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EVO Steering Bypass Kit From GM
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Post Bringing it up from the dead 
Having used the Saginaw pumps in MANY of my builds and having had to tune the pressure to better match the gear or rack, I can tell you guys a couple things. First, the valve actually works as a function of the "slug" (i.e., the valve and its shim height), the spring tension, and the pre-load on the spring provided by the nose of the fitting! If you mix and match parts, you're left with more experimentation, but that's the fun isn't it? Second, the valve for the EVO and non-EVO are, in fact, slightly different because the EVO is basically an electronic actuator pressing on the valve (someone with access to GMSPO catalog can confirm that quickly for at least the 1/2-ton trucks with lighter brakes it's different. I hadn't heard of the bypass kit out by GM until just searching the forum, and I had replaced my power steering pump ~5 months ago because it left me and recently I had problems traced to the EVO. Everyone I talked to said to remove it, so over the weekend I pulled the 98's EVO and replaced it with the valve slug, spring, fitting and pressure hose from a 96 model with the pump still in the truck. I found that the springs between the 98 and 96 are exactly the same in length and pressure, and as I said, the flow control valves are slightly different in bleed port size. Source of my parts was a $36 AC-Delco reman pump sans the reservoir and a $15 Edelmann hose for a 96. I DID NOT want the PITA of swapping the core again, just changing out the valve and fitting was plenty (plus I was ticked that my 5-month old pressure hose had to go - LOL)!!! Anyway, I vacuumed out my spendy GM Cold-Climate Power Steering Fluid and made the swap of parts. After refilling and bleeding, I knew the assist was going to be too high and confirmed with a drive on the highway. Came back, pulled the fluid and took out the valve, cooked off the epoxy with a torch to free the nut and used one shim from Borgeson kit I have left from tuning these pumps. I stacked up shims to meet where the factory had the nut and added one more, which equates to a drop of about 100 psi. Feels OK parked and up to 50mph on local roads, but still a little light on the highway. I'm concerned that another shim, and its 100psi reduction, will be too much as that is then the pressure for which rack and pinion operates... Plan to give a call to my buddy at Turn One in Michigan where they are the extreme experts in power steering to get some advice! My thought is that with the EVO dynamically adjusted pressure, GM was kinda lazy with tuning the steering gear itself and the only way to get the perfect feel back will be to have my gear done ($$$ OUCH!) I'll report anything I learn.

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I may have mis read your post but using the 1996 hose and fitting worked just fine for me in my 97 k1500.I don't believe I changed the valve but that was too long ago for me to remember the exact details.
Those pumps are surely aggravating

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stroker97k1500 wrote:
I may have mis read your post but using the 1996 hose and fitting worked just fine for me in my 97 k1500.I don't believe I changed the valve but that was too long ago for me to remember the exact details.
Those pumps are surely aggravating


It will work, but reading through the posts there were some complaints about the feel of the assist. We all know that can be very personal, but I was trying to point out that the porting on the valve is different between the EVO (larger port) vs. non-EVO pumps (smaller port), at least on the lighter brake optioned trucks (they seem to tie the pumps and components to brake RPOs regardless of hydro-boost or standard vacuum). I confirmed with GM parts counter that the valves are definitely different part numbers, which was no surprise based on my finding (ole drill bit size testing between ports). Anyway, smaller port provides more dampening so the feel would be better too. Thought I'd throw that out there for folks doing it as the valve, spring, and fitting, which is actually a restrictor, work in harmony for to tune the flow for level of pressure assist.

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Ry_Z71 wrote:
stroker97k1500 wrote:
I may have mis read your post but using the 1996 hose and fitting worked just fine for me in my 97 k1500.I don't believe I changed the valve but that was too long ago for me to remember the exact details.
Those pumps are surely aggravating


It will work, but reading through the posts there were some complaints about the feel of the assist. We all know that can be very personal, but I was trying to point out that the porting on the valve is different between the EVO (larger port) vs. non-EVO pumps (smaller port), at least on the lighter brake optioned trucks (they seem to tie the pumps and components to brake RPOs regardless of hydro-boost or standard vacuum). I confirmed with GM parts counter that the valves are definitely different part numbers, which was no surprise based on my finding (ole drill bit size testing between ports). Anyway, smaller port provides more dampening so the feel would be better too. Thought I'd throw that out there for folks doing it as the valve, spring, and fitting, which is actually a restrictor, work in harmony for to tune the flow for level of pressure assist.


