Dragster Brakes

Vertical mill with good part of one surface clamped down, face mill around the finished part of the top, then invert and repeat.

My vote is to pry open your wallet and spend 700 bucks on new ones.

If they are the flat kind that bolt onto the hub he would be best served by sending him to someone with a Blanchard grinder.

Before you start I would fixture them up and check the parallelism side to side. If they aren't all but perfect you'll never get rid of the chatter or pull even after they've been ground/milled.

To me it would be a royal PITA to attempt to shim one side to grind it parallel with the other, especially if it's the style with the bub built into the rotor. If they are the least out of parallel I would pass on the job. You could spend more time (money) trying to get them perfect than it would cost to buy new.

The style on the far right would be the most difficult to get parallel:

Best way would be to mimic a proper brake lathe and fixture two insert cutters, a left and right, on either side of the disk, adjusted so they cut at once and balance deflection. But it's a PITB to set up on a regular lathe, and by the time you cost out your time buying new might be the best move. Frankly, I'd want new (quality) rotors if I was going to actually put the car back on the strip.

Here is the way we do this:
If the rotors are the flat style that has a bolt on hat the process is pretty straight forward.
Take them to a good automotive machine shop...the sort of place that does real automotive machine work ...
Shop should have a dedicated flywheel surfacing machine...sort of like a small Blanchard grinder, having a rotary table and a grinding spindle above that runs a cup wheel.

Mount the rotor with a mechanical clamp in the center (machine has tapped holes in the rotary table) Register off the hat tabs on the side where they are flush....
Grind the opposite rotor face to clean. Flip over and use the just finished surface to register the rotor and grind the flush tab side...Do not grind the tabs...leave them full thickness.
Done!

Problem with the Blanchard is the magnetic chuck will pull the rotor flat and when released it will return to out of flat unless shimmed (time consuming)
By setting up on an original surface (tabs) and clamping in the center off the tabs will give a good reference that will run flat when mounted.

Grinding beats turning...won't leave phonograph lines in the surface and grinding can deal with hard spots in the rotors that cause bumps and depressions in the surface when turned....
Cheers Ross

AlfaGTA said:

Here is the way we do this:
If the rotors are the flat style that has a bolt on hat the process is pretty straight forward.
Take them to a good automotive machine shop...the sort of place that does real automotive machine work ...
Shop should have a dedicated flywheel surfacing machine...sort of like a small Blanchard grinder, having a rotary table and a grinding spindle above that runs a cup wheel.

Mount the rotor with a mechanical clamp in the center (machine has tapped holes in the rotary table) Register off the hat tabs on the side where they are flush....
Grind the opposite rotor face to clean. Flip over and use the just finished surface to register the rotor and grind the flush tab side...Do not grind the tabs...leave them full thickness.
Done!

Problem with the Blanchard is the magnetic chuck will pull the rotor flat and when released it will return to out of flat unless shimmed (time consuming)
By setting up on an original surface (tabs) and clamping in the center off the tabs will give a good reference that will run flat when mounted.

Grinding beats turning...won't leave phonograph lines in the surface and grinding can deal with hard spots in the rotors that cause bumps and depressions in the surface when turned....
Cheers Ross

Click to expand...

Yep. I've used a Peterson flywheel grinder to do some weird rotors years ago.

I turned a set of brake discs for my wifes car, the vibration at any speed over 10mph made the car undriveable. One of the disks was out of parrallel by .001. After I corrected that by turning both sides in the same setup it was fine.

If you cant turn both sides in the same setup to achieve perfect parrallelism, then I wouldn't bother doing it myself.

One thing hasn't been mentioned that may have a big impact on whether or not you do the job. Are the rotors case hardened of full hardened? In the last 30 years or more most rotors are only case hardened. I was going to turn a set for a 2004 Jeep and found not only would I need to go below the minimum thickness to get them true, I would also have needed to go beyond the thickness of the case hardening.

