hey all

I have a 1971 ford f250 highboy I recently bought and haven't had the chance to be really intimate with it yet.

Problem:
Anytime I rotate the tires (standing still, while moving, doesnt matter) the front tires start to shake. The shake is rather aggressive.

Notes:
The truck seems to be equipped with a bendix power assist setup and ive noticed while I rotate the wheel the return line seems to be collapsing near the PS.
Shop said they bled the system as well.

Does anyone know what could be causing this?

 

I don't know a ton about the power assist system, but I don't think either line is a "Return" line rather, they are both return lines (and pressure) depending on which way you are turning the wheel since it's basically just a hydraulic ram. if it were me, i'd replace that specific line just because it's a cheap try, but i'm guessing the control valve is the problem.

 

The comment about “standing still”, are you talking about jacking up the front end and rotating a tire by hand?
Straight rotational movements should not affect the steering at all. Should be strictly wheelbearings moving.
If you have a binding wheel bearing, it might be trying to move the steering system. Seems like you could be dealing with two separate issues.
At least if I understood your original statement correctly.

These trucks came with some pretty old design tires and yours may be very old, age-wise as well. Some of that back-and-forth might be from tire tread.
Do you have normal tires on this truck? Or skinny “Tera” type tires?

but yes, to replacing any hoses that seem suspect.
I don’t suppose you happen to have a video of this happening by any chance?

 

Here is a thread to read thru. 67 f100 4x4 steering components - Ford Truck Enthusiasts Forums (ford-trucks.com)
You will have to positively identify what system was swapped into your truck. Pictures might help, somebody might recognize what you have. But unless all the parts came from a donor truck it may be difficult to figure out. And even more difficult to fix.
Also you might want to read the sticky at the top of the forum page on 4x4 PS swaps.

 

sorry for such the late response! I’ve added the video and I hope it’ll help someone help me figure it out haha

 

I guess it didnt add to the previous post. here it is

 

this is related to the power steering components, no question. if you have a line collapsing, it's damaged and needs replacing that's for sure your first step followed by re-bleeding it. unless you have zero tools or a severe aversion to mechanical work, this is easy to do in your driveway. if that doesn't solve the issue, it could only be the ram you see in your video or the control valve or the PS pump itself. generally when a ram goes bad, it still works, it just leaks and doesn't give as much assistance. generally when a PS pump goes it's similar and gets louder. that's why i'm leaning towards the control valve. they aren't cheap. hopefully replacing that line solves the issue.

 

In your experience what do you think would cause the ram to flutter like in this video?

 

My '74 highboy would shake violently after hitting a shallow city street pothole at 35 mph, I would have to slow way down to stop the shake. I found a loose driver side spindle nut. The shake stopped after adjusting the spindle nut assembly.

 

As I said before in your other threads, to narrow down the many things that could be wrong, disconnect the PS pump belt and drive it. Then note any irregularities. That gives you a baseline. Then put the belt back on and check it again. You have 50 year old hydraulics. It won't be as smooth as an integrated PS box. The hoses will move when you stop a motion or reverse a motion. This is the same as farm/heavy equipment hydraulics.

 

i think it's the control valve, but I'm hoping it's not. I'm 99% certain this is related to the ram not getting a smooth steady supply of pressurized hydraulic fluid, but why that's happening could be a few things. could be air in the system, could be the pump not delivering enough fluid, could be the control valve not calling for pressure.

i would change that collapsing hose, make sure all the fittings are tight, make sure the reservoir is filled and thoroughly re-bleed the system.
if that doesn't fix it, you have the option of taking it to a hydraulic professional or being a parts changer. i think its incredibly unlikely to be a pump because it would have to be delivering almost no pressure for you to be creating enough vacuum by manually moving the steering via the wheel and you would have zero assit from the system. i think it's unlikely to be the ram itself, because generally when the seals go, you see oil leaking out of the ram or you lose power from the system if it's just the seal on the piston itself. it's possible a leaking seal could introduce air, but again, it would be pushing fluid out on the opposite stroke.... the only thing left is control valve.

for the advice on isolating the system by disconnecting the belt... not sure i'd do that. you will not only have manual steering, you'll have to be pushing the fluid in and out of that ram via your steering wheel and your manual steering gear and the only thing you might be able to get out of that would be if there was a loose ball joint, loose steering gear, loose rag joint, or loose pitman arm. none of those things would cause shaking while being stationary in your driveway. i think there might be some slight chance that if your steering gear wasn't just loose but the gears were actually chewed up it might be causing jumping causing a jerking motion to the control valve, but i don't think that's likely and i think you'd be better off testing for that by disconnecting the pitman arm from the drag link rather than taking the belt off the power steering pump.

changing that hose and re-bleeding isn't only the cheapest potential solution. it's maintenance that needs to happen anyways so you aren't out anything extra starting there.