Wilwood Pad Knockback

[67rally]

Quick background. Last year I was experiencing a little pad knockback on hard street cornering on my '67 Camaro. A quick pump of the pedal and the brakes were great. Bleeding the lines did nothing. At the time, I had a 12 bolt (c-clip) rear with 12.19" 4 piston Wilwood DynaPro's out back. (6 piston DynaPro's in the front, 7/8" Wilwood Dual MC, Wilwood Proportioning valve, manual brakes)

Fast forward to this year, I swapped out the 12 bolt for a Strange S60 with tapered bearings. I used the same rear brakes, with a new parking brake bracket from Wilwood, and my pad knockback was completely resolved. I have around 1000-1200 miles on it, and no hint of pumping the brakes, not even once. Until yesterday. I did my first autocross (actually and autocross school), and I had to double pump the brakes every time, all day. I don't want to have to tap the brakes constantly during a run.

I'm not willing to swap out to a full floating rear, and my research today points me in the direction of the Wilwood D154 floating calipers. Is there an easy way to just buy the D154's and the necessary brackets, or is the whole kit the way to go? Or is it even the right way to go? If there are better options out there, I'm open to suggestions. I would like to stick with Wilwood calipers, so they match the front though.


Other options I saw mentioned were switching to a bigger bore MC, or using a residual valve inline with the rear brakes. But both of those options sounded more like bandaid solutions. Thoughts?

[rrelco]

I have had the same issue with my 12 bolt what I had done is the rear end shop added material to my axles by welding build up so the axle didnt have any play, i did add the 10psi residual valve and my master is a 1.0 bore. i still have some play but not like it use to be.

[dontlifttoshift]

First make sure it is the rear brakes that are knocking back.

[67rally]

First make sure it is the rear brakes that are knocking back.

Interesting. I know the rears were the culprit before, since the problem was eliminated after swapping in the new rear w/tapered bearings. I suppose the rear could be fixed and its just the fronts that are knocking back on the course now. I'll have to find a vacant parking lot, do some maneuvers and coast to a stop. Remove the wheels and see which is the culprit.

I'm betting it's still the rears though, and that the tapered bearings were enough to eliminate the knockback on the street, but not on the AutoX.

[67rally]

^^^

Actually, here's a thought regarding my above post...

Let's say I take it to a vacant parking lot and make some hard turns and can replicate the knockback. Then pump the brakes back up, crank the proportioning valve all the way to the front (so there are no rear brakes) and perform the same manuevers.

Is it safe to assume that if I don't have knockback (with the rears blocked off), that the fronts are not the culprit, and if I do still have knockback that the fronts are part of the issue, but the rears may also be involved?

[Apogee]

^^^

Actually, here's a thought regarding my above post...

Let's say I take it to a vacant parking lot and make some hard turns and can replicate the knockback. Then pump the brakes back up, crank the proportioning valve all the way to the front (so there are no rear brakes) and perform the same manuevers.

Is it safe to assume that if I don't have knockback (with the rears blocked off), that the fronts are not the culprit, and if I do still have knockback that the fronts are part of the issue, but the rears may also be involved?

That's not how an adjustable proportioning valve works...even if you were to adjust it all the way to the minimum pressure setting, you'd still be getting 57% of the front line pressure to the rear. It is safe to assume that both the front and rear are contributing to your knockback issues since nothing is 100% rigid, however the rear is typically the larger contributor and therefore the first place people go in an effort to reduce the effects of knockback. That said, what are you running up front for spindles/knuckles, hubs, brakes, etc?

Tobin
KORE3

[67rally]

That's not how an adjustable proportioning valve works...even if you were to adjust it all the way to the minimum pressure setting, you'd still be getting 57% of the front line pressure to the rear. It is safe to assume that both the front and rear are contributing to your knockback issues since nothing is 100% rigid, however the rear is typically the larger contributor and therefore the first place people go in an effort to reduce the effects of knockback. That said, what are you running up front for spindles/knuckles, hubs, brakes, etc?

Tobin
KORE3

Thanks. The front brakes are a complete kit from Wilwood. They are the 12.19" drilled/slotted rotors (.81" thick) w/6 piston DynaPro calipers (http://www.wilwood.com/BrakeKits/Bra...o=140-10510-DR). Stock Camaro disc brake spindles. The hubs are the ones that come with the kit (http://www.wilwood.com/Hubs/HubProd....temno=270-7274).

The tire/wheel combo is nothing over the top. 18x8's w/5"bs and 245/40/18's Nitto 555's up front and 18x9's w/5.25"bs and 275/40/18 Nitto 555's in the rear.

[carguykeith]

I think to fully stop knock back it's either a floating rear or floating calipers, like Tobin said nothing is completely rigid. I'm pretty sure Wilwood has a floater kit out now that is comparable to what you currently have but you'd need to talk to them about exactly what parts you'd need to convert over.

