C5 X7 Steering Rack - Again!

[darbuck]

Thanks Jay, I am thinking on trying an annealed copper washer on the hydraulic pipes. I can't see how I could access thread in the housing with the rack in place if I was to tap it. I will just have to change seals and hope the copper does the trick. What do you think.

[MattBLancs]

If the pipes don't have any pin holes, then won't a new O-ring be sufficient?

Did I read on here of others using a slightly "fatter" section of O-ring to improve sealing ability?

[Jay-Bruce]

Thanks Jay, I am thinking on trying an annealed copper washer on the hydraulic pipes. I can't see how I could access thread in the housing with the rack in place if I was to tap it. I will just have to change seals and hope the copper does the trick. What do you think.

DONT DO IT!!!

Pinion housing is Aluminium, putting copper anywhere near anything aluminium results in a world of galvanically corrosive hurt.
I thought you knew better than that, having access to the ansys system? Anyways, here's a diagram showing how far apart Copper and Aluminium are on the galvanic table, and the further apart they are, the more they will interact with and eat each other.

In this case, the copper would be effectively eating the aluminium, as the washer would cause the aluminium pinion housing to do all sorts of self immolating reactions, sort of like this:

[darbuck]

Hi Jay, never checked it and assumed using copper like we do for injector seals in aluminium head was good practice. I appreciate you pulling me on this, I haven't had a chance to look at the Ansys and I seem to be forgetting useful information in place of other junk lately. It's very interesting to see that behaviour. So I would be better using a polymer/fibre washer if as Matt suggests a beefier o-ring doesn't work?

[darbuck]

If the pipes don't have any pin holes, then won't a new O-ring be sufficient?

Did I read on here of others using a slightly "fatter" section of O-ring to improve sealing ability?

Hi Matt, I am just concerned it won't hold because I think this is where the leak was coming from because it wasn't the shaft seal, but I changed out all the seals anyway.

[MattBLancs]

Ok, understand your thought process.

I would be tempted to back up the O-ring with RTV "gasket in a tube" sealant. A smear behind the O-ring and under the flange retained by the steel plate should help.

I agree with Jay on avoid another material into the mix. But also to add galvanic corrosion needs three things:
- Two disimilar metals (tick, have that already with aluminium and steel as standard)
- Electric connection between the two (tick, bolted together)
- exposure to the "electrolyte" (tick, water sprayed up from the road, effect enhanced by the salt chucked on the roads too)

However I am bringing this up as - injector seals don't have this issue as no electrolyte present. On a similar vein, thoroughly and liberally painting your nicely refreshed rack and all the pipework you can get at should not be overlooked in my opinion - keeps the electrolyte from the other two present items for galvanic corrosion to occur

[Dunkah]

Hi all, here we go again…….

I’ve finally got all the parts I need to refurb a rack and have modified the pinion housing to accept a boot.
Wondering now if anyone has ( or can tell me where to get ) a decent exploded view of the rack, particularly the pinion housing, just so I can be definitively sure that all the right parts are going in all the right places. Not too sure I want to trust looking at the one I currently have in the car as it’s a re manufactured unit and I’ve learnt at cost not to trust them.
Any help and advice greatly appreciated
Thanks all

[darbuck]

Hi Matt, I never considered it to be honest, copper grease seems to be the go to material to avoid galvanic corrosion aswell so never gave it much thought to be honest. In regards to RTV I did consider this but silicone reacts with hydraulic oil so would just make a mess and possibly cause damage if it got past the o-ring. Polyurethane would be a better idea here. Tiger seal is a brand of name for it, I am sure you are familiar with the material.I was reading up on copper and aluminium and found that large amounts of hydrogen are released when copper and aluminium react, looking at the picture Jay put up I think what we are seeing is hydrogen embrittlement rather than galvanic corrosion which would be worse because it would be right through the structure of the metal. A very interesting phenomenon all the same.

[MattBLancs]

I do know copper grease is a big no-no nowadays with stainless steel fabrications, there's a white grease used instead. I've bought myself a pot of "ceramic brake grease" (which is white and) also supposed to help in disimilar metal situations on braking systems = or at least their marketing drew me in and scored a sale from me on that basis!


There's RTV used on lots of engine sumps, does anyone wiser than me know if engine oil and hydraulic oils (or specifically LDS) are so different as to make this sealant ok with one fluid but not the other?

[MattBLancs]

This reads a lot like "buy my fancy grease" but an interesting article:
https://www.autotorque.news/the-afterma ... %20judder.

Pistonheads thread also seems to have garnered some experienced folks on a similar question:
https://www.pistonheads.com/gassing/top ... &t=1585308

[darbuck]

Interesting threads, basically copper grease is as I have suspected been accepted as good with lots of evidence to the contrary in my experience it's good on exhaust manifold bolts and the likes causes more problems on brakes than it solves. Stainless bolts I have seen fine in aluminium and seized and no obvious reasons for the difference in behaviour. So like those threads suggest in the words of Forrest gump "you never know what you are going to get" until you have tried it.

[myglaren]

I wonder if graphite would be useful in these applications. Graphite powder, not graphite grease.
Or Moly Grease (molybdenum disulphide).

[MattBLancs]

I wonder if graphite would be useful in these applications. Graphite powder, not graphite grease.
Or Moly Grease (molybdenum disulphide).

Sorry we are a little off (steering rack) topic but,

Moly grease is the CV joint grease I think, engineered not to thin out (reduce viscosity) with increasing temperature, so in theory could be a good candidate. I'd worry if there's an upper temperature at which the viscosity no longer plays ball - and whether brakes would likely be over that point??

But it's academic for me - I need to get using the tub of fancy ceramic grease, it's already likely to last me a couple of decades at current consumption!

Further off topic, but on the topics of "greases" and "consumption":
I've always thought a new pot of copper grease looks very much like some sort of exotic desert - not yet been tempted to taste yet!

[MattBLancs]

Interesting threads, basically copper grease is as I have suspected been accepted as good with lots of evidence to the contrary in my experience it's good on exhaust manifold bolts and the likes causes more problems on brakes than it solves. Stainless bolts I have seen fine in aluminium and seized and no obvious reasons for the difference in behaviour. So like those threads suggest in the words of Forrest gump "you never know what you are going to get" until you have tried it.

I agree, would slap copper grease on exhaust studs without a second thought. Recently undid a manifold that I'd have copper greased 30,000 miles ago and came apart without drama. Copper nuts there too, so warm fuzzy feeling about similar metal for a change there! I'm still chucking it on lots of steel fittings into aluminium component as force of habit. I think it does help there and most applications are likely away from continuous salt water spray.

It's weird about what will undo and what is seized solid - I normally revert to Sod's Law (i.e. the more pain it would cause, the less likely it'll come out cleanly!) which does generally play out correctly! Am learning to slow down a bit too - if something would pose a major pain if sheared then I'll wire brush, remember to add penetrating oil, back-forth-back-forth etc to try and recover it intact. And sometimes the less haste, more speed works....

[darbuck]

Yeah same here, patience pays off brute force and ignorance rarely if ever helps.As you say anything that can cause pain will there is a lot to be said for wire brush it will help Even the most stubborn bolts.a good lithium grease can make all the difference aswell. I wonder can you use marine grease as an antiseize