[T3] Cleaning Up

Jim Adney jadney at VWType3.org
Wed Jun 24 19:24:54 PDT 2015


On 24 Jun 2015 at 18:53, Craigs List wrote:

> What makes these calipers any different from modern calipers? Honest
> curiosity here. I had to rebuild a caliper from my 88 Beretta way back
> when. I've done them for my ex-wifes' 2001 F250. I think I might have even
> had to rebuild a caliper on an old Dodge Ramcharger I had.
> 
> Are these different because they were so early in the development of disc
> brakes? What is it about them that takes special tooling?

They have an axial pin in the caliper that is grabbed by a special 
mechanism in the piston, so that the pistons aren't as free to move 
as in "normal" calipers. The grab mechanism is sort of spring loaded 
so that it can slip when necessary, but most of the time, for small 
movements, it just deflects slightly rather than slipping.

I believe this mechanism is there to prevent hard turns from pushing 
the pistons back into the calipers, leaving the brakes requiring an 
extra pump or 2 before they are active. I SUSPECT this might have 
been necessary up to mid-'68, when VW made the stub axles thicker 
(and stiffer.) Mercedes doesn't do this, I don't think Opal and BMW 
ever did it, and Porsche only did it on the 914/4. I hear that some 
Toyotas also have these, but I'm not sure about that. 

The second thing is rust. Once the calipers seize up, the pistons 
take a LOT of force to push them out. I use hydraulic pressure to 
push them out and sometimes this takes over 1000 psi. I built a 
special hand pump to allow me to apply hydraulic pressure to force 
the pistons out. I hated doing this with air pressure, because they 
always came loose with a bang and possible damage to the parts. 
Hydraulic is gentle but persuasive.  

Third, there are 2 pistons, so the usual techniques only allow you to 
remove one piston at a time. I've made fixtures that allow me to 
remove one piston, plug that opening, then remove the other one. 
That's the only way that you're going to be able to get all your 
parts reliably clean before reassembly. Most modern calipers have 
just one piston in a floating caliper, or 2 pistons in a single bore. 
Both of those styles can be taken apart much easier than ours.

Finally there's the question of what do you do to slow down rust 
formation in the future. Choose the wrong lube and you'll be doing 
this all over again in 6 months with all new rubber parts. That's 
what happened to me on my first time, but that was in about 1971.

There's nothing I have that you couldn't duplicate if you wanted to 
invest the time and money. I didn't make all my fixtures at once. I 
made some and modified some and made new ones as problems arose. Not 
all my fixtures worked out well; there were several total failures. 
I've been lucky in that I have good access to lathes and mills, so I 
didn't have to pay a machine shop to make things for me, but that 
doesn't mean they were free. Some of the fixtures I have took me 3 
days in the shop to make. The only way I could justify doing all this 
was to commit to doing it for others as well as myself.

And with all that said, it's still a lot of work to overhaul a 
caliper. I should charge more.

And, I should add: If you have broken bleed valves, this is a lot 
more work and adds considerably to the price.  

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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