Pad knock back.....

[rrelco]

HELP.......running Wilwood 4 piston on the rear 12 bolt and now having pedal issues, what will a 10psi residual valve do in-line on the rear will that help any?

[SLO_Z28]

It will cause the pads to drag, and wont make it any better. You can go to a floating caliper setup, or take your car to a diff shop and have them make some thicker c-clips to get rid of some of the axle end play. I would go with the c-clip route first and see how much better it makes it.

It was fun getting a ride from you on saturday, that new engine really screams!

[rrelco]

James,

Thanks for the info there were some post on the residual valve for a fix i was just wondering if anybody has tried it, i am trying not to spend money right now.
and the 383 is very fun glad you like...

[pedro]

I used a 2psi and it didn't change anything. I ended up going with wilwood floating caliper kit from MCB. Selling the old setup paid for the new brakes and then some.

[SLO_Z28]

I used a 2psi and it didn't change anything. I ended up going with wilwood floating caliper kit from MCB. Selling the old setup paid for the new brakes and then some.

^This. Its like $700 for a full floating rear setup that has a e-brake from wilwood.

The alternative is the driving technique I mentioned, here is a good video:
6Dv3whihq8I

[rrelco]

so they dont use floating calipers? i know about the heal toe system pretty cool to watch, i did see him tap the brake a couple of times.

[Apogee]

X2 on the thicker c-clips ground to fit your axle grooves...ideally you would get your axial endplay to be as small as possible, but at least under .012".

What were you running before when you didn't have pedal issues? What size master cylinder are you running? Manual or power? What front brakes?

Tobin
KORE3

[rrelco]

I had CPP rear disc floating type, i just changed to Wilwood 6 piston front and 4 piston rear, i had a power master but then upgraded to a 383 with a big cam and i only got 1 good pedal so i changed that to a wilwood manual master with a 1.125 bore. and all this time i thought i had air in the system. but it pad knock back.

[Apogee]

Manual Wilwood (presumably Superlites?) brakes with a 1.125" bore master cylinder...and you're complaining about knockback, not pedal effort? Wow! What diameter rotors are you running? What front spindles? How much end play do you have in the rear axles? Considering you changed both the front and rear brakes at the same time, it's possible that your knockback issues are coming from both the front and rear of the car, if it is indeed knockback causing your low pedal.

Tobin
KORE3

[SLO_Z28]

I drove his car, it is definitely rear pad knock back. The pedal on his car actually feels great, about the same effort as my stock power brakes and nice and high...until you get knock back.

[JRouche]

Great thread. Im learning more about pad knockback than I have before.

I dont personally have an issue because I cant afford to race :( And I have a 9in on the back. But I think the better C clip idea is worth looking into.

You said you went with with a non power unit because the 383 wasnt pulling enough vacuum. Kinda curious what booster you had? Only cause my engine, a mild 350 is also a lil stingy with the vacuum. It will SLOOOOLY rise from around 2" of vacuum (full throttle run) to 9-12" after throttle lift (according to the EFI display) and it never seems to run out of vacuum in the canister. One throttle lift is enough to charge it for the next couple of braking sessions.

I have a 1985 cadillac selville booster, master cylinder and pedal. Oh and wilwood calipers up front and cadillac calipers on the back.

The booster is NOT cadillac BIG!. I have several inches of space between it and the small block. It is a perfect match for the wilwood brakes up front, stops like crazy. I have yet to dial in the rear brakes for the optimum use. I have a variable proportioning valve inline. Some day Ill take the car on a deserted street and tune that part up. Ill adjust it so the rear brakes lock and back off a bit on the knob and call it a day.

The rear brakes? Are they also parking brakes? I imagine not. Just had to ask cause some of the rear calipers Ive seen that were also parking brakes did have some issues with the parking mechanism causing some issues because they were not adjusting and holding the piston in, causing some soft brakes. NOT your case, you have solid brakes until you hit the esses right? Knockback. I agree. Dont discount what is going on up front. But you said you know its the rear knockback? Why? How can you point it to the rear and not the front?

