Loss of brakes & Brake bleeding

[DougT]

Hi all
Bit of a newbie on here & just got a 2002 90 LWB.

The brakes went poor recently, by poor I mean a long travel & poor stopping.
There was no fluid loss or apparent leaks so figured it must be master cylinder.

Replaced master cylinder & with ignition on (ABS) I bleed the load proportioning valve then Rear left, Rear right, Front left, front right.
I get a great pedal & think all is well.
I take a drive for 1/2 a mile & by that time I have virtually no brakes again & the pedal drops to near the floor - indicating I only have one useable circuit of brakes.

I have done the above 3 times & am getting bored with not having brakes!
- never had this much trouble bleeding brakes before

Is there anything I should be doing differently?
- do the load proportioning valves play up? - i.e. ingest air?

Thanks for any help

 

[fridayman]

Loss of brakes & Brake bleeding

Have you checked all the calipers for brake fluid leaks? A caliper seal may have failed. It could also be a hose that is bulging under pressure. I would also check the long brake pipes just inside the left chassis rail for leaks.

 

[DougT]

Have you checked all the calipers for brake fluid leaks? A caliper seal may have failed. It could also be a hose that is bulging under pressure. I would also check the long brake pipes just inside the left chassis rail for leaks.

Hi fridayman
- no, I haven't checked the calipers.
tbh, because of the good ground clearance I have left the wheels on to bleed the system as all the nipples are accessible, so haven't had a good look at the calipers.

Will check the calipers, hoses & pipes as you suggest.
- there was no fluid loss, just rubbish brakes.

Thanks

 

[bsmith123]

Hello

barring a leak if the brakes pump up and then you lose them later then I would think air

keep bleeding or you could get a reverse bleed kit which forces air up from the bleed nipple to the MC

 

[Chris]

You didn't mention bleeding the master cylinder. You may have done it, but if not then that could be the problem. We have to go on what you tell us. When you install a new MC, you need to put your finger over the connections and operate the piston so that it expels air and then draws in fluid from the reservoir.

Chris

 

[tim falce]

Have you tried pumping the pedal and pressing and holding it down hard hard without the engine running to see if it holds firm, if it holds at least it'll eliminate leaks.

 

[DougT]

Thanks for all your tips chaps.

Chris - I bled the master cylinder after fitting by having the pedal pressed with the union cracked open, & tightened when the pedal released.

I guess I will have to persevere & try again.
The reverse bleed system sounds worth a try - who makes them?

Thanks

 

[tim falce]

Thanks for all your tips chaps.

Chris - I bled the master cylinder after fitting by having the pedal pressed with the union cracked open, & tightened when the pedal released.

That reads that you released the pedal while the joint was open then tightened it with the pedal up, I assume I'm misreading it.

 

[Chris]

Yes you need to open the union completely and stick your finger over the end. Press the pedal until fluid comes out, then shut it off with pad of finger and let the pedal up. Repeat a couple of times, then remove finger whilst the pedal is up and stick the pipe back on.

Like I have said, we can only respond to what we read. Sorry if you've done it this way already. New cylinder, all bled at top and bottom with calipers in good condition, the only thing left really is the servo.

Chris

 

[DougT]

Thanks for your help guys
Hopefully I will have brakes when I can get back to try again.