I've been doing a little research into this - I've always thought the power steering on my vette was a little "limp", and not really quite as assistive as I think it should be.

Before I go checking pump pressures or swapping out components I was wondering about the spring inside the control valve - I've been reading Jim Shea's papers on the subject of the spring rate that was used in these valves (hopefully Mr. Shea might drop in on this thread ) and I understand you can get two different rates, 40 or 55lbs, the 40 lb one giving slightly lighter steering.

I have a couple of good second hand power steering control valves kicking around so decided to try and test the rates of the springs with weights and a digital caliper - hoping to find them rated at either 40 or 55 lbs/inch, then I'd simply stick the lighter one in my car. Simple....Well no!
Because now I'm completely confused, as both the springs I've checked are coming out at closer to 200 lb/in! What am I missing here?!

Has anyone else been **** enough to actually check the rate of their control valve spring (ok, I'm ready for the mockery ) and if so was it with a similar result?

I'm assuming that both of these springs are pretty typical, perhaps the quoted rates of "40" and "55" lbs aren't actually in lbs/inch?

Ultimately I just want to perk up the steering feel bit, and I know the solution may not even come from the spring at all. My existing one may just be fine. But in the meantime this little "experiment" has just raised the question!

 

The biggest improvement in steering assist I made was to replace my stock power steering pump with an AGR pump.

My system leaked for a long time and the original pump ran dry more than once. I believe if that happens, or if the system fluid gets dirty and is not replaced, excessive wear is caused which results in less pump capability.

The AGR pump was a bolt on and it finally enabled me to have power steering. This was a while ago so I don't have a part number for you. I'm sure that the folks at AGR can set you up with the correct model.

 

Theo,

Do yourself a favour and look up www.borgeson.com and check out their integral power steering box for the C3 Corvettes. The core is a NEW Delphi type that has the ram built into the steering box and only two hoses are needed to connect it to the pump.

The NEW control valve is built into the steering box and varies the amount of boost depending on steering wheel position. Minimum boost in the straight-ahead position, and increasing boost as the wheel is turned further up to maximum boost when parking.

This box will bolt straight in to your car and clear all standard exhaust systems and will look like it came from the factory that way. You will go from four turns lock-to-lock down to 2.7 turns. Driving pleasure will be greatly increased and you will have a far superior feel of the road.

Only two downsides to this conversion; you have to pay for it and you will kick yourself for not doing this swap sooner

I have two C3s and am in the process of fitting each with a Borgeson box and accessories.

Regards from Down Under

aussiejohn

 

Send a PM to Jim Shea and ask him to clarify. He is the most knowledgeable person on the Forum on the C3 steering system.

 

Boy, this question hasn't come up in the last couple years. You got me off of my butt and made me dig into the files and also Terry Rudy's Corvettefaq.com website.

Let's start with the easy one. A 40 lb or a 55 lb spring refers to the load that the spring exerts when compressed to a height of 0.38 inch. The 40 lb spring has a rate of 200 lbs/inch. I am not sure about the spring rate on the 55 lb spring.

I know that several years ago we discussed the fact that in 1976 the control valve was changed to use the lighter (40 lb) spring (for some reason.) I am not sure what spring is used in any control valve that you might purchase today.

Several years ago I talked with Mr. Robin Wilkie in the Tech Services Department of Vette Brakes & Products Inc. He was most helpful and offered to make valves available with 55 lb springs as a special service. I don't know if Mr. Wilkie is still available or not. I don't know if the special valves are available or not. Quite frankly, I do not recall anyone mentioning if they had success with the higher load spring or not.

Here is the address for my papers on higher load springs for the control valve:

http://jimshea.corvettefaq.com/wp-co...de10ap2010.pdf

I hope that it helps. I will update the paper if more information (good or bad) is forthcoming.

Jim Shea

 

I am sure VBP will still rebuild a vlv with the 55 lb spring. they offered to do it for me the last time I needed a PSV. That was two years ago. NOte it was specail order only and they needed my core. You'll have to phone them.

Anyhow I have since fitted the borgensen unit. .....

Carbster

 

The 40 lb. spring would make the steering system more sensitive. I had the original control valve on my car when I bought it and I liked the feel of the system because it didn't want to "hunt" on its own. The rebuild kit I put into it probably had a [new] 40 lb. spring and I think its a bit 'touchy' now. That's just one person's assessment, though.

If you like to have a light, easy to turn feel on the power steering, the 40 lb. spring is for you. If you don't...and you can find one...go with the 55 lb. spring.

 

Thanks to everyone for the various replies/suggestions.

My main priority is to make sure the stock system is top-notch and as good as I can get it before I opt to make any non-stock upgrades. I've just rebuilt the steering box and honed-to-fit my own pitiman shaft bushings, also the rag joint and tierod ends are good, so in general the steering is as slop-free as it's ever been, possibly better than new with the blueprinted steering box. The only "issue" I have is that it still just feels a little "powerless".

