Hydro boost / power steering issue?

[PMUT]

Hi all,

I had a really disappointing situation today.
Was driving down the hill and needed to brake (12% gradient). First brake was fine, with the second the steering wheel has started shaking left/right in a high frequency, so that I wasn't able to hold the line...
It got more worse when I hit the brake harder, I moved in the 2. gear and used the engine to slow down.

After I had the downhill behind me it has needed some time to normalize.
Hitting the brake afterwards was fine as usual, no issues, no vibrating steering wheel.

Any hints? Think maybe the belt has slipped due to the high amount of power steering pressure needed in a short time?

Power Steering fluid is in not under the fill level.

Any hints?

Greetings Ulrich

[RockwoodMike]

You should have been in second gear before you started down the hill..Your brakes got so hot that the heat was warping the disc brakes..Causing the steering wheel to shake with the speed of the wheel..

You should get your brakes inspected to be sure your discs are within specs for thickness and check for cracks..

Next time when you go down such a steep hill as you start down, shift into second..you will use the brakes less that way, saving them..

[PMUT]

Hi, it was at 40 km/h and i gone down to 30 km/h, so low speed but hard step on the brake.
No way the brake overheats in 5 seconds ... - or?
Bad initial description: The steering wheel was moving left/right without touching the brake for approx 10 secs afterwards.
So for me it looks more like it was an issue with the power steering pump or an valve in the hydro boost / steering box.

[Elandan2]

Sounds like a "death wobble". Common occurrence on solid axle vehicles with worn steering components. Check all the steering linkage, king pins, and wheel bearings for any wear. Also, the caster adjustment may be out.

[RockwoodMike]

You just need to get this thing up on stands and take a long look at it..How many miles on this?

[PMUT]

Two weeks ago, the car was in the yearly general inspection and passed it, with a worn steering this would have not happened.

I watched in the meantime some videos about and think its something different.
The death wobble looks like to starts quite often at fixed speed and can be reproduced.

In my case it started when I hardly hit the brake. I was since than driving now 200km without any issue and the rv drives like it drove the last years.

[Eyez Open]

Your brake rotors or calipers are more than probably the cause. Perhaps your axle/bearing setup is so slopped out simple break pressure unloads the system.


There is a bearing, race and spindle that all work together  towards one end. Smooth rotation of the hub.

Breaks on and its chaos.

It is simple enough to Jack the rig up, get in a sitting postion to use your legs to pressure/kick the tire sidewall ( forcefully)  "while" the tires are spinning. Care always comes first, any movement/wobble is not tolerable RV wheels are heavy...think heavy force.

Your tires spin freely when suspended.

[PMUT]

Hi thanks for your reply.

All that was tested by the inspector two weeks ago. No way here in europe they let you on the road with a worn brake or axle.
I tried test it by my own but recognized, that my electrical jacks are not able to get the tire of the ground ... too short. And my hydraulic jack seems to have a sealing issue and can't hold the pressure and height.

We managed the next 150 km driving, also with hills and hard steps in the brake, again without this issue has come back.

So if brakes or axle is worn we should have seen the issue again. But it's not reproducible.

[Eyez Open]

Unless they lifted the RV and preformed the above procedure you will not know I believe.

I will openly admit it is not too scientific...but it will expose almost any flaw in the system. It would seem your experiencing a extreme oscillation under heavy loads,you need to duplicate that.

If you have disc brakes a old piston caliper can hang up/ lock quite easily creating a pulsating drag. Doing that test really takes a heavy kick by the way...akin to breaking a 2x4 several attempts comes to mind.

Aside from that good luck be safe. A side note...there are very few left who know there way around these old rigs...heavy truck specialist would be my go to advise.

Speaking to inexperienced, it could be very possible your tire and rim are not mounted to the hub correctly meaning it was pinched on. I've seen that more than once.

[mytoolman]

I believe the "back and forth steering wheel jiggle you experienced was likely from a sticking valve in the power steering pump. Hydro boosted brakes put lots of pressure on  power steering pumps.   If the valves inside the power steering pump were a little sticky it could cause that type of jittery back and forth wheel....

When was the last time the power steering fluid was flushed?