Hi Folks, I think I know the answer to this but just want to confirm. Have a slight vibration upon braking in the steering wheel. I'm doing some work on the car and thought of having the front rotors turned down. I don't think they have ever been off the car so I should have the minimum 30mmt thickness the workshop specifies when done. When I looked at this on the lift, to remove the caliper, appears you have to disconnect the hard brake fluid lines to the hoses. Not too bad. Then proceed to unbolt, tap, finesse the rotor off. This will let all the brake fluid drain from car. I had a heck of a time getting the master cylinder bled and brakes back when I rebuilt the master cylinder. I don't know if there is any way around this but there is a drilled nut with cotter pin through it holding the brake lines and hoses that could be removed. Before I go where I have not been before can anyone offer some advice. This is for a 79 512BB. Thanks. Drew Altemara
I am not familiar with 512bbi ..but I am sure you can find a plastic plug /cap so that not all the fluid is drained ???
Thought about that. Maybe a good solution. Have to find something that brake fluid will not eat away too bad. Appreciate, Drew
The brake fluid drains out very slowly so you will have the time to put a small rubber plug in the end of the line. Find something that cones down to a small point and you will be fine to wedge it in. I do it all the time and happen to use some cone shaped plugs used for powder coating that do the job nicely. I'm sure any other soft material will work just fine. As for the brake rotors, take them to a place that machines flywheels and get them blanchard ground. It is a much better finish and process than traditional rotor turning and leaves a much better surface to bed pads to the rotors. While at it you may want to look at new pads as old ones tend to work harden over time even if the car does not have a lot of mileage. Pads are cheap enough that if you are going through all this trouble you are best to start from fresh all around. After re-connecting the calipers be sure to have a nice good brake flush then its time for a drive.
If you turn the rotors you need to replace the pads. So decide if you are ready to do that 1st. If you don't do that you might get lucky or have even more vibration and new noises. There is an art to replacing pads and rotors. That's why today to minimize the hassle at the dealerships they replace pads and rotors and don't turn or true them even if they are within spec because they want to avoid come backs. You should be able to just cap the line so the fluid does not drip out. If you get air in the master then you have to bench bleed that perhaps and it increases the difficulty of the job. Also on an old car the rubber bushing could be bad and that will cause the vibrations or in the steering rack ends or rack bushings. So make sure you got the diagnosis right so you don't chase your tail.
Thats not why they dont turn rotors. No one has an in house rotor machine anymore and very few mechanics know how to use one if they did. Taking rotors off, sending to machine shop and waiting to get them back burns a day with a car tying up a hoist not being worked on. Most cases they'd rather sell a set of rotors. There is no art to turning rotors. I have been doing it since American cars started to have disc brakes and I turned drums before that. We arced shoes too. Nothing to it.
On my truck I'll just replace pads as needed. Rarely, I'll have rotors dressed or turned especially since new ones are cheap enough. But on my wife's car its new BMW rotors and new BMW pads. I just don't want to hear the complaints for a noise only she can hear. There are times it is worth every penny to buy $300 pads that could have been $50 pads from NAPA.
I know people who have a repair shop, sometimes new rotors pulse when new. They have to take them off and true them. A lot of just on the market today. Some so called mechanics don't really know how to set up a rotor and brake lathe.
Hey Guys, Appreciate all the good advice. I'll pull the calipers and plug them with some bullet plastic from our shop. Does not have to hold for a lot of time. Apptrciate the comment about getting new pads as well. Thank you. Never thought of that but '"while you are in there" it makes a lot of sense. Again, thanks, Drew Altemara
I not would do so. the flywheel is grinding only on 1 side, not like a rotor on both sides. so sand both sides at the same time you also may use the bleeder nipple covers - if they are still there?
It is not a while you were in there. You want flat rotor and flat pads = no noise + max braking ability because max contact of pad to rotor. Yes you could wear in the pad to the rotor but that groves the rotor more because you got high contact points to wear out.
I have never seen that if done right. Just because a repair shop did it does not mean it was done right. A manufacturer of rotors makes zillions of them. They make them flat and true or they go out of business. Modern manufacturing is easily capable even the chinese. One thing i see all the time is old rotor come off new rotor go on. You must take 5 minutes and clean the hub contact surface to make sure you can have a flat rotor and this is the perfect time to clean and inspect the studs. No lube on studs!
It is not necessary to grind both sides at the same time. Blanchard grinding of brake rotors is a well known process among knowledgeable mechanics and race teams. It generates the absolute best surface for a new brake pad and there is zero issue getting both sides perfectly even. I have personally used this process for decades and am speaking from a position of a LOT of first hand experience.
you are right rob, but I know a lot of shops grinding flywheels but when they grind disks they fail. even it is only 5/100 of a mm
Thanks for the comments guys. I noticed that auto supply shops sell brass plugs for this purpose (or maybe some other). Anyone know the size I would need to buy to insert into the female rubber side end for the front brakes. This would make it easy.
Thought I would finish this thread off in the chance it may help someone else. I ended up plugging the brake lines from the calipers with fittings I had from a MC bench bleed kit. They fit perfectly into the brake lines and I just connected the hoses between the two lines. The calipers are held on by two 19mm socket sized bolts. On very tight after 46 years but with the help of a cheater bar they were not that bad. The rotor is held on by eight 13mm socket size nuts. I had to fuss with the dust shield from behind the rotor, held on by the caliper and an inside bolt but again not that bad. I cleaned the outside of the rotor where it contacts the hub with a small wire brush and applied penetrating oil to the front and rear. Hard to tell how much actually got in there. Put a 6 inch 2x4 behind the rotor and took a lead hammer and tapped away turning the rotor a quarter revolution at a time. About the 100th tab it came loose. The workshop manual says the front rotors are 32mm thick new and that is exactly what mine were. Looks like they were never turned. The minimum is 30mm. Took them to an old time shop I trusted and they took a maybe a tenth of a mm off each side. I am still over 31.5mm on each. They did a good job. Everything goes back together fairly easily except I somehow always have trouble getting the metal brake line from the caliper lined up with the hose fittings. But go slow, line it up and don't force anything for fear of stripping it. I put in new brake pads and bled the brakes with the help of my wife's foot. She was actually pretty good about it. I had replaced the front and rear brake hoses a couple of years ago and they looked to be in good shape. Car brakes great without any vibration. It's a long, dirty job and I'm still trying to get all the grease out from under my fingernails. Thanks for the help along the way guys. Drew Altemara
