front brake piston question

I have not been motivated to work on my wonderful 81 650 since I found out i will have to get a bonded title.Even though i have the original signed by the previous owner.Long story,not worth going into.Plus it has been 112 here, I have seen the temp at 101 at midnight. Now its cooling off, about 95.I had bought a new piston for the front brake.I had to use a grease gun to force the old one out.Then I screwed up once more and put the wrong size oil seal in the groove in the piston barrel.I bought a rebuild kit, the seal never would stay up in there.Yall told me it wasnt right, I persisted.Now I have the right one from chacal.Here is the problem.When I pump the brake lever the piston didnt move for awhile.But more fluid and the mightvac and it did. Having to add more fluid a couple times. So the caliper off, brake shoes off,fluid in the MC, pumped the lever many times.The piston has come out about a 1/2 inch.It probably is hanging up on the incorrectly sized oil seal I put in, its probably out of the groove.MY air compressor is 100 miles away.I dont want to do the grease thing again, thats a huge mess.Is there some way to grasp the piston and pull it out without damaging it? I really want to get this done and start riding it.First after its fixed i have to go to a town and stand in line about 3 hours to get a bonded title.I did that before.But then it will be mine. All input and guidance is appreciated.

 

I don’t think it would hang up on the seal. Does the brake lever feel really firm or soft? Unless it has air in it you should be able to push it out pumping the brakes. Perhaps you got some air in the system before you added fluid.

I don’t know about grabbing the cylinder with a vice grip—I’ve done it with an old car, but car parts are available and inexpensive. If you try that I would wrap it with something and go slow and easy.

 

it feels really soft.I have done brakes on cars, my only reference.On them you dont get good pedal till the system is properly bled.However with the caliper hanging in the breeze, no brake pads in it or mounted to the forks i wasnt sure if the lever resistance should be firm or not.The piston moved out about 1/2 inch.With the new pads installed and mounted to the forks I doubt the piston would ever move out that far.But I would think with no obstruction i.e. pads in the way, the piston should pump completely out or very close to it.

 

one more question, when do I start suspecting the master cylinder is part of the problem?

 

Right about now.............

 

I cheated. The last time I had to pop those pistons out, without a compressor at hand ... I just went to the nearest auto shop and they used their compressor, for a free cup of fancy overpriced coffee.

 

yep,len, mc rebuild kit next on the list.guess I will be starting a conversation.Soon I will have $100,000 in a $1000.00 bike.

 

Cruiser
Try this procedure, to bleed your caliper and remove the piston. Use a c-clamp to fully depress the piston back into the caliper bore, leave the c-clamp in place, holding the piston fully depressed into the bore. Re-bleed your caliper, when your lever is firm, remove the c-clamp. Pump the piston out of the caliper using your brake lever. The piston will just about drop out when it gets to the last seal. Watch the fluid level while doing this, add fluid as needed. Replace your caliper seals, polish the piston, lube piston and seals with break fluid. Re-install piston back into caliper, you will feel it go past the first seal and stop at the second seal, push the piston just a little ways past the second seal and then stop. Remove the bleeder fitting, and fill caliper with break fluid. Re-install bleeder fitting. Re-install break line, "again" use a c-clamp fully depress piston back into caliper bore, leave the c-clamp in place. bleed your caliper, until the lever is firm. Clean up your caliper, install your pads, re-attach caliper to the fork leg, pump your lever until firm, watch fluid level while doing this, add as needed. Good luck brother, riding season just around the corner for us.

Dan
Sugar Land Tx.

 

That is very helpful information.Thanks so much.I appreciate it.I know you are down near Houston.I figure about a month will be perfect weather.

 

If you can pull the piston out most of the way, it's probably the vacuum you've created that is not letting you pull it the rest of the way out. Open the bleeder screw. I have pulled them out using a spark plug boot puller. The jaws are rubber capped. I have also done it with regular pliers, but being very careful to grab only the lip of the piston. That only gets the dust seal around it, and the brake pad against it. Don't search or marr it anyway, but if you do a LITTLE, it's not going to be a problem.

 

thanks HF

 

I'm certainly not the expert but I just went through this entire process. in my view it's hard to beat the air compressor method of ejecting the piston, I'd find a compressor anywhere you can with a rubber nozzle tip. I put a paint stick with bunched up cloth to "catch" the piston because it can really pop - it only takes a few seconds to pop it. use as little pressure as you need to move it (no need for 120 psi)

...but it could be your MC or still too much air in the brake lines to build enough pressure to move it. I'd verify those two things first. pressure test the MC with a plug to see if you can build any pressure by pumping the lever. pretty simple test

 

Have one of these on hand, you just hold it tight to the caliper.