rotor refacing

[Bill Musarra]

I have a set of rotors that Fran furnished to me way back when I was searching for high performance brakes for the C-4 front suspension. I have just had a few problems with that setup. On the second drive of the car, I noticed the brakes grabbing and releasing. It seemed to get worse with more braking force aplied. So I checked the suspension and found two problems. The first was that the spacers in the polyurethane bushings(new), that hold the lower A arms on were a sloppy fit. The bolts that held the A arms in place are metric, measuring .454 as best I can measure. Being a DRB I am wondering why they made these this way. Original brakes that came on the car were worn out corvette units that probably were sourced from a junk yard. Do they have Corvette junkers in Australia? Remember I bought this car second hand and it had never been driven. Anyway, the front bolt is a grade 9 metric fully threaded bolt with a radiused head and looks like a factory item as it has a built in washer on it. It looks likd a Corvette item. Source??? The back bolt is a metric grade 8, 5 1/2" bolt due to a frame member next to the housing for the suspension. This may need updating to a grade 9. The spacers in the polys are 3/4"OD and .502 ID for a standard 1/2" bolt which will not go into the frame members. Had I known this in the early build stage I could have had them converted to the American standard. But that was then and this is now.
What I did was to get some 3/4 inch stock and drill it out to .002" over the bolt size. That solved the sloppiness.
Now the brake issue. When I recieved the brake adapters and rotors/calipers from Fran there was a slight problem. In shipping the box got dropped and the hub(s) were dented(only thing I could see that was amiss). By dented there were marks on the hub(s) that looked like someone had hit them with a hammer a time or two. I informed Fran at that point to see what should be done. We figured this was cosmetic and to leave well enough alone. It would never be seen and therefore would be more trouble than it was worth to persue anything further. Fran was very generous to help me out. He even sent the taps and dyes needed to install the components. All was assembled and torqued at that point. Move forward a couple of years. I pulled the calipers and checked the rotors for eveness and found the right front rotor had a very slight warp outward over about 20-30º of the face of the rotor. I took the hub off and repositioned the rotor on the hub and retorqued it to see if it was the hub. It made no difference, as I marked the rotor and it came up the same. I took it to Pep Boys to get it turned to true it up. They informed me that they could not turn the rotor as it was in their works a "throw away rotor" and for safety reasons they could not allow me to have that done and reinstalled on the car from a liability standpoint. Thier words, the rotor was wide and its face, thin with large internal fins for heat disipation(read high performance), and it probably would chatter even if they did it.
My question is should I try to reface this still new rotor the slight facing needed to get it true. I don't think it is more tha a few thousands at most. Or should I bite the bullet and get a new rotor?

Bill

 

[Mike Drew]

My question is should I try to reface this still new rotor the slight facing needed to get it true. I don't think it is more tha a few thousands at most. Or should I bite the bullet and get a new rotor?

I think the Boys at Pep Boys already answered your question for you.

Rotors are cheap. Brakes are important. 'Nuff said....

 

[Howard Jones]

Your rotor has a minimum spec for thickness that was established my GM or whoever. Try and find out what that is. A minimum reface cut would be OK in my opinion if you only need to remove a few thou to true it up. HOWEVER, the resulting thickness must remain within the minimum spec for your application.

Remember, the thickness of the rotor combined with pad wear can and will cause the pistons to extend out from the caliper. At some point too far is too far and you will get pistons that don't release at the time that is least desired. Ask me how I know!

Think track day, hot everything, big fast brake zone and then the left front doesn't release as you roll off the brakes at about 60 MPH to turn it the car for a right hander right on the limit. Can you say huge sideways slide that scares the shit out of you!

Brakes are a big deal, that doen't mean that you can't do maintenance to extend the life of good parts, but if its worn out then its worn out. Just replace stuff when it should be replaced and you will be fine.

 

[Cliff Beer]

Nothing wrong with turning a rotor. Inspect it and make sure you don't see any stress cracks or anything like that. And, as others have said, look for the minimum thickness stamp on it (or look it up online...) and make sure the thickness after turning is adequate.

Sounds like that rotor is still pretty fresh, no need to waste it unless there's something wrong with it.

I turn my own rotors on my lathe and they work just fine after they're true'd up.

ps. I heard a while back about an alfa romeo somewhere in the NE which was equipped with wooden rotors. Apparently the owner didn't like paying for new rotors so he just made new ones out of wood as necessary.

 

[Dimi Terleckyj]

Hi Bill

Stamped on the rotors should be the minimum thichness allowed.
As long as you don't machine past that point you are OK.

If you need new rotors contact Vette Brake Products in the US.

