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Power steering rack piston seal material

Power steering rack piston seal material

Power steering rack piston seal material

I hope this section is most suitable for this,

I am redesigning extremely rare rack internals into a new case/housing. The old case broke due to it being a prototype(marked as from factory) which had been I guess taken from the normal line, and brought into the factory workshop for some adjustments. It has been altered to fit a rally/race edition of the road car which has left it with some undesirable square shoulders which is where it fractured. Unbelievably they had also the rack turned down to a cylinder bore wall thickness of just 1.7mm under the mounting U clamps.(gravity sand cast aluminium)

The problem I have is that the main piston seal has been slightly scuffed while sliding past the fracture line.

Since this rack - made by TRW has no markings, bar a metal plate inscribed 'prototype' I am lost as to locating a new seal.

The seal is of the common rack piston design layout whereby it sits in a groove in the narrow piston and is internally supported by an o-ring.

The seal is of course round, and 2mm x 2mm in cross-section(square).
The metal piston is 40.6mm in o/a diameter, running in a 41mm bore.
The old piston seal resembles very dense cardboard, Im guessing this is graphite filled ptfe?

What materials spring to mind that I could perhaps make a new seal from?

I have done some searching on here, and ptfe/teflon comes up a bit, but there are a few 'againsts' also.

Obviously, something available off the shelf would be good, in bar or sheet form.

Perhaps this is a standard seal size? Any rack rebuild kits dont state sizes, just seal p/ns.

I have found the pdf below, concerning a rack redesign(no great detail) but they do mention this seal to be teflon.

What seal do you guys think I should go with? And remember, I need to be able to 'stretch' it onto the piston, and down into groove.

Many thanks,


RE: Power steering rack piston seal material

What's so special about this particular gear? If you are just changing the valve to a different profile, stuff a new gear and a special valve in there. Or, go with a different brand. ZF or others can provide swappable gears for most applications.

If all else fails, call up TRW and ask for a replacement part. They are at 34201 Van Dyke Ave.
P.O. Box 8008
Sterling Heights, MI 48311

A few phone numbers are for a Chief Engineer ('Craig') 810-977-1394 and a Product Engineer ('Michael') 810-977-1339.

Just beg for a replacement part given the seal dimensions or ask for an all new gear with your mount locations, ball to ball dimensions, 'C' Factor with the blah-blah valve profile, variable or fixed ratio rack and what rack preload thrust spring rate you want in there. (although you might want to be using the valve and 't' bar assembly already in your hands). My guess is that it's out of date or out of fashion anyways....

RE: Power steering rack piston seal material

As mentioned, the rack and internals are one off prototypes.

Wasn't/Isnt my job to locate a new rack/parts, owner(s) went down that route, and failed contacting many vendors worldwide. Some parts do exist Im told, but would require further machining, and a lot of case machining.

Owner wants to retain 'hard parts' but rehouse, which is where Im at.

If a 2mm x 2mm x 41mm seal size rings any bells with anyone, or what I could possibly make a new seal from let me know,



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