Brake Proportioning Valve

[bamelanc]

I have ’78 front axle with the disc with ‘74 stock rear drums. Master cylinder is aftermarket, but assuming it’s a OE replacement.

Having a MC designed for front/rear drums, what adjustments do I need to make for the front discs from the ’78 front axle? Upgrade MC to 75-80? Proportioning valve? Or both?

Need to make sure the hydraulic pressure is biased correctly.

Prefer to stick with what the OEM would recommend in this situation. Anyone with experience in this situation?

 

[kudzugypsy]

cityracer sells everything you need

 

[Pighead]

Anyone with experience in this situation?

Well, sorta. But in a '74 FJ55 (longer wheelbase).
I had great drums, could lock up 33s at will. Went to front Toyota discs in 2004 when i did the SOA and power steering. Kept the stock rebuilt master cylinder. No problem, great brakes. Don't know the bias but i don't drift it or rally it. It just stopped very well (now on 35s).
Few years later added Posers rear discs. Same master cylinder. Brakes worked great. Years later replaced the stock '74 master with an 80 series master. Still stops great. Never used a proportionning valve. Now on 37s.
I'm sure others will add more detail on how this can't possibly work and how you must match master fluid volumes and caliper volumes etc.
In my experience, just about any LandCruiser master will work pretty well as long as you drive it like a LandCruiser.

 

[bamelanc]

Hi

cityracer sells everything you need

I know where to get things…I need to know what things to get and why.

 

[Pighead]

Hi

I know where to get things…I need to know what things to get and why.

Try it with your current master then. See how you like it.
I found that the 80 series non-ABS master bolts right up and works nicely.

 

[bamelanc]

Try it with your current master then. See how you like it.
I found that the 80 series non-ABS master bolts right up and works nicely.

If I decide to upgrade the MC to a 75-80, is it required to upgrade the booster?

 

[Casey E]

If I decide to upgrade the MC to a 75-80, is it required to upgrade the booster?

No

 

[BJ40Verona]

Ciao bamelanc,
I did a front disk swap in 2014, with the original pump but I wasn't so good, so in 2021 during a MAJOR restoration I added rear disk, along with a new 4 disc pump from JT.
The answer is the same, my rig tends to block rear wheels (is without hard top so very light in the rear) and I can't leverage the full front brake capacity.
I've ordered some days ago a wildwood prop vale to see if I can manage this issue once for all.

My 2 cents

 

[JohnnyC]

A prop valve will be needed because of the small front brakes and ginormous rear brakes.
The imbalance can be mitigated by upgrading to the bigger 4runner front calipers & pads with an aggressive semi-met pad, and using the cheapest ceramic pad in the rear.

See Jim’s comments above… it makes a HUGE difference