Disk brakes sticking

[gcrump01]

Brake problem I've never encountered & I need some help.

1980 FJ40 -disk in front, drums in rear. After driving just 5 miles or so the front wheels don't roll freely and I smell burning brake pads. I'm jacking up the front & the wheels will turn, but it's hard to turn. Both sides are about the same in terms of difficulty to turn.

After about 30 minutes, it rolls freely again.

New master cylinder, new CityRacer booster & rear proportioning valve. Brake lines are new, brake pads are new, etc.

Any ideas? Where do I start?

 

[SouthBostonFJ40]

Check the adjustment on the pushrod from the booster into the master. There's a nut on the end of it. Sounds like it's too far out and putting pressure on the master.

 

[gcrump01]

I thought about that. What I don't understand is that it rolls fine right now, but if I drive it, it changes & starts dragging & sticking. Then, after a few minutes it rolls freely again. Why does it change?

 

[bikersmurf]

I had the same problem. When it's locked up, you'll find the brakes release if you loosen off the nuts holding the master cylinder to the booster.

Shorten the rod a smidge and the problem will go away.

 

[Racer65]

As noted above, you need to do that adjustment. I've mentioned elsewhere that I recommend watching this video. Most relevant part starts at the 30 minute mark.

 

[btbuild]

As noted above, you need to do that adjustment. I've mentioned elsewhere that I recommend watching this video. Most relevant part starts at the 30 minute mark.

Racer
I'm having somewhat the same problem with my stock booster push rod being to long by approximately 3/8" even when push rod is adjusted in as far as it can go. I have 4 wheel disk brake conversion with new master. Have you seen this issue before? I'm thinking I may have to cut down push rod.? 1/73 fj40 here is a pic of my master. Any advice would be a big help. I did completely remove adjusting nut just to see where booster would sit without the acorn adjustment nut on push rod and I still need approximately another 1/16 of a inch.

BTBUILD

 

[Rock_Hugger]

As others have said, the pushrod into the master cylinder is not fully releasing. There can not be any contact with the pushrod into the master or you WILL get exactly what you describe. Don't over think it. Make sure the pedal to booster is adjusted properly, then make sure the booster to master is adjusted properly.

 

[gcrump01]

OK, I've watched that video & it is helpful. I'll verify the pushrod setting with calipers tonight and adjust on the brake pedal side too - based on the FSM.

What's bothering me is that it changes while driving it - I assume due to temp changes as nothing mechanical is changing. I thought brake fluid was basically not compressible even at high operating temps, so I didn't expect it to change as it got warm. I can sit in the garage & press the brakes over & over & it never starts to drag.

 

[Cruiser Corps]

If they're close when cold, they'll grab when it all gets hot and everything expands (i.e. rotor, pads and caliper). I race motorcycles, and while it's a totally different braking setup, my front brake when cold is not very effective, the lever requires a long pull, and will almost touch the handlebar. After a couple laps when it's good and warm, I only have to use 1 finger, and barely touch it to get full force. If it were set to that tolerance while cold, I'd be boiling my brake fluid within a few laps.

- Josh

 

[lc69hunter]

When I did my conversion, I had the same issue. My solution, rather than shortening the rod, was to very carefully and gently grind down the adjusting nut on the end. I was able to get the gap I needed in the master cylinder. We are talking millimeters not inches.

 

[gcrump01]

Thanks guys. Pushrod adjustment did the trick. I now have about .15 clearance (FSM says .1-.5).
Also adjusted the brake pedal side for less pedal travel before the brakes catch. No dragging even after several miles.

 

[Racer65]

Racer
I'm having somewhat the same problem with my stock booster push rod being to long by approximately 3/8" even when push rod is adjusted in as far as it can go. I have 4 wheel disk brake conversion with new master. Have you seen this issue before? I'm thinking I may have to cut down push rod.? 1/73 fj40 here is a pic of my master. Any advice would be a big help. I did completely remove adjusting nut just to see where booster would sit without the acorn adjustment nut on push rod and I still need approximately another 1/16 of a inch.

BTBUILD

View attachment 1499606

Personally I wouldn't grind down the push rod if my life depended on it.
Is your pedal side adjusted per FSM? There shouldn't be any residual resistance when you release the brake pedal.
I think the real issue is that your stock booster is a drum brake booster and it's coupled to a disc brake MC. You can bet the two engineers never talked because the two pieces are from different generations.

 

[btbuild]

Personally I wouldn't grind down the push rod if my life depended on it.
Is your pedal side adjusted per FSM? There shouldn't be any residual resistance when you release the brake pedal.
I think the real issue is that your stock booster is a drum brake booster and it's coupled to a disc brake MC. You can bet the two engineers never talked because the two pieces are from different generations.

I did adjust pedal per FSM. And I also know the correct procedure to adjust push rod. I did not know I had to change booster. Thank you!!! That makes the most sense why things are not meshing well.
I know I have the ability to modify push rod, the part that's inside booster but not positive it will work. I may try just for fun but most likely I will be ordering a booster from ya.
Thanks again.

BTBUILD

 

[bikersmurf]

If your booster is still good you shouldn't need to order a new one.

 

[btbuild]

If your booster is still good you shouldn't need to order a new one.

It was good when I took it off. Push rod at this time is way to long. And won't allow me to get even close enough to mount master cylyder. Even when adjustment nut on master is dialed all the way in. I'm baffled!

 

[bikersmurf]

Something isn't fitting right. Have you tried pushing the rod in further? Is the brake pedal partially depressed?

The rod will pull out and go back in. How far does it stick out?

 

[btbuild]

Yes I adjusted pedal height per FSM. I have pulled it out and tried pushing rod in further, dead stop. I will have to measure how far rod sticks past booster. When I try to put master on booster mounting bolts I'm left with approx 3/8" between booster and master. When I get home I'll check in mm.