Hot Rod Forum banner

Reliable GM PS Pumps

2K views 9 replies 4 participants last post by  '48 Austin 
#1 ·
My '75 GMC K25 with 350 has a stock steering setup that uses a standard GM pump connected to a heavy duty variable ratio steering box (its a 4x4). All fittings and hoses are relatively new, but stock. Tires are stock size (245/75R16) and truck weighs about 5000 lbs. The truck is heavy enough that good power steering is a needed for any kind of maneuvering, and I'd like to get rid of the pump whine just because it sounds bad.

I replaced the PS pump with a rebuilt when I installed a new crate engine and the pump whined and had uneven/jerky power assist. I decided it must be the pump, so I replaced it again, but had very similar results.

I haven't found a parts store that sells a new unit for the old pumps (only rebuilt), so that doesn't seem to be an easy option. Is there something I can do to get these rebuilt pumps to be more quiet (no whine) and work smoothly, or should I look at switching to a type II pump? The switch to Type II seems to get quite expensive compared to the old style pump, but it would be worth it if it worked well.

Thanks,

Bruced
 
#2 ·
https://www.google.com/search?q=gm+...X&ved=0ahUKEwiurJb0urvMAhWEND4KHSaBDf4QsAQIYA


Check above site. Make sure PS belt is tight. Make sure fluid is full when hot and clear without bubbles. Whine or growl is caused by air in system or a relief valve that is set for too low a pressure, which can also cause jerky steering you describe. There's also a possibility you have a steering box problem. The pressure relief valve is located behind the pressure hose fitting on the back of the pump. Remove the hose and fitting to remove the relief valve and spring. Use a magnet to get plunger and spring out. Completely disassemble the relief plunger check for any foreign material and completely clean and reassemble plunger. The large plunger spring controls the system pressure. These pumps were used on small lightweight cars to 4 WD 1 ton trucks. The difference is the spring and plunger to supply higher pressure for bigger vehicles. Try stretching the spring so it is 1/8" longer free length than it was originally. Reassemble and fill system and see if things improve. If no improvement, you my have a worn steering box. If every thing is good, low system pressure was your problem. Don't go nuts stretching the spring. On many vehicle you can get at the relief valve from the bottom without removing the pump. Have a catch pan ready to collect the oil. Don't reuse the oil. Use clean PS fluid only.
 
#3 ·
Thanks very much for the suggestions. I never returned the first replacement pump so I still have it in the box. I'll use that one as a trial case and see what I find when I disassemble it and try your suggestions.

If the steering box is worn, will it help to play with the sector shaft tension adjustment to take out some of the play? My GMC shop manual has a procedure that does not sound that complicated. As I mentioned in my first post, my shop manual says this is a variable ratio box, if that makes any difference.

Bruce
 
#4 ·
Wanking on that spring wont do diddy.


Look at the photo here


The shims in the valve itself will change the pressure
(They are calling them washers)


IIRC , installing shims lowers the pressure. Removing them increases it. A few thou at a time should be the way to go until you get the desired effect
 

Attachments

#6 · (Edited)
According to my 1975 Chevrolet Factory Issued Service Manual for Chevelle, Camaro, Monte Carlo, Nova, and full size Chevrolet, it goes through a 4 plus page detailed explanation of the PS pump and the pressure relief valves and the 2 relief valve springs. Long story short, the small spring and ball control the absolute max pressure the system will generate. This only comes into play when steering system reaches the lock or when the front wheels are against a curb or buried in mud or sand (exact words from the manual). The max pressure can be increased by removing a small shim under the ball seat/retaining bolt shown in LATECH's picture. This may or may not solve a jerky felling when maneuvering like when tight parking or backing up a trailer with minimal vehicle movement. The larger spring acting on the spool valve is more of a flow control valve that modulates based on the demands on the system in almost all driving conditions, like driving down the road and turning into or out of a driveway. Usually adjusting the larger spring is all that is necessary to get rid of the jerky feeling. The large spring controls pressure by modulating flow in the 200-400 PSI area. But, I will agree there can be times when removing a shim on the small spring and ball will help. The spec according to the manual is 1250-1350PSI as adjusted by shimming. As you can see removing shims from the small spring and ball can have dramatic effects on max pressure and going overboard can cause an excessive system pressure that can rupture seals and hoses. That's why I go for the large spring adjustment first. I did this on a Street Rod 2 weeks ago that had the jerky problem and the problem went away. Customer was very happy and there was no increase in max pressure that could cause future parts failure.
In a situation where someone is using a Ford Mustang II Rack and Pinion powered by a GM PS Pump, shims have to be added to the small spring retaining bolt to reduce max system pressure. As said GM runs between 1250-1350 PSI. MII racks require a little more than half that amount. Also the large spring pressure needs to be reduced to avoid the over sensitive power assist complaint. There are also restrictors (where the high pressure hose threads into) which have a smaller orifice to help with an over sensitive issue. Street Rod set ups can be a challenge because of the wide range of tire sizes, wheel backspacing, front end weight, and steering wheel diameters.
 
#9 ·
I have used a pair of good channel locks ,like Knipex, to grab the body ( not the machined surface of course) of the valve to hold it so as to unscrew the end of the valve. Usually it holds well and I am able to loosen it.But you know, every now and then you run across one that doesn't want to budge.


Good idea on the copper pipe to hold with.


Austin...sorry I seemed a bit snarky on the post about the spring. You did post good info.
I am Sorry Friend.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top