[T3] Cleaning Up

[Craigs List]

Thanks for the info. That was what I was wondering.

Along those lines, how much to send my calipers over for a rebuild?

Adam
On Jun 24, 2015 9:25 PM, "Jim Adney" <jadney at vwtype3.org> wrote:

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