Notes on Power Steering Issues

Power Steering Article

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I have a 98 wagon with a Mile Marker 10500 2 speed hydraulic winch. I've had it for years now and the winch has never given me any problems. I have gone through at least 4 power steering boxes (under warranty) since I've had the truck which in my opinion is not normal.

The last incident occurred when I was in Colorado In early September 2003 on my way to the Hummer Club's Durango/Moab event. I had occasion to use the winch for the first time in months. The next morning when I was pulling out of the motel I had no power steering for about 2 minutes. The brakes were fine. When I arrived in Durango I mentioned this to one of the factory tech's at the event and he said that I probably had some air in the system that worked it's way out. He recommended that I use GM Power Steering fluid which would cut down on Cavitation. I also complained of a soft brake pedal with a bit of brake fluid lost in the rear system. I bled the brakes and they were fine. I was able to drive the whole Durango/ Moab event without much of a problem except the occasional 'stiffness' in the steering.

When I returned home I had my idler, pitman, center link and power steering pump replaced on my GMPP warranty which is up May 2004. They didn't want to replace the steering box again. The truck still had intermittent periods where it steers hard. My next step was to have GMPP replace the power steering box again. Since my truck will be out of warranty soon I figured it's finally time to get to the bottom of the problem. I don't want to throw parts at the problem and see it go away until the next time I use the winch. I want to get to the 'real' cause of the problem.

I asked Jim Bella who used to work for AMG if he had any insight into the problem. He wrote back saying " I recall some hydro-boost problems,fluid foaming, and intermixing of P/S & brake fluids and concerns relating to AMG's certifications to DOT/FMVSS 105, 106 116, 208,but Doug Hamlin at AMG is the undisputed "expert' on H1 & Mile Marker problems".

I called Doug Hamlin in customer service at AMG to see what he knew about the problem. He told me that the problem was due to the Mile Marker winch causing a pressure spike in the system that would blow out the seals in the power steering box. He suggested that I put an overpressure valve in the circuit to prevent the spike. He went on to say that AMG is not warranting any power steering components on trucks with Milemarker winches. Knowing that the AMG installs these winches on many of the military HMMWV's I asked him what the Army was doing about the problem. He said that the Army doesn't do anything about the problem. He went on to say that the Army specifically orders the Hmmwv's with the Mile Marker winches and their (the army) primary concern is getting out of stuck battle field situations. According to Doug the Army doesn't care if they have to replace steering box's.

I started looking in my Grainger catalog for hydraulic overpressure valves but I'm not a hydraulics' engineer and really didn't know what to get. This whole thing didn't sit well with me. I didn't want to write an article with incorrect information so I called one of my hydraulic engineer friends who has a Hummer with a Milemarker. He doubted that the winch could cause a spike in pressure. He said you might blow it by stalling the winch and overheating the fluid. Turning the wheel over hard while using the winch might put an unusual high pressure on one side of the steering piston blowing out the teflon spool seal.

I figured if there was an endemic problem Milemarker would already have a fix so I decided to call them and get their side of the story.

The guys at MM knew who I was from my this website. I made it clear to them that I wanted to write a fair article about the steering and now possible winch problem. They requested that I put into writing my problem and what AMG said.

The guy I spoke to at the factory was incensed when I told him what AMG said. I must have really hit a hot button with them. He said that the winch itself could not produce a pressure spike because it's pretty much a benign resistance (hydraulic motor) in series with the PS pump. He said that AMG has some kind of sweetheart deal with Warn and they have had nothing but trouble getting in there.

I was told that MM worked directly with the Army (not with AMG) to get their winches approved for service. That must be why Doug said that the Army 'orders' them to put the MM's on the trucks. Mile Marker said that AMG had enough problems with the hmmwv's to cause the Army to launch it's own investigation. AMG pointed the finger at MM and visa versa so the Army had it's own investigators take a handful of trucks and test them out.

He said that the Army investigation determined that the problem is in the hydroboost. Reading between the lines in our conversation he said that it was a poor design and had QC problems.He said that the spool valve gets caught between ports and leaks causing loss of pressure in the system. Some worked, some didn't. He said that the spool valve was undersized and internal parts weren't made of high enough quality steel.He said that AMG knows all of this but doesn't want to spend the money to fix the problem. I asked if they had a copy of the Army's results. He said that the Army doesn't release results for the public and they found out by talking to Army engineers that were familiar with the study. So my next mission is to learn about and test the hydroboost.

