Brake Questions - 1995 90Q

Mike Arman armanmik at
Fri Oct 15 19:08:30 EDT 2004

>"Greville Bowles" <zaphod at>
>Subject: Brake Questions - 1995 90Q
>It seems that my rear disks have all but rusted away after 2 years and (I'm
>guessing) 40,000 km (24,000 mi). (They are Brembo that were slotted and
>cadmium coated.) Large chunks of rust fell off while removing the calipers.
>Obviously, the brakes are not functioning properly and I doubt that the pads
>were even making contact with the disks.

>  I had it in mind to ask the list about brake
>bias and whether or not it is possible to adjust it. I now have to replace
>the disks so I'm asking now.
>My questions:
>Can I adjust the front to rear bias in this braking system? If so, I'll need
>advice on how to do that. (The beauty of being a novice is that there is
>always lots to learn.)
>Can anyone suggest a possible cause for this malfunction? George & I will
>pull the wheels off again when the new rotors arrive. What should we be
>looking at besides the obvious (calipers seized)

Had this problem on my 86 5KS - rear brakes were just along for the ride.

Problem was a frozen proportioning valve, which on the 5K is just forward 
and inboard of the left rear wheel. It is an aluminum block with brake 
lines going in, and a spring loaded lever which presses on two small 
plungers under the lever. Mine was locked solid.

I found one in a you-pull-it junkyard for $2.00 (YMMV), installed it, bled 
the brakes and it worked perfectly - you check them by pressing on the two 
plungers, if they move, it means the proportioning valve is OK, if not, it 
is junk.

After I got my car fixed, I decided to open the bad proportioning valve to 
see what was inside. Despite many years of practice in taking things apart 
(and even putting some of them back together), a large selection of 
implements of mechanical destruction in English, metric and even Whitworth 
sizes, some LONG breaker bars, a 50 pound bench vise, some inventive 
profanity and finally the use of heat, even a lot of it, I absolutely 
couldn't get it apart or open, and for me, that's VERY unusual. It is still 
on the shelf, sitting there smugly, and I'm thinking about trying a 
tactical nuclear weapon next . . .

Best Regards,

Mike Arman

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