LSD option - Wavetrac Differentials?
09-30-2011 | 10:02 PM
#31
Rennlist Member
Joined: Aug 2003
Posts: 4,699
Likes: 80
From: Midwest - US
For sure you dont want a locked diff for auto-x or street use, but more than one pro team has used locked diffs for full/high speed road course racing. I have the trans from the #3 US Escort/Cup car sitting in the garage w/ a locked diff that was done by Kelly Moss; they locked the diffs on their Firehawk S2s too. And the original trans from my Escort car was locked, likely by Fred Baker/Bedford Porsche, when it was pro raced in World Challenge and IMSA Supercar races.
It does induce push on shorter/tighter tracks. But the cars can be setup w/ enough rear spring to still rotate on higher speed corners. These LSDs are not welded up open diffs, they are factory ZFs that have been stacked w/ additional plates to basically lock them. And these were done in the late 80's and early 90's, before Guard existed so a superior aftermarket replacement LSD was not yet available.
Some other good LSD/TBD discussions and info:
Old Pelican thread where Paul Guard offers some of his perspective:
http://forums.pelicanparts.com/porsc...d-915-a-3.html
Comment from Cervelli that gives some insight into lock up under varying conditions:
Article written by/for Torsen on the fuction of the Torque Biasing/gear type differential:
http://www.torsen.com/files/Traction...ol_Article.pdf
It does induce push on shorter/tighter tracks. But the cars can be setup w/ enough rear spring to still rotate on higher speed corners. These LSDs are not welded up open diffs, they are factory ZFs that have been stacked w/ additional plates to basically lock them. And these were done in the late 80's and early 90's, before Guard existed so a superior aftermarket replacement LSD was not yet available.
Some other good LSD/TBD discussions and info:
Old Pelican thread where Paul Guard offers some of his perspective:
http://forums.pelicanparts.com/porsc...d-915-a-3.html
Comment from Cervelli that gives some insight into lock up under varying conditions:
Remember that the degree of lockup is a function of input torque as well
as the characteristics of the differential (in most cases).
So a diff with 40/65 ramps actually locks up much harder under
acceleration than it does on deceleration. This also means that by using a
different gear in a given corner (especially on entry), you are changing
the input torque and hence the lockup.
Downshifting to the lowest possible gear generates the highest possible
degree of lockup, which may or may not be desireble.
Chris Cervelli
as the characteristics of the differential (in most cases).
So a diff with 40/65 ramps actually locks up much harder under
acceleration than it does on deceleration. This also means that by using a
different gear in a given corner (especially on entry), you are changing
the input torque and hence the lockup.
Downshifting to the lowest possible gear generates the highest possible
degree of lockup, which may or may not be desireble.
Chris Cervelli
http://www.torsen.com/files/Traction...ol_Article.pdf
09-30-2011 | 10:27 PM
#32
Drifting
Joined: Aug 2006
Posts: 2,659
Likes: 1
From: Tucson and Greer Arizona
Thanks for sharing we can lock a RWD diff, and still have good driveability at the track.
Great information, thanks for the links.
10-01-2011 | 01:23 AM
#33
Rennlist Junkie Forever
Joined: Dec 2001
Posts: 5,978
Likes: 2
From: Los Angeles
Years ago, when I was 17.. when mini trucks were in.... (going way back), I used to break my Datsun truck spider gears all the time (yes I used to build up those engines too... big time).
I ended up welding spider gears. It worked... they never broke again. But the truck was always spinning the inside tire on any tight turn (like a gas station for example).
I was afraid it would snap the axle, and it probably would if it had any real weight in the bed.
Those were the days....
TonyG
I ended up welding spider gears. It worked... they never broke again. But the truck was always spinning the inside tire on any tight turn (like a gas station for example).
I was afraid it would snap the axle, and it probably would if it had any real weight in the bed.
Those were the days....
TonyG
10-01-2011 | 01:25 AM
#34
Rennlist Junkie Forever
Joined: Dec 2001
Posts: 5,978
Likes: 2
From: Los Angeles
For sure you dont want a locked diff for auto-x or street use, but more than one pro team has used locked diffs for full/high speed road course racing. I have the trans from the #3 US Escort/Cup car sitting in the garage w/ a locked diff that was done by Kelly Moss; they locked the diffs on their Firehawk S2s too. And the original trans from my Escort car was locked, likely by Fred Baker/Bedford Porsche, when it was pro raced in World Challenge and IMSA Supercar races.
