Brake bleeding

[Downton1960]

Hi

No never done a gravity bleed but happy to try as have the tubing, do you keep the master depressed by weighting the pedal?

Dave

[Downton1960]

Some progress, I forgot I had a vacuum testing tool by sealey which actually has a pot in the kit for brake bleeding

Had a quick go this evening and now have a pedal albeit more spongy than I would like but I have also found an issue, the new minispares Cooper S regulating valve has a tiny weep where the spring retaining nut screws in the valve housing, it has a copper washer as a seal which is very shiny so not annealed.

Anyone taken one of these apart before as looks dead simple and I will fix if so rather than wait for a replacement with endless email justifications to minispares?

Don’t think it was my real issue as changed this since the problem began but certainly not going to leave it no matter how minuscule the weep ( found with tissue when checking all the joints for the tenth time).

Dave

[Herbert]

deleted comment

[davidnutland]

I have been having problems with a new system on a Sebring Sprite I am building, brake pedal was very spongy and I could not get rid of the air in the back section, I was advised to buy a new pump oil can connect it to one side and a tube to a jar with some fluid on the other, then you just pump the fluid and air from one side until the air bubbles clear on the other. you can do the same front to back side to side etc.

[mk1]

Have you tried bypassing the servo yet? Still sounds like air in the servo to me.

[iain1967s]

I will make a servo bypass pipe up one evening this week as want to eliminate it being at fault.

Any details on this bypass pipe?

I want to pull the servo out of my Mk1 to refurbish it, but I don't want to keep the car off the road.

So I was wondering if there was an off-the-shelf flexi hose or pipe available with the correct female threads to take both of the flared brake pipe ends that usually go into the servo.

You know, something like "a Renault Dauphine A8 rear brake hose has the correct female couplings at both ends" (made-up example...)

Such a device would let me bypass the servo but keep the brakes working without boost assist...

[GraemeC]

If they could be straightened out, something like this would work:
https://www.compbrake.com/product/3-8-x ... e-fitting/

Or even a T-piece with one leg blocked off.

Easy enough to make something with a short length of brake pipe and a couple of female fittings though (if you have a flare tool)

[Herbert]

I had a great tip (from an F1 technician) on how to bleed the brakes (and this is what they did at Williams)
Use an easy bleed system, but do not fill it up with brake fluid.
1. Top your master cylinder
2. Get your spare wheel and take the pressure down to 15 psi. Plug the air bleed nozzle on the tyre valve.
3. From your farthest wheel, take out 100 cc of fluid.
4. Undo the easy bleed pipes from the tyre pressure and master cylinder

now do the next 3 corners and apply the same rule for each.
Do the "round" once more, hence a total of 800 cc would have passed thru the system, this way you've renewed all fluid from the system.

The reason your tyre pressure is low is so that the air bubbles in the system are not compressed and will flow.

Its worked every time.

Thanks Dave Gear !
Roland

and btw, it could be that the servo seals havnt been put back right.

[pdb]

When you are ready to work on the rear cylinders depress the pedal VERY slowly and gently. If you depress the pedal rapidly and with a lot of force you can/will shuttle the spool in the rear mounted proportioning valve. Once that shifts you cannot get fluid (or air) out of the rear brake lines.

I think the most common mistake when bleeding early Mini rear brakes is to pump pressure before opening the bleed screw

[woodypup59]

Ref the weepy regulator valve.

I'd try nipping it up with a large spanner.

Copper washers, even annealed, still need some welly to seal.

In case no-one has said, get the back of the car up as high as you can to ease the fluid pushing air out from where the tube goes over the rear s/frame. This is favourite place for an airlock / bubble.

[iain1967s]

I also need to bypass the servo but keep the brakes working without boost assist...

Easy enough to make something with a short length of brake pipe and a couple of female fittings though (if you have a flare tool)

Thanks. Wife bought me a flaring tool set for Xmas so I made a bypass.

ps. apologies for hijacking the thread

[timmy201]

I thought I’d add my query on here rather than starting a new thread.

