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Tips
Tips

Rebuild front calipers on a BT7

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dvu101

Jedi Hopeful
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I have tried for hours spread out over the months since December to get the pistons out of my extra set of calipers. THe set in the car are dragging and sticking. I got one piston out of each side. I think (?) I searched past posts and did not see anything? I have tried all kinds of DW40 type products combined with about 80 to 100 PSI (that got the two pistons out) but the other two will not let go. Any ideas?


Thanks Scott
 
Hi Scott,
This tech tip was in the back of a Moss catalog. It worked pretty well for me. I used a thinner piece of metal though, only 1/8" thick. I did a couple things differently. I substituted a bolt that was a good length in the plug instead of cutting it. When the tool is in place, I put the caliper on the bench with the piston to be removed on the top. That way, you use your body weight to push the piston down and out of the caliper.
 
Seems to me that in the distant past I have used a grease gun to accomplish this task. Substitute a grease nipple for a bleeder valve on the caliper. The psi on the grease gun will be more than 100 psi. Just be sure to clean very thoroughly afterwards. Of course also make sure that the grease nipple is of the same thread as the bleed valve.
 
I tried the grease gun trick but could not find a grease fitting that fit. Any ideas?
 
You might try heating the body of the caliper with a propane torch. That might make the caliper body expand enough to release the piston.
 
Hello,

i have an additional idea to the proposal of Randy Gay.
Heat the caliperhousing and cool the piston down with ice spray in combination with grease pressure ( not compressible) Do you try to push the piston inward, with the big tool on your workdesk :wall:? (I don`t know the word of the tool) For first moving of the piston(only an idea)

Michel- who design anti skid systems
 
Hello,

it is spray out of a aerosol can( normally gas if that evaporate, gives cooling up to -52°C)
But it should be not burnable !! Because oft he heat of the caliper !

Bye Michel- who use in Germany a spray called - 75 Kältespray -
 
I've used a "thermal shock" to separate rusted pistons from calipers on several occasions. Heat the thing, I use a MAPP/Oxygen gas torch in the piston and body, then when good and hot drop it in a bucket of water. Works every time for me. But, if you do this you're committed since the cooling will suck water into the piston bore. But even calpiers handed back to me by a brake shop that could not get the pistones out came apart this way.
 
Here's the setup I use. From left to right:

1/2 of a 3/16" brake line and fitting with bubble flare
3/16" compression fitting to 1/4" NPT adapter coupling
1/4" X 1/4" NPT coupling
Hose on grease gun with 1/4" NPT male fitting.

The silver cylinder in the top of the photo is the adapter that has to be removed from the grease gun

This has never failed me. One hint: If you have synthetic grease in your gun, be prepared for a miserable clean-up job. Most solvents won't touch it.

Marv J
 

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For those of you with big sockets this modification to the Moss tech tip worked like a champ for me. Went to Ace Hardware with caliper half in hand to get the right size rubber stopper ($1.85). Drilled a hole in it and put a long carriage bolt up through it (a piece of all thread would work better but I already had the carriage bolt). Oh yea - i sprayed a little penetrating oil around the edge of the caliper before I left for the store. Compressed the rubber stopper inside the cup, put a large socket from a 3/4 inch set over top of the piston with the bolt coming up through drive hole. Washer on top of that and another nut and she fell right apart with a few turns. In fact, I had my 3 yr old little girl out helping (you can't start them out too young) and she was the one turning the wrench to pull the pieces apart. When the fell apart with a thud - she thought she had broken it and I got "Sorry Daddy" so it cost me another $2 in ice-cream to let her know I was really happy.

Sorry - I can't seem to add an image... just comes up as a link. Any help on this would be appreciated

Also - when re-assembling the calipers... other than the o-ring - should anything be put between the capliper halves?

Thanks for the help
 
When my calipers were playing up, my expert used compressed air to drive out the pistons, but they were not siezed up. I have heard that the grease gun method gives good results and I would have thought that drilling and tapping the piston may work with a bolt, depending on the meat in the piston head to give a good thread length, but if it is that bad, re-assemble and trade them in for re-built calipers off the shelf. Over here I guess that would increase the overall cost by around 100%, that is the down side.

Bob
 
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