Gonna learn something now :) I think you are gonna work this brake deal out. Funny about cars, for me anyway. Once one issue is worked out one other steps up, ERRRR!! :) JR

[Skip Fix]

My TA when stock had so much freeplay in the C clip on hard turns the brake drum rubbed on the backing plate. Dealers never could figure it out under warranty until I did the first brake job(semi metallic shoes-talk about no cold stop!) and saw the wear-out of warranty of course.

[rrelco]

Great thread. Im learning more about pad knockback than I have before.

I dont personally have an issue because I cant afford to race :( And I have a 9in on the back. But I think the better C clip idea is worth looking into.

You said you went with with a non power unit because the 383 wasnt pulling enough vacuum. Kinda curious what booster you had? Only cause my engine, a mild 350 is also a lil stingy with the vacuum. It will SLOOOOLY rise from around 2" of vacuum (full throttle run) to 9-12" after throttle lift (according to the EFI display) and it never seems to run out of vacuum in the canister. One throttle lift is enough to charge it for the next couple of braking sessions.

I have a 1985 cadillac selville booster, master cylinder and pedal. Oh and wilwood calipers up front and cadillac calipers on the back.

The booster is NOT cadillac BIG!. I have several inches of space between it and the small block. It is a perfect match for the wilwood brakes up front, stops like crazy. I have yet to dial in the rear brakes for the optimum use. I have a variable proportioning valve inline. Some day Ill take the car on a deserted street and tune that part up. Ill adjust it so the rear brakes lock and back off a bit on the knob and call it a day.

The rear brakes? Are they also parking brakes? I imagine not. Just had to ask cause some of the rear calipers Ive seen that were also parking brakes did have some issues with the parking mechanism causing some issues because they were not adjusting and holding the piston in, causing some soft brakes. NOT your case, you have solid brakes until you hit the esses right? Knockback. I agree. Dont discount what is going on up front. But you said you know its the rear knockback? Why? How can you point it to the rear and not the front?

Gonna learn something now :) I think you are gonna work this brake deal out. Funny about cars, for me anyway. Once one issue is worked out one other steps up, ERRRR!! :) JR

I had the CPP Dual Diaphram I think it was a 8" the motor had ideling issues that I had to figure out so when I hit the brakes it wanted to die. so I did a bunch of stuff to figure it out the first thing was to remove the vacuum canister on the distributer,after doing that the motor ran way better 383 in my case dont like any advanced.

Wilwood uses the hat type parking brake the piston is not used as a parking brake small shoes. CPP uses the Cadillac caliper and if you dont set it correctly within .25 inch you will burn up your rotors and you must always set the parking brake everytime you park so that it will adjust.

I am sure its the rear I have ATS spindels up front and there is no play, but the rear has alot, I need to get meassurment.

GM engineers know whats going on they use full floating calipers probable due to that same issue.

I did make a call the Coast Drivline and he has no way of making new c-clips and has never done that in his 30 years, he also said there is a reason for the axels to have end play you have to remove the pin then push the axels in to remove the c-clip.

either I learn how to tap when I come up to a corner or buy Wilwoods floating caliper.

its only MONEY....

[SLO_Z28]

I did make a call the Coast Drivline and he has no way of making new c-clips and has never done that in his 30 years, he also said there is a reason for the axels to have end play you have to remove the pin then push the axels in to remove the c-clip.


Sounds like you got someone over there that has no idea what they're doing. Im getting some metal work done at the shop behind there (really cool place if you have never seen it), so Ill roll by there and talk to them in person.

[Vegas69]

I've been to the dark side of the moon and back on this whole deal. Bottom line, how many fixed calipers do you see from the factory on a ford 9" or 12 bolt? NONE Some guys get away with it with power brakes and stock width wheels. They also get away with it if the ***** foot their car around. A floating rear caliper, floating axle, or Corvette style bearing pack are the only way to CURE it.