New parts installed:
7.5” calipers (I put in new seals and pistons)
Front brake hoses
Rear spacer drums

Master and rear cylinders are the same as before and weren’t disturbed. Front calipers have been gravity bled

The issue:
First press of the pedal is soft till about halfway down, second press or after a pump it’s nice and firm from the top. The front left caliper has both pads loose in the caliper after sitting, they aren’t held against the disc like the right side (not sure if this is normal). (Edit)

My thoughts for what to do next:
2 person bleed
Remove pads and make sure pistons are pushing out properly and lubricate with brake fluid
Check rear drum adjustment
Any other ideas?

[greyghost]

sounds like one of your callipers is sticking the pad should be against the disc
id start there

[mk1]

What Greyghost says. A calliper having loose brake pads is VERY ODD!

[MiNiKiN]

What is "gravity bleeding"? I reckon I know what it might be and that it may well not work on a Mini brake system.

*suppose this is pushing and leaving applied the brake pedal or lever (on MCs) and leave overnight for air bubbles to seep upwards through pipes escaping via the master cylinder.

[bwaminispeed]

Gravity bleeding, is just opening a bleeder, and, waiting till the fluid starts to flow by by itself (gravity), no pumping necessary.....

Either one at a time, or, all 4 at a time....

Once the bubbles stop, close up the bleeders, and, your done......hopefully.....

I find, it usually works on most Mini's.......

[timmy201]

sounds like one of your callipers is sticking the pad should be against the disc
id start there

Thanks for that, it’s my first time dealing with discs, so I wasn’t sure how far back the pistons were supposed to go. The right side keeps a little pressure on the pads, but the wheel spins by hand. The left ones rattle when I poke them

What Greyghost says. A calliper having loose brake pads is VERY ODD!

Thanks Mark. Good to know it’s not normal

What is "gravity bleeding"? I reckon I know what it might be and that it may well not work on a Mini brake system.

*suppose this is pushing and leaving applied the brake pedal or lever (on MCs) and leave overnight for air bubbles to seep upwards through pipes escaping via the master cylinder.

As mentioned above it’s just opening the bleeder (with a clear hose attached) and waiting for clear fluid to come through. I didn’t have a helper to press on the pedal at the time

Gravity bleeding, is just opening a bleeder, and, waiting till the fluid starts to flow by by itself (gravity), no pumping necessary.....

Either one at a time, or, all 4 at a time....

Once the bubbles stop, close up the bleeders, and, your done......hopefully.....

I find, it usually works on most Mini's.......

I did each front side by itself, then both together, pumped the pedal with them closed and then bled again. There’s definitely a chance there’s still an air bubble somewhere

I think the next thing to try will be taking out the pads and seeing what the pistons are doing. I guess they might be a bit stuck on the brake seal grease or just need to be pushed in and out a few times to get brake fluid on the seals.

[GraemeC]

I think the next thing to try will be taking out the pads and seeing what the pistons are doing. I guess they might be a bit stuck on the brake seal grease or just need to be pushed in and out a few times to get brake fluid on the seals.

I think this will be your answer.

Remove the pads and carefully push the pedal and move the pistons out so about 1/4”-1/2” of the piston shows. Wipe a finger dipped in brake fluid around that exposed bit of piston then push them back in, wipe up any fluid and put the pads back in.

This will make sure the seals slide on the piston easily and will also get them to settle in the right orientation so they don’t want to ‘pull’ the pistons back.

[MiNiKiN]

Still not convinced your gravity bleeding worked - in any upwards bend of the brake line the brake fluid will just drip past the air-bubble that'll stick there like sh*t on a shovel.
If you haven't got a helper, use at least a syringe to create some vacuum

my2p

[nick@dunsdale]

if you wanted to double check the master cylinder what i have done when been in your shoes a few times
is disconnect the brakepipe from the top of the master cylinder and screw in a blank
the pedal should be solid when pressed very lightly
Hold the pedal to see if there is any fade
leave it for 30 mins and see if there is any drop on the pedal
I have never tried this next idea but the blank could be then moved with master cylinder reconnected and then move the blank to the blank of the servo
and repeat brake pedal test. this would tell you if the problem lies at the servo.

Its a pity you cant clamp hoses as it would be very easy with a pedal test, clamp all four hose's
and try the pedal as each clamp is removed it's was usually the rear for me.

I am purely a bodyshop man and may be giving poor advice apologies in advance

Plenty good advice already been given thats the methods i used to follow to try and pinpoint where the problem lay