[urq] UrQ brake booster/servo

[Renneisen, Eric 475]

Jim Furdyn wrote:
> You mentioned that you have a document that you 
> were working on about the differences between 
> the two brake boosters. May I have a copy of 
> that?

Sure, I'll send you a copy when I get home this evening.

> Also, I'll assume that the later P/N is the 
> aluminum booster (857 612 107 A) compared to the 
> earlier one (857 612 107). 

Careful here.  I don't see 857 612 107 in either the US or Euro versions
of the family album.  The later cars ('88+) have 859 612 107, but their
hydraulic system is completely different (similar to the non-turbo 20V
stuff).

As far as I can tell, the P/N didn't change when they went from Fe to
Al.  It's probably just a change the supplier (Ate) made without
changing functionality.  I suppose this means that you might find an Fe
booster on an early bimmer 7-series.  The one I got was from '84, I
think, and it's Al.

> My question is, are these two boosters interchangeable? 
> The reason I ask is I was offered your BMW replacement 
> and want to know what (if any) mods needed to be done 
> in order to make it work. You said that the rod that 
> goes to the brake pedal is shorter, can this be removed 
> and replaced with the correct one from the original 
> booster?

The Fe and Al boosters on the urq are definitely interchangeable.  When
the rebuild of my original Al went sour, I picked up an Fe unit (thanks
Dan!), rebuilt it, and it's on the car now.  I am 99.999% certain that
you can take the rod (with attached plunger) from your Fe booster and
use it in the E23 bimmer Al booster.  I have the Audi and bimmer Al
units apart on my bench right now, and everything but the rod length is
identical.  I have pictures of the innards of both Audi units
side-by-side, and I'm certain that the rod/plunger piece is the same.
There are other pieces that are slightly different, but that one should
be all you need to make it work.

Eric Renneisen
'93 S4
'86 urq
'85 urq
Chattanooga, TN


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