Modifying the Power Steering Pump

Anyone have any experience or knowledge of the SOHC's power steering pump?

I want to take one apart and see how it can be modified for more volume and/or higher pressure.

I've read a few threads on PBB on tweaking the Toyota pumps (higher pressure) and I'd like to see if the same can be done to the SOHC's pump.

Of course a smaller pulley would mean greater flow per unit of time so if anyone knows of another pulley (aftermarket or from another vehicle) that fits, that would be fantastic.

Here's an interesting idea--

http://www.patentstorm.us/patents/5557977-description.html

The link didn't work for me. What did it say? Try the set up that is in the 89 Lincoln Continental. It has an electric boost pump connected to the rack & pinion which kicks on when the engine is at a low idle (parking). It won't turn on at highway speeds. You could connect this with a sensor on the steering column. I have electric steering on my 88. I have a magnet on the column with a reed switch on a bracket. Your column has a wheel with holes (from a picture on your other thread). You could make an optical sensor with an LED/photo transistor or photo diode set up. It could use an MSD rev switch which is preset to function at a specific RPM range. Another set up could use a hall effect sensor from an older style distributor. Could you post a link to that Toyota pump article?

Here's one thread on how to turn up the PSI on the Toyota pump:
http://www.pirate4x4.com/forum/archive/index.php/t-441049.html

To sum it up, I think the biggest thing is basically to stiffen up the bypass valve so that the pressure before the valve goes to bypass mode is higher than normal.


But I think eventually I will have to switch over to a Saginaw pump cauz they're PSI rating is just so much higher and are available widely.

I imagine my pump is the same as yours because... why wouldn't they be. Right?

section525 said:

I imagine my pump is the same as yours because... why wouldn't they be. Right?

Click to expand...

No. I believe your pump, since you have the 5.0L, is the more common Saginaw type -- greater PSI -- good for you, sucks for me <- ahah

EDIT -- nevermind, looks like we pretty much have the same pump! I looked it up on PartsAmerica.com for a '96 5.0L Explorer. So negate what I just said. I guess its the 4.0L OHV that has the Saginaw type, I've seen it on SavageWolf's vehicle.

Oh and here's another article on how to increase the pressure -- from West Texas Off-Road: http://westtexasoffroad.homestead.com/powersteering.html

Same general idea as the Toyota modification .

A quick Exploded diagram of the SOHC pump:


For reference, an unmodified SOHC pump will max out at this PSI:



After a few days of messing around with the SOHC's pump, I have come to the conclusion that this pump can not be modified very easily for more pressure. The reason is because its flow piston can not be opened w/o damaging it.

Below are two flow pistons -- both of which are from the SOHC's pump. You can see that in order to open (and therefore modify) the flow piston, you have to pretty much destroy it.


In the image above, the ball bearing that operates as the valve is missing as it popped out somewhere during grinding. But typically, in order to modify the pump for more pressure, the spring inside the flow piston is made "stiffer" by compressing it more -- which increases the pump's bypass pressure. However, I could not find an easy way of opening the flow piston w/o damaging it.

For reference, the picture below compares the SOHC's flow piston (on the left) with that from a Jeep (Grand Cherokee). You can see that the flow piston from the Jeep has a hex cap which allows easy access to the spring inside.



So having said all that, my only option now is to go with another pump.

I found a pump from a Chevy Lumina (last generation) that I thought would work because its modifiable in pressure. It also has the same pulley as the SOHC -- same diameter and same number of ribs. However, I think it has a smaller displacement compared to the original SOHC pump because its body is just slightly shorter than the SOHC's. I did also look at a pump for a Jeep Grand Cherokee and I think this has about the same displacement as the SOHC's pump. Unfortunately, the Jeep's puley is larger than the SOHC's and its wider. So I think the plan is to use the lumina's pulley on the Jeep's pump.

Below are just rambings of what I found with the Lumina's pump:


After all of the fittings and such are removed, here is what the SOHC's pump (on the right) looks like alongside the Jeep's pump (on the left):


The SOHC's pump's input has this weird 90 degree swivel input thing so it had to be removed and fortunately fit pretty well in the Lumina's pump. Hopefully it will fit just as well in the Jeep's pump.

