Rear Brakes; what am I missing?

[33fromSD]

Hey All

On my 33 I have the 8.8 moser rear end with the optional 11.65" rotor / caliper kit from FFR.

The last couple of times I cruised, I get a feeling of drag or resistance when I push in the clutch when shifting between gears. I do not get that "coasting" feeling when the clutch is pushed in. I'm also not getting the roll back when at a stop light and the clutch is in.

In preparation for working on my shocks this weekend, I lifted the car in the rear, I put the car in neutral, the emergency brake in off (I even removed the cable end from the caliper) and I cannot turn the rear wheels at all. Am I missing something? This should be no different than my other cars with manual transmissions, I can turn those wheels (with slight resistance from the brakes obviously) when the car is in the air, and is in neutral with the brake off.

Bad Calipers (seem odd)? Bad M/C?

Thoughts? Ideas?

Jim

[michael everson]

Try forcing the parking brake lever all the way back against the stop and see if the problem goes away. I had a few calipers where the parking brake was stuck slightly on. Ended up buying new ones.
Mike

[wallace18]

Try forcing the parking brake lever all the way back against the stop and see if the problem goes away. I had a few calipers where the parking brake was stuck slightly on. Ended up buying new ones.
Mike

Agreed. I have had to free up 3 sets of the FFR rear calipers on some kits I built.

[ggunter]

I assume you have two master cylinders, one front on rear? If so the rear master cylinder push rod may be too tight causing the bleed hole in the resivouir not to uncover when the brake is released and holding pressure in the system. Open your bleeder on one of the rear calipers and see if the wheels will turn, if it does your holding pressure in the system. OR.. one of your ebrake levers are not releasing.

[ggunter]

And if your system is holding pressure, all you have to do is shorten the master cyl push rod, for the rear, adjustment till you can feel about 1/32 of play in it.

[33fromSD]

I'll check the emergency brake mechanism on the calibers themselves, I have the cables physically disconnected so it's not the brake mechanism.

Also I'm thinking it may me the M/C; Look at the push rod in the pic, I had both rods (front & rear) equal lengths threaded into the clevis (still are) but look how far the rear m/c plunger is pushed in (circled in red). Also, I can wiggle the balance bar so it's not like it's tight on the rear side.

Almost seems like the wildwood m/c depressed but never released on the rear side? Could a stuck emergency brake mechanism cause the m/c not to release?

fullsizeoutput_66.jpeg

[ggunter]

You should have a tiny bit of looseness on the push rods when released, just open a bleeder and it will tell you imediately if you are holding pressure, if your wheels will then turn.

[33fromSD]

Update....I indeed was missing something. I jacked the car up by the frame (in front of the differential) which caused the drive shaft to set against the frame. Now that I jacked up the differential slightly to get the drive shaft off the frame I can turn the rotors a little more. Still tight though.

The push rods both have a little looseness.

Still not sure why the m/c for the rear is depressed as much as it is.

[33fromSD]

I loosened bleeders / retighted them to not let air into the system, no changes on the rear m/c but as noted above, both push rods on the front & rear m/c are loose with there brake pedal is depressed. Looking at it, it just looks like rubber boot on the rear m/c is not coming back on the rod like the front boot does. Not sure why.

I'm guessing this is all stupidity on my part and my initial issue was the drive shaft hitting the frame which lead me to the M/C boot looking wrong thinking I had an issue, however, with that said it doesn't answer why it's not coasting like it should with the clutch in..

I'll play with the brake bias a bit to make sure I'm not too much on the rear.

Thanks for the help everyone.

Jim

[NAZ]

It is common for the balance bar to be skewed a bit with the pedal all the way rear or all the way forward. For systems that have different size M/C and/or pistons front to rear, the balance bar should be adjusted so that at midway on the stroke (moderate pedal pressure) the balance bar should be at a right angle to the M/C push rods. This will explain the set-up and reason for it better. https://www.wilwood.com/PDF/DataSheets/ds1102.pdf

Sounds like you have eliminated the rear M/C as a cause of the dragging sensation. That leaves something else as the cause, and likely the parking brake as suggested above.