The unit I rebuilt and put on a 99 Tahoe when I did thos retrofit was off of my 96. So, in this case the truck got the 96 model pump complete with valve, spring, and fitting all from a 96, non-EVO setup. The adjustment to the valve (the end nut epoxied into place) was measured to be "shimmed" to the same distance as the valve that came out of the 99 Tahoe's stock pump when I disasembled it. To make a long story short, the only thing that was not swapped over to 96 model equipment was the steering gearbox itself, so I know the overboosted condition on the 99 Tahoe has to be becasue of the difference in the gearboxes. They do call for a different box between EVO and non-EVO Tahoes.

Do you have any pics of the valve you're talking about? I assume it is the spool valve with the nut epoxied on the end. I could discern no differences in the 96 valve and the 99 Tahoe valve when I had the two pumps apart, but perhaps I missed something.

EDIT: OK, I just looked at the part numbers and I can see where the spool valve is a different number for 96 and 99 GMT400s (non-EVO and EVO). I do recall that they are shimmed the same though, as I measured both. I did not take note of the port sizes though, so I might go take a look at that. I still have some pumps out in the garage I can look at.

This would not be the cause of my overboosted feel on the 99 Tahoe though, since I swapped out everything... I rebuilt and put in a COMPLETE 96 model pump and hoses, so I know my issue is the existing gearbox. I've still never tried shimming out the epoxied nut farther to try to lower the pressure even though I have the shim kit to do so. Someone here tried it and said it had no effect, but I never got to try it myself. My mom drives this 99 Tahoe, and she says she actually prefers the way it steers so easily now, so I've abandoned any plans to change it at this point.

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OK... nevermind. I've re-read your post up top a few tmes now and I think I follow better what you were saying. I think my mind is a little slower than usual tonight or something.

I didn't notice at first that you said you swapped in a 96 model flow control valve (spool valve). So, you essentially have the same thing I do... a COMPLETE 96 model pump (with 96 flow control valve) and hoses but still with the 98 model EVO gearbox, right? If I'm reading you correctly it seems shimming out the epoxied nut on the flow control valve DID actually make a discernible difference for you, even while retaining the EVO gerabox. That is good to know.


Good info. Glad you mentioned this.

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When I put in my hydro boost last year, I swapped out my 97 pump to a 2003 that came out of a Yukon. The tank had the extra return line. So I got rid of the 97 used my pulley on the pump, everything was a good swap. I ended up using a line from a 95 because that pump used a different line off the back, The 95 wasn't the exact line but it works for me. I haven't had any issues with the pump or my steering. Knock on wood.

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JR96CK wrote:
OK... nevermind. I've re-read your post up top a few tmes now and I think I follow better what you were saying. I think my mind is a little slower than usual tonight or something.

I didn't notice at first that you said you swapped in a 96 model flow control valve (spool valve). So, you essentially have the same thing I do... a COMPLETE 96 model pump (with 96 flow control valve) and hoses but still with the 98 model EVO gearbox, right? If I'm reading you correctly it seems shimming out the epoxied nut on the flow control valve DID actually make a discernible difference for you, even while retaining the EVO gerabox. That is good to know.


Good info. Glad you mentioned this.


JR96CK, you seem to be following me now! Very Happy

The feeling of over-assist left has to be in the steering gear itself. If I shim the pump valve any more, it'll be below standard operating pressure for a gear and at a rack's operational pressure. In your case, it could be nothing more than taking some slack off the thrust bearing and over-center pre-loads from many miles, but my gear isn't that old. I installed a NOS gear because my original gear was leaking after 214K. So, I highly suspect it's more of an internal issue (different torsion bar). Tearing down a gear to swap in a thicker torsion bar (effectively makes stiffer feel) is minimum a few hundred bucks. If the gear between the 96 non-EVO and later EVO trucks is a different part number, I bet that's the difference!

