Solving Pad Knockback

[Payton King]

re-read my post and it was not clear. The .70 and .75 is the master bore size that i am running. I have twin masters with a balance bar.

I was runnng the Wilwood BP10's and they never stopped well. Went to a Carbotech pad and it was night and day difference. The Carbotech Ax6 is an autocross pad that you can also use on the street. Easy on rotors, they are dusty and every once in a while I will get a small amount of noise. The cold mu on those are .52. I believe the cold on the bp10's is .32 or .35.

Per Carbotech's rec these are not a track pad for the front and will not handle the heat. Running street tires on the track they reccommended XP10's for the front and AX6's on the rear. If I move up to more aggressive rubber or a really tough braking track I will need to move up their line.

Give Carbotech a call and they can give you the info that you are looking for....

[a67]

re-read my post and it was not clear. The .70 and .75 is the master bore size that i am running. I have twin masters with a balance bar.

I was runnng the Wilwood BP10's and they never stopped well. Went to a Carbotech pad and it was night and day difference. The Carbotech Ax6 is an autocross pad that you can also use on the street. Easy on rotors, they are dusty and every once in a while I will get a small amount of noise. The cold mu on those are .52. I believe the cold on the bp10's is .32 or .35.

Per Carbotech's rec these are not a track pad for the front and will not handle the heat. Running street tires on the track they reccommended XP10's for the front and AX6's on the rear. If I move up to more aggressive rubber or a really tough braking track I will need to move up their line.

Give Carbotech a call and they can give you the info that you are looking for....

OK, thanks for the info on the M/C bore size. That makes sense.

The AX6 at .52 mu puts them in the upper range of a G rating. Good friction level for street use.

Bob.

[Van B]

The 1" master totally transformed my car. I beat it as hard as I could on the street with not a hint of knockback. I can't believe the difference. I like the feel better as well. It firmer but with a much higher pedal and it gives me way more confidence. I don't know if the 7/8 was never right or this one made that much difference. There was no fluid behind the bore and the seals looked fine. The bore was scored and the front fluid was nasty with some fine particles. I think it was from the excessive pumping I did in my 8-10 races and street driving. Bottom line is, I'm happy !!!

What master did you go with? What did you have on the car. I am fighting the same thing. Here is my current setup. I think it is a 15/16 bore.

[MarkM66]

Lever arm, eh? My 7 3/8 BS (11") wheel would have approximately half that, I think. That's gotta be why the original Wilwood bearing retainers didn't cause me any problems.

Very nice analysis.

jp

I'm confused, wouldn't more backspacing cause more 'lever arm', so yours would be twice that...

[a67]

I'm confused, wouldn't more backspacing cause more 'lever arm', so yours would be twice that...

More back space moves the wheel in on the axle. The mounting flange of the wheel is closer to the outside.

Bob.

[Vegas69]

What master did you go with? What did you have on the car. I am fighting the same thing. Here is my current setup. I think it is a 15/16 bore.

Hang in there. I'm running a 1" bore Wilwood now. However, I found out yesterday that there is some residual pressure in the system at all times. The piston design was different from the 7/8 to 1" and I used the same push rod which seemed fine. One it's in the car the angle isn't perfect between the rod and pedal arm and puts just a touch of pressure on the system.(Atleast that's what I think) My brakes locked up yesterday and nearly stranded me. Strange since the night before it seemed fine after an adjustment in the rod length. Must of been the temp difference. Anyway, I'm not sure it's fixed my problem totally until I get the pressure out of the system at rest. So I get to start over and re bleed the system and bench bleed.

[parsonsj]

wouldn't more backspacing cause more 'lever arm'

Only after a point. Matt's lever arm measurement is from the wheel centerline. Todd's wheel's backspacing has the bearing retainer 4.088" inboard of the wheel centerline. More backspacing will move the bearing retainer closer to the wheel centerline, reducing that lever arm, and the force with which the axle is pulled from the center as the car goes around a turn.

I doubt the M/C bore size has anything to do with knockback unless there is some residual pressure in the system.

jp

[Van B]

I doubt the M/C bore size has anything to do with knockback unless there is some residual pressure in the system.jp

Probably not, but if the MC is not moving enough volume it will be harder to overcome knockback. I have been going through this for three plus years now. I thought I found a bad MC last year but when I ran at Faceoff at Road America I realized my problem was not cured.

The manufacurer of my brakes can't even tell me for sure. They are guessing...

[a67]

...One it's in the car the angle isn't perfect between the rod and pedal arm and puts just a touch of pressure on the system.(Atleast that's what I think) My brakes locked up yesterday and nearly stranded me...

