Work continued on the VFR750 – the brake calipers being the next to receive attention. They had been removed and tied up with a bungee – usually a sign that they have been binding which makes the bike very hard to push around. I undid the unions and took them over to the bench so I could have a proper look – it wasn’t good.
It quickly became obvious that somebody had tried to save a few quid by doing a rebuild job themselves – which is fine if you have the correct tools and know how to use them. If, however all your tool kit comprises of is 14 hammers in various sizes, a pair of mole grips, some gaffer tape and a tin of WD40 you really are best leaving potentially life saving brakes well alone.
Somebody had tried and failed with these and three out of four of the pistons had suffered deep score marks from the serrated jaws of a pair of mole grips. It is really important to understand that when you fit nice new brake pads the pistons will have to be retracted right back in to the caliper body. Any scoring on the outer 1/3 of the piston length will be right where the seals are and they will leak. The leaking fluid can get on your pads and really balls your otherwise splendid day right up.
If a score is big enough to feel with your nail it’s big enough to leak – the seals will not take up major deformation either, which you can get from mole grips.
The only tool to use for the job is a proper expanding removal tool, they are not expensive to buy, cheap ones can be had for less than an hour’s labour at a decent bike shop. They won’t last a lifetime but they will get the job done if used correctly. Always be sure to use the largest collet that will fit in your piston, if you use one that is too small you will probably break it by trying to expand it too far. I did exactly that with the largest one in my set – I should have used thin shims to make up the difference but I was too lazy and I paid the price. Prick.
Anyway here is the tool in use. I like to hold the tool in the vice so I can twist the caliper while applying gentle pressure to pull it off the piston, it usually works pretty well although the lever on the tommy bar is way too short on these cheap jobs and a ring spanner is required to get it really tight. If you do need to twist the caliper always do it in the opposite direction to the tommy bar screw otherwise you will just loosen it off and get nowhere fast.
If the caliper is totally siezed – they often are – you may need to apply gentle heat to soften up the rubber seals and make them pliable – don’t overdo it, there are other rubber components that you don’t want to damage, just focus some heat on the bore you are working on at the time and try again. It will come out eventually but thy can be a total sod, the grooves that the seals fit in become corroded and expand making the seals far tighter than they should be.
I have ordered new pistons – they are really expensive when you need 4 of them, I only needed 3 as fortunately Mr Molegrip only had enough energy to shag up 3 of them. Probably had sore knuckles from where they were dragging on the floor.
While I await delivery of the pistons I decided to get the rear caliper off to see if that is any better. Fortunately Mr Neanderthal hadn’t got around to “fixing” that one and it was in very good condition, the seals were good, nearly new pads too. All I had to so was bleed it and it’s good to go. Bleeding can sometimes be really easy or really hard, this one was ridiculously easy, it just bled straight through without any faff or stress. Only problem is the rear brake switch is missing it’s bracket so I can’t quite finish the job. I don’t have one, I could make one but it’s a lot of hassle. I found one for sale on line for a tenner so I just ordered it and will fit it when it gets here. I was going to do an oil change but I am about 1 litre short of oil so I will have to order some of that as well!! It’s really not going according to plan today. I suppose I should do some of the electrics on the chopper instead or any one of the 150 other jobs I should be doing. I probably won’t though 🙂
Article provided by David Powell of Boston Bike Bits.