The Borgeson box looks good, but as aussiejohn says it's not cheap! Maybe a mod for some time down the line if I can't get the stock system performing to my expectations.

Jim, thanks for "getting off your butt" for me and looking back at the archives! What you're saying all makes sense - the height of the spring when it's installed in the valve is, by my measurement, very damn close to 0.38". So essentially the "rating" is not the actual spring rate, but just the preload present when the valve is assembled.

My "experimental observation" of 201 and 207lb/inch for the two springs I've tested is encouraging given what you said - looks like those are definitely a pair of "40lb" springs then. So using either of those should give the lightest steering.

Thanks for the link to your papers, in actual fact it's those very papers about spring rate that got me thinking about which spring(s) I had in the first place - but your info about the 200lb/inch seems to have confirmed that for me!

I'm going to put a new control valve in very soon anyway, and will install it with one of the springs I've tested, now I know that they're both the lighter type. If that doesn't improve the assistance, I guess I'm left looking at the pump pressure being low, or there being a cross leak in the power ram - all something I can test by hooking up a pressure guage. That'll probably be my next port of call.

Are new pump pressure regulator springs available? Just wondering if it's possible to push up the assist pressure a little on the stock pump...

 

Put a new Power Steering Control Valve on my 75
now when i'm stopped and have my foot on the brake
I can turn the steering wheel left and it will
turn fine, but when I turn the wheel right it won't
turn at all, take my foot off the brake and it
turns right and left just fine, anyone have any ideas why
It worked fine before the change.

 

TheoUK,
One of the other changes that occurred within the C3 power steering system from 1968 through 1982 was the amount of flow (NOTE, NOT PRESSURE) that the various pumps produced. Here are the flows through the years:

1968-69 Max flow was 1.75 gallons per minute
1970-73 Max flow 1.60 gpm
1974-81 Max flow 2.90 gpm
1982 Max flow 1.9 gpm (probably reduced for improved fuel economy.)

Increased flow would tend to make the control valve more responsive and the effort would feel lighter.

Here would be one tip. If you can find a power steering pump from a known original 1974 through 1979 Vette, it will have the higher flow discharge fitting. You most likely don't want a 1980 and later discharge fitting because it would have a metric o-ring port and would require a special power steering hose assembly. Since all Vette pumps after 1974 had an interference fit pulley, all of them with a smooth driveshaft (except the 1980-1982 pumps) would have the higher flow discharge valves.

Another pump fact: The throat of the discharge fitting is a major controlling element as to the amount of oil that the pump discharges. It isn't quite as simple as just drilling out the throat of the discharge fitting. If you take a fitting out of the pump and look closely at it, behind the hex head is an o-ring. Just behind the o-ring at the bottom of the next groove (somewhere on the diameter) you will see a very small hole. That hole is called the P-hole and it communicates pressure back to the pump and regulates the flow control plunger behind the discharge fitting.

By going in and disturbing the diameters and surface finishes, you really don't know what you might end up with. But if you want to try, here is a guideline.

As a rule of thumb, for every 0.016 inch on the diameter that the throat is opened up, the pump will flow an additional 1/2 gallon per minute.

0.1144 inch throat diameter = 2.0 gallons per minute
0.130 inch throat diameter = 2.5 gallons per minute
0.144 inch throat diameter = 3.0 gallons per minute

Some people have complained about jerky steering when they have drilled out the fitting. They have disturbed the surface finish of the throat of the discharge fitting and/or may have caused a burr to cover the P-hole.

If you want more flow driving down the road, this will increase the flow from the pump. Obviously, once you open up the throat of the discharge fitting, there is no turning back.

One warning: The pressure relief on all C2/C3 Corvettes was set at 950 psi. A lot of GM steering systems have much higher pressure reliefs. The special Corvette power steering hoses were designed to operate with 950 psi max pressures. Changing the pressures that your Vette pump produces will cause hose leaks.

TPIboy,
It is best to start your own thread outlining your problem. It just confuses the issues with two seperate questions and answers. Having said this, you need to balance your control valve.

Jim Shea

 

Jim, thanks very much for the detailed info.

Just out of interest, I assume these flow ratings are at zero/ambient delivery pressure?

Not easy to test flow, but I do intend to test the pressure of my pump next. My vette is an 80, so has metric fittings on the pump.

I'm taking from what you've written that, unless it's been replaced by someone, my pump should have the higher 2.9gpm flow output, right?


Let's say I isolate and test the pump output and it's low on pressure - that will mean one of two things. Either the pump is worn out or there's an issue with the flow control/pressure relief. In the second eventuality, can one adjust the pressure relief to a higher pressure, or even buy new springs if the old one's gone soft?