TR6 rotor specifications help

[ichthos]

While I am waiting for insurance stuff to get cleared, I am working on the front brakes. Took my rotors into Les Schwab to get turned, but they said they can't find any specs for my brakes. Does anyone know what the minimum thickness that the rotors can be turned? They specifically asked for "minimum machine two" not sure what that means totallly. Nothing in either my Haynes or Bentley seems to state this that I can see. Any help would be appreciated.
Kevin

 

[Gliderman8]

Kevin-
I found this rotor info on the Buckeye Triumph technical page: https://www.buckeyetriumphs.org/technical/Brakes/Front/Front.htm
It appears that 0.45 inches may be the minimum thickness. See the info below....

Rotors: There is always a question as to whether the rotors should be resurfaced. I don't have the rotors resurfaced unless they have been gouged (pads wore through) or the rotors are not running true. I removed the rotors from the hubs on the first TR I rebuilt. After I reassembled everything I found that the rotors didn't run true and kicked the pads back so that the pedal went to the floor each time I applied the brakes. If I pumped the brakes quickly I could get the pads against the rotors and the brakes would function. I must have reassembled the rotors to different hubs or got the orientation different. Resurfacing fixed this. I have an old Haynes manual that says to be sure to make a locating mark on each piece if separating the rotor from the hub. (Should have read that before I took the rotors off the hub.) They also list the maximum run out at .002 inches. Neither the Factory TR6 manual nor the Bentley manual mention resurfacing the rotors or list any specifications as to the minimum thickness. I polled the 6-PACK e-mail list and Dick Taylor passed on that the new rotors are about 1/2 inch thick and several others pointed out that some rotors have markings on the inside that say the the minimum thickness is 0.45 inches. I had two sets on rotors in the workshop, one set was unmarked and the other set had the 0.45 minimum thickness cast into the rotor.
The rotors I decided to use for his project originally came off a '76 and were later used on a '73. They have a thickness of 0.50 inches indicating they have never be resurfaced. The rotor surfaces were heavily pitted from corrosion. I degreased and basted the hubs along with the the brake dust shield and the hose bracket. These components are shown in next photo below. If you look closely you can see the pits in the rotor surface. This was before I had them resurfaced.
Recall that the rotors were 0.50 inches thick before resurfacing. After resurfacing they measured ???? (I'll fill this in when I actually get them resurfaced)

 

[ichthos]

Thanks, Elliot. With it starting at 0.50, that sure doesn't allow much to be taken off. Puzzling why you would not find this information in any manual. A couple of nasty groves, but hopefully enough to get them turned. If not, I guess it will be time to decide on what type of rotors to buy.

 

[TR3driver]

The "Owners Workshop Manual" gives minimum rotor thickness as .440". Page 97, section 10.3

If you do replace them, I strongly suggest checking carefully for runout, thickness variation and balance. The last set I bought turned out to be horrible in all 3 respects. The book mentions that runout should be no more than .002" but doesn't give a measurement for thickness variation. My experience has been that even .001" TV will cause noticeable pulsation in the brakes.

PS, there is a service bulletin for the TR3 that suggests the disc be replaced if damaged; machined only if replacement is "not possible". It also limits the amount removed from each side to .025", and notes to ensure that there is still a radius between the outside braking surface and the center "top hat".

 

[DNK]

Randall- Should new disc be turned slightly then?

 

[ichthos]

Thanks for the information. So, runout can only be checked on the car, correct? If so, it seems like I am out of luck if runout is too great in that most places will not take them back once they are on the car. One of the YouTube videos I watched stated that anything below 1/1000 is okay in that you can't feel anything at that amount. It seems like I am going to have to buy new rotors, and then go in to have them checked if I feel any vibration. Should I start a new thread for recommendations for who to buy from and what type I should get? I have found that paying more money does not always equate to better parts.

 

[TR3driver]

Thickness variation can be checked before mounting them, just measure the thickness at several places around the rotor (same distance in from the edge) and compare. I haven't been in the habit of checking it, but I will from now on.

The rotors have to be mounted to the hub to check runout; and frequently you can get the runout below spec by fiddling with the mount. Turn 180 degrees and remount, or sand just a bit from the mounting surface. A normal part of installing new rotors.


Personally, I never turn them at all, but follow the factory advice in that old TR3 service bulletin. Either run them the way they are (after breaking the glaze) or replace them. They were presumably machined correctly to start with, and if they have warped just sitting in the box, then the casting is bad and they will quickly warp again in service.

Wouldn't hurt to start a new thread about rotors; I'm interested to hear what folks have to say. But I will stick with the stock type rotors; pretty much everything I have read says that cross-drilling and slotting have more disadvantages than advantages.

 

[ichthos]

Got the rotors turned. Apparently one was slightly warped. Odd that I did't feel it when I braked. Not enough to turn them again, but I think I will start a new thread on the best type of rotors so I am ready for the next time. Just waiting on a couple more parts from Moss. The new stainless steel pistons look nice. Thanks for all your help.
Kevin

 

[TR3driver]

Got the rotors turned. Apparently one was slightly warped. Odd that I did't feel it when I braked.

Runout doesn't usually show up that way. As long as the thickness is constant, the pistons and pads just follow the rotor as it waves back and forth while turning.