[72BBSwinger]

Does the Dana have Ford or Mopar bearings? Are they adjustable? If the front wheel bearings have ANY slop that will cause it also.

[67rally]

Does the Dana have Ford or Mopar bearings? Are they adjustable? If the front wheel bearings have ANY slop that will cause it also.

I believe they are they Strange A1013 tapered bearings which are non-adjustable. I'll check my paperwork when I'm back home.

Front wheel bearings have less than 4000 miles on them. In fact nothing on the car has more than 4000 miles except the body.

[67rally]

I think to fully stop knock back it's either a floating rear or floating calipers, like Tobin said nothing is completely rigid. I'm pretty sure Wilwood has a floater kit out now that is comparable to what you currently have but you'd need to talk to them about exactly what parts you'd need to convert over.

Yes, I'm pretty sure it's the D154 calipers. If it is just the rear brakes, I'm going to contact Strange and Wilwood both to make sure I have the right parts for my application.

[72BBSwinger]

I wasn't questioning the quality of your front bearings or the competence of the installer. If they have ANY wiggle when you have the front tires off the ground it can cause knockback. Even an 1/8 of a turn on the spindle nut can make a difference. It's the down side to a manual brake setup. I have rear drums and experienced this problem on my fronts.

[67rally]

I wasn't questioning the quality of your front bearings or the competence of the installer. If they have ANY wiggle when you have the front tires off the ground it can cause knockback. Even an 1/8 of a turn on the spindle nut can make a difference. It's the down side to a manual brake setup. I have rear drums and experienced this problem on my fronts.

Thanks, I'll check them out.

I took the Camaro to an empty parking lot in an industrial park at 5am today. Did a series of hard left and right turns, coasted to a stop. Got out, jacked the car up and a security guard rolled up in his golf cart. I explained what I was doing and why. He said "explain it to the cops when they get here, or get out of here before they arrive. Your choice." Needless to say, that didn't go so well. I'll jack the front end up tonight when I get home and see if there's any play in the front wheel bearings.

[71RS/SS396]

Thanks, I'll check them out.

I took the Camaro to an empty parking lot in an industrial park at 5am today. Did a series of hard left and right turns, coasted to a stop. Got out, jacked the car up and a security guard rolled up in his golf cart. I explained what I was doing and why. He said "explain it to the cops when they get here, or get out of here before they arrive. Your choice." Needless to say, that didn't go so well. I'll jack the front end up tonight when I get home and see if there's any play in the front wheel bearings.

Unbolt the calipers from the brackets when you check for play. I fought a car for several months with a knock back problem, with the calipers installed all seemed fine, but once I removed the calipers the problem was obvious. I would check the axles for lateral movement with the calipers removed, even with tapered roller bearings you can have movement if the retainers are incorrect.

[67rally]

Unbolt the calipers from the brackets when you check for play. I fought a car for several months with a knock back problem, with the calipers installed all seemed fine, but once I removed the calipers the problem was obvious. I would check the axles for lateral movement with the calipers removed, even with tapered roller bearings you can have movement if the retainers are incorrect.

Is this just because the brake pads were holding the rotors from moving when you went to check? If so, I should just be able to remove the brake pads when I check right? I safety wired my caliper bolts, so if I don't have to remove them it would save a step.

[72BBSwinger]

Yes, no pads, same result.

[67rally]

Alright, I removed the front brake pads and set up a dial indicato with the magnetic base on the rotor and the indicator tip on the end of the spindle to measure endplay. Bothe sides were between .001 and .002. So I think we can rule that out. I still need to do the parking lot test, which probably won't happen until Wed. at the earliest.

[WelderJay]

Alright, I removed the front brake pads and set up a dial indicato with the magnetic base on the rotor and the indicator tip on the end of the spindle to measure endplay. Bothe sides were between .001 and .002. So I think we can rule that out. I still need to do the parking lot test, which probably won't happen until Wed. at the earliest.

Did you ever get this figured out? I am having the same issues with my manual wilwood setup, I am wondering if different sized c clips would help shim the lateral play from the axle? Everything front and rear is new except the rear end which was narrowed, one new axle, new bearings and seals and new fixed caliper 4 piston wilwood kit.

[67rally]

I haven't addressed this yet, but I don't have c clips with my Strange S60. I'm going to go with the floating calipers as a few people have said they resolved their issue.

The c clip eliminator took care of my issues on the street but not on the track.

[Skip Fix]

If you don't need E brakes there are a number of ways to get D154 calipers on the rear, just depends on the rotor you want to use. If you had a 10/12 bolt bolt pattern on the Dana even the 79-81 Trans Am brackets and rotors would work, just use either Wilwoods dual piston D154 or any GM metric caliper-not th efactory rear ratchet caliper. Lots of weld on brackets on the circle track side.
http://www.speedwaymotors.com/GM-10-...Kit,14015.html

Speedway aslo has the weld on brackets and a few other kits.