MileMarker sent me this bulletin. Oil Temperature Expectations

Typical power steering pumps operate at about 150-220 degrees. This will not break down the fluid at any quick rate. When it reaches about 230 degrees it can loose viscosity. When it reaches about 275degrees it can be in the area of loosing any lubrication qualities that it had to start with. Note that these fluids are not synthetic. When using good quality synthetic oil in this application it can go up to 325-350 degrees before it can have the loss of viscosity and lubrication properties. With synthetic oils the losing of viscosity and total oil failure can occur almost at the same temperature .

This information is from JR Macmillan.

A Good fluid to recommend is Amsoil @ Their synthetic transmission fluid is great for those that can use this, it must be recommended by the vehicle manufacture for transmission fluid use in the power steering system.

Royal purple @ lists Max EZ, it can be mixed with many fluids and claims it doesn't affect the seals and protects against rust and corrosion.

Lucas oil @ has an additive product #10011 which smoothes the operation of the system and is 100% petroleum based and a seal conditioner.

Justice brothers has a replacement fluid @ they claim works well, no part #.

Neo Synthetic oil @ offers a replacement that is inexpensive, no part #.

I checked the hydroboost using the procedure in the AMG shop manual. My hydroboost seemed fine. Still in a quandary I started to email different Hummer tech's to get their opinion. The following are some of the responses.

In my personal experience, through 2 trucks with MM, I've replaced one box. I always felt it was more of a big tire/non-factory offset/off-roading combo more than anything else. And now that I'm running 40" MTRS on Hutchinson wheels, I'm just going through idler/pitman arms. Mainly after aggressive Kinzalow drives.

AMG always has said that the MM are the source of all evil. I wouldn't trust their opinion as far as I could throw a 2 piece wheel with runflats! Their basis is, in my opinion, based upon the issues that when a truck shows up and has a MM winch, that must be the problem. Convenient, but hardly empirical.

Still; nobody knows the answer!!!

Next I decided to educate myself on how power steering gears work. Maybe if I fully understood it I would find out the answer. I began my search in 2 old automotive textbooks I had. One Motor Services Automotive Encyclopedia copyright 1965 and the other, Stockel auto service and repair copyright 1969. I found the exact model illustrated in both books so it looks like the unit we have in our trucks is at least 37 year old design.

The box used in our trucks is a GM Saginaw recirculating ball self-contained (integral) power steering system which incorporates a power piston geared to the pitman shaft, as an integral part of the steering gear. A control valve is also incorporated in the housing. It is an inline design because the ball nut, power piston, worm shaft and control valve are all in line.

Next I decided to see if anyone made a better steering box as a replacement. The only company I found that sold a replacement was AGR in Texas. I went to their web page and discovered according to AGR that the Hummer already uses the largest Saginaw steering gear available and the highest capacity GM power steering pump. The main reason to get their product would be if you were going to install their 'Rock Ram' steering system which has special fittings installed in their rebuilt version of the Saginaw Gear. Otherwise it looked like a nice unit to use as a rebuilt replacement if you don't want to spend the bucks on a new steering gear.

I finally decided that I was going to fix my steering wheat her GMPP wanted to pay for a new box or not. I went down to the shop and spoke to a mechanic who rebuilds Hummer steering boxes. The following are what he sees going wrong with boxes.

First it's leaky plastic/ teflon seals on the power piston and spool valve.

Second the cylinders are scored.

Stripped splined shaft

Third massive damage like teeth broken off the pitman shaft.

We removed my gear from the truck and took it apart. The first thing we did is move the piston in and out. It moved with less resistance then it should have indicating a poor seal. When we pulled the rest of it apart the cylinder wasn't scored and there were no broken parts. The only way to really know is to test the box on a hydraulic test stand.

What ruined the seals? Did the fluid overheat one time and cause the plastic seals to leak? Was there some kind of pressure surge developed that caused the leak? Who knows?

Scot Smith said that I have been thinking about hooking up a separate system that would power the winch and not interfere with the steering system....It would consist of a separate power steering pump with a larger reservoir and a filter for heavy use, and it would be hooked directly to the winch.....I was hoping that this would keep the winch separate from the steering to eliminate any problems that might occur between the 2. Scot built a separate system but he has his own steering and axle shop.

Do you think the AGR box is any stronger then the stock Hummer one? No I think the box is the same it just has the fittings for the hydraulic ram........But I think you can get it with a tighter steering gear so that it turns quicker...the one we got from howe had a tighter gear they said... Will the AGR box work without the ram cylinder? Yes the box is basically the same as the hummers the fittings can be capped off when not in use.... When you drive with the whole AGR setup (cylinder and all) does the wheel return straight after you make a turn? No from what I recall you need to steer it where you want it.

