19 replies to this topic

[Jed Sanders]

Hi all,

I have a completely standard 1976 Clubman saloon, which I have just replaced both pairs of brake cylinders in the front drums as well as the rear brake lines.
I have been bleeding the system (as per the Haynes) with an easy bleed, but cannot get rid of what seems to be an air lock in the system.
No further air is being expelled from bleeding the system and the first press of the brake has no, to little resistance but the following get better and better.
The master cylinder has been topped up throughout the bleeding process.

From the Haynes manual I beleive that it has a single circuit braking system.

Has anyone else experienced this or know of a reason for it?

Any help much appreciated.

[lrostoke]

Have you adjusted all the brake shoes with the adjusters on the backplates..

Not sure what layout is on that year, but my 84 as drums all round and its like this

rear ones turn the adjust till the wheel locks, then back off a qtr turn on the adjuster.

front ones mines twin cylinder..I just a adjust till you can feel the shoes biting slightly on both adjusters.

plus also it can take a while for the brakes to bed in.

[Jed Sanders]

I have tried adjusting the shoes and beleive them to be correct.
The first pump has no resistance, the second about 40% and third being pretty much how they should feel.
Which feels like air in the system.
I've put quite a lot of fluid through the system and all the old fluid is now flushed out.

Puzzled.

[nicksuth]

Sounds like "air" to me? I did see a tip sometime ago for wheel cylinders where the shoes were removed and the pistons were pushed as far back in as posible and then a clamp fitted over them to ensure there was no possible air pockets left at the piston end of the cylinders. Worth a try?

[Jed Sanders]

Cheers Nick,

That sounds like its definately worth a try, what with 4 new cylinders fitted.
Ill give it a go.

[giz]

someone once told me to bleed brakes with them un adjusted and then adjust them after the bleeding is finished, i've never tried it though as i normaly bleed them fully adjusted. are you sure that the master cylinder isn't failing?

[ANON]

chances are you've got air trapped where the pipe loops over from the top of the m/cyl, pressure bleed should shift it no problem

[dklawson]

I disagree about air being in the system.

You said...
"The first pump has no resistance, the second about 40% and third being pretty much how they should feel. "

If there is air in the system, the brakes typically continue to have a spongy feel. Since there is increasing resistance with multiple pedal pumps, I suspect this is one of two things.
1) Brakes shoes on in the wrong position (yes, there is a proper orientation and it does matter) and/or,
2) Out of adjustment shoes.

Sorry that this picture is so grainy, but take a look at:
http://home.mindspri...nityBrakes2.jpg
Note where the "relieved" edge of the friction material is relative to the direction of drum rotation. Make sure your left and right side shoes are oriented as shown in the JPG.

As for the shoe adjustment, elevate the wheel and tighten the adjuster until the wheel won't rotate, then back off 1/4 turn and spin the elevated wheel. The wheel should spin with audible drag and stop rotating within about 1 revolution. Pump the brakes to center everything and repeat the test to make sure the wheel still can be heard and stops within about a turn.

[lrostoke]

I'm with Doug, like I said in my 1st reply, its amazing how much the pedal travel is altered by the slightest moving of the adjusters.
Also make sure the return springs are on correctly, just had a situation where I rebuilt front brakes and was struggling to get them right only to notice I'd fitted return springs wrong way up, and the coiled section of the spring was catching against the adjuster cam and knocking the shoes out of line.
An easy way to test if it is the adjusters and not air would be to just adjust all the shoes full on and try the pedal.

[huntface]

Hi, I had a similar problem with my 77 clubby.

No pressure in the pedal on the first push, bit more on the 2nd and so on.

Turned out to be a duff brake bias valve

[dklawson]

Turned out to be a duff brake bias valve

That's a good point. Bleeding the rear brakes can be a real problem due to the bias valve shifting during the bleeding process. I've heard lots of different methods for getting around that. The one that seems to work for quite a few people is gravity bleeding the rear wheel cylinders.

[Jed Sanders]

Thanks for all the replies chaps.
My fronts are twin setup and everything is on correctly.
After clamping the front cylinders shut it has improved but not quite there yet.

I will look into the brake bias valve as well, as I did change the hard lines from it to the now new braided link pipe.

Cheers, Jed

[nicksuth]

If you've fitted braided flexible lines of any length they do need to be securely tied/fixed back to something as they tend to thrash around when pressurised.

[Jed Sanders]

They are secured from the bracket on the swing arm to the bracket on the subframe.
I didnt want to tie them down due to the rear swing arm travel.
I take it you would recomend further flexible fixings?

[nicksuth]

Just watch them while someone else presses the brake a few times, if they look secure then you've probably done enough, if they jump around a bit, consider further fixings.