But your comment on the driveshaft rubbing caught my attention. It's important that the driveshaft never rub anything throughout the entire range of suspension motion. That include when jacking the rear tires off the ground and the shocks are at full droop. A spinning driveshaft that contacts anything is a potential problem including a catastrophic failure of the driveshaft. If the driveshaft is rubbing, I suggest you correct that before drive the car.

[33fromSD]

It is common for the balance bar to be skewed a bit with the pedal all the way rear or all the way forward. For systems that have different size M/C and/or pistons front to rear, the balance bar should be adjusted so that at midway on the stroke (moderate pedal pressure) the balance bar should be at a right angle to the M/C push rods. This will explain the set-up and reason for it better. https://www.wilwood.com/PDF/DataSheets/ds1102.pdf

Sounds like you have eliminated the rear M/C as a cause of the dragging sensation. That leaves something else as the cause, and likely the parking brake as suggested above.

But your comment on the driveshaft rubbing caught my attention. It's important that the driveshaft never rub anything throughout the entire range of suspension motion. That include when jacking the rear tires off the ground and the shocks are at full droop. A spinning driveshaft that contacts anything is a potential problem including a catastrophic failure of the driveshaft. If the driveshaft is rubbing, I suggest you correct that before drive the car.

Agree on the drive shaft comment NAZ, that took me by surprise too. I'll need to recheck the pinion angles (again). These things have very little clearance on them as you know so I'll see what I can do, but in parallel to checking everything for clearance I know for sure I'm going to add limit straps to the rear end to make sure the rear axle can never lower enough to have the drive shaft hit the frame.

I guess the positive note is there are no scraps or marks on the drive shaft in that area so it has never hit the frame when driving, but I agree that it doesn't guarantee that it couldn't happen.

Jim

[NAZ]

I set my rear ride height at 6.875" which is much higher than most do on their hot rods to facilitate running 30" wrinkle wall slicks (which grow ~1.5" at 150 MPH). And I run a "Glide" trans which is much shorter than the typical trans run in these cars so I ended up setting my engine/trans angled down in front ~1.5-deg slopped down in front which is opposite of a typical installation. That elevates the trans output shaft enough that I don't have driveshaft clearance issues. Not sure you can get away with that as my chassis and doghouse cover are very different than yours (all custom fabrication) but this may give you an idea how to deal with your driveshaft clearance issue. There's always a workaround, just have to be creative as some are more work and $$ than others.

[33fromSD]

I set my rear ride height at 6.875" which is much higher than most do on their hot rods to facilitate running 30" wrinkle wall slicks (which grow ~1.5" at 150 MPH). And I run a "Glide" trans which is much shorter than the typical trans run in these cars so I ended up setting my engine/trans angled down in front ~1.5-deg slopped down in front which is opposite of a typical installation. That elevates the trans output shaft enough that I don't have driveshaft clearance issues. Not sure you can get away with that as my chassis and doghouse cover are very different than yours (all custom fabrication) but this may give you an idea how to deal with your driveshaft clearance issue. There's always a workaround, just have to be creative as some are more work and $$ than others.

Fully agree

Jim

[33fromSD]

After I swapped the shocks today I also played around with the brakes a little more. I changed the bias bar slightly to edge a little more towards front braking, that seemed to really loosen up the braking system. I was probably a little too much on the rear. I also went through the emergency brake system to ensure everything was functioning properly. All looks good.

Finally, I readjusted my drive line angles so now I have a 1/4" of clearance between the drive shaft and the frame when I left the car by the frame and the rear end hangs by the suspension and I now have about 3/4 - 1" of clearance between the frame and driveshaft at ride height. I think I'm good now.

But never let it be said that I don't cover myself because I also to be safe installed limit straps on the rear end (front the upper shock hole which being used to a 3" limit strap clap you install on the rear end) to insure that the 1/4" gap maintains even if the car is lifted by the frame or for some reason the rear goes airborne momentarily.

Thanks for all the help everyone.

Jim