Callipers overhaul problems.

[Mickg99]

Hi, hope you can help me. I am trying to overhaul the rear brake calliper on a 1997 vmax and am replacing one of the pistons In the calliper but I cannot get the new piston seated with the new seals in place. It fits snugly without the seals but won’t fit with the seals in place. Can anyone offer advice on what I am doing wrong? Old piston never recessed properly and so caused uneven wear on the pads, hence the need to overhaul the calliper. Using the Haynes manual for instructions. Thanks.

 

[Fire-medic]

Are you lubricating the square o-ring and the bore, & the piston with brake fluid before assembly? You're using new o-rings, yes?

 

[TK3333]

Recheck your part #'s and are you sure its a stock caliper? Mike the 2 pistons both ways. Got the 2 different o-rings in the right slots?
I used a little of the rubber grease that came with the o-rings. I thought thats what its was for. Pistons slid right in.

 

[Mickg99]

Thanks Guys, yes lubed both seal and dust cover with brake fluid, also new piston but still doesn’t fit in. Did you split the calliper to fit yours in? I haven’t as the Haynes manual says not to but you tube shows most repairs done with callipers split.
All original parts, I think. I bought the bike in Alexandria, VA in 2004 but had to get the rear rotor replaced in 2005 as it was worn out. So thinking now this has been a long term problem that I didn’t spot. New Piston was off eBay and fitted well without the seals. Old seals were corroded so maybe the new ones are not sitting correctly so I will clean the calliper again and refit the seals and try again to seat the piston.

 

[Wirenut]

I rebuilt mine a couple years ago. Didn’t have any issues. I did split the caliper and unfortunately the gasket in between the halves did not come with the rebuild kit. And I lost one of them during the disassembly so I went to the local rubber gasket maker place and they cut me some new ones. You might be able to reuse them anyways.

 

[TK3333]

I did split the caliper and reused the 2 o-rings with no problem. The factory repair manual also said never take it apart. Too late.

 

[Mickg99]

Thanks again, I think I will split it as it is too difficult to work on when it is in one piece. Wemoto sell the gaskets so that will help.

 

[82ndCowboy]

I would take a caliper (measuring ruler, not brake component). Measure the diameter of the pistons and the channels for the o rings and compare them to the original.
The problem with Ebay these days is there are billions of counterfeit parts made cheaply in China being sold as name brand parts.

 

[user 16790]

have you removed all traces of hardened brake fluid from the seal grooves, if any is left in there it could make the seals too tight against the piston

 

[02GF74]

+1 what JT says.
then check both seals are the same and then measure up the piston to see if the one that does not fit is the same as the other.

also worth trying to swap the pistons over to see how they fit; either:
1. the problem stays on the same side = something wrong with that 1/2 of the calliper
2. moves to other side = bad piston.
3. both fit = result
4. non fit = WTF?

note that you can hold one piston in place with a cable tie and use compressed air to pop the other one out.

 

[one2dmax]

Likely you have something holding the seals out. Check and reclean the gives that they seat in.

 

[Mickg99]

Took the seals out yesterday as advised and cleaned the recesses again, then reseated them. Put the original Yamaha piston back in and after a bit of fiddling around it went in and was flush with the calliper. Used two cable ties on it aa 02gf74 suggested and then used the brake hydraulic system To try and dislodge the other piston. Didn’t work, the piston I had recessed came out and the opposite one didn’t move so both stuck out again and not moving at all. Think my next step is to separate the calliper and work on one side at a time to see there is a problem with the piston or calliper shapes/ structures as advised. Friend has good workshop so going to visit him.

 

[Fire-medic]

Hook a grease gun to the bleeder & I guarantee it will come out. You probably need more than nylon tie wraps to hold the one that moves. I use 2 C clamps & the brake pads to sandwich the ok caliper piston to keep it from moving. I've never had a caliper defeat the grease gun method.

 

[Mickg99]

Thanks for your advice, I’ll try that and I wanted to say thanks to everyone who has responded to my post, it is sage wisdom and much appreciated.

 

[TK3333]

This goes without saying but am gonna say it anyway. Wear safety glasses. Grease guns can produce alot of pressure and you dont want projectile grease in the eyes. Mine werent seized and still came out with velocity using air and trying to go EASY.

 

[Patrick Byrne]

I have struggled with this same caliper problem. When I found my rear brake pad completely worn on the inside I realized I had a stuck caliper. First I tried to loosen it with no luck. Decided to split the caliper and was able to release the stuck caliper with a grease gun. Orings and pistons looked ok, so I thoroughly cleaned the caliper and re assembled. I noticed during reassembly that the pistons were not sliding smoothly at all in the caliper so figured the problem was not solved. I gave it a shot and the rear rotor was substantially heating up during braking again because the pistons were not moving freely. I ordered a new set of pistons and seals and tried again..... Thoroughly cleaned the calipers of any residue using a brass brush etc.. Put in the new piston and seals and although they moved better in the caliper body, they were not nearly as smooth / free moving as I was hoping. I re assembled anyway and bled the system again and the problem remains. Maybe to a lesser extent, but the rear rotor still gets hot, especially compared to the front rotors which just gets slightly warm. any suggestions folks?

 

[02GF74]

have you checked the run out of the disc - side to side wobble when turning the wheel?

also check the rear brake has some free play, the piston insidethe master cylinder shouldbe able to retract fully.

 

[Fire-medic]

Assuming that the rear master cyl. is operating properly, and that the rear brake line isn't collapsing internally:
Either turn the pistons or hone the caliper. Sounds like you don't need-much. No, I've never had to do that to one of my bikes, but I did have an aftermarket set of pads I had to 'introduce' to my belt sander, to remove a bit of material so that the rotor wouldn't drag, it also was the rear on a VMax. The pistons were fully-retracted, and the caliper was too-tight to the pads.

I have had collapsed lines before, on bikes, cars, and trucks.

 

[user 16790]

the solidified brake fluid in the seal grooves can be hard to see and remove, many times I have found this to be the problem with pistons that don't move smoothly by finger pressure,
I clean the grooves out with a small allen key that I have ground the short part of into a tapered chisel, with this you can slide it around the seal groove without gouging it

 

[Fire-medic]

Using a Dremel tool or equivalent and a brass disc-shaped 1-1/2" wire wheel brush is how I remove debris and accretions of brake fluid, a spritz of brake cleaner or carb cleaner before (to soften deposits) & after (to rinse-away any of what the brass bristle brush dislodges), has worked-well on even decades-old nasty dried-out, seized caliper/piston assemblies. I also like a bicarbonate of soda blaster to remove deposits in the master cylinders. I only do that during a removal of the master cyl. from use, where it gets thoroughly disassembled, cleaned/rinsed, and rebuilt to be returned to service.

Be-sure to use eye protection as the Harbor Freight wire brushes are gonna make you look like a porcupine as the bristles shed during use. This is a good time to use a shop apron.