It does induce push on shorter/tighter tracks. But the cars can be setup w/ enough rear spring to still rotate on higher speed corners. These LSDs are not welded up open diffs, they are factory ZFs that have been stacked w/ additional plates to basically lock them. And these were done in the late 80's and early 90's, before Guard existed so a superior aftermarket replacement LSD was not yet available.
Some other good LSD/TBD discussions and info:
Old Pelican thread where Paul Guard offers some of his perspective:
http://forums.pelicanparts.com/porsc...d-915-a-3.html
Comment from Cervelli that gives some insight into lock up under varying conditions:
Article written by/for Torsen on the fuction of the Torque Biasing/gear type differential:
http://www.torsen.com/files/Traction...ol_Article.pdf
It does induce push on shorter/tighter tracks. But the cars can be setup w/ enough rear spring to still rotate on higher speed corners. These LSDs are not welded up open diffs, they are factory ZFs that have been stacked w/ additional plates to basically lock them. And these were done in the late 80's and early 90's, before Guard existed so a superior aftermarket replacement LSD was not yet available.
Some other good LSD/TBD discussions and info:
Old Pelican thread where Paul Guard offers some of his perspective:
http://forums.pelicanparts.com/porsc...d-915-a-3.html
Comment from Cervelli that gives some insight into lock up under varying conditions:
Article written by/for Torsen on the fuction of the Torque Biasing/gear type differential:
http://www.torsen.com/files/Traction...ol_Article.pdf
I think it's quoted incorrectly because there is a LOT more breaking HP than there ever is acceleration HP. Didn't Porsche even used to quote braking HP equivalent numbers?
TonyG
10-01-2011 | 09:20 AM
#35
Three Wheelin'
Joined: Sep 2004
Posts: 1,269
Likes: 0
From: Tennesee
Years ago, when I was 17.. when mini trucks were in.... (going way back), I used to break my Datsun truck spider gears all the time (yes I used to build up those engines too... big time).
I ended up welding spider gears. It worked... they never broke again. But the truck was always spinning the inside tire on any tight turn (like a gas station for example).
I was afraid it would snap the axle, and it probably would if it had any real weight in the bed.
Those were the days....
TonyG
I ended up welding spider gears. It worked... they never broke again. But the truck was always spinning the inside tire on any tight turn (like a gas station for example).
I was afraid it would snap the axle, and it probably would if it had any real weight in the bed.
Those were the days....
TonyG
10-01-2011 | 01:38 PM
#37
Rennlist Junkie Forever
Joined: Dec 2001
Posts: 5,978
Likes: 2
From: Los Angeles
TonyG
10-01-2011 | 05:10 PM
#41
Rennlist Junkie Forever
Joined: Dec 2001
Posts: 5,978
Likes: 2
From: Los Angeles
Just pulled the differential from the last transmission I broke.
Once it was on the bench, it took me less than 15 minutes to get it out. No special tools.
Here's the order:
1. Unbolt the transmission to transaxle case bolts.
2. And it's a little tricky. I turn the transmission so that it's standing on its input shaft, on a block of wood. Then we pick the transmission, and drop it on to it's input shaft, about 4" drops. This will seperate the transmission from the transaxle case.
3. Unbolt stub axles (allen wrench on drill gun helps)
4. Unbold and pull side plate (tap around sides to push off)
5. Reach in and pull out differential & ring gear.
15 minutes once it was on the bench. Just got done doing it 5 minutes ago.
TonyG
10-01-2011 | 05:52 PM
#42
Rennlist Junkie Forever
Joined: Dec 2001
Posts: 5,978
Likes: 2
From: Los Angeles
Here's a few pics of the trans that blew 2nd gear a few weeks ago at Laguna Seca.
PS> I just pulled this apart and it took less than 15 minutes to get it apart (see previous post)
TonyG
PS> I just pulled this apart and it took less than 15 minutes to get it apart (see previous post)
TonyG
10-04-2011 | 12:43 AM
#44
Rennlist Member
Joined: Aug 2003
Posts: 4,699
Likes: 80
From: Midwest - US
There is some concern about the lash and preload w/ the ring/pinion setup when swapping differentials. The factory manual does state that the differential bearing spacing should be checked/re-shimmed when changing the differential housing.
Dimensionally, the only reason that would be necessary is if the housings are not machined within the tolerance required for setting lash and preload, which is somewhat surprising. I would expect that the bearing race seats and the ring gear land tolerance could be held tight enough that reshimming should not be necessary, but apparently the factory doesn’t think so. The replacement diff housing should at least be checked to compare dimensions w/ the original diff.
What has Matt or Paul said about the tolerance of their Guard LSD housing? Do they recommend checking/resetting the diff shims when replacing a factory ZF dif w/ their LSD?
