Differential Rebuilding
Le Mans Master
Joined: Aug 2010
Posts: 5,339
Likes: 546
From: Central Texas
You don't use Track Dogg 2 to get a good (cheap)deal, You use him when You want it done right. If You want it done cheaply use one of the exchange services that most of the major vendors offer, they can probably beat most any local shop on price, but add in shipping.
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
Mike,
You have a 3.08 diff built on the 180 day of 1977. Looking at your pics you have the usual stub axle wear. I would want to see the case where the stub axle seal is for any damage. Going by the gap in the preload springs your clutches are worn out. You have average wear on the spider gears but your ring gear is worn out. Time for a new ring and pinion.
Even with keeping the stock engine and hp there are several areas that need to be addressed. New clutchpacks will wear approx. .010 in the first 1,000 miles of use. This sounds like nothing to be worried about, it's just ten thousandths of an inch.And it will just sit in the bottom of the housing. In reality it's metal shavings from 34 surfaces being deposited into your gear lube. The ring gear acts as a scoop picking up lube, and particles, from the bottom of the housing. It then throws everything into the upper passage into the cavity between the pinion bearings. From there lube, and particles, must pass thru the bearings to return back to the rear of the housing to be recirculated again. This "roping effect" is strong enough to pick up a snap ring and throw it into the passage where it gets stuck, as many people here have seen. Changing the gear lube will help but it will not get the debris out from between the pinion bearings, where most of it ends up.
Another issue with initial clutch wear is it has a dramatic effect of spider gear backlash. Proper backlash is .001-.005. Ten thousandths clutch wear equals .007 increase in backlash. I bring this up because, to my knowledge, there are only three people in the country that can properly pre-seat posi clutches. To the average company rebuilding differentials this is 2 hours of wasted time.
Another big issue that nearly all rebuilders don't do is removing the factory defects in the carrier. Again, to them, is just a waste of time. It lasted for forty years and it will last another 40, right? But yet they can't explain why one diff has had the crap beat out of it and is fine yet another one was never abused and the carrier cracked. I have seen more cracked carriers this year than in the past 30. The deburring process costs anywhere from $85 to $150. Only one person doesn't charge for doing it .
In another thread I touched on cap stretch. This is becoming a bigger problem as these diffs get older. Metal fatigue sets in and clearances open up. And is rarely, if ever, even checked.
The reason I am bringing this up is to show the difference between a stock rebuild and a hand built diff. Hand built diffs take time. A lot of it. There is a huge difference between preferred and allowable clearances and preloads.
Mike, the springs inside the carrier are preload springs. They have nothing to do with the shimming of the clutches. As power is increased more pressure is applied to the clutches and the springs aren't needed. But under light load and unequal traction conditions the clutches will slip without the preload. There are pros and cons to using the springs.
Mike
You have a 3.08 diff built on the 180 day of 1977. Looking at your pics you have the usual stub axle wear. I would want to see the case where the stub axle seal is for any damage. Going by the gap in the preload springs your clutches are worn out. You have average wear on the spider gears but your ring gear is worn out. Time for a new ring and pinion.
Even with keeping the stock engine and hp there are several areas that need to be addressed. New clutchpacks will wear approx. .010 in the first 1,000 miles of use. This sounds like nothing to be worried about, it's just ten thousandths of an inch.And it will just sit in the bottom of the housing. In reality it's metal shavings from 34 surfaces being deposited into your gear lube. The ring gear acts as a scoop picking up lube, and particles, from the bottom of the housing. It then throws everything into the upper passage into the cavity between the pinion bearings. From there lube, and particles, must pass thru the bearings to return back to the rear of the housing to be recirculated again. This "roping effect" is strong enough to pick up a snap ring and throw it into the passage where it gets stuck, as many people here have seen. Changing the gear lube will help but it will not get the debris out from between the pinion bearings, where most of it ends up.
Another issue with initial clutch wear is it has a dramatic effect of spider gear backlash. Proper backlash is .001-.005. Ten thousandths clutch wear equals .007 increase in backlash. I bring this up because, to my knowledge, there are only three people in the country that can properly pre-seat posi clutches. To the average company rebuilding differentials this is 2 hours of wasted time.
Another big issue that nearly all rebuilders don't do is removing the factory defects in the carrier. Again, to them, is just a waste of time. It lasted for forty years and it will last another 40, right? But yet they can't explain why one diff has had the crap beat out of it and is fine yet another one was never abused and the carrier cracked. I have seen more cracked carriers this year than in the past 30. The deburring process costs anywhere from $85 to $150. Only one person doesn't charge for doing it .
In another thread I touched on cap stretch. This is becoming a bigger problem as these diffs get older. Metal fatigue sets in and clearances open up. And is rarely, if ever, even checked.
The reason I am bringing this up is to show the difference between a stock rebuild and a hand built diff. Hand built diffs take time. A lot of it. There is a huge difference between preferred and allowable clearances and preloads.
Mike, the springs inside the carrier are preload springs. They have nothing to do with the shimming of the clutches. As power is increased more pressure is applied to the clutches and the springs aren't needed. But under light load and unequal traction conditions the clutches will slip without the preload. There are pros and cons to using the springs.
Mike
