Caliper rebuild tips please.

[Simon Davey]

8 minutes ago, jedibiker said:

Just for reference, I had the one way valve thing and didnt like it. I tried the way i did the car which is the 1 man bleed system, tube, bottle and tie wrap. Put some fluid in the bottle covering the bottle so the pip can sit in it no air.

drill hole in the cap for the pipe and a tiny breather hole.

attach pipe to nipple and secure with tie wrap. fill resevoir and undo nipple and pump brakes, when fluid low, lock off nipple with brake down, refill, open and pump til no air, works great.

 

I think the 1 way valve I had was cheap crap as needed to much pressure.

 

I agree, the one way valve is useless. 

I must have done something wrong. 

I've ridden the bike, the brakes work very well, but I don't get max pressure until the lever gets 1/2 inch from the grip. 

I've tried the vacuum pump, had a great vacuum which pulled air through. 

I've tried pumping the lever until it's hard, then used a cable tie to pull the lever back to the grip over night, this gave my great pressure, but within 15 minutes, the pressure had gone. 

I've put a whole litre of fluid through. 

Next is the reverse bleed. 

Edited May 19 by Simon Davey

[jedibiker]

12 minutes ago, Simon Davey said:

 

I agree, the one way valve is useless. 

I must have done something wrong. 

I've ridden the bike, the brakes work very well, but I don't get max pressure until the lever gets 1/2 inch from the grip. 

I've tried the vacuum pump, had a great vacuum which pulled air through. 

I've tried pumping the lever until it's hard, then used a cable tie to pull the lever back to the grip over night, this gave my great pressure, but within 15 minutes, the pressure had gone. 

I've put a whole litre of fluid through. 

Next is the reverse bleed. 

Does yours have a bleed nipple on the lever to? near the master cylinder? seems odd its take so long to bleed but I had one once where it took ages, and i think i used to much red rubber grease, only use brake fluid now to rebuild as per haynes.

[Simon Davey]

No bleed nipple, but I did open the master cylinder banjo to let a little through. 

It turns out I do actually have a local workshop in Haverhill, I had no Idea there was one so close, until I just had a bike chat with a guy at Sainsbury's. 

I'm going to get it in there, I think my front wheel bearing has gone, there's an awful non-engine noise. 

[Fozzie]

Is it getting to a good pressure, and then losing it over time? That sounds like a leak. Just to double check you got your banjos snug (about 25nm is usually all they take), and have a copper washer either side of the banjo fitting (Bolt-Washer-Banjo-Washer)? I've dropped the lower washer without noticing in the past. If it stays spongey the whole time, with a long travel on the lever, then it sounds like air in the system. 

Clean the whole assembly down with brake cleaner, and dry it off, inspect for leaks and then pump the brake lever a dozen times. Leave it and then come back an hour later to look for any wet points where the brake fluid might be escaping to check for leaks/air getting into the system.

 

Another tip is if there's no leaks, leave the brake reservoir cap off, with the brake level tied on. Leave it for several hours. As the reservoir is the highest point, trapped air bubbles through the open valve. I often give the calipers several taps with a hammer, and move the brake lines about to encourage any air bubbles to rise up to the reservoir. 

 

I did my brakes on the SV this weekend, and it took 250ml of brake fluid front and back to be fully bled through. I used a one way valve with the pipe fed into a glass jar. They generally work ok with a method of 4-5 pumps of the lever and holding on the last pull, crack the bleed nipple for 1 second, close nipple, release the lever, repeat. I have a vacuum tool but it's shoddy ebay quality. You have to spend some money to get something good, the best being compressor driven.

[Simon Davey]

29 minutes ago, Fozzie said:

Is it getting to a good pressure, and then losing it over time? That sounds like a leak. Just to double check you got your banjos snug (about 25nm is usually all they take), and have a copper washer either side of the banjo fitting (Bolt-Washer-Banjo-Washer)? I've dropped the lower washer without noticing in the past. If it stays spongey the whole time, with a long travel on the lever, then it sounds like air in the system. 

Clean the whole assembly down with brake cleaner, and dry it off, inspect for leaks and then pump the brake lever a dozen times. Leave it and then come back an hour later to look for any wet points where the brake fluid might be escaping to check for leaks/air getting into the system.

 

Another tip is if there's no leaks, leave the brake reservoir cap off, with the brake level tied on. Leave it for several hours. As the reservoir is the highest point, trapped air bubbles through the open valve. I often give the calipers several taps with a hammer, and move the brake lines about to encourage any air bubbles to rise up to the reservoir. 

 

I did my brakes on the SV this weekend, and it took 250ml of brake fluid front and back to be fully bled through. I used a one way valve with the pipe fed into a glass jar. They generally work ok with a method of 4-5 pumps of the lever and holding on the last pull, crack the bleed nipple for 1 second, close nipple, release the lever, repeat. I have a vacuum tool but it's shoddy ebay quality. You have to spend some money to get something good, the best being compressor driven.

 

Cheers @Fozzie

Yes, tried all the above, I'm not actually losing fluid, although it would be difficult to tell as it would be a tiny amount. 

Reason for the caliper rebuild was poor braking, and having to top up twice in 400 miles. 

I've tried the cable tie trick a few times, it works well, but the pressure ebbs away quite quickly. 

I'm going to pull the calipers off to check for leaks around the piston seals, as all the banjos are dry, but I'll leave the brake lines conected. Whilst doing that, I'm going wind the calipers back and open the bleed valve, as there could be air trapped behind the pistons. 

Thanks for the help. 

Edited May 20 by Simon Davey

[Fozzie]

It's a sealed system, so it sounds like it's getting out somewhere, but very slowly. 

A torn main seal letting small amounts of fluid by could possibly be obscured by a good dust seal, so you wouldn't see an obvious leak. The pistons get hot with use, which combined with the air flow at speed, might be enough to boil off any that builds up and gets by the dust seal. 

[Simon Davey]

1 hour ago, Fozzie said:

It's a sealed system, so it sounds like it's getting out somewhere, but very slowly. 

A torn main seal letting small amounts of fluid by could possibly be obscured by a good dust seal, so you wouldn't see an obvious leak. The pistons get hot with use, which combined with the air flow at speed, might be enough to boil off any that builds up and gets by the dust seal. 

 

Although a leak does seem obvious, when I pump the brakes, then cable tie the lever over night, it doesn't lose pressure, which it would if there were a leak.

Before I do anything drastic, I'm going to clamp the opposite line to one that I'm bleeding.

Both lines come from a "T" above the mudguard, so clamping one may help.

I know you can buy the plastic clamps that don't damage the hose, but a chap showed me that you could put two small socket on a pair of mole grips so it clamps, but very kindly.