If manual brakes (I think they are and didn't go back reading posts to find out), is there a return spring for the brake pedal? It may be that the weight of the pedal is tapping the M/C piston as the car gets bumped around.

Bob.

[Vegas69]

Wilwood has a stiff spring on the piston. They don't recommend a return spring and I never has any issue with the 7/8. I'm pretty sure I know why....

[David Pozzi]

Hang in there. I'm running a 1" bore Wilwood now. However, I found out yesterday that there is some residual pressure in the system at all times. The piston design was different from the 7/8 to 1" and I used the same push rod which seemed fine. One it's in the car the angle isn't perfect between the rod and pedal arm and puts just a touch of pressure on the system.(Atleast that's what I think) My brakes locked up yesterday and nearly stranded me. Strange since the night before it seemed fine after an adjustment in the rod length. Must of been the temp difference. Anyway, I'm not sure it's fixed my problem totally until I get the pressure out of the system at rest. So I get to start over and re bleed the system and bench bleed.

Steve Rupp chaged the Willwood 7/8" master to a 1" and his brakes locked up too. Now that the pushrod was shortened it's OK.

[The GMR]

Very good thread. Surprised I just stumbled onto this.

I have been talking to Wilwood about this very issue for some time now.

One solution is to upgrade to a Full-Floater system for the rear end.

Jason

[Vegas69]

Steve Rupp chaged the Willwood 7/8" master to a 1" and his brakes locked up too. Now that the pushrod was shortened it's OK.

It's weird, I adjusted it shorter the night before and drove for 30-40 minutes with no problems. When I got home I did roll the car back and forth and I could hear the front brakes drag which was strange I thought. The next day is was hotter and I didn't make it more than 5-6 miles and they locked up solid. I tried going shorter to no avail... I'm going to swap over to a factory type pushrod instead of the beveled aftermarket. I wasn't thrilled when I put it together and didn't think about the slighty angle needed to put in the clevis pin. On the bench when I moved the rod up or down it pushed the piston. Should of known but....

[dontlifttoshift]

Soooo, I don't have a knock back problem (drum brakes) but my retainers are bent and this seemed like a relevant thread. It's a currie 9" with their axles and Timken set 20 tapered bearings. I have the 360 degree "heavy duty" retainer plates. When I pulled the car apart I noticed some play in the axles but didn't really worry about it. i got all my rear suspension sorted out, welded all my brackets on, and had the housing straightened. The races were trashed by the time they got out so I bought new bearings and noticed the retainers rocking on the bench. When I assembled the rear end originally it went together very well, I pushed the axles home by hand and "set" them with a deadblow hammer and tightened up the hardware.

Any ideas on how I can prevent these retainers from bending again?

Donny

[dontlifttoshift]

I just got off the phone with Currie. They told me it was normal to bow a little, about .015", and that would happen on assembly. I get that.

These measure .065" at the middle. That seems excessive to me and hardly normal.

[Bryce]

how much does your bearing protrude from the axle ends. I think .020" is about normal. If you have more than that then maybe when you torque the retainers on you bent them.

[Vegas69]

That's what I was thinking. ARe you sure you have the right retainers?

[dontlifttoshift]

Yeah, everything went together fine the first time. I dont recall the plates bending when I tightened them but I do remember that the axles were nice and tight with no endplay and then they were loose when I took them apart. I am not sure what the right retainer would be. It's just a flat plate, no relief cut into the back. I need to measure the bearings/seals and the depth on my housing but I can't believe it would be wrong. This entire assembly came from currie.

Thanks
Donny

[mwhizard]

I had bad knockback on my wilwood rears and narrowed it down to my axle float. I bought new moser axles, and at the time put in a truetrac. I still had enough float with all new hardware to lose pedal feel. I am running the clip axles still so what I did was made my own spacer that goes between the axles on the truetrac. Basically took feeler gauges and figured out how much clearance there was on the supplied spacer, then made a new one on a lathe out of steel. It made a world of difference, but I still have a bit. I've heard of using a 2pound residual valve, is that something I should consider? Oh, and the system is 7/8 master, manual brakes, disk brake proportioning valve plus inline adjustable proportioning valve, 6 piston wilwoods up front and 4 piston wilwoods on the back.

[Vegas69]

If you have one of the older Wilwood kits, the retainer was wrong and they have an updated retainer that has the proper lip and is thicker steel. I've shimmed by axles and have a 2psi residual. I didn't find that either did much good. I'm getting ready to convert to a floating caliper.