Cant get rear disc brakes to lock

[Groundhog]

Disclaimer: I searched....
i cannot get the rear brakes to lock up on gravel
76-fj 40 w/ new rdb conversion monte calipers, mid 90's 80 series non abs m/c, wildwood proportioning valve, mico line lock

booster rod adjustment is ok

as shown in the picture the rear m/c port feeds the p-valve then runs through a mico line lock to the rears. front port feeds fronts.
the p-valve is wide open. I saw threads regarding the mystery port swap but found no conclusive evidence.

did i really need the p-valve?
is it restricting too much?
anyone ever swap ports?

 

[Groundhog]

forgot the pic

 

[Groundhog]

yes; the truck was on its side when i took the picture.

 

[Fast Eddy]

did i really need the p-valve?
is it restricting too much?

Maybe not and it sounds like yes. I would have expected that valve to be adjustable to almost no restriction though. Is it possible that those calipers need more volume than you're getting from that master?

I have an fzj80 rear end with Toyota OEM calipers. I use an fzj80 master and a booster from a 4runner. When I put it together it was easy, due to the brake line routing, to just include the OEM '76 proportioning valve, and it just happens to work perfectly. All four lock at the same time on gravel.

 

[Eshu Elegua]

my friend install Toyota rear disc brakes on my 40 ,TLC calipers,stock 1976 booster and MC..no PV, stop on a dime

 

[Morse_FJ40]

Eddy,

I thought that the cruisers including my '78 came with residual valves, not proportioning valves.

Res. Valves maintained a constant pressure for the drums, where the prop. Valeve only allows a certain amount of fluid through.

Question.... Did you get rid of all of your stock LC hard brakelines??

 

[effjay76]

I have a similar set up, only difference is I have the stock 40 series master, and I have the opposite problem, rears lock up first.

 

[Groundhog]

Eddy,
Question.... Did you get rid of all of your stock LC hard brakelines??

new hoses are braided stainless from m/c to a Mico line lock under the drivers seat then to frame on passenger side just in front of the fire wall
lines are hard lines down passenger side frame front & back to axles

 

[DSRTRDR]

I have the stock 40 drum brake master and a prop valve in the rear circuit - no residual valves anywhere - it works

 

[Poser]

Too much hose brother...


Rigid steel tubing does not expand like hose does.

Been there, done that.

 

[reddingcruiser]

2X on the flexible brake hose!!!!! It's easy to get from point A to Point B, but at the price of line pressure.

 

[UZJ40]

Good to know! I'm glad I read this before purchasing brake lines. Thanks Poser

Too much hose brother...


Rigid steel tubing does not expand like hose does.

Been there, done that.

 

[AlexJet]

In my past experience not locking brakes needed proportional valve, then problem usually got fixed.

 

[Poser]

In my past experience not locking brakes needed proportional valve, then problem usually got fixed.

How does this work?

A proportioning valve does not generate flow or pressure...

 

[AlexJet]

If pressure is not enough on the rear, it readjust the pressure to lock rear earlier. If pressure is not there, then it won't help.

 

[Poser]

If pressure is not enough on the rear, it readjust the pressure to lock rear earlier. If pressure is not there, then it won't help.

Is your native language French?

 

[Groundhog]

With the p-valve set for max psi to rears, I gave 2 small pumps before braking in neutral. I may have a little air still hiding. Im also gonna snug the push rod a little more. Does the rod always need to be adjusted from the booster side or cAn I get it from the pedal side also? Should this set up w/the 80 m/c even needed the p-valve? I'll give a report after bleed/rod lengthening. I heard if you tie a brick to it it'll lengthen!

 

[Fast Eddy]

Eddy,

I thought that the cruisers including my '78 came with residual valves, not proportioning valves.

Question.... Did you get rid of all of your stock LC hard brakelines??

Your understanding of the valve types is right on. A '78 has both. The proportioning valve is #60. It is not adjustable. It bolts on with the bottom two bolts of the master. I kept it and all my original steel lines.

Too much hose brother...

Rigid steel tubing does not expand like hose does.

2X on the flexible brake hose!!!!! It's easy to get from point A to Point B, but at the price of line pressure.

With the p-valve set for max psi to rears, I gave 2 small pumps before braking in neutral. I may have a little air still hiding. Im also gonna snug the push rod a little more. Does the rod always need to be adjusted from the booster side or cAn I get it from the pedal side also? Should this set up w/the 80 m/c even needed the p-valve? I'll give a report after bleed/rod lengthening. I heard if you tie a brick to it it'll lengthen!

Is your native language French? I assume you read the two informed opinions quoted above? I'm no expert, but I'm guessing nothing will help with the flexible hose in the circuit.

 

[Pighead]

Is your native language French?

Is your native language French? .

There's no need for insults...

 

[Groundhog]

Is your native language French? I assume you read the two informed opinions quoted above? I'm no expert, but I'm guessing nothing will help with the flexible hose in the circuit.

I posted the problem and I am not French. The French guy was trying to help. There is no OME p-valve on this system. It is as described. I believe there is a rogue air bubble somewhere. I will check the pressure loss of the lines as well.