brake help please (1 Viewer)

[abecker]

Hi all,

So, originally i put 4 wheel disc brakes on my SWB. Achieved by putting a '76 axle on the front and monte carlo rotors and calipers on the back. At the time the available space did not allow for me to fit a booster in and was using a single reservoir MC. I drove it like this for approximately 100 miles with no problems other than having to lift my arse off the seat and put all 155lbs of body weight on the pedal to stop it when someone hastily pulled out in front of me.

I then siwtched to a supra MC (dual res) and 80 series booster. bled the lines and worked out some hub locking issues. Test drove on dirt and all seemed fine but only got about 5 miles in at the time but only at my decision (no limiting problems).

I now took it for a longer drive. coming off the dirt onto hardtop I made it about a total of 3 miles (dirt and pavement) and it felt like the brakes were "coming on" or being applied. After pulling over and pondering my situation for about 15 minutes I figured I'd try it again. Made it a very similar distance and the same happened. So i got a tow from a friend. Upon arrival all four wheels were pretty hot.

I'm not sure what the problem is. I plan to jack up the front and spin the wheels by hand to see what happens initially. Then take them off and look for any rotor scorching.

In the meantime - I checked the vacuum hose on the booster and its connected. I don't think air in the lines would be the problem. And I don't have much play in the brake pedal.

The only other problem I have is that I also found the radiator was a little dry at the time.

Any ideas on whats going wrong?

TIA,

Aaron

 

[SHREG]

I think this is related to the booster push rod. pull the booster, there is a small rod that will be exposed. this rod has an adjustment. Loosen and adjust that push rod back a bit. That should do the trick. I bled my brakes about 1000 times before I found that mine was applying pressure, it builds, and eventually locks the breaks up.

i hope this helps.

 

[2fpower]

So, you are talking about the push rod between the booster and the master cylinder. Good idea.

I was going to recommend giving more space on the rod between the pedal and the booster.

 

[abecker]

thank you gentlemen. that gives me a promising start!

much appreciated,

Aaron

 

[FJ45Dude]

abecker,

Wanted to toss out one more possible cause based on your description. The lines might be routed too close to the exhaust manifold and are heating up the brake fluid causing it to expand and 'apply' the brakes. I struggled with this issue many years back on my '71 and it had to re-route the lines to 'cure' it. Stumped me for a while wondering why everything was fine until the motor got good and hot.

Of course if you did not change the routing going to the dual, this is very unlikely. Wanted to toss this out.

Cheers!

 

[abecker]

Oh no! Thanks fj45dude, I was actually wondering before I felt the wheels if I was getting a fuel vaporlock because it is pretty hot in the engine compartment. Im hoping less work will fix it and do not want to be re-running brakelines at this point. Thanks for the heads up though, it is appreciated.

Aaron

 

[Tancruiser]

Check the rod in going into your booster mine did this and would lock up the rear brakes there should be a little clearance not touching at all , keep adjusting it and you will get it .

 

[abecker]

Ok, sorry for the delay, I have a 2 yr old, single dad. So I have about 6 hours every other weekend to try to work this out. On top of that, when I started I noticed a casting plug leaking, so I adjusted the pushrod but was afraid to drive ...or more so crack the block, then realized I needed to get all my gauges working to do this, so after 6 hrs, at best, every other weekend for like 6 weeks,I have a pretty nice looking and functioning gauge cluster - THANKS RUDI!!

Now, I adjusted the booster pushrod, still got brakes while driving a few miles, got annoyed and tightened the nut all the way, no thread showing on the rod, still problem today.

in retrospect, wondering, I pulled the rod forward, adjusted, put mc back on....would neglecting to push the rod all the way back in by hand be a cause now? I just assumed putting the mc on and having vacuum would make it all settle back into place.

I can offer the following too. Pulled vacuum hose at booster end, still had pressure, stiff as hell pedal, shouldnt that have relieved pressure? Let rotors cool, drove using transmission only, no brakes, 2 miles later, felt them on again, barely able to overcome them and not feel the need to downshift although it was close to that point. Also, after installing the booster it sat for a year.

I think the next suggestion will be to cut the rod... Do you think its still the rod, or something I did wrong like not physically manually pushing the rod back in, or frozen calipers or like FJ45DUDE! said, lines too close to engine?

I think next step is to space mc out 1/2inch w just washers, just to see if it works before I fab a spacer. But wanted to get some input.

I cant drive my rig anywhere ...not having any fun.

 

[friel01]

before you go cutting things, try adjusting the rod connected to the pedal. I had same issue with mine. I cant explain the functioning behind it, but mine wasn't pushing the rod far enough, like it needs to go a certain distance before it can start to release the pressure on the line when you let off, if it doesn't make it that far, every step on the brakes just slowly increases the pressure more and more until the brakes drag and ultimately lock. I adjusted the pedal rod to push a little further, and all was good since.

 

[abecker]

So, you are talking about the push rod between the booster and the master cylinder. Good idea.

I was going to recommend giving more space on the rod between the pedal and the booster.

before you go cutting things, try adjusting the rod connected to the pedal. I had same issue with mine. I cant explain the functioning behind it, but mine wasn't pushing the rod far enough, like it needs to go a certain distance before it can start to release the pressure on the line when you let off, if it doesn't make it that far, every step on the brakes just slowly increases the pressure more and more until the brakes drag and ultimately lock. I adjusted the pedal rod to push a little further, and all was good since.

OK, thanks for these responses. Round 2 approach. will update ASAP, hopefully one week not three.

 

[abecker]

ongoing

well, once i got into this i found a casting (freeze) plug dripping. Now that all of those on the drivers side are replaced, and after shortening the booster rod all the way, and adjusting the pedal, I still had the locking brake problem. I spaced out the MC with a single washer on each post and now have no locking problem.

My question is: Was the solution just that the newly created space is allowing the pressure to release from the booster and MC? I ask because I wanted to fab a spacing plate to keep it all mostly clean in there, but I don't want to waste the time doing this if its just going to trap pressure again and revert back to locking brakes....although I highly doubt I would be getting a complete seal when doing so.

I guess I'm just curious and looking to learn more....

- Aaron

 

[Marcfj-45]

I had the same problem try all these tricks !
But mine is the cylinder in the caliper didn't retract .... I just found that !!!!
Now need to know why ?!?