letting gravity bleed the brakes

[les]

In that case----we agree!

[xpress]

bmc, keep calm and carry oil! i have a short push on the brakes but they are positioned quite low. doesn't seem too bad to me though!

[lesrollins]

Well I have tried to bleed the brakes again today as I was to busy over the weekend.

First approach.
Handbrake fully slackened off, snail cams fully tightened so shoes are tight on the drums. Son pumps pedal keeps pressure on release bleed nipple, once pedal travel reaches floor tighten bleed nipple each brake was done at least six times. In the order N/S/R, O/S/R, N/S/F, O/S/F.

Second approach
As above but with snail cams fully slacked off so drum spins free.

Third approach
As above but with snail cams fully tightened then cams released by three clicks on each wheel.

Fresh brake fluid was used on all occasions whilst topping up the master cylinder anything going into the jar was not used to top up the master cylinder. The pedal adjustment onto the master cylinder as been adjusted and is fine.
As I have put in the previous thread all the following items are new master cylinder, all wheel cylinders, copper washers, brake pipes, all brake shoes, flexi hoses replaced with new braided ones, hand brake cables, dust covers.
Whilst bleeding the brakes the pedal pressure is good, but if you leave it for about an hour the pedal will travel straight to the floor, once the pedal is pumped the pressure is good again.When bleeding the brakes on this occasion there were some fine air bubbles but all was bled until there were no more air bubbles. All the wheels lock up when the brakes are applied, the car is on jacks all the way round so I went round trying to turn the wheels when the brakes were applied. There is no fluid loss anywhere on the system.
As anyone got any ideas would a pressure pump help to eliminate any air if its still in there. Just wondered if the rear wheel cylinders might still have air in them I thought I read that they can cause a problem because of the way the bleed nipple was situated. I will try any ideas tomorrow. Thanks

[MarkyB]

Were the fine air bubbles from every bleed nipple or just one?

I have a feeling that until the brakes get some actual use there is every chance that the shoes haven't got into the optimum positions.

A small plus point of discs is that this isn't an issue.

[xpress]

i agree, perhaps the brakes need a bit of use to bed in. i don't have any issue of pedal hitting the floor at any time, never have experienced this. to les; how about undoing the bleed nipples a little and leaving them overnight, to test out bmc's theory of bleeding air from the system/gravity?

[rayofleamington]

Whilst bleeding the brakes the pedal pressure is good, but if you leave it for about an hour the pedal will travel straight to the floor, once the pedal is pumped the pressure is good again.

Unfortunately I've come across this once and it turned out to be a faulty new master cylinder. However much they were bled there was always a some of air in the system. Myself and Cam bled the brakes TWICE each on that car but they remained pretty poor until 2 years later the m/c was replaced AGAIN! After that they were ok.

If your problem relates to air in the rear cylinders then after some use they should bleed out better as long as the banjo union to the bleed nipple is pointing upwards (this acts as an air trap)

[lesrollins]

Thanks for all the advice it just becomes a bit of a pain when you are almost there. I will need to change the direction of the rear bleed nipple as they are both facing the front so I will need to slacken the banjo off so they are facing up. If your m/c was faulty because it was loosing in air didn,t it allow fluid to escape.
After I spin the bleed nipples to the up postion and ensure there is no more air in the system I will stick the wheels on the car and take it for a small test drive. Another theory I read regarding air in the system was to put the front wheels on ramps and the rear wheels on the floor then bleed the two rear wheels then swap the ramps to the rear of the car and then bleed the front brakes, because the master cylinder would always be higher than the cylinders being bled.
The fine air bubbles were from the back cylinders.
Must remember to pump the brake once before I hit the car in front Gulp !

[xpress]

i think they will firm up once they've bed in unless something you've missed. good luck!

[bmcecosse]

I would be very sceptical of the new master cylinder....... Some Mini lads swear by jamming the brake pedal ON overnight with a long stick wedged into the seat or anything solid. Not ever used it myself - I just pass on the trick!

[MarkyB]

I've done it myself but rate it as a bit of a bodge.
I believe it forces the air into the fluid like CO2 into a fizzy drink, can't think of the right word at the moment.
It's said to lower the boiling point of the fluid but it hasn't given me a problem with my sedate driving style.

Common on bikes too, using strong elastic bands on the lever.

[bmcecosse]

Ahh - right - hadn't thought of it working like that - I just assumed it was maybe stretching out the master cylinder seals - something like that.

[kennatt]

on changing over to 8 inch I had a very similar problem and found that the secondhand snail cams were worn and alowing the shoes to drop out of adjustment,readjust and after a while needed to readjust(Pedal to the floor on first use)just might be your problem,try fully adjusting and then use brakes and see if you then have lost the adjustment,Honestly can't see that it is air because pumping the brake dosen't normally get rid of the problem of air ,if theres that much in then you wouldn't get much of a pedal at all and it would be soft and springy.

[xpress]

you would know if you had lost the adjustment though, right? ie, if you tested and the clicks were in the same place? how high should the pedal be before travel, and how high should the pedal be before braking action is observed? also, how low to the floor should you be able to press the pedal before full braking effect is experienced? also, how firm and heavy should the action be, as much as you can describe with words and similes?

[lesrollins]

Many thanks to all regarding the advice on the brakes, after following advice, nipples sticking up ( enough to hang you coat off them ) and letting gravity bleed the brakes they are now working perfect or as good as they should be. Thanks

[MarkyB]

Ahem, this is a family forum .
Great news about the brakes, I'll give that method a try next time.

[rayofleamington]

If your m/c was faulty because it was loosing in air didn,t it allow fluid to escape.

During bleeding it wasn't possible to know - we put so much fluid into the m/c that some was spilled (not being the type to use a funel + patience)
Afterwards the level wasn't dropping so it didn't appear to be leaking out, however to get air in the secondary seal must not have been working correctly so fluid out was a possibility. I did wonder if the seal had been put in the wrong way round!