Been chasing this issue for awhile. Master appears to be stock toyota. I had a poor brake pedal and even worse pedal height that basically no matter how much you adjusted the rear shoes it didnt change. I finally gave up and adjusted the booster pushrod and everything seemed fine for about a month. Pedal worked fine, was much higher than before and stopped well.

Fast forward to the other day and I noticed again, hmm pedal is low but truck still stops...Adjusted the pushrod again and its better but it baffles me why I needed to adjust it again.

There is no hissing, the booster is holding air it seems. Truck off pump up the pedal it doesnt seem to sink. Truck on, pump up pedal and yea it does slightly sink. I can barely fit my foot under it, when before I know I could easily fit a my foot with workboot (much larger than my sneaker today) in the gap easily.

I think the seals in the master are bad, whatcha think?

How many miles on this master cylinder?

Have you noticed if yer brake fluid has been black before any recent bleeds? There is a rebuild kit from Toyota...not sure on the part number though.

With all the stuff you've been doing to yer T-100...probably wouldn't hurt to take a shot at it. Just keep in mind that if you go fer a rebuild, the bore might be hosed with corrosion. Just prepare yerself fer that possibility. <img src="/forums/images/graemlins/wink.gif" alt="" />

Honestly no idea how old the master is or how many miles.

Fluid hasnt been black at all that I recall. I honestly think I might just pick up a rebuilt one in the end depending on price. Willing to be the inside is corroded should I take that route.

I just dont know what would cause this besides a bad master. No signs of lost fluid, no leaks, everything in the brake system is new.

Just adjusted the pushrod, everything was fine and now its bad again. Thats what baffles me. Doesnt hiss so cant be a bad booster and the lines to the booster and other vac lins appear ok.

Truck has 1" bore master right? I think I want a firmer pedal period so the 1 1/16" bore is what I might aim for. Does it matter when it says non abs vs abs? I do have abs btw.

Edit: found this post on TTORA, seems they are all the same abs or not. http://www.ttora.com/forum/showthread.php?t=144432

Did it git worse when the weather got colder? If so, the rubber seals in the master are probably bad as the rubber will shrink in colder weather. <img src="/forums/images/graemlins/wink.gif" alt="" />

Firmer pedal? You mean you want more effort to have the same stopping power? Going with a bigger bore size will require more force on the pedal to stop the same distance than with the stock bore size. <img src="/forums/images/graemlins/wink.gif" alt="" />

It has been cold for some time now, were talking about 25-50F most days (hi/lo). This past week or so its been a bit colder but nothing insane.

The thing is I dont understand why after adjusting the pushrod it either unadjusted itself or the master got worse..IDK. Its only been maybe 2 months max since I adjusted it.

I will say since I adjusted it, it was fine up until a week or so ago.

I had thought the larger master would make the pedal be firmer as in the travel would be less maybe? Pushing more fluid in the end. Either way the larger master is only 1/16" vs the smaller 7/8" (or whatever it is) the old trucks were vs the 1" masters.

I think Im going to is wait and see how it goes, if the pedal sinks again Im just gonna try replacing the master.

I could really use some advice guys. I know Im annoying with all my issues, but Im desperate at this point. I adjusted the pushrod the pedal went down again by today, its been less than a week.

There are no external leaks at the master, either at the seals or at the fittings either. No fluid loss at all that I can find, reservoir is full to the top. No leaks at any of the calipers or wheel cyls or lines. Everythings new but booster and master.

Using the haynes and toy FSM I come up with the following after using the test procedures for the booster they outline:
Q. Engine stopped and press pedal several times, pedal travel shouldnt change.
A. pedal travel becomes less.

Q.Brake pedal fully depressed start engine, pedal should sink a little when engine starts
A. Pedal sinks at least a good inch or better

Q. Depress brake pedal, stop engine and hold.
A. Pedal doesnt seem to sink I think, its hard to tell b/c it sinks a little if any.

Q. Start engine, let run for a min. Turn off and then press brake pedal several times. Pedal travel will decrease
A. Pedal travel does decrease.

I also rechecked the pushrod, yep its adjusted where I had it last I measure. I did notice theres quite a bit of in and out play at the rod-is that normal? Also noticed if I grip the rod with pliers (so I can adjust it) it hisses if I dont keep the pliers straight.

No leaks anywhere, not even at the master seal. I just adjusted the pushrod again maybe 1/8" at most and bingo firm pedal again. Maybe the springs or whatevers inside the masters wore out? At this point its either replace one or the other-master being much cheaper first.

IDK...

I say buy a new master and a rebuild kit, pull yer old master out, disassemble it and inspect/check it. If it's rebuildable, rebuild it. If not, install the new master and return the rebuild kit and old master as a core. <img src="/forums/images/graemlins/wink.gif" alt="" />

Kinda how Im leaning right now too. Soooo frustrating still with these stupid problems.

Im gonna buy the slightly larger master, I like the firmer pedal feel. Up sizing on the old trucks was drastic, were only talking 1/16" larger vs 5/8" to 1". Mostly doing it cause its cheaper. Rebuild kit from toyota is only 10 bucks less so why bother lol...

Going to buy a master come monday, I think your right Bam-the seals are bad. Temps changed and all of the sudden brakes got much better vs just a few days ago when it was colder and brakes were good but not like i barely touch the pedal and it stops. I backed off the pushrod a good bit today.

Gonna call toyota and see if I can determine if my truck has a 1" or 1 1/16" master, its not labeled at all-how can you tell otherwise inside overall diameter?

Almost all OEM Toyota master's I've seen have the bore size cast into it somewhere. Alternatively, you can measure the bore size at the rear of the master when you remove it to adjust the booster push rod, etc.

Also don't forget when troubleshooting/adjusting your brakes that there's also a pedal pushrod adjustment on the backside of the booster.