T100 large bore MC

[satchel]

Does anyone know the part number or a link to the 1 1/16 bore size master cylinder that was available on the T100? All I'm finding are the 1" bore. I did the 4runner conversion with calipers and booster, and the t100 master cylinder, but while the pedal is firmer for sure, it also is way too sensitive. If I let my foot rest on the brake pedal it almost throws me through the window, hoping this will help some.

 

[cruisermatt]

That's with the stock master cylinder? I'll trade you my T100 master cylinder.

 

[satchel]

It brakes very sensitive with all three MC I have used, the stock 62 has more pedal travel and I have a 4runner and t100 MC both a 1 inch bore that are firm and way too sensitive. I think it is the booster that made everything overly sensitive so if I can take a little of that leverage away with a bigger bore it may work. If yours is a 1 1/16 bore I'll trade you but I want to make sure.

 

[OSS]

I may be thinking about this wrong... But if the 4Runner booster is providing too much assist, that means that a small brake pedal movement creates a large piston movement in the booster, which isn't matched to the rest of the system.

If the brakes are now too sensitive & want to throw you through the windshield with just a tap on the pedal, that means that TOO much brake fluid is getting pressed down the lines to the brakes at a given pedal pressure and that the booster isn't matched to the geometry of the cruiser's pedal movement.

That being so...it would seem to me... a larger master cylinder bore would only exacerbate the sensitivity because it will press even MORE brake fluid down the line for a given pedal extension.

To take this concept to the extreme, if a theoretical 1/8" bore master cylinder was installed, (as a theoretical example) the brake pedal travel would be very far and the pedal sensitivity would be extremely poor because very little fluid would get pressed down the lines compared to a large bore MC.

I'm thinking... a larger bored MC will only make sensitivity worse.

 

[satchel]

From everything I have read, a larger bore is firmer and reduces pressure, smaller bore travels further and increases pressure. I need less pressure. Larger = more volume, less pressure according to all the posts here and elsewhere, but yeah, it is counterintuitive. The stock 62 MC does seem to make it brake even harder, more sensitive, just takes more travel to get to that point, which is like a lot of nothing then a lot of braking.

Here's one such excerpt, "Generally speaking, if the master cylinder bore is too large, the driver will feel a very hard pedal feel with minimal pedal travel, and will have a difficult time generating the necessary pressure to effectively operate the brake system. If the master cylinder bore size is too small, the driver will be able to generate a lot of pressure, but the pedal may have an excessively long stroke or a very spongy feel. And if the bore size is way too small, the pedal or master cylinder may bottom out before enough volume is pumped to operate the calipers. The best advice would be to consult with the manufacturer of the brake system you will be using and work with them to pick the right size for your application."

source: Braking Systems - Popular Hot Rodding Magazine

Regardless, anyone know of or have a link to a larger than 1" bore MC that would fit up to the stock booster?

 

[satchel]

Looks like this one might work, for future ref. I needed to search for the 1 ton T100.... Brake Master Cylinder - Remfd

NMC P3261

 

[Spike Strip]

Try adjusting the Brake Booster rod, first.

Also, I agree with OSS - Bigger MC is going to require more pedal pressure. You'd be better off with a MC that's closer to ratio Toyota Engineers built into the 4Runner system. 15/16" MC.

Otherwise, if you're dead-set on a 1 1/16" -- If you cross-ref, you might be able to find the Aisin Asco Advics one. You want a 1-Ton early 90s T100 V6.

More Information for RAYBESTOS MC390149

 

[satchel]

Brake booster rod is adjusted, no play, very firm pedal right off the bat.

I used the stock 4 runner MC that goes with the calipers and the booster, all from the same 4runner setup, and as best I can tell they are all 1" not 15/16. Anyway, still way too sensitive, so looking for less hydraulic pressure, more foot pressure. Worth a shot.

 

[Spike Strip]

I've got the the 4Runner setup also, with a 1" T100 master. Pedal is very firm and takes more pressure than I'd like, but it's not going to make me go to a 15/16" . Stops great. I wouldn't characterize it as sensitive at all ... Everything was new or reman Toyota / Aisin.

Stock early 90s V6 4Runner MC is 15/16" with the S13 calipers.

You're the first person on MUD I've read having this issue.

If all those MCs didn't work for you (and I'm not sure what you mean exactly by a 'sensitive' pedal) then I'd look at other things before throwing money at another MC.

 

[satchel]

By sensitive, I mean when I go to brake, in most cars I would cover the brake pedal with my foot and start applying pressure as needed. In this case, almost as soon as I touch the pedal it is braking hard. It's firm, but way sensitive, like 100 times more braking right off the bat than my wife's uzj100. If you were just to relax your foot onto the pedal, not applying any real force, it would be locking up the brakes.

I'll keep troubleshooting. I'm sure it's related to the 4runner booster applying too much boost, but the stock fj62 booster was way too weak, so trying to find a middle ground on all these parts hasn't been easy.

I'll post up if I find a good solution.

 

[OSS]

I'll just leave these two quotes here.

but while the pedal is firmer for sure, it also is way too sensitive.

Here's one such excerpt,....If the master cylinder bore size is too small, the driver will be able to generate a lot of pressure, but the pedal may have an excessively long stroke or a very spongy feel.

'Spongy feel' is the opposite of 'too sensitive'. The pedal needs more sponge and less sensitivity.

 

[satchel]

And this is what I am going for, "Generally speaking, if the master cylinder bore is too large, the driver will feel a very hard pedal feel with minimal pedal travel, and will have a difficult time generating the necessary pressure to effectively operate the brake system."

I want to have a harder time generating pressure with my foot, and I want it to be firm, it's way too easy to generate pressure at the moment. I've tried the smaller bore using my stock fj62 master, it is spongy for a while, then instant lock up and that is way worse than current cause i'm guessing when it is going to lock up instead of my current firm pedal.

Either way, from experience over the last 2 days, smaller bore used creates more pedal travel before locking up hard at some point pushing down the pedal (like guessing when it will happen), larger bore is much more firm and slightly less sensitive braking than the smaller bore, meaning a little more foot pressure. I want even more foot pressure to actuate.

 

[cruisermatt]

I re-read your first post not at 5am grogginess. I'm not sure I have what you want, I don't remember exactly which bore it is (I swapped it years ago).

I want very firm pedal and lots of pressure. So I guess I'm going hydroboost

 

[satchel]

If you haven't tried the 94 4runner booster I would. That's what has gotten my truck stopping at such a ridiculous rate.

 

[NookShneer]

Toyota brake reference for everyone to enjoy.

Brake Master Cylinder and Brake Booster Specs for Toyota 4x4s | Roundforge

 

[satchel]

Just threw in the larger bore t100 mc and I think it's exactly what I was looking for. Not quite as sensitive as the 1 inch bore and a little more foot pressure required to lock up the brakes.

 

[Tapage]

you have now 1" and previously you had ..?

 

[satchel]

I now have 1 1/16 bore, I previously tried 1 inch and 7/8 inch. 7/8 had a lot of pedal travel and about half way down it would suddenly lock up, very sensitive and a bit of a guessing game as to when it would happen. The 1 inch was much firmer, almost no pedal travel, but as soon as I touch the brakes, while they were firm, would almost lock up the tires. Too much pressure going to the brakes for the amount of foot I was putting into it. The 1 1/16 is just as firm, no travel, and requires a little more push of the foot to get the brakes to lock, not as much pressure going to the brakes and not as sensitive.