I purchased upgrade brakes from them for my DRB with Corvette suspension to change from C4 to C5 and their service and prices are great.
I have used their upgrade kits 3 times now with no problems.

I have no hesitation in referring them to anybody.

Dimi.

 

[Dave]

Get a new rotor from Fran and run a 1/2 drill bit through the suspension brackets so you can run 1/2 inch bolts.......

 

[Scott]

Bill,
I ran into the same problems with rotors on an RCR. I did have three of them re-cut, and the warp just came right back. The solution was to buy new short-trac rotors made by wilwood. (no problems after that) If you like, post a pic of the rotor, and I can give you a part number/source. Or send a PM. Best, Scott

 

[Randy V]

How about posting up some pics of these rotors that have failed?

There are some very inexpensive stock-car rotors that are good for one or two races before they are toast.. I used to use them. They are typically uni-directional rather than curved vane and are sandwich sand-casted.. If the parting line in the vanes shows any offset between the right and left sides, don't even think of using them for anything more than a paper-weight..

 

[EGLITOM]

You probably got some Wilwood rotors from Fran. If you check out there Website they have different rotor types of even the same dimernsion. Some are lighter , less expensive material . less exact machining , not tempered , where as other types are heavy duty with bigger wall thicknesses, more expensive ( high carbon steel) , tempered and machined to tighter tolerances.
THe brake discs of my car had a slight warp as well after the first heat cycle ( i probably have been to less cautios in getting them bedded in, as a fact a gave a sh... about that and hit the brakes as hard i needed to slow me down going probably to fast also for some first rides). Anyway the warp was about 1-2/10th of a millimeter, which resulted in severe chattering of the steering when i fully applied the brake pressure.
We took the rotors of and my son machined them still mounted on there hubs in a double action ( simultaneous cutting from the front and back side of the disc) lathe which they have in the Porsche dealership for exactly that purpose.
We where able to get them down to a warp of max 2/100 of a mill.
They have stayed like this ever since and believe me they have seen some severe heat cycles since them and braking is very smooth without any slightest chattering.

So it is all about hwo much they are warped and what was the cause for it. I would use a dial on a magnetic arm and put it on the rotor to measure exact the warp and than go from there. If it is more than 2-3 /10ths of a mill, i would buy new one, if it is below that you could decide to go for machining them. This will still be within there standard wear tolerance , which of course need to be respected.

TOM

 

[Rich Roy]

Make sure "all" mating surfaces are spotless and free of any surface rust on the hub to rotor contact areas. Even a little amount of rust from humidity in the air can add up once it's measured at the outer perimeter of the rotor. It sounds minute, but adds up to enough at the outer surface to result in being out of round laterally, especially on large diameter rotors. There are also variable sized rotor shims available for the Corvette rotors as G.M. does not recommend resurfacing rotors.(but does offer the on car cutting "J" tools to do it). The shims are tapered from one side to the other and fit between the rotor and hub. I would make sure all surfaces are clean first. Then if possible do an "on car" cut so any warp in the hub could be eliminated. Is this getting too anal or what?

 

[Bill Musarra]

I had a light surfacing at a Goodyear shop that I kinow the guys. I then went to put them on the car and noticed a slight buildup of what looked like rust or oxidation on the bell(outside). I took great pains to remove this oxidation and put the bells back on. I tightened them up gradually, spinning the disc as I went, and noticed the warp was still there, but less of it. This gave me the suspicion that the warp was actually a bend in the bell. So I loosened them up and tightened them at the warp(outward) to lateral of it and then the lug(s) opposite the warp. I noticed that spinning the rotor as I slowly tightened them the warp was disapearing. I loosened them and tightened again and the warp now could not be notided. On driving only the slightest bit of grabbing of the disc could be detected. So I think the bell is the problem here. This is probably some left over from the dings it got in shipping from Fran's. Since this is from years ago when I first got them there is no since in trying to redress the issue. It seems to me that the mounting face of the bell got dinged and it bent toward the inside of the bell(?) Options at this point are to try and square the bell or replace it. I have it down to the point that the grabbing is so slightly noticeable that it is felt only in the steering wheel. It is not noticeable with the "seat of the pants". I will work with this a bit more over the winter as this weekend is the last chance to get the car out. Supposed to be close to 70 tomorrow and I am going to the Caffiene and Octane cruise in up in Alfaretta off Windward Parkway. It is the biggest cruise in in the state. Lots of exotics usually show up. Then it is parked til spring and I can get some of the little things done like the nutserts for the windows and things like that.
Thanks for the valuable imput and the learning experience of you guys that have "been there done that"

Bill

 

[mark b.]

i had the shoulders on the studs protruding from the hub on my jbl and had a heck of time finding the source, they were interfering with the hat to hub mating.