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1982 R100RT rear brake caliper master cylinder reassembly

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Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

OK! I've decided to return to my 1982 R100RT project bike that had suffered the $2000 dollar O-ring problem and I'm making good progress. On checking the rear caliper reservoir found it empty. Added fluid and pumped but got nothing in fluid flow. I removed the master cylinder and found the plunger frozen forward. A sharp rap dislodged it and the plunger spring returned. I figured I'd better check it out for pitting and found pitting to be quit minimal and looking pretty good after my cleaning and sanding job. So I've purchased a new rebuild kit from euromotoelectrics which consists of a new plunger and an external end seal that will need to be pressed into the master Cylinder's end. So my question is how should I accomplish this given one chance to do it right and no second chances! The kit furnishes a slightly over sized washer and a rubber gasket that proceeds it in the assembly process. I could use a long socket to push it in with a vise or a hammer, but I'm wondering if I should be using a special mandrel the keeps the washer from deforming or that deforms it in a specific way. I'm also wondering if such a tool exist through the club and is able to be loaned or rented. I reset the old piston with a hammer, turned my back to get something and heard a twang as the plungers spring pushed the seal out of the cylinder..... I never found it. Are you surprised?

 
Posted : 12/05/2018 00:00
Richard W
(@wobbly)
Posts: 2549
Member
 

I'd try pressing the washer into place with a "deepwell" socket squeezed in a bench vice. I don't think this fit is as tight as normal pressed-together parts.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 12/06/2018 18:20
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

Would a "deep well socket" have a thick wall like an impact socket? I was thinking if something could press it to form a concave bend to the washer it would perhaps have a better bite on the steel case...

 
Posted : 12/06/2018 20:07
Richard W
(@wobbly)
Posts: 2549
Member
 

The rear brake pedal and the actuating rod adjustment take ALL the piston return spring pressure once the m/c is installed in the bike. IMHO, the washer is simply there to hold everything together during the trip from the bench to the bike.

I must be missing something important. I don't remember having to take any extra steps like you describe when rebuilding my rear m/c. I do remember cursing a lot trying to get the m/c remounted and the linkage back in place !

I also remember the caliper needs to be removed from the bike and canted to a more appropriate physical position to get all the air to chase out. You'll find that job would be much simpler and quicker if one of the caliper mounting bolts was about 2mm shorter. You have my permission to shorten that bolt. πŸ˜†

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 12/08/2018 00:19
Lee Nyboer
 5499
(@5499)
Posts: 20
Eminent Member
Topic starter
 

I see what you mean about the bench to the bike. I'd removed the pedal, the pump and the linkage all in one unit because I knew I could not get my fingers in there and that's the way it's going back in. I'll shorten the bolt as well. Thanks for your help

 
Posted : 12/08/2018 01:03

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