soft brakes

Post by **g_land** » Fri Feb 03, 2006 11:41 am

folks,

i spent 2 hours bleeding brakes last night to no avail. the pedal is still very soft on the first press, after pumping pressure does build up but its the first pump that really lets it down

at this stage i'm confident that there is no air in the system, we bled it about 3 times last night, including using a vacuum pump to make sure all the air was gone

does anyone have any pointers as to where to try next, BTW i have new BMC, new brake lines, new cylinders and shoes in all drums. its basically a full new system

thank for the help guys

George

Post by **rayofleamington** » Fri Feb 03, 2006 11:55 am

its basically a full new system

did you prime the cylinders at the rear?

Post by **g_land** » Fri Feb 03, 2006 12:17 pm

rayofleamington wrote: did you prime the cylinders at the rear?

i don't think so, what do you mean

Post by **paulk** » Fri Feb 03, 2006 12:31 pm

Also you can get an airlock in the brake light switch. Mine showed soft brakes and no lights but when I primed the switch I got the lights back.

Shame I've now stripped the M/C and found corrosion in the bore near the 2nd seal so I now need a new M/c any way. May as well change all the brake pipes while I'm at it

Post by **rayofleamington** » Fri Feb 03, 2006 3:10 pm

i don't think so, what do you mean

The rear bleed nipples only bleed the pipes - not the actual cylinder. If there's air in the cylinder it tends to stay there.

Post by **g_land** » Fri Feb 03, 2006 3:46 pm

ok how do i bleed or prime the cylinder

i take it this has to be done at the front too.

Post by **Willie** » Fri Feb 03, 2006 6:06 pm

Since you have new linings and,presumably, have not done many miles on them then the brakes will not have bedded in yet and will not feel as positive as they will. If you inspect the rubbing marks on the linings you will find that surprisingly little of the area is actually rubbing on the drum,a situation which will rapidly change.

The other possibility is that the linings are too far from the drums, it is useful to set them up so that they are slightly rubbing with the new linings so that they bed in more quickly.

Post by SR » Fri Feb 03, 2006 6:11 pm

wowah!!!!!! nice one willie

Post by **bmcecosse** » Fri Feb 03, 2006 8:21 pm

To get the last bit of air out the rear cylinders - slacken off the adjustment on the shoes (and the handbrake) and then bleed them - the cylinders will then be able to stroke out - and on the way back will expell the last of the air through the bleeders. If the brakes pump up hard at the second press it will be air. Keep going. Try the oumping up hard method - then your helper opens and closes the nipple briefly while you keep pressure on the pedal. That too will chase out the last of the air.

Post by **g_land** » Fri Feb 03, 2006 8:32 pm

bmc we did that method pump hard, hold and release air from pipes, there is no air in the pipes

we also used a vacuum pump to suck the air out of the pipes so i'm fairly confident there is no air in the pipes

the cylinders in another matter

willie - thanks for that, that could be it, i'll try adjucting them and bring her for a spin on monday

any other suggetsions welcome

George

Post by **rayofleamington** » Fri Feb 03, 2006 11:42 pm

For the rear cylinders, my preffered way is to unadjust the shoes, which allows the pistons to travel a bit - then just cycle then a dozen times to help flush any remaining air out. The T-piece needs to be upright to make sure any air coming out is trapped under the bleed screw.

However - I think Willie has probably made the most useful point - new brake shoes are well known for being a bad fit to the drums, therefore you can get a poor pedal until the shoes have worn to fit the drums snugly.
You can speed the 'bedding' process by overadjusting the brakes, but that gives brake drag and poor brakes in the short term (i.e. it's a comment not a recommendation ;-) )

Good luck

Post by **bmcecosse** » Sat Feb 04, 2006 4:53 pm

Or just left foot brake as you drive along - that way you can control when the brakes are on - and when they are not! But try not to overheat them - the nasty non-asbestos linings these days are easily damaged.

Post by **Onne** » Sat Feb 04, 2006 6:49 pm

nasty non asbestos at least aren't asbestos. Which helps if you don't change em yourselves...

Post by **mkwc** » Sun Feb 05, 2006 9:52 am

Get yourself three break line clamps ( if desperate use vise grips and soften the jaws with cardboard ).

Put a clamp on each of the rubber hoses two front one back, then push the brake peddle it should be solid if it isn't then there is air in the system.

Make sure that all of the wheels have the brakes adjusted normally.

If the master cyl is hard then remove the clamp from the rear hose, and check the peddle again, if the peddle is soft then there is air in the back line bleed the system again with the front clamps locked off.

When there is no more air in the back line replace the clamp on the rear hose and remove the offside front clamp and repeat the same procedure.
repeat the same for the right front.
This way you get a full master cylinder of fluid through the line that you are bleeding.

If this fails go around and adjust all the brakes so that they are locked on hard and repeat the process again but I don't think that it will be nesessary.

Regards Mark

Post by **bmcecosse** » Sun Feb 05, 2006 10:43 am

I really don't like clamping the flexi hoses - very easily damaged. Any I have ever done this to - have failed (ballooning) shortyly after.