Does anyone know specifically what the differences are in a PS control valve with the different markings on the cap covering the adjustment nut? In the Service Manual, there is reference to the one with the "X" marking being for the Corvette, and that others with no marking were for different Chevrolets of the time. Mine on my 67 SB has a "C". I don't know if I have the right or wrong valve in place.
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Re: Marking on PS control valve cap - 'X', or 'C'
Tim----
I believe that both "X" and "C" were used for the Corvette valve over the many years of its manufacture (i.e. 1963 to the present). There are several very similar valves that were used for other GM applications. They differ only with respect to one of the springs in the assembly. The "X" and "C" denote the ones with the Corvette spring. As far as which marking is considered "correct" for your year, I don't know.In Appreciation of John Hinckley -
Re: Marking on PS control valve cap - 'X', or 'C'
The Corvette control valve utilized a 55-pound centering spring, and it was identified by the "X" stamped on the end cap; the other application (Chevy II) used a 30-pound spring, and was identified either by a "C" stamped on the end cap or by no stamping on the cap at all.Comment
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Re: Marking on PS control valve cap - 'X', or 'C'
Uh oh. Sounds like I might have the wrong valve in place (or at least the wrong cap!) assuming John is right. Is there any way to tell without disassembly which spring is installed? I bet there isn't. How do I tell the difference WITH disassembly I wonder? I purchased this valve several years ago from Chicago Corvette and it clearly was supposed to be for the Corvette, but my car was not running and hadn't been for some time and I didn't have another valve to compare with. It's been running for the last year, but I can say that the steering assist seems a bit too much. I would expect that a weaker spring would result in more control valve movement, which would then result in greater assist. I wonder how many Vette owners out there have the wrong PS valve spring on their car and don't realize it?Comment
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Re: Marking on PS control valve cap - 'X', or 'C'
Tim, if your control valve has been rebuilt (Chicago Corvette?), it is very likely to have the "C" stamped cap. It may have nothing to do with your valve spring or the proper application. I don't think the X cap was ever available as a service part...If you have one, it should be preserved and re-installed if the the control valve is rebuilt.Comment
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X or C plus rebuilders =?
Tim Just for fun I checked 68-69TI&JG= says X is correct. 70-72 TI&JG = X correct 73-74 TI&JG it says C is correct 75-77 TI&JG= C is correct 78-79 and 80-82 TI&JG just a cap no letter stated. Now with this information if correct a 68- 72 valve had an X and 73 and later had a C by the manuals. I have removed the X from 73's to be correct to the manual. I really don't think the rebuilders care about the cap but I would hope they know about the spring. I wonder if the survey to make the manuals was full of rebuilt parts with C on them or in fact it is correct and did the valve change? LyleLyle
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Re: X or C plus rebuilders =?
What I really wonder is what effect having the "wrong" spring in the valve has on steering feel? It sounds like different Vettes had different caps, but did they have different springs too?Comment
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Re: Marking on PS control valve cap - 'X', or 'C'
Tim-----
OK, here's the deal: 1963-1973 Corvettes used control valve GM #5691955. This valve used a 55 pound centering spring which was denoted by an adapter cover stamped with an "X".
1976-82 Corvettes used a control valve of GM #7825636. This valve used a 40 pound centering spring which was denoted by an adapter cover stamped with a "C".
In October, 1982, the GM #5691955 valve assembly was discontinued from SERVICE and was replaced by the GM #7825636 which remains available in SERVICE. Also, I believe that most new "reproduction" valves are built to the same standards as the GM #7825636 valve. So, for the past 22 years, the only valve you could obtain in SERVICE was the valve with the 40 pound centering spring and the "C" stamped cover. Another distinguishing feature of the 7825636 valve is the hose guide. The GM #5691955 did not have this feature. The hose guide for the 7825636 valve was GM #7819613.
Now, in case folks are wondering what happened in 1974 and 1975, here's what happened: the 1974 valve was GM #7816806. I don't know which spring and cover this valve had but I strongly suspect that it was the 40 pound with "C" stamped cover. For 1975 the valve was GM #7819980. This valve also replaced the 1974 valve for SERVICE in October, 1975. I do not know what the centering spring and cover stamping were for this valve, either, but I strongly suspect that it was the 40 pound with "C" stamped cover. The GM #7819980 valve was discontinued in August, 1982 and was replaced by the GM #7825636. The GM #7816806 and the GM #7819980 also used a hose guide, but it was different than the later 7825636. It was GM #7817342. This MAY have been the only difference between the 74-75 valves and the 76+ valve. I do not know what the differences in configuration of these brackets are.
With respect to "rebuilt" valves, there's no telling what components that they may contain. All of the parts for the above-referenced valves are interchangeable. When rebuilders "do their thing", they strip down the valves to component parts, clean them up as required, and re-assemble the valves with new wear parts and seals. No attempt is usually made in a commercial parts rebuilding operation to "keep the components of the original valves together"; it's totally impractical when you're mass-producing rebuilt valves. The valves are not rebuilt "one at a time", from start to finish. About the only way you get this is to rebuild an original valve yourself. Of course, most of the time you have no way of knowing if the valve you have is an original valve or a rebuilt valve that was "installed along the way" and contains a "mixture" of internal components.In Appreciation of John HinckleyComment
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Thanks Joe !!!
Joe I bought a 75 a while back and I have noticed it has less power and you need to use more effort than my 73's. It may need work but the valve may be the difference. LyleLyle
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Re: Marking on PS control valve cap - 'X', or 'C'
Great information Joe. I would agree that unless you have rebuilt your own original PS valve, there is no telling what spring you have inside. Since the purpose of the spring is to control the amount of pressure assist by reacting to the load from the pittman arm to the steering linkage, it makes sense that the higher rate 55 lb spring would produce less assist (as felt by the driver)than the later 40 lb spring. This would mean that C2 and early C3 Vettes would have had less assist than later C3's. Is this the way folks who had these cars new remember it? Maybe there are some folks out there who have experience with the different control valve springs and years of Vettes who can offer insight into the difference in "feel". GM changed the spring rate for some reason, maybe because the steering wheel size was reduced slightly more assist was needed to compensate?
In any case, I have generally felt that my car had a bit too much assist. I just figured that's the way it was, but now I am starting to wonder about the spring in the valve. Assuming that the stated spring rates are based on 1 inch deflection (lbs/inch), then it should be fairly easy to check the spring when the valve is disassembled. Before I start taking my valve apart I will see how this string finishes out.Comment
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