:o Steering Rack Help!

[Drew32]

Hi all,
I have a 1987 944 that I am near completing the rebuild after picking it up earlier this year. My issue is that after rebuilding the rack (I did it myself with the Rennbay kit) it locks up real bad when turning left while on the ground. When the car is on jack stands it turns fine. As soon as I put the car on the ground it has a bad mechanical lock up when turning to the left.
It was fine before even though the car wasnt running, I was able to turn the wheels no problem with the engine off and on the ground. I rebuilt the rack twice, just to make sure I made no mistakes.
Any ideas? Could it be the lines? I can't see it being anything other than a damaged rack. It was leaking which is why I had to rebuild it.

[Drew32]

Just wanted to make an update. When I have the engine off, car on the ground, the wheels turn fine with no lock. Looks like I need to chase a hydraulic issue

[huskerick1]

Drew - Hi, I rebuild these racks and does sound like a hydraulic issue for sure. I know you mentioned rebuilding it twice, but it may be the main spool valve/relief valve is giving you issues. For when there is no hydraulic pressure, you note it turns normally. So, surely something to do with fluid pressure. Do ensure you connected the high pressure line/return line in the correct location, as it's possible to get them backwards.
In rare cases, an upper spring mount with a failed bearing can also cause binding...

[DrTruth]

Originally Posted by huskerick1

Drew - Hi, I rebuild these racks and does sound like a hydraulic issue for sure. I know you mentioned rebuilding it twice, but it may be the main spool valve/relief valve is giving you issues. For when there is no hydraulic pressure, you note it turns normally. So, surely something to do with fluid pressure. Do ensure you connected the high pressure line/return line in the correct location, as it's possible to get them backwards.
In rare cases, an upper spring mount with a failed bearing can also cause binding...

+1. Lines reversed.

[Monkey Wrench]

I know nothing about steering racks but I do work with hydraulic packs quite often.

basiclally you have a pump, it generates flow. it runs all the time.

to have pressure you need restriction so a hydraulic pack includes a pressure relief valve, this is a ball bearing fited to a seat which is like a O sitting within a V
with a compression spring behind it often there may be a grub screw ( setscrew) to adjust the spring pressure.

more spring pressure, adjusts to a higher system pressure limit threshold.

normally the pump always runs, the ball maintains the system's designed pressure, when presure is used by actuators motors etc it is there at the ready.

the rest of the time the unit runs in basically an idle state, returning all the fluid to the tank. basically wasting energy.

if the soemthing like dirt gets behind the ball, or seat is damaged. it may not seal properly.

to resurface the seat, an old trick, use a new steel ball take a hammer and punch and give it a tap. then change the bearing in case it is damaged.

the hydraulics shop I work with has a set of ball bearings braised to a rod, they put very fine lapping compound on them to fit the seats to the size of ball. the ball is simply a ball bearing but should be the correct size.

if the spring got misplaced or ball went missing, or maybe the setscrew behind the ball ball got tightened down too much , or any debris in the area of the spring and seat. its stuff to look for.

a very similar spring and seat arrangement is often used as a check valve, fluid can only leave if it pushes the ball up ( away ) from the seat. fluod pressure the other way pushes the ball into the seat and it seals, it won't allow fluid to move in the reverse direction.

about the particulars of the sterring rack itself , others can help more than I can.. this is just very basic info common to most hydraulic systems. evem a car jack or pallet jack uses the same basic principle, if it limits hydraulic pressure

the fluid gets returned and you can bring the cylinder to its physical limit, then pump all day it is pumping fluid but then simply overcoming the limit of the pressure relief valve... returning the fluid to the tank ( reservoir)

one problem with those tiny ball bearings, they bounce really well if they hit the floor and they have a habit of hiding really well.