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Post Confirmed - steering gears are different. 
Based upon talking to the expert at Turn One. Non-EVO gears from 88-96 1/2-tons are pretty much unchanged over that span of years, but are different that EVO gears of 1/2-tons from 97-2000 GMT-400s. Side by side the older gears are not as robust and the forward end of the housing for the rack piston was enlarged to accommodate slightly larger internals. Piston, valve and torsion bar are all different, and these all effect feel of the assist.

Also, I was correct in that the pump valve should not be shimmed any more than for an extra 100psi reduction as I did for both safety (you may have insufficient assist for panic maneuvers) and because of undue stress on the internals of the pump and gear.

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Newbie on this board. I'm on my 4th speed sensor in my 1999 C1500 Suburban It's failed. I unplugged the wire on the bottom of the PS pump and the problem went away. However, I now have a PS fluid leak. I'm going to do the bypass kit.

I'm trying to understand how best to do this. I have a leaking high pressure hose that needs to be replaced too (at least i think that what's leaking). Do I order the 19168825 bypass kit and a 1999 hose since adapters are included? Or do I order the bypass kit with a different hose for say a 1996 since I have to replace the hose anyway and not use the adapter?

Looking at the available parts, I see there is a Hydroboost feature. In reading about it, it appears to be more prevalent in the 2500 truck but I never found any info that tells me how to determine whether or not I have it. Suggestions here?

I need the truck drivable so I can't get it wring and then wait on parts to come from out of town. I need to do this in one go.

Also, when flushing the system, do I use PS fluid, as specified by GM, or is Dexron transmission fluid the way to go?

Thanks for any help.

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Good info info, Ry... have been wanting to investigate those questions for a while now myself. Do you have a PS pump pressure gauge to see how much difference the shims make? The 99 and 96 pumps I took apart were each shimmed .024" on the flow control valve. I found an articla online somewhere a while back where they added in shims and measured the pressure reduction. Will try to see if I can find that info and post it when time allows.

510,

Welcome to the board. You can do two things, essentially. It has beena couple of years since I did this, so I'm working from memory here.

1) Buy a new 99 hose and the EVO bypass kit from GM. This is NOT my personal preference. This is really only cost effective if you can re-use your existing hose. The EVO adapter from GM (which is a bit expensive, I think) is basically just made to make the bend in the metal section that the 99 model hose lacks due to the EVO solenoid being there. The 96 hose had this bend made into though, hence option #2 below.

2) Since you have to replace your hose anyway, I would suggest doing what I did and just get a 96 model hose with the correct bend already in it. This will be far cheaper than the GM adapter. What you will be missing, however, is the flow control fitting from the 96 (threads into the back of the pump). The 99 doesn't use this since the EVO fitting takes the place of this part, so your truck will be missing this piece. You can most likely get this piece from a dealer or possibly just get one for a few bucks out of a salvage yard. Even with this added expense you will probably come out ahead in terms of cost as opposed to option #1 above with the GM adapter. In addition, this approach of retrofitting back to the older hose just makes for a cleaner install, IMO.

One other thing which Ry_Z71 has just mentioned is that the flow control valve (the "spool" valve inside the pump behind the high pressure hose fitting) is ported slightly differently between the EVO and non-EVO trucks (96 and 99 respectively). You would most likely be fine using the 99 valve, but I used a complete 96 model pump when I did my swap, so I cannot tell you for certain how this will feel with the 99 flow control, valve.

Really, if it were me I might go grab a used 96 or earlier pump out of a salvage yard since it will have the flow control fitting you need AND the older style flow control valve inside. You can get an AC-Delco rebuild kit for around $15-$20 on RockAuto (I posted a 5% discount code over in the Classified Section here the other day) and rebuild the pump yourself. Also, look up a pressure hose for a 96 model truck... they have them for around $15 on RA. Gates makes the hoses for AC-Delco, so either brand is a good choice, whichever is cheaper (usually Gates).

