Rear Brake/Load Compensator

[poseidon]

Hi - any advice on how to adjust the rear brake compensator valve would be appreciated. The rear brakes on the truck have become steadily more aggressive and often lock up alarmingly under quite moderate braking. Also, rear brakes are tending to 'clunk' on suddenly as the truck comes to a normal braked stop. I see a rod, connected between the end of the Panhard Rod and the Compensator valve assembly, and expect this may be adjustable. Any clues on how to go about this?....Keith

[BUSHWHACKER]

Does the truck have any suspension lift?

[poseidon]

Yes, a 2" lift. Also, the braking issue emerged around the time I changed the trucks wheels from an oversize set to standard wheels and tyres....k

[NiftyNev]

Best bet is to get the brakes professionally adjusted but here is some info that may help. Brakes may have been modified somehow to compensate for the bigger tyres.

http://www.toyotasurf.asn.au/forum/v...highlight=lspv

Nev

[poseidon]

thanks Nev - that's a useful link and I see from it that you've visited this territory before. It's pretty heavy duty tech stuff and I'd kinda hoped somebody would say something simple like '2 turns clockwise on the adjusting nuts will cure it'. Nothings ever simple on the 4 Runner and I'm a bit uneasy about trial and error adjustments when braking system is involved. I could maybe live with the rear end locking up under harder braking, but it is pretty alarming and I'd rather have it sorted. Pro help on my limited budget is probably the very last resort.

The linking rod between the Panhard Rod/adjuster and the Compensator Valve assembly is a bit bent - I wonder if simply straightening it could help and do the same as resetting the adjuster screws...Keith

[NiftyNev]

Avoid bending the rod unless it is actually bent out of shape. This is the only pic I can find of one at the moment. Should be a straight section then a curve down to the panhard connection.

http://postimage.org/image/2rwbjiuec/

Nev

[poseidon]

OK - I'm glad I asked, as the shape of the rod on my truck looks the same as the pic, so it's not bent out of alignment. Pity, as that might have been an easy fix. It's hard to see how the tiny adjustment available using the nuts will make much difference to the actuation at the valve, if they work by changing the effective length of this rod. The angles seem all wrong to achieve any significant mechanical advantage, but I'm not really sure how this all works....K

[BUSHWHACKER]

The valve works via the up and down movement of the body in relation to the axle.
When the cargo area is fully loaded, the rear end sags under the weight which lowers the body.
The rod from the LSPV pivots from a fixed point on the axle. As the body lowers, the rod moves a piston in the LSPV to increase braking force (allows more fluid pressure) to the rear wheels.

[KERRSURF]

The design of the valve allows only a little bit of movement, you may find yours has stuck open, allowing too great a braking force to the rear. I have the opposite, I have bought a new valve because mines is stuck closed.

[poseidon]

Thanks for these comments - I now understand a bit better how the valve might work and how small adjustments on the panhard pivot can make significant impact on the valve opening at the other end of the rod. My problem seems to be a bit intermittent and the rear brakes don't always lock up violently. That maybe ties in with a sticking valve. I've given both ends a good 'waggle' around (as the actress said to the bishop) and some WD40. The boot on the valve has a tiny split and may have allowed some crud in to stick the valve, but no sign of fluid leakage.

Is this an MOT issue????? Maybe I stick half a ton of logs in the back when I present it for test?....keith

[KERRSURF]

Do what it needs to work properly, although a new valve might be in order for proper braking.
My truck sat idle for months so I suspect this is what caused the valve to corrode.