4 Wheel disc, soft pedal

-
TurboGLH

TurboGLH

FABO Gold Member
FABO Gold Member
Joined
Jul 29, 2017
Messages
638
Reaction score
725
Location
CT
I've been fighting a soft pedal all year, there's air in the rear brakes, but they bleed completely clear.

Car has new front lines/braded hoses, all three rear hoses are new(rubber) and new lines. Only original line is the steel one front to back.

Front is new 11"/2.75" rotors/calipers. New 15/16" M/C. All from Cass. Drum/Drum Distribution block.
Rear is a right stuff 11" disc kit. I didn't want parking brake provisions, and they were the only vendor to offer them that way.

I've bleed the brakes the regular way multiple times, vacuum bled them multiple times, and just recently used a pressure bleeder. I've taken the calipers off the rear brackets, I've angled them every which way, they always have a stream of air free fluid.

I'd swear at this point that it's just how the pedal feels on a 15/16 MC, but if I pinch off the rear hose, the pedal instantly gets better.

Two questions.

1: What's the normal pedal travel on a 15/16" M/C?
2: The few people who've bleed these successfully, any tips?
 
Came with my rear disc kit

1002211903.jpg
 
I switched to a 1” M/C cause I didn’t like the soft pedal on my four disc brakes.
 
I think that kit uses the GM Caddy calipers. Did you adjust the parking brakes or have them hooked up?
 
dano said:
I think that kit uses the GM Caddy calipers. Did you adjust the parking brakes or have them hooked up?
Click to expand...

This is the kit without parking brakes, so no adjustment or hookup to be done.
 
My first thought since you say you have bleed the brakes is the small 15/16 bore of the MC. And you really shouldn't be pinching the rear brake hose.
 
TurboGLH said:
Correct.
Click to expand...
Check with an assistant for one or both over-returning, is there a visable gap using a small flashlight tight to the rotor & peering in opposite through towards light. If the pins are not moving free(I've seen too much heavy caliper grease develop enuff suction in blind- hole setups to actually pull the caliper towards the bracket & rotor, compressing the piston & leaving a gap between outer pad to rotor.), do the brackets align the caliper(s) with the rotor(s) properly w/o flexing/binding/pushback? Some piston seals drag/hang up in the bore & cause the piston to over-retract when the pressure is released. I've seen all of these in the field. That's where I'd start...good luck! How about a couple pics of the setup..?
 
I know you said you pulled the Calipers off to bleed them are the bleeders at the top of the calipers ,grasping at straws here ?
 
SGBARRACUDA said:
My first thought since you say you have bleed the brakes is the small 15/16 bore of the MC. And you really shouldn't be pinching the rear brake hose.
Click to expand...

Normally I wouldn't, but the need to diag overrides that. If I need to replace the hose afterwards, fine. But I wanted to narrow down the problem, if possible.

Killer6 said:
Check with an assistant for one or both over-returning, is there a visable gap using a small flashlight tight to the rotor & peering in opposite through towards light. If the pins are not moving free(I've seen too much heavy caliper grease develop enuff suction in blind- hole setups to actually pull the caliper towards the bracket & rotor, compressing the piston & leaving a gap between outer pad to rotor.), do the brackets align the caliper(s) with the rotor(s) properly w/o flexing/binding/pushback? Some piston seals drag/hang up in the bore & cause the piston to over-retract when the pressure is released. I've seen all of these in the field. That's where I'd start...good luck! How about a couple pics of the setup..?
Click to expand...

I can't answer any of those for certain tonight, but good things to check for. I might pull the calipers tomorrow and check that they extend and don't retract on their own. The caliper pins don't go into a blind hole, so that's probably not an issue. But checking freedom of movement on the pins themselves is another good one to check.

Biff said:
I know you said you pulled the Calipers off to bleed them are the bleeders at the top of the calipers ,grasping at straws here ?
Click to expand...

Yes, bleeders are up, I removed them, used a block to simulate the rotor and tried rolling them around while using the vacuum bleeder. Nothing,.
 
TurboGLH said:
Normally I wouldn't, but the need to diag overrides that. If I need to replace the hose afterwards, fine. But I wanted to narrow down the problem, if possible.