If you want the easier option of not rebuilding it yourself (alhtough not hard to do at all), I would order up an AC-Delco pump (NOT A1 Cardone or any other aftermarket brand... they suck) for a 96 or earlier model truck and turn in your 99 model for core. Might be an easier option for you. That way you have a pump which is already built and has the earlier flow control valve and the fitting already there.

Lastly, as far as fluid goes, I have used Redline Synthetic Power Steering Fluid for the last 15 years with nothing but excellent results. It far exceeds anything else out there. The 99 Tahoe I was working on in this thread was on its original pump with 125,000 miles on it when I disassembled it for this swap. I had switched it over to Redline within the first year after the truck was bought and then changed it about every 20-25,000 miles thereafter (this is my mom's truck on which I do all the maintenance). When I took it apart, the pump was in SUPERB shape inside. As a sidenote, I have NEVER had power steering pump whine one any vehicle I've owned when using Redline. I've used several items from their product line and have always been impressed with their products.

These days I add a Tablespoon of Molybdenum Disulfide into the PSF reservoir whenever I service the system. Just one more trick you can employ which works very well, along with adding a Magnefine filter on the retirn line. These last two steps are optional though, just personal preference. Just swap in a good rebuilt non-EVO pump, the correct hose or hoase and adapter (if you prefer), some Redline PSF, and I assure you you will never have any issues.

Hope this helps.

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Here are some part numbers I dug up:

1996 Flow Control Valve:

GM #7809221
List $48.01

1999 Flow Control Valve (just for reference):

GM #26065843
List $23.10

1996 Flow Control Fitting

GM #26009894
List $27.51

The above prices are list. You can find much better prices online. If your local delaer cannot help you out with a better price, I suggest GM Parts Direct or GM Parts Giant.

As far as your question about hydroboost, your PS pump will be the same either way. The only difference is a return port on the reservoir for the hydroboost trucks. If you have a large round balck canister behind the master cylinder, you have regular vacuum brakes. If you have some hydraulic lines running to a piece of hardware behind the master cylinder, you have hydroboost.

As far as used pumps for rebuild purposes or robbing parts from, the pick and pull yards around me have them for around $15. Pulling the flow control valve and fitting out of a salvage yard pump and getting the rebuild kit below for your pump (or you could go ahead and rebuild the salvage yard pump... either way) would get you in business. Another $15 for the hose, and some fluid, and should able to keep this whole thing right under $100 total.

Rebuild kit:

GM #19146544

Just looked and it's only about $11 for this kit on RockAuto. Cheaper than I remembered. There is one kit (also Delco) which is $9 but it does NOT include the shaft bushing. I highly recommend replacing the shaft bushing though. Worth the $2 and the minimal effort to do so.

Here is the 96 model hose:

Gates #353950 $29.79 at RockAuto (prior to discount, before shipping). Slightly more expensie than I remembered in my previous post, but still not bad. I double checked that this is in fact the part number I used.

Lastly, I added a power steering cooler onto the 99 Tahoe I was working on but again, this is optional. This does not affect which pressure hose you use, only the return hoses. Here is the link to my thread with the part numbers for those parts if you decide to add one. The hydroboost trucks come with them already, but it is beneficial to vacuum boosted trucks as well.

http://www.pacificp.com/forum/viewtopic.php?t=10572

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Thanks for the quick replies. This is very helpful.

I looked this morning and I do not have Hydroboost. I ordered this truck new and this is the original PS pump and hoses. I have 142K on the clock so I'm guessing the pump will need replacing before too long anyway. That being said, I'll replace the pump and both hoses to be done with it. What's the saying, "there's never time and money to do it right but there's always time and money to do it twice"?

Based on info above, I'll order a 1996 pump and 1996 high pressure hose. I looked at my return hose and it has a clamp on one end and a crimp fitting on the other. Is there a part number for this hose? Or are you guys using a pipe cutter to remove the crimp on the return line and then just using a fuel line hose clamped on both ends? With no pressure, this would work but the new hoses are cheap enough that it's probably not worth doing this way. Just replace the line.

