USA_Z

I have a question for those of you running the APRacing CP8350 Caliper setup on their C5's. I purchased a used setup from a fellow forum member that had a little over a season's worth of use on them. I finally got to really test them this past weekend with a 3 day event. I absolutely loved how the calipers performed as I had constant solid pedal feel and increased trust in my braking power compared to what I had with the stock setup on my C5 Z06.

However, like my stock setup, I noticed very bad longitudinal taper of the brake pads on the second day. I was running new Wilwood type A pads that came with the calipers for this event. I also have SDK race hubs in the front that are solid with no slop at all.

Is the pad taper I experienced normal, I thought that would go away with the 4-piston setup, or should I maybe look into getting the calipers rebuilt?

C5ZEE06

that's a terrific caliper design. I bet some new seals on the pistons would go a long way in curing that taper.

Olitho

If they are wearing in a parallelogram fashion, it is my opinion that it is the spindle flexing. On high speed, high grip tracks with good DOT-R tires the ears on the spindle where the calipers mount provide some flex.

I am installing the new ZR1 spindles that are stronger and in three weeks after racing at Laguna Seca I should be able to corroborate that believe I have. I have beein using that set-up for about four years until just recently I went to the larger Endurance Kit version from AP.

USA_Z

I forgot to mention that I am running with the upgraded C6 knuckles that have additional strengthening support. These came with the setup and were definitely different than the stock C5 knuckles I took off. I don't know if they are the same as the ZR1 knuckles or not though.

I'm also not 100% sure about the parallelogram wear pattern but all 4 pads have pretty much the same exact wear pattern with a top of caliper/pad to bottom of caliper/pad taper. No taper in the horizontal (side to side).

USA_Z

I'm kind of leaning towards getting them replaced. At the very least I'd be starting from a known wear point for future reference.

RedLS1GTO

I pulled a brilliant move not long ago and accidentally deleted all of my PMs so I don't remember where my parts all went...

Was it my setup that you bought?

USA_Z

Actually yes, I should have just contacted you. Did you have any pad taper when you were running these?

argonaut

I used those calipers for about two seasons and experienced slight pad taper - nothing like stock calipers however. Note there are two different designs of the mounting brackets. Essex Parts is selling there own design now and its different than the original design when those calipers first came out for Vettes. That might be your problem, I'm pretty sure you have the older ones (If you got those from Brian I know something of their history). I'd contact Essex and see about getting the newer brackets.

Olitho

I still think this is more of a spindle/knuckle issue rather than mounting bracket as I have used both and I get taper with both.

RX-Ben

considering the pics of the cracked c5 spindle, at the mounting bosses, hardly seems like a stretch that the lack of strength could lead to other issues, like taper.

RedLS1GTO

Damn. I'm glad to hear that you liked them but sorry they weren't perfect for you.

They are definitely the "old" mounting bracket design.

The only issue I ever had with them was the first time out with the Ferodo 1.11 "deep" pads. It was COLD (~40°) and I had ducts on the car. They never got to temp, made a ton of noise, and wore very badly (chunked/tapered). I switched on day 2 to a used set of the Wilwood A that I carried as spares. I also taped up the ducts. They worked like a champ. The second time out I used a new set of Hawk DTC 70s. When I measured them, they had very minimal taper but nothing at a level that I would be at all concerned about. I'm surprised that you are seeing bad taper with the Wilwood A pads with the C6 spindles on it.

If I had to guess, I am also in the camp that it is a spindle/knuckle/whatever issue vs. a caliper issue.

RedLS1GTO

I can tell you for certain that prior to what you have done, the seals have 2 HPDE weekends at VIR and some minimal street use on them.

Olitho

I prefer the DTC-70s over the Ferodos.

There is a new DTC-80, or whatever name they will give it, that you should try.

It saves on rotor wear by laying down a thicker base layer of pad onto the rotor so you get essentially pad material frictioning against pad material. That is my layperson version of what I was told by the Hawk guys when doing some testing with their new pads.

