Brake Bleeding Problems on LWB Coloado

[MikeC]

Help!! A couple of months ago, I renewed all 5 flexible brake hoses on my 1997 LWB 3.0 GX Colorado and generally cleaned up discs, callipers, pads etc. Brake fluid changed -all OK and no issues at all.

During this work, I noted that the rigid brake pipes over the left rear axle were badly corroded and needed replacing. Ordered new ones from Mr T. The old pipes were removed OK, but to get the top pipe on the Load Sensing Valve free, necessitated the removal of the valve. Again, no huge problems other than usual corrosion! All freed and cleaned up, including bleed nipple.

Everything refitted to the car and bleeding commenced. BIG PROBLEM! Despite repeated attemps there is obviously air trapped somewhere in the system and the brake pedal is ineffective - asmall amount of pressure can be pumped up and help but falls away as soon as pedal is released.

Does anyone have any ideas or guidance for this one? Is there any Toyota guidance/Service Bulletin/procedure? I have searched through forums but can't seem to get a definite answer.

Hope someone can help.

 

[BobMurphy]

Mike,

This type of problem crops-up from time-to-time I'm afraid and there are a few posts about it here and on other sites.

It is possible to 'flip' the master cylinder seals by over-enthusiastic brake pedal pumping, resulting in loss of pressure. A Master Cylinder Repair Kit will sort that if the bore isn't scored.

Apart from that there are a few things you can try that might narrow down the source of the problem.

1. Clamp-off the rear flexi-hose where it drops from the body to the rear axle. If the brakes then go tight the front and the load-sensing valve are OK and the problem is in the rear (or in the other half of the master cylinder).

2. Clamp-off the front and check for pressure - that will test the rear and the other half of the master cylinder.

3. Was the load-sensing valve working?? it may now be stuck having been disturbed.

4. Are you getting fluid from the bleed nipple on the load-sensing valve??

5. A 'pressure brake bleeder' (I use a Gunson system) will push fluid through without you having to pump the pedal, that can be very effective at removing trapped air. I drive mine from a spare tyre - but keep the pressure low (DAMHIK ).

6. Did you replace/remove all three brake pipes at the load-sensing valve?? did they go back correctly?? It won't work if they have been cross-connected.

Fortunately I haven't had many problems with mine when replacing fixed pipes, flexi-pipes, LSV, calipers & pads so others may have some better ideas than me.

Best of luck with the search.

Bob.

 

[MikeC]

Hello Bob
Thanks for your input, I should have replied years ago to tie up the thread!

The problem was simply with the load sensing valve - I overlooked the bleed nipple.
Once bled, absolutely no problems at all. She always gets a 2 yearly brake fluid change and I will overhaul the calliper pistons, seals and boots this year - last done 2010 ish

Thanks again
Mike