If the diff housing dimensions are ok, the other issue is removing the diff bearings off the old differential. If new bearings are used, you do need to set the lash/preload. So you would need to reuse the old bearings if you choose not to reshim the diff. Pretty hard to pull the old bearings off the diff w/o damaginig the cages. The races are pretty tight to the diff housing. W/o a press and special dies, you typically have to grab them w/ a gear puller which very often damages the cages, as shown. Need to be careful.
Dimensionally, the only reason that would be necessary is if the housings are not machined within the tolerance required for setting lash and preload, which is somewhat surprising. I would expect that the bearing race seats and the ring gear land tolerance could be held tight enough that reshimming should not be necessary, but apparently the factory doesn’t think so. The replacement diff housing should at least be checked to compare dimensions w/ the original diff.
What has Matt or Paul said about the tolerance of their Guard LSD housing? Do they recommend checking/resetting the diff shims when replacing a factory ZF dif w/ their LSD?
If the diff housing dimensions are ok, the other issue is removing the diff bearings off the old differential. If new bearings are used, you do need to set the lash/preload. So you would need to reuse the old bearings if you choose not to reshim the diff. Pretty hard to pull the old bearings off the diff w/o damaginig the cages. The races are pretty tight to the diff housing. W/o a press and special dies, you typically have to grab them w/ a gear puller which very often damages the cages, as shown. Need to be careful.
10-04-2011 | 02:10 AM
#45
Rennlist Junkie Forever
Joined: Dec 2001
Posts: 5,978
Likes: 2
From: Los Angeles
There is some concern about the lash and preload w/ the ring/pinion setup when swapping differentials. The factory manual does state that the differential bearing spacing should be checked/re-shimmed when changing the differential housing.
Dimensionally, the only reason that would be necessary is if the housings are not machined within the tolerance required for setting lash and preload, which is somewhat surprising. I would expect that the bearing race seats and the ring gear land tolerance could be held tight enough that reshimming should not be necessary, but apparently the factory doesn’t think so. The replacement diff housing should at least be checked to compare dimensions w/ the original diff.
What has Matt or Paul said about the tolerance of their Guard LSD housing? Do they recommend checking/resetting the diff shims when replacing a factory ZF dif w/ their LSD?
If the diff housing dimensions are ok, the other issue is removing the diff bearings off the old differential. If new bearings are used, you do need to set the lash/preload. So you would need to reuse the old bearings if you choose not to reshim the diff. Pretty hard to pull the old bearings off the diff w/o damaginig the cages. The races are pretty tight to the diff housing. W/o a press and special dies, you typically have to grab them w/ a gear puller which very often damages the cages, as shown. Need to be careful.
Dimensionally, the only reason that would be necessary is if the housings are not machined within the tolerance required for setting lash and preload, which is somewhat surprising. I would expect that the bearing race seats and the ring gear land tolerance could be held tight enough that reshimming should not be necessary, but apparently the factory doesn’t think so. The replacement diff housing should at least be checked to compare dimensions w/ the original diff.
What has Matt or Paul said about the tolerance of their Guard LSD housing? Do they recommend checking/resetting the diff shims when replacing a factory ZF dif w/ their LSD?
If the diff housing dimensions are ok, the other issue is removing the diff bearings off the old differential. If new bearings are used, you do need to set the lash/preload. So you would need to reuse the old bearings if you choose not to reshim the diff. Pretty hard to pull the old bearings off the diff w/o damaginig the cages. The races are pretty tight to the diff housing. W/o a press and special dies, you typically have to grab them w/ a gear puller which very often damages the cages, as shown. Need to be careful.
The reality is that if you only change the diff (and nothing else), the specs are so close that it almost doesn't matter.
Not to say that it's not possible that things could be way off, but based on my last 6 diff swaps (in a AOR, 5R, 5S, etc.. trans...), that has not been the case. I just slip it in and go.
That said... I've been experiencing a lot of transmission failures in the last 3 years of racing. The last being a shredded 2nd gear, then a trans with bad synchros, a factory LSD that busted apart, and trans that for some reason, lost its oil somewhere. The list goes on.
But even with a diff swap in to each of those transmissions, in no case was there any R&P whine/growl, and after dissasembly, there has never been any sign of R&P weird wear patterns, nor has there ever been a R&P failure.
So to answer your question...
The reason I slip in a different diff and go, is because I change nothing else. If you change a diff carrier bearing, change a ring gear, change a side plate, then all bets are off. The R&P lash must be set (and that's a big job for sure).
TonyG