[opelgtman1973]

I'm going to be replacing the rotors on my '73 GT as part of a complete brake system rebuild project. I may have more questions as I go, but right off the bat something in the instructions that came with the rotors stumped me.

It says that after fastening the new rotors, you need to use a magnetic comparator to make sure the rotors are true. I found out what that contraption is on the net, but it doesn't seem like something I could afford if I could find one. I've seen other people replace rotors and they didn't use any special tools. I honestly don't remember if they even checked the rotors after putting them on.

The only thing I found on this board about rotors was to watch out for twisting off frozen bolts. That pretty much goes for anything on these 30 year old cars, though. Been there, done that. Although, on another thread, I read about the candle wax trick, and I have my torch and some candles ready just in case the Liquid Wrench fails me

Anyway, what do people normally do after replacing rotors to make sure they're true?

 

[BQS4]

the thing you're checking for when you use this "contraption" is for disc "run out", this contraption is just an ordinary dial caliper mounted to a strong magnet to hold it on various metal surfaces, both on the edge and on the braking surface. The edge is not as important as the brake surface. Edge true-ness is more like a tire that is not balanced right. Brake surface true-ness is to make sure it is as flat as can be, because if it's not, it's not that the car won't stop, you'll get a "pulsating" feeling from your brake pedal. Taking your new rotors and having them turned on a brake lathe will straighten this up, the process is called "truing". If you have a good brake shop nearby, they will understand this and take off just enough material to do this, and not gouge out a layer of un-necessary material. Now, this does not really have to be done with all rotors, even new ones. But, there are people who are true sticklers for exact-ness, so, it's up to you. Generally, it's about $25 +/- to turn a rotor, no matter how much material is removed.
HTH,
Gene

 

[ddoyle]

I put lots of new rotors on lots of different cars. It is very seldom we have found them out of spec, possibly 1 in 500. I would just skip the measurements in your case. If by chance you had a problem, pedal pulsation, I would send it back and get another one. I would not be happy about turning a new rotor. With new or machined rotors, wash them with soap and hot water. To break in new pads and or rotors, 20 to 30 stops from 25-35 MPH at moderate pressure. Allow some time for the rotors to cool between stops. Avoid(if possible) hard stops for about 200 miles. This will will help set the pads to rotors, and give better performance, less chance of noise, and help prevent glazing of rotors. Be sure to lube all sliding or metel to metal surfaces, I use synthetic moly, it works the best. I seldom have a comeback on my brake work.

DAN

 

[opelgtman1973]

Thanks for the info. I think I'll skip the measurements as Dan suggested, cross my fingers, see if there's any pulsation, and take it from there. I'll go with your other suggestions as well. It may be hard to avoid hard stops for the first 200 miles here in L.A., so I think I'll try to sneak out to the 'burbs and break 'em in (no pun intended ).

 

[opelgtman1973]

Follow-up questions on lube

I'm getting ready to replace not just the rotors, but also the calipers (pre-loaded with new pads), upper ball joints, front inner and outer wheel bearings, and rear brake shoes.

I got some synthetic moly that Dan suggested, and I also have lithium grease.

My question is what parts need to be lubed, and with which type of grease. Sorry if this sounds like a dumb question. I have somewhat of an idea from watching others and reading manuals, but this is my first time with each of these and I want to make sure I do it right.

 

[ddoyle]

Since the opel uses a fixed caliper, not a whole lot to lube on these. Use the moly where the pistons contact the back of the pads. If you look at your old pads usually you can see a round ring where the piston hits the pad. You dont need a whole lot of lube here, just a light coat. And keep the moly off any rubber parts(piston boots). You may also put a light coat on the pad retaining pins, just where they contact the pads and the spring.
I also like to use a small amount of anti-seize(the moly will do) wher the pins are seated in the caliper to prevent them from getting stuck. I hope this helps.

DAN

 

[ddoyle]

You can also get synthetic grease for the wheel bearings also. MUCH better!!!

DAN

 

[opelgtman1973]

Since the opel uses a fixed caliper, not a whole lot to lube on these. Use the moly where the pistons contact the back of the pads. If you look at your old pads usually you can see a round ring where the piston hits the pad. You dont need a whole lot of lube here, just a light coat. And keep the moly off any rubber parts(piston boots). You may also put a light coat on the pad retaining pins, just where they contact the pads and the spring.
I also like to use a small amount of anti-seize(the moly will do) wher the pins are seated in the caliper to prevent them from getting stuck. I hope this helps.
DAN

Dan,

I got sidetracked, but now I'm back to the front brakes. I just want to clarify this before I go further. I'm actually replacing the old calipers with rebuilt ones that are loaded with new pads already. Can I assume that since they're rebuilt and loaded, they should already be pre-lubed? I was thinking that I just may be able to remove and replace the whole thing and that should be it.

And thanks for mentioning the synthetic wheel bearing grease. I'm trying to go synthetic with as much of the fluids/lube as possible, but I didn't even see the Mobil 1 wheel bearing grease the first time I was at the parts store. I exchanged the lithium I bought for that. A few bucks more, but it'll be worth it in the long run.

 

[ddoyle]

Scott, I have never seen a loaded caliper that came with the parts pre-lubed. You should be able to tell by looking at the back of one of the pads, it will likely be dry.

DAN

 

[opelgtman1973]

Scott, I have never seen a loaded caliper that came with the parts pre-lubed. You should be able to tell by looking at the back of one of the pads, it will likely be dry.
DAN

You're right, they're dry. Thanks for clarifying it for me. Will proceed with lube per your previous instructions.