So I've read somewhere that new (not OEM for the FJ40 necessarily, but that fit) master cylinders don't require the use of proportioning valve because they've got the front of rear balance built into them. Can anyone confirm or deny this?
I am NOT a brake expert, nor have I read what you've read. I have run the stock '74 55 master cylinder with 4 wheel drums, with Toyota front discs then with Poser rear discs. Then added the 80 master. I have never run, nor felt the need for, a proportioning valve. Some people swear by them, Toyota felt a need for them (I don't know why). Wagons are different from 40s, YMMV.
Why do you ask?
I don't necessarily consider myself a brake expert, but when I converted my 12/79-build 40 to 4-wheel disc brakes, it needed a proportioning valve, both with the stock master cyl and with the non-ABS FZJ80 master that I am currently running. My rear discs locked up way too soon without one.
Asking because I'm making the master brake lines RN and I don't want to have to come back and add the proportioning valve if I can avoid it. I purposely bought a non-abs Toyota-spec friendly unit to try and take advantage of the built in front/rear bias balance.
My truck is a 10/75, with front discs, converted rear discs from drums.
@1911 - That's basically what I tried to buy. Based on your experience, sounds like it'd be better to go ahead and have one. I'm never lucky like Pighead above.
It was cheap. Hell, I've bought 2 different units now. I can buy another one - was hoping someone would confirm or deny the whole thing. Or just run the proportioning valve. I have 2 new ones of those too. Just like the clean look without it. Less to fiddle with.
I highly doubt it is built into your master. There is a lot of difference in the vehicles listed, how would they determine the right amount of adjustment for all 3? Also, if you bought one and hooked it up to your existing system for an 81-89 land cruiser you would have 2 proportioning valves.
You could always install a valve someplace where you can't see it. When i did my 1st 4 wheel discs back in the 90's, I played around with the bias for about 3 days and haven't touched it since. I run a stk 76 FJ40 and later m/c.
While there somewhere in the automotive universe be master cylinders with "built in bias" there is nothing like that going on in any master cylinder you are going to buy at the parts store and bolt into your Cruiser.
What you have heard about most likely, is the lack of a 5 (or so) lbs residual valve in the rear brake circuit of the RDB equipped '80 series.
If you have a modded up rig, with suspension, tire and brake changes... Spend the few bucks for an adjustable proportioning valve and maybe some external residual valves so when you are all done you can get the most from your system.
In my '40 I am running an '80 series M/C, F&R 2 pound residuals, adjustable proportioning valve, F&R line locks (irrelevant for normal driving use)Toyota 4x40 calipers and plain old '40 series rotors at all four corners. The tires are bigger now and it does not see the road anymore but when I was running 40 inch boggers the brakes were so effective I never did work up the courage to try a full slam panic stop on pavement just to test it. With the soft and flexy suspension the rig has, it felt like it was gonna somersault ass over nose any time I came close to doing so.
My experience with the '78 40 with front factory discs and converted rear disc with stock MC was that without an adjustable proportioning valve, firm braking on any "loose" surface caused the rears to lock up. I also tried an offbrand valve originally with improved but less than stellar results. Finally went with a Wilwood valve and was able to dial the front/back proportion in.
Pressure is resistance to flow. Brakes work by moving fluid from the MC to WCs, so while people treat hydraulic oil as incompressible, the brake components are not equal in resistance and fluid will flow towards the path of least resistance, engaging that brake first, or require less fluid for a smaller cylinder/stroke combination. Disc vs drum, front vs back, aftermarket GM calipers... flow from a MC could be internally proportioned if everything were the same across models and perfectly adjusted for stroke for engagement, but odds are flow has to be adjusted to equalize (or bias) braking force.
Modern cars do this in much more sophisticated ways that a prop valve, using manifolds with dynamic valving for ABS, traction control and "limited slip" based on wheel sensors, just look at all the lines on the fire wall of a recent Toyota.