USA_Z

Interesting that you mention this cold day issue. That could be part of my problem as well. This was a 3 day weekend and the first was non-stop rain and very cold so the pads never got up to temperature while on the track. I could have done most of the "damage" then but didn't notice until I checked after day 2. I have a set of CL enduro pads I wanted to try so I'll give them a go on a more normal weekend and see how things go before I do anything. Well, I might go ahead and get the newer designed bracket.

RedLS1GTO

I recommend that you get some heat paint or some of the sticker kind of temperature indicators so you know exactly where you are with them. I think there were still some in random places when I mailed them off if I remember correctly. If they are not up to temp you can see all sorts of bad things out of them.

USA_Z

Thanks, I'll look into getting more of those. There are a couple (1 caliper and 1 rotor hat) in place when you sent those. They never seem to change but haven't paid that much attention to them. I'll get some new ones and pay attention. I swear this HPDE hobby is getting more and more involved. LOL

CP Thunder

Might try knocking down the leading edges of the pad backing plate where it contacts the glide plate......make sure they don't hang up. I had that problem with our Wilwoods ..... not so much with the APs but got into the practice.

jimtway

I've been suffering the same pad taper issue for years, also suspect the spindles. I've tried all the "tricks" to get rid of it: new bearings, better rotors, replace spindle, rebuild calipers, better fluid, sacrifice a chicken, carve "oli is slow" into underneath his seat. None have improved the taper.

I've got a new set of the ZR1 splindles on the shop table awaiting install. Hopefully, I'll have some info on how they do by the end of the summer.

flink

I have SL6R's on the BMW. I have a lot of issues with taper causing a squidgy pedal. It's worse for me because I have unboosted brakes. This requires 3x greater mechanical advantage via the pedal ratio and master/slave cyl sizing. So the pads only move 1/3 as far per inch of pedal travel so I can only tolerate 1/3rd as much taper as a boosted setup.

I get longitudinal taper on the inboard pads (dues to the caliper twisting) and radial taper on the outboard ones (due to the caliper sides opening up).

I can "fix" the inboard ones by flipping side-to-side but that doesn't work with the radial taper.

I took some backing plates to a machine shop and had them machine them into thin tapered wedges: 0.4, 0.8 and 1.2 degrees. Insert those behind the pads to square them up. This works OKish.

I use a vast number of pads and when I've accumulated 20 or so I have a session with some 20 grit paper on the belt sander to reflatten them. This works OKish as well.

I discovered that when the bridge bolt is tight, the caliper opens up 6 thou but when the bolt is loose the caliper opens 17 thou. I said "ah-hah", as there's no bridge bolt on the inside of the caliper so the bolt's stiffness will be causeing the caliper halves to go non-parallel. So I now run with half a mm play in the bridge bolt (locknuts..). Alas this doesn't seem to help.

It's all a monstrous pain in the rear. I've concluded that the calipers (and possibly the aluminum mounts) just aren't stiff enough. Brembos or something are in my future.

RedLS1GTO

Random thought... has anybody correlated ABS to taper issues or the breaking mounts?

Without any scientific data to show where/how forces act on those points under braking, it seems to me that the cyclic loading caused by ABS would cause a much faster fatigue than a more consistent braking motion. ABS cycles at 10 Hz(?). If you are in it regularly, it wouldn't take long at all for that to add up to a fatigue situation for the aluminum knuckles.

I don't know the exact aluminum that these knuckles are made from, but as a representation:



The numbers may seem large, but how many cycles would a car see on a race track? In real-world application it would obviously have a lot more variables, complex loads, etc. I am just putting out a very simplified example.

As a completely arbitrary example, say.... 4-5 hard braking zones on a "normal" track? You hit ABS for 2 seconds in 2 of them with 2-3 modulations of your own doing. That gives 25+ cycles at PER LAP on the spindles. Given the forces that you see with big brakes, slicks, etc... it really starts to add up.