In this case a new set of rotors only cost about $100.00 each

It's a dragster. Buff the big chunks off by hand with a scotchbrite pad, and drive it around the parking lot twice with the brake pedal down slightly. Brakes are for staging, parachute is for stopping!
If it's a show car, or it has to look like new, get ahold of Aerospace Brakes in Florida-they should be able to make you a pair of rotors for much less than that.

Sell the customer custom hub adaptors to fit a standard stud layout he can take to the shop with a brake lathe. That way he'll have 'em for next time, too.

That way you're not on the hook for anything used on the car in a competition venue, either.

Chip

projectnut said:

One thing hasn't been mentioned that may have a big impact on whether or not you do the job. Are the rotors case hardened of full hardened? In the last 30 years or more most rotors are only case hardened. I was going to turn a set for a 2004 Jeep and found not only would I need to go below the minimum thickness to get them true, I would also have needed to go beyond the thickness of the case hardening.

In this case a new set of rotors only cost about $100.00 each

Click to expand...

None of the rotors I've bought in the last 20-30 years have been hardened, even the stainless motorcycle rotors. Maybe it's because i buy cheap rotors.

Other than aircraft and motorcycle applications I have never seen one other than cast iron. Well there is formula one but this ain't no formula one. If a disc was case hardened it wouldn't be for long. They can get red hot and good bye case hardening then.

DrHook said:

It's a dragster. Buff the big chunks off by hand with a scotchbrite pad, and drive it around the parking lot twice with the brake pedal down slightly. Brakes are for staging, parachute is for stopping!
If it's a show car, or it has to look like new, get ahold of Aerospace Brakes in Florida-they should be able to make you a pair of rotors for much less than that.

Click to expand...

Back 20 years ago we had a Mercedes 450 SL with the factory service manual.

Was great as it showed how to make many of the "special tools" needed.

Anyway for brake service we were floored!

It was something like this...

Remove calipers and existing pads.

Install rotor polishing pads into calipers and re - assemble

Drive (some specified speed) and come to a controlled stop in (some distance) (some number of times)

Repeat first steps to remove polishing pads and place new ones.

DONE

This was the brake maintenance section and somewhere else it had instruction for rotor thickness or other issues.

Assume the rotors are parallel and surface not grooved but grooves just do not wear the pad until it wears down anyway.

A dragster is not going to care much with a slightly pitted surface as some high performance ones have holes for cooling.

If the top line of the day Mercedes sports roadster used simple sanding of a rotor to clean up and declare the rotor and that met the performance expectations then using a scotch Brite pad in a rotary tool yo deglaze and remove rust may be just fine.

Old school brake lathes turned between center cones but back then most rotors were front wheel and in the hub so bearing races used for the centers to grip
Another simple option is locate someone with the turn the rotor while on the car lathes as they seem to be common now due to the many bolt patterns or other variables and they could do them on the dragster and call it a day.

But before you do anything that related to removing metal get documentation confirming minimum thickness (usually cast in somewhere and confirm they can be touched.

Lastly considering the danger involved make sure any and all work is on paper and paper has clear release of liability.

We did work on an oil filter remote mount kit and had the owner mark it as scrap before we touched it and the work was "prototype on scrap for future fit" and was cash and no names but that was not a part that could matter in safety.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

Never seen a brake lathe that used the bolt pattern to line up the rotor. That's what the hole in the hub is for. Take it to a store that has a brake lathe and that knows how to use it. Pay them $15 each and charge him $25.

maybe I'm missing something here? on a standard engine lathe, I made cast Suzuki road bike discs fit my klr on-off roader. ignored the "brake lathe" concept. cnc milled the od to size. lathe chucked on the od, flat face in. faced the inner brake face to dimension -.005 from the hub face. faced the hub face to dimension. flipped, chucked on the od again, faced the outer side. flat // <.002. no chudder at all.

I did my somewhat rusty unobtanium rear disks flat on the mill with a rotary table. Smooth as silk when stopping. They were just a smidge too large for my lathe.

Chip