Im trying to narrow this issue down to either the booster or the master.

About a year ago I replaced my rear axle due to a faulty bearing that caused a leak at the seal that wouldnt go away. After that point I had a low pedal, not really mushy just very low. 6-8 months ago I replaced everything in the brake system besides the LSPV, booster and master. No matter what bleeding process (pump method, machine, etc), tool or whatever I did it didnt seem to help. I also bench bled the master 2x, same results. I am losing no fluid at all and besides the booster and master everything and I mean everything in the breaking systems new. Before I replaced the axle I had no issues..I wonder if we damaged the master?

More interestingly I noticed then when the weather would warm up (winter days from 35F morning to about 50F daytime or so) or the engine would heat up fully the pedal got better, higher if thats possible. I decided what the heck Ill adjust the booster pushrod. Bingo. Problem seemed solved, then it got SUPER cold and I had to adjust it again. Then it warmed up and WHOA its adjusted too much, so I backed it off. The temps fluctuated like crazy during this time and every week I would adjust it, didnt have time to mess with it otherwise.

One day that solidified the temperature related problem was it was freezing that morning in the spring, like 35F. Then it jumped to about 60F. Pedal was super low that morning but fine later that night.

I did all the booster checks the FSM talks about, seems to be fine. I concluded the seals in the master are internally leaking perhaps? Its very strange its temp dependent. Right now pedals fine but once it gets cold again Im thinking its gonna get low again.

Ideas? I think Im going to try a master since its only 100 bucks vs a booster thats over 200. But still..whats going on?

 

you are bleeding your lspv right? With the new rear end, the rear bleed screws are at the correct position? Sounds to me like theres air in the system. When gasses (air), are cold, they contract, when they warm up, they expand. Seems condusive to your problem.

 

Totally bled, wheel cylinders are in the correct spots. Infact I bled it with a machine, then the pump method using a bottle myself then the pump method with a friend. No amount of bleeding cures this. I also bench bled the master. Only once I adjusted the booster pushrod did it solve my issue. Once it got warm outside it was to far adjusted, then I backed it off. But cold weather it was adjusted more. The master as far as I can tell is original for 245k as is the booster.

Air in the lines would matter imho as you pump up the pedal more it would compress and thus be fine once pumped up. It isnt like that. The truck stops fine but the actual pedal travel is longer/shorter depending on temps.

 

Did you adjust the rear brakes?

 

Yep, rear brakes are 100% adjusted. Believe me I did everything imaginable besides replacing the master or booster. Trust me this isnt my first rodeo doing brakes on these trucks, I havent overlooked anything I think.

Everything thats new: lines, calipers (tried 2 sets just to be sure!), wheel cylinders, drums, shoes, springs, adjusters and pads. I also doubly checked the drums, calipers are releasing and pins are greased up nicely, rear shoes are working correctly.

Like i said earlier, I did everything imaginable and the only thing that helped was adjusting the pushrod. Ive been wondering for eons if perhaps my master is internally leaking, as all the booster failure tests the FSM outlines come out good.

Guess only way to find out is to buy a master and see if it helps.

 

Did it fix?

 

Didnt buy a master or a booster yet, havent had time. Probably gonna buy a maste rin the next week or two and report back.

Either the master is internally leaking or the boosters bad. Master is MUCH cheaper than a booster tho.

 

Let us know