Bleeding Defender Brakes - Any secrets ?

[Bushie]

I've just replaced the vacuum pump, booster and pads on my defender (98 Tdi - no ABS).

After bleeding the brakes a few times I'm stuffed if I can get anything like a decent pedal.

I've tried pressure bleed, normal bleeding (pedal) and another pressure bleed, with basically no air except on the initial bleed.

Pedal is still VERY spongy and the brakes pretty much ineffective.

Any secrets ?

Prior to replacing the booster the brakes were rock hard, but probably more effective than they are now.

I suppose next step will be to pull the master off again and put a seal kit through it, but given it was fine prior to this I'm a bit reluctant.


Martyn

[marting]

If, while bleeding the brakes, you have pushed the pedal right to the floor, the seals in the master cylinder are run through a section of the cylinder they don't normally touch. This 'unwiped' section of the cylinder may have corrosion or some build up that can damage the master cylinder seals during the bleeding process, making it impossible to get a decent pedal.
I have always bled brakes by using one of the 'one-person' bleed units readily available from repco or the likes, and only taking the pedal through its normal stroke.
Good luck,
Martin

[Xtreme]

I had similar problems with mine about 18 months ago. Mine is a Td5 with ABS but after replacing the Master cylinder and the ABS Modulator and overhauling the front calipers plus trying every system of bleeding known to man, the eventual fix was achieved by removing (without disconnecting the hydraulics, placing an appropriate sized spacer between the pistons and then bleeding with the bleed nipple at the highest point - when fitted, there is a possible air space above the nipple. Needless to say that this solution was achieved by me but by a highly qualified engineer who has designed and built numerous special vehicles based on Land Rovers.

The symtoms I had were a spongy pedal to the extent that if pressure was held on the pedal, it would gradually go right to the floor - with no loss of fluid from the system.
The problem reared its ugley head after I replaced both the front and rear axles - complete, hub to hub.

A test that can be done to detect where the problem is to clamp off individual wheels/calipers or pairs of calipers (both rear or both front). If pedal comes good then problem has been isolated to area that has been clamped off.

Hope you sort it out soon.

[Xtreme]

If, while bleeding the brakes, you have pushed the pedal right to the floor, the seals in the master cylinder are run through a section of the cylinder they don't normally touch. This 'unwiped' section of the cylinder may have corrosion or some build up that can damage the master cylinder seals during the bleeding process, making it impossible to get a decent pedal.
I have always bled brakes by using one of the 'one-person' bleed units readily available from repco or the likes, and only taking the pedal through its normal stroke.
Good luck,
Martin

Agree with this and this is what I thought had caused my problem and why I replaced the master cylinder but alas, in my case it was not the problem. So I now have a spare used master cylinder sitting on the shelf.

[tazd]

just got on here to post the same question! replaced rear brakes.(pads and rotors) and new master cylinder. bled several times and feels good then start up and brakes are nothing. pump a few times and then they are fine, but after 5min of driving hit the brakes and almost to the floor again and hardly anything.
no fluid loss and no air in system when bleeding got me puzzled aswell.

Strange thing the other day was the pedal was as hard as hard, soon as hit the pedal brakes on, like this for about 30min of driving then when i started up again went back to soft nothingness.

[rick130]

Unless you were changing fluid due to age/contamination, did you really need to bleed ? :D

They are a **** of a thing to bleed, the hardest of any system I've ever tried.

In the finish I made a pressure bleeder, it was the only way I can get the air out and get a decent pedal, I'd reckon a vacuum bleeder would be even better.

I tried bleeding the way we always bled race car systems and that wouldn't work, (effective on any race car I ever worked on) so tried the old fashioned pump the pedal and hold and that didn't work either, so whenever I need to bleed I use the pressure bleeder.
If I had a vacuum bleeder I'd use that instead, It'd probably be even more effective.

How much fluid are you pushing through ?
Are you starting at the longest line first ?

Have you tried doing a complete end or even four wheels at a time ?
This is how race car systems are bled and what I try and do on Deefer except I use the pressure bleeder. ie. I open all four calipers and pump the fluid through. Seems to work, and you get all the old stuff out quickly.

[tazd]

started at front drivers side as (rave) says then worked to the back. even did the back first then came to the front. putting through about 300-400ml of fluid per bleed.

rang a brake place the other day and they said "oh they are easy never any troubles with them. but cant help you for 2weeks" so i just make sure i pump the brakes a bit before getting into town. or park out of town a bit.

[scott oz]

started at front drivers side as (rave) says then worked to the back. even did the back first then came to the front. putting through about 300-400ml of fluid per bleed.

rang a brake place the other day and they said "oh they are easy never any troubles with them. but cant help you for 2weeks" so i just make sure i pump the brakes a bit before getting into town. or park out of town a bit.

I was always told to start at the rear passanger side then drivers side rear then front passanger then final drives side front.

[abaddonxi]

I was always told to start at the rear passanger side then drivers side rear then front passanger then final drives side front.

x2.

[lochie]

G'day Bushie.I have the same model Deefer ,from new ,and every second year I change the brake fluid.I always bleed the brakes .1.lhd rear passenger 2. rhd rear pax.3. front pax 4. driver. I keep the master brake cylinder topped up as I bleed the system and I've never had the problem you now have .During the time Ive owned the vehicle the brake master cyl.vacuum pump ,brake boost ,rotors have been replaced with out any issue .What I am saying is under normal circumstances the brake system has been straight forward.I wonder if you are dragging in air to the system through a pin hole ,a union not sealing properly or a faulty brake hose.I hope this is of some use .Cheers Lochie

[rovercare]

http://www.aulro.com/afvb/1437759-post83.html

[Bushie]

Figured I should show what the problem turned out to be,

It was twofold, first issue was a hole in the seal under the reservoir (rear port), although I'm not 100% convinced this was really a problem. It *may* have been allowing air to draw back into the system when the brake was released.

https://www.aulro.com/afvb/images/imported/2011/04/413.jpg

However after replacing the master cylinder seals, and being pleased the master cylinder was in very good condition the brakes were still strange feeling, way too much pedal travel.

My son then asked me should 'that' be moving (master cylinder). Something I certainly hadn't noticed (after all its hard to watch the m/cyl when you put your foot on the brake.

YouTube - booster1.avi

That was an after market booster (couldn't get a genuine one at the time, will have to see if I can return for credit). I'd reckon that movement was translating to more than 20mm at the pedal giving it the weird feeling. Anyhow new booster on and all now feels as it should. THe after market booster was also deeper than original moving master cylinder forward (maybe 10mm)

At least I know the brakes should be OK for a while, new vacuum pump, new booster, overhauled master cylinder all new fluid and new pads.


Martyn

[Quirk]

Hi Roger,
It appears that I have the same issue with my shorty. The spacer that you have fitted was it specifically made and what sizes is it. I have tried 2 brand new master cylinders and still every week or 2 I go from a good peddle to nothing and when the system is bled there is heaps of air but no fluid loss.
Cheers
Mark

[Xtreme]

Hi Roger,
It appears that I have the same issue with my shorty. The spacer that you have fitted was it specifically made and what sizes is it. I have tried 2 brand new master cylinders and still every week or 2 I go from a good peddle to nothing and when the system is bled there is heaps of air but no fluid loss.
Cheers
Mark
The spacer you need is simply to take the place of the disc rotor and stop the caliper pistons from coming out further than they do under normal operation. So the spacer needs to be about as thick as the disc rotor.
HTH