I have a problem with the power steering on my 73 that I have not found any mention of in any of the forum posts that I've searched. Here's what's happening:

For some time now, when making turns at low speed, there's a noticable humming or whining noise accompanied by a matching vigration from the steering wheel. It also seems that the power assist is not really "assisting" like it used to. Then last week, while parking I blew the high pressure hose. It actually blew both ends of the hose off of the metal off the couplings. I've ordered a new hose, but I know there's something else going on. There are no leaks, at least there were none before I blew the hose.

Has anyone else experinced this sort of problem? If so, what was your resolution? I know that I could start replacing everything from the pump on down, but that's a shot gun approach that empties the wallet really quickly. I'd rather target the problem and fix what needs to be fixed. Anyone got any suggestions?

 

There are only two typical ways for a hose to blow out of the fitting. Either extremely high pressure or extremely high temperatures.

C2/C3 Corvettes have Saginaw P-pumps that have pressure relief settings of 950 to 1000 psi. Most GM P-pumps today have pressure relief settings in the 1450 psi range. The pressure relief setting is controlled by a sliding flow control valve inside the pump.

Any chance that someone installed a high pressure pump or swapped a flow control valve that had a high pressure setting into your pump? The only time that the pump actually goes into pressure relief is when the steering wheel is at full lock. So it could be possible to have a high pressure valve in a pump but virtually never see real high pressures if you don't reach near full lock.

The other way to blow a fitting is very high temperatures. If a pump is held in pressure relief and at the same time engine rpms are raised. The common way of doing this in Michigan is in the winter. People try to park their cars; get stuck in the snow; and try to gun their motor and turn their steering wheel at the same time. This type maneuver can really spike the fluid temperature blow a hose and/or ruin the power steering pump. Autocrossing can also get you into a high temperature problem.

Another way to create high pressure (and temperature) is to have some type of blockage in the system. This could cause the pump to work full time against the blockage and elevate steering fluid temperatures. Steering fluid temperatures (driving on a highway during a hot summer day) would be in the 220 degree range. Short drives and cooler days would see the temperature in the 180 degree range. (To actually blow a hose I would suspect that fluid temperatures would have to get in the 350 to 400 degree range. You might take a look at the plastic capstick on your pump reservoir. I have seen melted sticks from extreme over temperatures.)

Jim

 

Since I'm the original owner of the '73 (yea I know, that really rare) I know for sure exactly the service history on this Vette. I've actually done 95% of the work that's ever been done myself.

As for the history on the power steering, About 15 years ago I replaced both the pump and the control valve with rebuilt ones. The hoses were all replaced at that time as well. The ram has never been replaced or rebuilt. About 2 years ago the steering started to exhibit that odd humming or whining noise that I described in the original post. And like I said, there does not seem to be great power assist anymore, especially at low speeds, like when parallel parking. This Vette sees very few miles per year anymore, usually less than 1000 miles. So I've put off working on it, partly because I don't drive it much and partly because it's a real b_tch to get at the pump on a 454.
Anyway, I doubt that high temps were to blame, because I had only driven about 3 miles when I blew the hose. I was turning hard though, although I was no where near the limits on the wheel at the time. I was however experiencing almost no power boost at all when it happened. I have not yet received the new hose, so the ol' '73 is sitting in the garage with the left front jacked up waiting for the hose. I doubt that I have a pump problem. I sounds a feels like the pump is straining all the time when I make any turn to get the job done. Something down-stream is wrong, but I can't figure out what it might be. Do you suppose that the control valve could be a fault? If so is there any way short of ordering another new one and installing it to test it out?

 

Usually the noise of a cavitation pump is caused by high pressures or low fluid levels in the reservoir. My guess in this situation, its high pressures. Probably caused by a bad steering ram cylinder. If it is leaking internally by the diaphragm, it will load both sides and make it very hard to turn. That will increase pressures and cause the noise in the pump and hard steering.

 

I did not know that an internal leak in the ram would cause such a problem. I think your analysis seems very reasonable and based of this I'm going to order a new or rebuilt ram and see if that corrects the problem.

 

Please dont blame me if it dont. But, I have seen that problem before.

 

I've got 1 more. Bad crimps

Years ago we had thousands of hoses fail because of bad crimps and sued Sunstrand, the hose manufacturer.

Doesnt sound like that is the case here though.
Hoses deteriorate over time, just like the brake hoses do.
When the steering valve is centered, there is a return port open back to the pump and there should be very, very low pressure, really just friction in the circuit length.
Sounds like the rebuilt valve is probably at fault, but a service life of 15 years on the hoses is really pretty good.

Absolutely make sure you flush out the pump, and the rest of the system as best I could, especially removing the flow/relief valve for cleaning. Put it all back together and see if you get the relief noises in the neutral position.

 

You can disconnect the ram at the frame and try to move the piston by hand with the engine off. If there is no fluid in the system due to the blown hose the piston should move freely. If it sticks or is really hard to move you have probably found the problem.

The 79 basket case that I bought a few years ago had a siezed ram and I could barely turn the wheel with the engine off.



Rick B.

 

Usually if a pressure hose has a bad crimp it will fail at the fitting fairly soon in use. The hoses were replaced 15 years ago. Most hoses begin to seep or leak at the fitting as they get old. Or the hose itself begins to leak where it bends. They typically don't blow the hose out of the fitting.

Jim

 

Here's an update. I still don't have the new hose. They must have shipped it around the horn or something. But I took off the ram and was going to rebuild it myself when I noticed that right at the center was some serious pitting and deterioration. I assume that may have caused the internal seal to fail as was suggested earlier. So I found a rebuilt cylindar and installed it. Now I'm awaiting the new hose. perhaps a donky will walk up to my door one day soon with a package. Until then I can't report my results. Stay tuned.

 

The internal leakage referred to earlier was at the piston seal.
The pitting on the rod won't affect that, but can rip the rod/gland seal at the rod end of the cylinder and cause external leaks.

Hope you get your hose soon.

 

Well, the ol' 73 is back together and the diagnosis of a bad slave cylindar was a correct one. The new cylindar fixed the problem. Thanks everyone for your help.

PS to noosie: There was never an external leak, but internally the cylindar must have been leaking because all I relaced was the slave cylindar and the blown hose and the power steering works as good a new.