Bearing change effect runout?
Tech Contributor
Joined: Aug 1999
Posts: 15,175
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From: Connecticut, USA
sounds like you're speaking of the front wheels. If the rotors were true before they should be after installation of new bearings and proper adjustment. However I recommend checking the runout as part of the procedure.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
If you front rotors are still riveted on the hub and they are out over 005" a good parts store or machine shop can kiss cut them to true them up. The key is getting a guy who understands that a micrometer is not a c-clamp and he takes the time to properly setup rotors. When I was a kid I brought in my front rotors to the local parts store on a Saturday to get cut for $8. The manager had a wise guy punk who didn't want to do them because it was close to noon and he wanted to go home. The manager had the kid cut them and he wrecked them. Proper bearing setup should not have much play in them and if the runout is under 005 and you're using lip seal calipers you should be good. If the rotors are not riveted on and you have runout I would first check the mating surfaces and touch a grinder at the rivet holes in the hub and the backside of the rotor hat, then recheck them.
If you buy a Chinese indicator be careful because the cheap ones use cheap parts and I have seen them stick from weak springs inside, resulting in false readings. Hum, maybe that is why their stuff doesn't fit a lot of times. If you want a quality tool that lasts check on ebay for a Starrett, my personal favorite.
If you buy a Chinese indicator be careful because the cheap ones use cheap parts and I have seen them stick from weak springs inside, resulting in false readings. Hum, maybe that is why their stuff doesn't fit a lot of times. If you want a quality tool that lasts check on ebay for a Starrett, my personal favorite.
Thread Starter
Intermediate
Joined: Jan 2020
Posts: 34
Likes: 8
Truly invaluable advice, GTR1999! I'm going now to look for the Starrett...saved me the time I always put in to tool reviews before buying, while trying to not go broke. My rotors appear original but with rivets drilled, so especially grateful for this particular tip. I know I need a good alignment, and found an alignment and brake shop nearby that's been in business for decades that works on old stuff too, if I need them cut.
Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
Good luck. The brakes on these cars work great for 95% of the driving they are used for. If you are going to go road racing that is different. Once properly setup there is nothing wrong with them at all. If you want to stay on top of them bleed them once a year and they will last a long time.
Melting Slicks
Joined: Jun 2014
Posts: 2,236
Likes: 498
From: NJ
If you front rotors are still riveted on the hub and they are out over 005" a good parts store or machine shop can kiss cut them to true them up. The key is getting a guy who understands that a micrometer is not a c-clamp and he takes the time to properly setup rotors. When I was a kid I brought in my front rotors to the local parts store on a Saturday to get cut for $8. The manager had a wise guy punk who didn't want to do them because it was close to noon and he wanted to go home. The manager had the kid cut them and he wrecked them. Proper bearing setup should not have much play in them and if the runout is under 005 and you're using lip seal calipers you should be good. If the rotors are not riveted on and you have runout I would first check the mating surfaces and touch a grinder at the rivet holes in the hub and the backside of the rotor hat, then recheck them.
If you buy a Chinese indicator be careful because the cheap ones use cheap parts and I have seen them stick from weak springs inside, resulting in false readings. Hum, maybe that is why their stuff doesn't fit a lot of times. If you want a quality tool that lasts check on ebay for a Starrett, my personal favorite.
If you buy a Chinese indicator be careful because the cheap ones use cheap parts and I have seen them stick from weak springs inside, resulting in false readings. Hum, maybe that is why their stuff doesn't fit a lot of times. If you want a quality tool that lasts check on ebay for a Starrett, my personal favorite.
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Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
Us Gear almost always setups center to toe on the drive. The pattern is perfect between the root and crown which is the true indicator of gear centering. That gear set has been perfect and quiet for 15 years, Just saying.
Melting Slicks
Joined: Jun 2014
Posts: 2,236
Likes: 498
From: NJ
Maybe they are using those cheap dial indicators to setup the Diff. LOL. Sometimes they will lower the contact area, especially on a high horsepower car, to increase the strength of the ring gear. But usually the contact area is a little higher on your average car.
Thread Starter
Intermediate
Joined: Jan 2020
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Tech Contributor
Joined: Aug 1999
Posts: 15,175
Likes: 3,990
From: Connecticut, USA
As I assume you are aware, there is only so much adjustment to dial in the pattern. Pinion depth and lash, the cut of the gears is out of control of the builder and personally I think the GM gears of the 60-70's were the best of all. I am building a 1480 12 bolt vette diff now, the gears are special cut Richmond, the pattern is center to toe drive & center to heel coast, there is no way it will ever be "text book". I personally machined this posi case and there is under 001" variance through 360*. The root to crown is equal and the gear mesh is smooth, a slight change in pinion shim will result in a noisy mesh and gear set and today even with the text book patterns the gears can have a whine in the 45-60 mph range as that is the way they are cut. US Gear prints it in their setup paper now - expect to hear a gear whine. Yeah, a lot of things have changed for sure.
Sorry to take this away from the original posters question. I will step away from it now, point was made, life goes on and we all have more important things to be concerned about today.
Last edited by GTR1999; Jun 2, 2020 at 11:34 AM.