It looks like the the serpentine pulley needs to be removed to replace the pump. It likely takes a puller to remove. If so, I need to have that handy before starting the project.

Lastly, the high pressure hose is in a recess on the steering box. A wrench, including a flare wrench, won't go down in that recess to remove the hose. What's the trick to removing the hose from the steering box? Is there a special GM took for this task?

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JR, yes I have a PS pressure test kit.

510man, if you order a reman 96 pump, you may not get the needed flow control valve, its spring, and the fitting. Quite commonly, remans require you to swap over these pieces before installing. AC-Delco remans used to always come with them, but I have been told it's increasingly rare. The one I purchases, which was just a pump core, did, but it was also a shelf-sitter according to the parts shop.

You can also order a return line with the crimped flex hose such that there's just a hose clamp at the pump. I know for a fact that Edlemann makes one because it's what I used. Just order the one for a 99. Many folks don't bother and simple cut the crimp and original hose off the return using a hacksaw or dremel and slip on new hose with clamps. I personally prefer clean as-stock look.

I also agree on switching to synthetic fluid, but that's more because my applications build lots of heat regularly (towing long distances or much motor in cramped quarters). I like GM's Cold Climate PS fluid myself. In any event, you need to thoroughly flush your gear, and I recommend doing that first with fresh conventional fluid because it's cheap and you'll need plenty to clean the gear out. Once clean, then flush with synthetic to remove the conventional. Make sure the gear is turned side to side while flushing.

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I didn't find a 1996 Delco conventional PS pump at RockAuto. Called them too. They don't have it. In fact, I didn't find an AC Delco at Advance, Pep, O'reilly, Auto Zone or NAPA. Delco needs to realize its hard to buy their stuff if nobody sells it. RockAuto has the 1995 Delco. However, when I checked the 1995 against the 1996, here's what I found:

Pressure hose 1995 = Gates 359190 1996 = Gates 353950
Delco pump 1995 = 36-517095 1996 = 36-517134

1992 - 1995 seem to be the same. 1996 is different. So is the 1996 model year the only choice here?

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510man wrote:
I didn't find a 1996 Delco conventional PS pump at RockAuto. Called them too. They don't have it. In fact, I didn't find an AC Delco at Advance, Pep, O'reilly, Auto Zone or NAPA. Delco needs to realize its hard to buy their stuff if nobody sells it. RockAuto has the 1995 Delco. However, when I checked the 1995 against the 1996, here's what I found:

Pressure hose 1995 = Gates 359190 1996 = Gates 353950
Delco pump 1995 = 36-517095 1996 = 36-517134

1992 - 1995 seem to be the same. 1996 is different. So is the 1996 model year the only choice here?


It's the brackets, geometry and mounting difference. Remember 96-2000 Vortec motors, 92-95 tbi™ motors. The pump base rotation speed is different and may change how it's valved. I can't say for sure, because I haven't had a tbi™ motor in ages!

eVILBay has a bunch of the ACDelco remans up for sale for the 96.

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I'm making progress. RockAuto has the Delco Part # 36517131 reman pump listed for the C1500 pickup but not the Suburban. Should be the same pump so I now have the pump and hose figured out.

In addition, I need the 1996 Flow Control Valve GM #7809221, correct? If the pump has it installed, I'll return it. RockAuto doesn't have this part that I can find so I'll get it locally.

I do not need the 1996 Flow Control Fitting GM #26009894 as it would already be in the new pump, correct?

Also need confirmation I need a puller to remove the pulley and help with how the high pressure hose is removed from the steering box since the hex nut is in a recess. I think that's it.

Sorry for all the questions but I'd like to get it right on the first try. Thanks for all the help.

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510man wrote:
I'm making progress. RockAuto has the Delco Part # 36517131 reman pump listed for the C1500 pickup but not the Suburban. Should be the same pump so I now have the pump and hose figured out.

