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I'm slowly re-building my diff with new 3.73 gears (the last set from Tom's until '09, I believe!:thud
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As part of the re-build I'm tuning the posi unit as per Gary Ramadei's paper. :thumbsup:
Reading various posts here and on other forums, I noticed some people asking how much drag was enough when shimming the side gears to pre-load the clutch plates.
This is my first Corvette differential but I've rebuilt three clutch type LSD's for UK vehicles (2 for a '79 Escort RS2000, and 1 for a Sunbeam Lotus), so I think I can make an educted guess as to how much slip I'm looking for for tractable street use.
With this type of build, having no springs to pre-load the clutches, I wanted to be sure that both sides produced exactly the same amount of drag. So I hooked a spring balance on to the ring spanner, and rotated the unit, keeping the balance at 90degs to rotation, and reading the "weight" produced.
This was after I had finally selected 035" shims in both sides, and was happy with the hands-on "feel" of the unit.
It confirmed the drag was the same on both sides.
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The drag measured was 8lbs with the balance 10.25" from the centre. This (by my calcs) equates to 6.3ft-lbs of drag.
Another point of note that my be of interest: The clutches were left; coated with GM diff aditive, installed in the carrier and preloaded, for two weeks (while I scooted off to Azerbaijan for some offshore work!! :down
When I returned I found the action of the diff had very noticably smoothed out. Prior to leaving the diff had felt notchy regardless of how small the shims were, and I spent my working time convincing myself that the springs were going back in.
After two weeks covered in fluid and crushed up together the notchiness had gone, and I was back in the springless zone :laughing:
I haven't spoken to Gary about this specific finding, but thought it may be of interest to anyone else maybe wrestling with a similar problem.
A final point - the drag I set for the previous cars, if I would jack-up one drive wheel and leave the g/box in neutral. The raised wheel could be turned by hand but took some effort.
Out of curiosity, I re-installed the Corvette springs, with 020 shims, and checked the feel - I could not budge the damn thing!
The pre-load is immense, no wonder standard diffs clunk and grind on corners. :crazy:
I will post another thread once the diff is back in the car. To confirm whether this method of tuning really does work, and whether 6.3ft-lbs is too much, too little or bang on the money
The only "while I'm at it" items I am undertaking, is to replace the drive shaft UJ's and to notch the diff crossmember to raise the diff 1/2" to impove my driveshaft angles.
.As part of the re-build I'm tuning the posi unit as per Gary Ramadei's paper. :thumbsup:
Reading various posts here and on other forums, I noticed some people asking how much drag was enough when shimming the side gears to pre-load the clutch plates.
This is my first Corvette differential but I've rebuilt three clutch type LSD's for UK vehicles (2 for a '79 Escort RS2000, and 1 for a Sunbeam Lotus), so I think I can make an educted guess as to how much slip I'm looking for for tractable street use.
With this type of build, having no springs to pre-load the clutches, I wanted to be sure that both sides produced exactly the same amount of drag. So I hooked a spring balance on to the ring spanner, and rotated the unit, keeping the balance at 90degs to rotation, and reading the "weight" produced.
This was after I had finally selected 035" shims in both sides, and was happy with the hands-on "feel" of the unit.
It confirmed the drag was the same on both sides.
The drag measured was 8lbs with the balance 10.25" from the centre. This (by my calcs) equates to 6.3ft-lbs of drag.
Another point of note that my be of interest: The clutches were left; coated with GM diff aditive, installed in the carrier and preloaded, for two weeks (while I scooted off to Azerbaijan for some offshore work!! :down
When I returned I found the action of the diff had very noticably smoothed out. Prior to leaving the diff had felt notchy regardless of how small the shims were, and I spent my working time convincing myself that the springs were going back in.
After two weeks covered in fluid and crushed up together the notchiness had gone, and I was back in the springless zone :laughing:
I haven't spoken to Gary about this specific finding, but thought it may be of interest to anyone else maybe wrestling with a similar problem.
A final point - the drag I set for the previous cars, if I would jack-up one drive wheel and leave the g/box in neutral. The raised wheel could be turned by hand but took some effort.
Out of curiosity, I re-installed the Corvette springs, with 020 shims, and checked the feel - I could not budge the damn thing!
The pre-load is immense, no wonder standard diffs clunk and grind on corners. :crazy:
I will post another thread once the diff is back in the car. To confirm whether this method of tuning really does work, and whether 6.3ft-lbs is too much, too little or bang on the money
The only "while I'm at it" items I am undertaking, is to replace the drive shaft UJ's and to notch the diff crossmember to raise the diff 1/2" to impove my driveshaft angles.