Today I picked up the pump from the Jeep Grand Cherokee.

But first lets take a quick look at the three pumps (and their associated pulleys).. on the left is the stock SOHC pump, in the middle is the Chevy Lumina pump, and on the right is the Jeep pump


So now on to the Jeep pump.


A few parts of the Jeep pump:

From left to right: spring, flow piston, and the main fitting.

Flow piston opened (couldnt do this with the stupid SOHC's flow piston):

From left to right: cap, ball bearing, limiting stud, spring, flow piston housing.

This is the washer I'm using (from Home Depot) to compress the flow piston's spring a little bit more (measured it as 0.61 mm thick with the calipers):


This is where the washer goes in the flow piston's internals:



So after that, the flow piston is finished and was buttoned up.
Then its onto modifying the main fitting.

Drilling the main fitting's center port for more flow:


I was forced to stop because I had to help my friend with his blazer (ball joint broke) but I only have one more hole to drill in the main fitting and its time to put this Jeep pump with a Chevy Lumina pulley on the Ford Explorer

sweetness

cant wait to see how you mount and plumb this sucka

410Fortune said:

cant wait to see how you mount and plumb this sucka

Click to expand...

Mounting the pump will be no problem as the Explorer's pump has a Saginaw "TC" mounting pattern (and dimension.. but not internals) .. so mounting the Jeep pump (or the Chevy Lumina's pump for that matter since they are both Saginaw TC's) will be cake since the mounting holes should all line up.

The biggest problem I foresee is putting the pulley on because the 4.0 SOHC's engine layout does not allow the pump to be mounted with the pulley on. So the pulley has to be mounted onto the pump after the pump has been bolted to the engine. And of course I'm using the Chevy Lumina's pulley since it has the same diameter and grooves as the stock SOHC's pump.

As for the high pressure fitting, the stock SOHC's lines bolt directly onto the Saginaw TC's main fitting so this should be no problem. And the input hose is also cake since there's nothing to it.. just a gravity fed (no pressure) 5/8" hose.


So to sum up some questions that might be asked and to put things into perspective:
Q: Why am I not using the stock SOHC pump?
A: The stock SOHC's pump can not be easily modified for more pressure (the flow piston does easily allow the modification)

Q: Why am I using the Chevy Lumina's pulley?
A: The SOHC's pulley mounts differently so it can not be used on a Saginaw-TC pump. On the other hand, the Chevy Lumina's pulley mounts directly onto any TC pump and it has the same diameter and number of ribs as the SOHC's pump (which means its compatible with the SOHC's serpentine belt).

Q: Why are you using the Jeep's pump instead of the Chevy Lumina's?
A: IDK (my BFF Jill), I thought the Jeep pump had a larger displacement but I now doubt this as the two TC pumps are exactly the same dimension. So I could have just gone with the Chevy Lumina's pump which would have eliminated swapping pulleys. But I already had the pulleys removed when I did the dimensional measurements so I just went with the Jeep pump since it didn't have as much crud on its body. And as stated previously, the pulley needs to be removed anyway in order to mount a TC pump onto the SOHC block.

For anyone following this in the future and just to keep the story together, all this pump effort is going towards my full hydro steering .. thread here:http://www.explorerforum.com/forums/showthread.php?t=188452

Had a few minutes today so all I did was finish the main fitting .. which basically meant drilling out a tiny hole p about 180 degrees from the original .. hopefully for easier fluid flow out of the pump.

Sooo today.. right, today.

Well turns out that the Jeep Grand Cherokee pump can not be used for two reasons:
1) The SOHC pump has threaded tabs on its body which the mounting bolts then grip on. The Grand Cherokee's pump has tabs on its body but the holes are not threaded. And unfortunately you can't just tap these holes because in order to do so, you need to step up in bolt sizes and drill out the aluminum bracket that the pump bolts to (and there's no room to get a drill there).
2) The Lumina's pulley has a main shaft that is differnt diameter than the Jeep's. Sooo only the Jeep's pulley can be mounted on to the Jeep pump and only the Lumina's pulley can be mounted on the Lumina's pump.