In addition, I need the 1996 Flow Control Valve GM #7809221, correct? If the pump has it installed, I'll return it. RockAuto doesn't have this part that I can find so I'll get it locally.

I do not need the 1996 Flow Control Fitting GM #26009894 as it would already be in the new pump, correct?

Also need confirmation I need a puller to remove the pulley and help with how the high pressure hose is removed from the steering box since the hex nut is in a recess. I think that's it.

Sorry for all the questions but I'd like to get it right on the first try. Thanks for all the help.


That pump is for RPO JB7 brakes, so be sure that's what you got. The full reman for RPO JB5 or JB6 brakes is 36-517134 according to the Delco catalog. My hardcover catalog says either of those pumps are complete, meaning they should have the valve and fittings already, BUT my catalog is 4 years old and since I was told it's becoming rare you may want to check. As for the flow control valve, its spring, and the fitting, they are dealer-only items.

You can rent a simple puller from Advance, AutoZone, etc. Should be zero issue getting the line off with a proper flare nut wrench.

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Post Pic is worth 1,000 words.... 
This thread used to have some pics of mine posted, but my web hosting expired. I've just re-uploaded some pics I thought might help.

As far as any special tools, you may wish to procure a tool for the clutch fan. Not totally necessary to remove this to do the pump, but makes life easier if you do:



Here is a shot of the pump pulley tool kit:



Here is a shot of the new lines installed and everything back together on the 99 Tahoe I was working on back in summer 2011 when I did this. The fitting atop the pump on the left is the high pressure hose, and the one on the right is the return hose. As far as the hex nut being inaccessible with a wrench (recommend you use a flare nut wrench to keep from rounding it off), are you referring to the plastic collar seen in this pic which goes around the fitting? That is not a problem, as it's easy to move that back out of the way and expose the hex nut on the fitting. You'll have no issue with that. That is the only thing I can think of that would obscure your access to the hydraulic fitting. Note that in the pic below my return line setup will look different from yours, as I added on a cooler. The line goes from the gearbox out to the cooler and then comes back to the pump. Yours should go straight from the gearbox back to the pump (to the reservoir, to be more precise).



Once you have the old pump removed, the pic below shows the problematic EVO solenoid we are talking about, having been removed from the back of the pump. This threads into the back of the pump and then the high pressure hose attaches to the front side of this fitting (where the red plastic plug is seen in this pic). This is what you are deleting:



This is the fitting which you will need from the 96 or earlier pump which replaces the EVO solenoid. The high pressure hose threads directly into the back of this. This is why the bend on the EVO and non-EVO pressure hose is different, as the EVO hose threads into the front side of the pump onto the EVO solenoid housing (as seen above), but the 96 and older hose must have a u-bend in it to connect directly to the older style fitting seen below on the back side of the pump.



Lastly, this is the aforementioned flow control fitting (right) and flow control valve (left, a.k.a. "spool valve") which we have been mentioning. This shows how the line-up goes into the back of the pump. These are the pieces I gave GM part numbers for in a previous post (does not include the spring you see in the pic).



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Perfect!! Pics help a lot! Thanks for posting them.

So now I see I need the pump, hoses, 1996 fitting, 1996 spool valve, a puller and a flare wrench. I assumed the plastic collar was metal. Good to know it is easy to move out of the way.

I think I'm good now. Looks like I need one order for the pump and hoses and a second dealer order for the fitting and valve (or a JY visit). I'll be glad to move off the EVO and the sensor replacement every six months.

Thanks for all the help.

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Glad the pics help.

If you're ordering up a 96 model pump, you may want to wait until it arrives to see if it includes the 96 flow valve and fitting already. I concur with Ry_Z71 that they may or may not be including one or both parts on reman pumps now, so I would hate to spend the money at the dealer for parts you might get as part of the new pump. Just a suggestion, unless you're just in a time crunch and HAVE to make sure you have everything all at once. I understand how that is too.

I was looking on RA myself and find it quite strange that the pumps are out of stock for non-hyrdoboost trucks. Curious. Hrm

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