I can't answer any of those for certain tonight, but good things to check for. I might pull the calipers tomorrow and check that they extend and don't retract on their own. The caliper pins don't go into a blind hole, so that's probably not an issue. But checking freedom of movement on the pins themselves is another good one to check.



Yes, bleeders are up, I removed them, used a block to simulate the rotor and tried rolling them around while using the vacuum bleeder. Nothing,.
Click to expand...
Chit that sucks
 
I would obtain whatever fittings you need to block off the system at various points. Then see how hard it gets with the rear plugged off,etc
I can only tell you my "example." Before I tore my car apart, I used the factory 67 non power drum master--just poked holes in the residual valves. The front brakes are common 73/74 Duster/ demon, the rears are Lincoln Versailles rear axle and factory Linc disc brakes. I dont remember off hand how far the master goes, maybe ? 20-30% of travel and then it is just plain rock hard. I could lock them up easy at 70. My legs are not that strong anymore, I'm 73 now
 
Are you running GM front calipers on the rear? If so, what is the bore size?

Unless you have special, small bore circle track GM Metric calipers, you will end up with a soft pedal when paired with a 15/16" bore master cylinder.
 
67Dart273 said:
I would obtain whatever fittings you need to block off the system at various points. Then see how hard it gets with the rear plugged off,etc
I can only tell you my "example." Before I tore my car apart, I used the factory 67 non power drum master--just poked holes in the residual valves. The front brakes are common 73/74 Duster/ demon, the rears are Lincoln Versailles rear axle and factory Linc disc brakes. I dont remember off hand how far the master goes, maybe ? 20-30% of travel and then it is just plain rock hard. I could lock them up easy at 70. My legs are not that strong anymore, I'm 73 now
Click to expand...
As soon as the rear hoses are pinched the pedal's rock hard.......
 
Realize there is a very small amount of retraction that is normal/designed in, & is what keeps the pads close without dragging. I've used blocks to do various things, but the wood will make it difficult to judge due to it's compressibilty......on car & rotor is best......
As long as You're not crushing the hoses, pinching good/fresh ones just enough won't hurt 'em, it's done all the time. Have You tried isolating the fronts? If the pedal responds the same either way, that master may need upsized as other's have suggested, good luck!
 
DoctorDiff said:
Are you running GM front calipers on the rear? If so, what is the bore size?

Unless you have special, small bore circle track GM Metric calipers, you will end up with a soft pedal when paired with a 15/16" bore master cylinder.
Click to expand...

Yes, kit uses the GM front calipers as rears.

Car is on the floor currently so I'll need to verify later today, but I looked up the kit I bought, got the caliper p/n and did some digging. 2.5" is the bore size according to the almighty Google.
 
Seems like your fighting the advice that has been given. You need a larger bore MC. Or keep beating your head against the wall. You are not the first person to encounter this with a 15/16 bore. Same as a rock hard pedal. MC bore size is to large.
 
SGBARRACUDA said:
Seems like your fighting the advice that has been given. You need a larger bore MC. Or keep beating your head against the wall. You are not the first person to encounter this with a 15/16 bore. Same as a rock hard pedal. MC bore size is to large.
Click to expand...

Not sure how you're getting that impression, I haven't had a chance to go out to the garage yet, c so I'm answering the questions people have asked.

These calipers, apparently, are tough to bleed when used in the rear, so they had me doubting my first impression, which is a small MC. Just bouncing info off others before I make a move.
 
TurboGLH said:
Not sure how you're getting that impression, I haven't had a chance to go out to the garage yet, c so I'm answering the questions people have asked.

These calipers, apparently, are tough to bleed when used in the rear, so they had me doubting my first impression, which is a small MC. Just bouncing info off others before I make a move.
Click to expand...
Off topic here ,but you have a omni GLH.?
 
TurboGLH said:
I did, not anymore unfortunately. Still one of my favorite cars.
Click to expand...
I have a 89 CS. Daytona still and no is a CLub sport not a carol Shelby you probably already know this but the CS is 400lbs lighter and same power plant . Fun car for bbq technology :thumbsup:
 
You must log in or register to reply here.
-

Back
Top