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TR2/3/3A TR3A Disk Brake Rebuilding

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rlandrum

rlandrum

Jedi Trainee
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I've purchased all new internals (piston and rubber) for my TR3A brake calipurs.

Using the carb cleaner and blowtorch method, I got the pistons out of the old calipurs.

Then we painted the calipurs. Now I'm reassembling, and I'm having some trouble getting the new pistons in...

Here's the trouble: I can't seem to get the rubber boot to stay in the notch cut in the calipur. Once I do get it into the notch, and I start to slide the piston in, it stops about 1/4 inch in (on the inner o-ring, perhaps), and refuses to go any further.

I hesitate to fab up some sort of special tool to fit into my press just to re-install the pistons. Mainly, I don't want to risk gouging the new pistons, or tearing the new o-ring, or worse, destroying the calipur.

Anyone ever done this rebuild before? Any suggestions?

Thanks,

Rob
 
Rob: Either a compatable (Girling) grease or some brake fluid (which will make a mess of your paint job) on the O-ring seal and the boot I.D. before you introduce the piston. You can slime the piston O.D. with a film of fluid too. This can be nerve wracking on the first go, so be patient and persevere!
 
I'll see if the local parts store has some red grease and try that.

I tried it the other night with a thin film of brake fluid. It didn't want to budge. Maybe I'll let the o-ring soak in the fluid while I clean paint off my trunion...
 
meh. A challenge, fer sure. A set of pliers are made with a tapered, "scalloped" set of jaws which open as the handles are squeezed to facilitate rotating the "puck" as you apply pressure into the bore. A "spreader" type jaw. NAPA may have such a tool. Inquire.
 
I have never had the problem you describe -- for me the tricky bit is always getting the boot over the piston whilst keeping the other end of the boot in its groove.

To get past that point I use a combination of low pressure compressed air and a small hook tool made out of 12 ga solid Cu wire. Once it has the boot around it everything just slides home.

Are you sure the boot is staying in the groove as you push the piston in? You might try inserting the piston w/o the boot just to see if you can tell what is happening in there.
 
Where did you buy your parts? If from VB, do not use Dot 5.
My slave cylinder lasted only 2 months with that combination. Also, my friend, with me as a witness, came within inches of becoming intimate with a Bugeye in his nicely restored AH 100.
We would have been safer had we been drunk.
 
They way we do it at work is to put the boot over the piston first. Then take the piston with the boot attached hanging down below the bottom of the piston. Then wiggle the lip of the boot into the groove of the caliper. Push the piston home.

Also, make sure that the groove for the boot lip is REALLY CLEAN. Any rust or debris in there will not allow the boot lip to seat properly.
 
Update on the brake rebuild. The trick was a combination of greased parts and steady pressure. After my son cleaned the cylinders and got the grunge and scale out of the grooves, I lightly greased the o-ring which went into place easily. I also lightly greased the boot rubber and fitted it into the thin groove in the top of the cylinder. I then carefully placed the lightly greased piston into the center of the boot rubber and used the hook tool to flip the inside edge of the boot rubber upwards so it would slide up the outside of the piston as the piston was pressed into the cylinder. Now, what to use to apply the pressure. After thinking a bit I grabbed a large woodworking C-clamp. After padding the clamp pressure points with some folded paper towels ( to protect the piston and also the shiny new caliper paint) I slowly tightened the clamp. I noticed that the clamp would tighten down and then after waiting 10 seconds, I could give it another turn or so. It became apparent that it took slow pressure to insert the piston. I had to move the head of the C-clamp from side to side on one piston, but they all went in nicely, After seating the piston properly, the boot rubber pretty much just inserted itself into the groove in the top of the piston and I used the hook tool to tuck it in the odd place or two. Once we got the hang of it, it took 5-10 minutes per cylinder.
 
Whatever my son had on the bench - some kind of generic red semi-transparent grease, I think. I used very little - a teensy dab on my fingertip - just enough to put a shine on the surface of the seal and piston so it wasn't totally metal to metal or rubber to metal. It really helped put the rubber in place and let it slide against the piston as it was inserted.
 
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