Carrera rotor replacement - what could go wrong

[redmill]

Long story short:
87 911 - DE use, drive to/from track
My Mechanic: 20+ years, independent porsche only, aircooled specialist, very encouraging about DIY eg refused to change pads years ago, put car on lift , showed me how (nice). Lets you work on cars with his tools for aggravating fixes like broke window lift

Buddy: mechanically good, not as OCD as me, swapped out complete brakes on non911s

Buddy offered to swap out pulsing rotors with me. Mechanic had discouraged me from DIY rotor swap years back. Mentioned tension on bearings needed to be accurate.

So.... what the hell was the mechanic talking about?

What can go wrong with a rotor swap? Got the bleeding/pad change down pat.

Any favor DIY' pages for stock rotor swap outs? Did a halfhearted search here.

[CharlesJones]

I changed my front rotors. The only complication is that you have to take the whole hub off to get the rotors off, which means when you put it back on again you have to tighten the spindle correctly, otherwise your bearings might be too tight or too loose. I think that is what you're mechanic is talking about.

However, there is a rule-of-thumb method of testing bearing tightness (involving pushing the thrust washer with the end of a screw driver) which isn't too difficult and worked fine for me. You can try searching for that here - there are threads about it, and it is described in rotor-swap threads. It really shouldn't be anything to discourage a DIY rotor swap.

[Zeke]

And that ain't a big deal. Tighten them up until you feel a slight resistance, drive and recheck. I usually go about a 1/16th turn or 20 degrees past the last point of a freewheel feel.

[CCM911]

Charles is correct, in that you use the end of a screwdriver to move the thrust washer. And as a second check, I always put the wheel back on and then check for play by holding at 9 O'clock and 3 O'clock positions and try to feel for any slop. Then I repeat, holding on the 12 O'clock and 6 O'clock positions. So between the screwdriver and the "wheel test", I can feel if there is excesive play in the bearing.

This is a filthy job. No two ways about it, as the wheel bearing and all of the associated grease live in the hub. Oh, while you are at it, now would be a good time to replace the front wheel bearings if there is any doubt as to their age or condition.

[gtc]

I don't know how you can measure bearing tension "accuracy." If you have the Bentley manual, the job is fairly straightforward, albeit a bit dirty. I would suggest buying a pair of the front wheel bearing outer seals, as they are easy to mess up if you're repacking the bearings.

[john walker's workshop]

medium torque with your thumb and forefinger is all they need. you take up the slack and not much more. the calipers need to come off too. fronts brake line is separated at the tab on the strut behind the rotor, so you will need to bleed the stsyem on reassembly. on the rears, remove the C clip on the swing arm tab, move caliper forward off the rotor and push the metal line through the tab and lay the caliper on the swing arm.

[m110]

Originally Posted by redmill

So.... what the hell was the mechanic talking about?

What can go wrong with a rotor swap? Got the bleeding/pad change down pat.

Too tight: burn out the bearing pronto. I saw a car that a third world mechanic had torqued the nut down (a Mercedes but similar). Bearing overheated, failed on the highway, wheel fell off. Mind you the other side was TIGHT so results may vary. Too loose and you get a clunk, botched handling.

[47silver]

If all that you are going to do is to replace the rotors you will need good tools for the job:

1. good tubing line wrench for the fitting on the caliper. Dont do it without a good wrench.
2. 1/2 inch torque wrench (mine were 94#)
3. Good long allen socket wrench.
4. good 3/8 torque wrench for the clinch bolt.
5. good 19mm socket for the caliper bolts.
6. tools to remove the grease cap (tough job for some.
7. a soft plug for the end of the brake line fitting to plug it after you remove it...i think a cotton swab may work (i let mine drain as i was replacing hoses,etc.).
1. Jack up car and put on stands. i have a midrise lift which is better than a cold beer at times),
2. remove wheels.
3. remove the grease cap. I used the blunt end of a small bar to hit the cap from the inside out to remove it. a few hits is all it took.
4. remove the tubing connection to the rotor. (brake fluid will drain out. if you have the plug use it). I dont think you can leave this fitting on to get the caliper off.
5. remove the caliper bolts and lift off the caliper.
6. loosen the clinch nut and spin it off.
7. remove the hug.
8. If the bearings are over 75000 then time to make a decision. replace or not.
9 remove bolts that hold the rotor on 13mm?
10. put on the rotor and tighten to torque in a star manner.
11. clean rotor with brake cleaner.
12. repack bearings and install the hub.
13. slide on outside bearing.
14. put onwasher and clinch nut.
15. tighten as per above advice.
16. put on the caliper, clean the threads on the bolts. use new washers.
17. tighten to torque .
18.clean the threads on the brake fitting.
19. as Grady stated elsewhere put on some anti lock to the fitting after you slide it back up the pipe and some on the threads.
20 . put the brake pad in.
21. bleed the brakes
22. put on wheel tighten with 3 bolts and spin it check for play if ok take th wheel off and put on the grease cap.
I estimate if you have all of the tools and parts you can do this in less than 8 hours. If you dont have the tools dont try it.

Now if you want to rebuild the calipers, replace hoses etc that is another story.
I would buy the restored calipers that eric from OMG performance sells and boltthem on.

[DanielDudley]

Do it with your friend. Clean ALL the old grease out before repacking. It is very good to regrease these bearings. They can last the life of the car if maintained. Always replace the seals.

If you follow Milt or John's advice, you are in the ballpark. Turn them by hand and they will spin smoothly and freely if not too tight. The difference between just right and way too tight is that extra 1/16 Milt is talking about.

If you have any doubt, go for a drive, pull the pads and check for slop. the only timt you might ever have a problem with a bearing preload is if you make them too tight or you fail to seat new bearing races properly and they seat themselves later, causing a lot of slop.