Bleeding brakes

[r1ot]

May seem pretty elementry but I'm having a bit of bother.

On my kit car with dry lines I've started bleeding the brakes through, the master cylinder is a tandem type. I've been using an eazybleed as I'm working on my own. I pushed all the brake fluid through initially and got a steady flow on all four corners. Now I'm trying to get all the air out of the system. I'm bleeding from the n/s rear caliper as it is the furthest away from the master cylinder and then working on diagonals. There seems to be a lot of air in the rear braking circuit how long will it take to get all the air out and what is the best way to do it?

I've checked all the unions and they are all tight and not leaking. The front circuit is fine with all the air bubbles out. There is a T piece at the rear which is higher than the master cylinder reserviour but should that really make a difference?

[anonymous-user]

On my Tiger the rear brakes bled almost immediately, with new fluid through a dry system. It has a T-piece on top of the diff but I don't think it's higher than the master cylinder, although I can't see why that would make a difference anyway.

Is your master cylinder OK? My first one was not working correctly but it was obvious to see because it wouldn't allow fluid to flow and therefore the easi-bleed overloaded it and blew out brake fluid all over the chassis

I think the correct approach is to start at the corner farthest from the master cylinder and work towards the closest one - open the bleed nipple, bleed until no air comes out, then move on. Then I suppose to be sure go all round once more to make sure no more bubbles come out.

Edited by jimsupersix on Monday 19th March 20:23

[steve_d]

jimsupersix said:

....I think the correct approach is to start at the corner farthest from the master cylinder and work towards the closest one - open the bleed nipple, bleed until no air comes out, then move on.....

Agreed
Make sure you are not putting too much pressure into the easibleed. All this does is compress the bubbles making them smaller and harder to get out.

Steve

[GreenV8S]

Air bubbles will be very reluctant to go downhill so look at the geometry of the master cylinder, pipes and callipers etc and make sure you don't have any high spots that will retain air pockets.

[cnhss1]

now heres a trick that ive used for years after being told about it by a wise old sage. God knows how or why it works, but it does!
bleed the brakes until your happy you cant get them better, irrespective of how crap the pedal is. depress the brake pedal as hard as you can and then wedge bit of wood on pedal and back to the seat rail so the pedal is effectively jammed on. Leave overnight. when you remove it next morning for some reason the pedal will be either perfect or hell of a lot better! repeat the bleeding or the above method if necessary.
I know you'll not believe me, but hand on heart its worked for me many times when sytems have been stripped on road and race cars.

[grahambell]

r1ot said:

There is a T piece at the rear which is higher than the master cylinder reserviour but should that really make a difference?

Very possibly. Air bubbles have an obvious tendency to rise in liquids, and as GreenV8S has said, there can be problems trying to make them go 'downhill' - especially with steep gradients - so could well be that you're getting an air pocket at the high point.

Normal solution to this in pipe systems is to put high point vents it. For your brake system you could try 'venting' it by cracking open one of the T piece joints while someone presses the pedal and hopefully force any air out that way.

An alternative that can work on systems you can't seem to bleed by pumping the pedal is to suck the fluid through rather than pushing it. Obviously you need a vacuum pump to do this (you can get small hand operated jobs from Car Builder Solutions among others) but it can make all the difference because you're sucking the air through rather than compressing it.

Something else that can make a difference is to give the calipers a few whacks with a copper hammer or something to help dislodge air bubbles that sometimes latch onto rough surfaces rather than rising.

Good luck.

[350zwelgje]

Did you fill the master cylinder with brake fluid before installing it/connecting the brake pipes to it? It could be that the master retains air then, and traditional bleeding isn't curing it. Think that a previous post is linked to this: pushing the brake pedal down for a night could help the air from the master cylinder to escape to the reservoir perhaps, and that that is the reason why it works in some cases.

Also think that pumping the brake pedal, due to 'pulsation' is more effective to get air to the end of the brake lines/down hill then the constant 'action' by an easy bleed kit.

Rob

[r1ot]

I've been bleeding the furthest most caliper now and I'm still getting air bubbles although they are getting less and less. I tried unbolting the caliper (still in contact with the disc) and rotating it so that the bleed screw is higher that the inlet to encourage the last of the air out and still the braking effect is still poor. I'll try leaving the pedal pressed down overnight to see if that improves things. Failing that I'll have to see if I can borrow/scrounge/steal a vacuum bleeder from somewhere to bleed the brakes.

I was told to try to do a final bleed from the pedal itself not using the easybleed as this will bleed out the last of the air. I'll report back if there is any results

[r1ot]

Right, I tried putting a piece of wood on the pedal and wedging it down overnight and low and behold it has worked. The brakes are a hell of a lot better . I managed to get the last of the air out by removing the caliper from the car and holding the pistons back with a pair of wooden wedges and holding the bleed screw as high as possible as the last of the air popped out and then refitting them. Now the pedal feels a lot better.

The reason the car wouldn't slow down very well is a cock up on my part. The suspension settings at the front were too hard with almost no travel at all. So under hard braking the wheels were almost leaving the ground! Now with the suspension slackened off all round the car not only does it feel less nervous it does also stop as well. The car is going to the garage tomorrow to have the suspension set up properly and also make sure the tracking/camber is correct as well

[r1ot]

New update, getting the suspension set up but the brakes have thrown a new spanner in the mix. It turns out the rear calipers don't work or at least very poorly. Another ebay purchase down the swanny. The calipers I bought were "re conditioned" and nice and shiny but they fail to exert braking effect. A new set of calipers have been bought and will be fitted tomorrow.

Nice driving it down to Dastek never took it much above 50 but by christ it got there fast, world going backwards and all that..

[d-man]

cnhss1 said:

now heres a trick that ive used for years after being told about it by a wise old sage. God knows how or why it works, but it does!
bleed the brakes until your happy you cant get them better, irrespective of how crap the pedal is. depress the brake pedal as hard as you can and then wedge bit of wood on pedal and back to the seat rail so the pedal is effectively jammed on. Leave overnight. when you remove it next morning for some reason the pedal will be either perfect or hell of a lot better!

I was in exactly the same situation, kit car with a completely dry brake system and having no luck at all getting a decent pedal by bleeding using easy bleed / pedal pumping or anything else. Searched on here last night and found this thread, tried this and my brakes are absolutely sorted now Top tip, thanks