WICruiser

I am in process of rebuilding my calipers and am having trouble installing the piston with outter seal. The WSM says to install the seal over the piston then to install the seal into the groove in the caliper, but when I try this I can not get the seal into the groove. If I remove the seal from the piston I can install it into the groove in the caliper but then I can not get the seal over the piston.

Is there a trick to this installation or are my fat fingers just not nimble enough?


FYI this is a floating caliper, single piston type.

the flyin' scotsman

Clean everthing spotless with brake cleaner and lube the piston and seal well with fresh brake fluid.

I install the seal in the caliper then piston ensuring its square to the seal.

Landseer

A whiff of dielectric grease works too.

WallyP

Some brake rubber is specifically compounded for brake fluid - I would be hesitant to put anything other than brake fluid on it as a lubricant.

WICruiser

I can get the piston into the piston seal OK, it is the expansion seal that seals the piston and caliper from allowing dirt into the bore.

If I install the seal on to the piston as shown in the WSM, should the seal slip into the groove in the caliper as I install the piston? It almost reads like I need to get the seal into the groove in the caliper before the piston enters the bore but I can not seem to get the seal into place. If the chamfer on the entry to the caliper bore is designed to allow the seal to slide into place as the piston is being installed I may be just making it harder than it is.

My concern is getting the piston into the bore and the seal not going into place resulting in the seal being cut as I install the piston.

GlenL

It's all harder than it looks. The seal can get distorted and cut it if it gets caught on the piston. I always end up putting it together and then taking it apart to make sure it went right...then putting it together again.

It's the "boot" that's causing problems. I out the small end around the piston first and then the large end into the groove inside the piston bore. Then slide the piston in. After getting the piston mostly in slide the small end into the groove around the piston. That gives enough flexibility to get it all together.

WICruiser

Thanks Glenn

That is what I thought I needed to do, so I guess I need to figure out how to hold everything in place while I get the large end into the groove in the piston bore. Maybe I can support the piston in location with something that will free up my fingers to manipulate the seal into the groove.

Cortina

Been there too , only one thing worked for me !!

(plenty of b fluid as lube)

Put seal on piston - pull down as far as you can , so the seal is hanging in mid air (only just still on piston by a few mm) . Suspend piston well above bore (nice and square and steady) . Now work the seal lip into that groove ... only when it is fully home can you then gently get the pistion to engage the bore , and gently squeeze it home.

Not a 2 minute job .. I found that I could not get the rubber into the groove after the piston was in place ... I almost could ... but NOT !.
Make sure piston orientation is correct or very close before you start !!

good luck ... the 2nd one is easy after first !

WICruiser

Thanks for the detailed help.

Just to close this out I found that using a folded shop towel to support the piston in line with the bore allowed me to lay the caliper with the seal hanging on as described by Cortine into the bottom of the groove. then using both hands I (because I didn't need to hold the piston) I was able to guide the seal into the groove working from bottom to top on both sides until the top popped into place. Then proceed to push the piston into the bore.

As Glenn said I ended up pushing the piston into the bore and then using air pressure to move the piston back out and confirm that the seal was in place.