Soooo.. I moved all of the modified parts to the Lumina's pump.

Then tack welded the feed tube fitting onto the Lumina's pump:


Also had to shave/grind down the aluminum bracket under the pump so it would clear this feed fitting:


So its time to mount the pump!

(note I had to notch the plastic fan shrowd just a little bit so I can get the pulley tool in the tight area. a small drill bit on a dremel worked really well, kind of like a router).

So I hook up the feed tube to the reservoir and filled the reservoir with fluid .. then started the engine... sounded fine for a second, then a whirl, then a grrrl.. then pop!!! OH NOOO! fluid everywhere.. Danger Will Ribinson, Danger!!


So I stop the engine as fast as I could and fluid is just gushing. After a few minutes of calm-down-you-can-do-this session, I got back up over the hood (it sucks working in the engine bay of a lifted vehicle), I removed the pump and what did I find?

Yey!!! the pump blew its back side off! Yey! Hurray!! Happy happy joy joy!



So if anyone is interested in seeing how our pump works, here you go:

(the centrifugal, as opposed to the centripetal, force keeps those vanes extended and the fluid fills between the vanes until its spun out to the high pressure side).


At first I realized that that I had left the high-pressure hose cap on. I use this cap to keep dirt from getting in the hose during installation. And as I just said, I left this cap on and never connected the pump to the rest of the system. Initially I thought, oh that must have been it! The pump built up too much pressure behind it and blew its back side off! But now that I think about it, I think it that my ignoraneous (yes thats a word) self forgot to shave the pin that the check ball-bearing sits on inside the flow piston. And even with the cap on, the pump should have gone to bypass so the pressure should not have built up high enough to cause the back to blow.


FOOORtunately, I have another Chevy Lumina pump (can never have enough of these damn things), so I transfered everything over and shaved the pin that had caused the recent happy-event. The Lumina pump has a shim on it to space it out (for lower pressure), so for now all I did was remove this shim. I did not put a washer in the flow piston's spring. So after about an hour of transfering and replumbing, I cranked the engine, ran the engine a few minutes to verify the system isn't going to go boom again, and started the bleed process. I was then able to get a baseline reading for this pump and, with the shim removed and no washer, I read about 1,200 PSI. I took the Explorer out on the street for like 3 minutes just to see how it does and felt just like with the SOHC's pump when the vehicle is stopped (gets hard about 1/3 of the way left or right) -- which makes sense cauz they both put out about the same pressure.


Pic above shows the shim, which is the non-golden washer. Again I didn't install the brass washer (pictures in the middle of the shim) this time around to get a baseline reading. You can also see the grinded down pin thing to the right of the spring.

So next step is to then stack a shim under the flow piston's spring and get another reading -- hopefully I'll get to this Friday maybe?

That pump looks very similar to the internal pump in an AXOD transaxle.

Yesterday I got around to removing the pump and installing the #4 washer in the flow piston to up the pressure on the (Lumina) pump. The new config maxed out the 1,500 PSI pressure gauge that I've been using so, for now, all I can say is that the max pressure is greater than 1,500 PSI. I ordered a 3,000 PSI gauge so that'll come in sometime this week.

And then....

Wow sorry for not updating this..

Basically I stopped updating this thread because the stock SOHC's pump can not be modified for greater pressure -- that is without using an external relief valve to control the upper pressure limit.

Sooo.. the rest of the story is in my hydro steering thread (sorry for the mixup):
http://www.explorerforum.com/forums/showthread.php?t=188452

But right now I'm using the modified Lumina pump, but soon I will try to use the SOHC's pump again (with the bypass feature removed) in conjunction with the external Prince Hydraulics relief valve. And the reason why I want to revert back to a stock SOHC's pump is because its far easier to remove and install than the Lumina's pump (the pulley is easier to remove on the SOHC pump).

Can I have dibs on the Lumina pump, when you are done with it?

Sure sure.

The pulley has a few minor defects so if you're going to run it as a DD, I'd replace the pulley. Typically about $16-$20 at most parts store
http://www.partsamerica.com/ProductDetail.aspx?MfrCode=RNB&MfrPartNumber=300201&PartType=140&PTSet=A

Thanks IZ.