Brake Piston Problem 4L0

[webbo]

Hi, I have a problem with my front calipers. I have a very early 4L0 using FA64 pads on the front brakes. I have compleatly rebuilt the calipers but cannot get the calipers over the discs. I think it's because the pistons are too long. They are all the way in but still stick out of the caliper body by 4mm. I'm hoping that someone has calipers off there bike and can measure the amount the pistons stick out when fully home so I can get the pistons I have turned down. I cannot compare them to the old pistons as I damaged them taking them out and stupidly binned 'em Bit of a difficult problem to explain but photos should show what I mean! Cheers.

[bare]

how big is the problem interference betwixt pads and disc?
If not too large it would be simple to rub your pads on a sheet of 80 grit sandpaper until they are thin enough to fit in.

[webbo]

Did think of that, If I took 2mm off each pad it would probably fit, but it would be nice to get the pistons right. Cheers.

[marsbar350]

can you get the pistons out?
if you can measure the chamber and you piston to make sure theres nothing stopping them going right back

[flames]

hi dude,ive got the later brakes on mine,but as far as i know they have the same pistons.they r stripped bare at mo so no resistance whatsoever,i get 2mm of piston showing @ the bottom of the pad,and about 1mm at the top.are you sure your pistons r all the way in and havent 'rocked' or are both calipers the same.if you do strip them down,before you cut the piston,mine measures 36.5mm. HTH.

[flames]

btw even without seals or fluid in the calipers,the pistons are still an arse to get all the way in.

[bare]

Apr 6, 2012 19:56:45 GMT 1 webbo said:

Did think of that, If I took 2mm off each pad it would probably fit, but it would be nice to get the pistons right. Cheers.

Fair chance that the real problem stems form the oddball pads rather than the caliper pistons.

[robin]

I had a set of early and later 4L0 calipers, piston against piston I think one piston IS slightly longer than the other, but cant remember which is which (sorry), I would worry a bit if piston is such a tight fit without seals?

Hope that helps

Robin

[pepsisteve]

most caliper pistons i have seen usualy go in to just above flush with thte caliper body.

[webbo]

Thanks for the replys. I have removed the pistons and there is no obstructions and both pistons are all the way in. They both stick out the same amount so I'm sure they are just too long. As stated by robin they fitted a different piston to the very early models. The parts are long discontinued by Yam so just trying to work out how much to get them turned by by! I reacon if I get 3 mm taken off then that would give me approx 1mm protruding from the body. Any thoughts??
Cheers.

[oldelsieboy]

Apr 9, 2012 12:03:18 GMT 1 webbo said:

Thanks for the replys. I have removed the pistons and there is no obstructions and both pistons are all the way in. They both stick out the same amount so I'm sure they are just too long. As stated by robin they fitted a different piston to the very early models. The parts are long discontinued by Yam so just trying to work out how much to get them turned by by! I reacon if I get 3 mm taken off then that would give me approx 1mm protruding from the body. Any thoughts??
Cheers.

How do they compare to the dims I pm'ed you?

OEB

[webbo]

Hi OEB, The dims you sent are the same as the pistons I've been supplied. Cheers.

[robin]

From memory I turned off 2 - 3mm off of a pattern piston to match an genuine piston, I wrapped the piston with a couple of layers of Duck tape to stop the jaws of the lathe marking the finish. Even if you machined off enough to make it flush with the caliper face you would still have 3 -4 mm clear of the seal face, and with minimum thickness pads / disc it would never pop out of the cylinder.

[webbo]

Thanks Robin, I've got a local engineering company to take 3mm off so it should work!