Toyota Vs. GM master cylinders (1 Viewer)

[Spook50]

It's going in my 62 so I figured this would be the best place to ask...

Correct me if I'm wrong, but Toyota's master cylinders are set up so the forward fitting goes to the front brake lines and the aft fitting to the rear lines IIRC.

I saw that Sky Manufacturing offers an adapter that allows bolting a GM master cylinder to a Toyota booster. Sounds like a simple plug n' play setup, right? Problem is, I don't know if GM master cylinders are set up the same way Toyotas are (ie: front/front and rear/rear), or if they're reversed like how Chrysler MCs are (front fitting to rear brakes and rear fitting to front brakes).

Anyone know which is the case for a GM MC?

 

[FL cruiser]

I know the particular GM master I chose is set up the same as Toyota front/front and rear/rear.
On a GM, the side with the larger Reservoir area is for the front brakes.

 

[Spook50]

I know the particular GM master I chose is set up the same as Toyota front/front and rear/rear.
On a GM, the side with the larger Reservoir area is for the front brakes.

Cool, I think that's how the one I'm eyeballing is too. 9/16 front and 1/2 rear. Now I just gotta find fittings that'll accept the 3/16" factory hard lines.

 

[Bomar]

Which master are you running? Are there benefits over the Marlin Crawler MC?

 

[Spook50]

Which master are you running? Are there benefits over the Marlin Crawler MC?

According to Sky Manufacturing, their adapter is for use with GM master cylinders made to bolt onto hydroboosters. It doesn't have anything to do with a hydroboost conversion; just adapts that style of MC to a Toyota vacuum booster. They recommended a MC from an '86 full ton, which has a 1 5/16" bore. Given the noticeable difference I had when I went from the factory 7/8" bore to the 80 series 1" bore (which is exactly what Marlin sells), I think jumping up an extra 5/16" would make for way too little pedal travel before locking the brakes. There's a 1 1/4" bore MC that was used on hydroboosted Chevy Astro vans, so I'm going to give that a shot. It's a dual reservoir MC and doesn't look nearly as huge as the 1 5/16" bore full ton unit (which is heavy as hell and possibly might not even clear the hood because that reservoir is so tall).

 

[Mace]

What brakes are you currently running and what tire size??

 

[Spook50]

What brakes are you currently running and what tire size??

The 4Runner front calipers (which led to swapping in the 1" bore master cylinder) and Chevy Monte Carlo front calipers in the back for my rear discs. The piston area in the rears is HUGE and gives me a ton of pedal travel. Too much for me to be comfortable with. I'm hoping the 1 1/4" bore master cylinder will be the right volume to offset that. Possible 1 1/4" may be too much, but from there I can go either bigger (not likely to be necessary) or smaller, so I'll use it as my jump-off point.

No ebrake hardware on the rears, since I didn't like how the Eldo calipers worked when using a hand brake. They're made for a pedal-type ebrake that can put a LOT more force on the mechanism. I'll be installing a transfer case ebrake hopefully sooner rather than later. Just have to order the stuff for it.

I'm on just 31" mudders, too.

 

[ntsqd]

I think that you've got the cart before the horse. Prime importance is that the front brake's hydraulic leverage be correct and how the pedal feels, then with those parts fixed in place sort out the rear brakes.

If you've got too much rear piston area you have too much rear bias and going to a larger bore m/c only won't fix that. You would also need to increase the front piston area, most likely very significantly.

 

[Spook50]

I think that you've got the cart before the horse. Prime importance is that the front brake's hydraulic leverage be correct and how the pedal feels, then with those parts fixed in place sort out the rear brakes.

If you've got too much rear piston area you have too much rear bias and going to a larger bore m/c only won't fix that. You would also need to increase the front piston area, most likely very significantly.

This I know. Problem is there are no larger front calipers available (already running the 4Runner ones), and no rears available with a smaller bore. I'm stuck with the biasing I have, so I'm on to the next step of correcting the pedal travel and then proportioning the rears as best I can with the Wilwood proportioning valve I installed when I went to rear disc. I know a larger bore MC won't correct the biasing on its own, but it'll at least move more fluid so the overall pedal travel will be decreased and then I can work on finding the ideal proportioning between the front and the rear.

 

[ntsqd]

IME you'll never find it that way and you'll have an extremely stiff pedal that doesn't do much stopping unless you go to hydra-boost, which will just cover rather than fix the problem.

Going to the D52 GM fronts (2-15/16" piston) will bring you closer. As a guess and depending on pedal ratio you'll want a 1-1/32" to 1-1/4" m/c bore with such a combo.

Alternately early Volvo rear discs and Mercedes rear discs were fixed 2 piston ATE calipers. I've no idea what rotor thickness or piston diameter they used, but being a rear caliper they should be closer to being right. Even the early bug/T3 front disc calipers are possibles, and some of them are ATE calipers too.

In the wilwood line I'd look specifically at the DynaPro calipers as they were designed just for this sort of situation. Stiff little forgings too, few in the whole wilwood line that are stiffer.

 

[Mace]

Spook, are you running any sort of residual valve in the rear?

 

[lehiguy]

I'm very interested in the outcome of this as I too have the GM calipers in the rear. I run a residual valve, stock MC and front calipers. I know I need a larger MC, and that is coming up. I planned on getting 4-runner calipers for the front as well as the 4-runner/FJ80 MC but it sounds like you have already done that and you need still more MC size?

 

[Spook50]

I'm very interested in the outcome of this as I too have the GM calipers in the rear. I run a residual valve, stock MC and front calipers. I know I need a larger MC, and that is coming up. I planned on getting 4-runner calipers for the front as well as the 4-runner/FJ80 MC but it sounds like you have already done that and you need still more MC size?

It works, but there is still alot of pedal travel. More than I'd care to have.

ntsqd, I don't think I can put any different calipers on the front or the rear without more fab work, unless you know of something that'll work with a 60/62 series semi float rear (or a larger caliper that's compatible with the fronts for that matter). If there are bolt-in (or at least close to it) options available, I'd love to know 'em. I'm using the TSM caliper brackets on the back.

Joel, yes I've got a residual valve on my rear line. It made a significant difference when I installed it. I think it might be a 10lb. I'd have to go out and double check. Whether it's a 10 or a 2, it's whichever one TSM recommended at the time.

 

[ntsqd]

Any direction that you go from here will require more fab work. The Volvo and Merc calipers are fixed body designs so they most likely mount like the OE fronts do. I know that the Bug/T3 calipers mount that way. What I don't know is if their piston sizes make them candidates or not.

An RPV will reduce the fluid needed to make the pads contact the rotors, but you have to be careful of excessive pad dragging. Though I've read of folks using the 10 lbs. RPV's on disc systems, they are intended for drum brakes. The 2lbs. RPV's are intended for discs. The m/c should already have this valve in it, at least the domestic stuff does. Normally they are hidden under the sealing cone in the outlet ports.