I was talking to a friend about the reinforcing plate where the steering box gets bolted tot he frame. He was concerned that welding on the frame to install the plate was a bad idea unless the frame is already cracked. What do you think? If the frame is not cracked you don't have to weld the plate on.....The only reason I recommend it be welded is so it does not create side to side movement....Thats why if welded it should only be in 1 inch sections just to attach it to the frame...The plate will work well by itself because it sandwiches the frame rail between the box and the plate to fix the problem.

I think that there quite well could be an issue of hydraulics that is contributing to the failure, perhaps in concert with other parameters, such as stress from off road activity, heat, fluid failures in the lubrication or cooling or cavitation areas or several of these acting at once.

I would say it is definitely a HOT button issue. It seems that this is about to blow out into the public's attention. Hydraulic winches are great. I have used many of them on wreckers and they have many advantages, but I think that the idea of tying them to a power steering system may prove to be over ambitious to say the least. Perhaps hydraulic winches should have their own conventional hydraulic pump/reservoir system such as in a wrecker or ramp truck.

I know Doug's reputation, which precedes him, which is very positive. He may want to steer you straight and he may also be mindful of restrictions he has on full disclosure of all he may know, due to corporate decisions. But regarding the Army warrantee, I can tell you that the Army buys the vehicle with very little in the way of what we would call a warrantee. They only have a catastrophic failure of materials clause in their contract which is very limited. They are not concerned with warrantee issues to speak of like we are.

When I arrived in Durango I mentioned this to one of the factory tech's at the event and he said that I probably had some air in the system that worked it's way out. He recommended that I use GM Power Steering fluid which would cut down on Cavitation. I also complained of a soft brake pedal with a bit of brake fluid lost in the rear system. I bled the brakes and they were fine.

I find that situation certainly not explained reasonably by the tech's opinion either. A fluid change may remedy the problem with the fluid, however it would seem probable that the negative effect to your power steering pump had already taken place. Air as you know doesn't just enter these systems when unbroken. I think the tech just was incorrect and speaking to an issue that he had no real answer for. Of course that leaves the possibility that there is a known issue which he may or may not have known about that is being kept confidential. Obviously something IS going on and some people are in the know. There may in fact be a way, if AMG or Milemarker wished to do so of performing certain tests to demonstrate repeatability of the failure, to a scientific standard. Perhaps that has actually already been done. Would they want to release such information. Big money is at work here involving the players and their contracts. Army, other govt agencies, AMG, Milemarker, Warn etc. It would be unwise to believe that all is unknown in this area. Power steering boxes just like we have in our trucks have been very reliable in many makes and models. It would not be unheard of to go get a box out of a salvage yard from a 4X4 truck that have over 100,000 miles on it and over 10 years in age and have it be fine. The failure rate with the Hummer is strange. I wonder if anyone has cross referenced the incidence of failure to milemarker equipment being attached. Apparently AMG has, or so it seems from their warrantee stance

Put a wad of grease on the output shaft to keep salt out.

Bob here. Any issues you know of with regard to this static steering being a "normal" and "acceptable" condition? My truck never had it, now it does, AMG can't/won't fix it and it is very annoying, not to say it concerns me. Any experience with this, is there a way to fix it?

I get in my truck, start it up. Temperature of engine or weather is irrelevant. While truck is parked (it does not make a difference if the trucks transmission is in park or drive), I at times cannot turn my steering wheel. It is as if I have no power steering. As soon as I step on the accelerator and the truck begins to move, the steering goes back to "normal". In the past, this would happen even when under forward motion at slow speeds (like in a parking lot trying to park...that was a nightmare not being able to turn the wheel). AMG is telling me this is normal "static steering". They have documentation on this but refuse to forward it to me. Hmmm, my truck never did it in the past, and after 7+ weeks of not having my truck (it was in the repair shop getting this steering problem looked at), the problem still exists. AMG sent two engineers out on 3 occasions, and still this is a problem. But AMG says this is acceptable. They offered me a 1 yr 12,000 mile extension on my warranty, but I have GMPP for 6 years, 75,000 miles. Currently 34,000 miles on the truck.

As you already know This is not normal. Make sure your tire pressure is not low. I keep my gsa's at 37 psi cold. All you have to do is sit in another few trucks and see how they do for comparison. When I had your problem it turned out to be the steering gear.

Brand new MTR's, I have varied the psi, it makes no diff.

My truck is not operating properly in my opinion......and steering is an important function if one is to drive safely. I am going to send them a letter requesting in writing that my truck's condition, according to them, is "normal" and "safe".

It might be the steering shaft or U joints binding. Removing the steering shaft is not that bad. Changing out the joints can be a pain. They are pressed in pretty tight. Spicer # for the joint is 5-92x.