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Old 06-14-2021, 05:06 AM   #1
dalek
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Default So my differential is 3.73 and open

Threads like https://forums.turbobricks.com/showthread.php?t=358061 made me become more interested in my diff. Because my car is a 91 turbo, I thought it had a 3.73:1 LSD, but since the sticker that goes in the rear axle is just a mirror, I needed another way to find out.

https://www.turbobricks.com/mods.php?content=art0014 states "Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs." I had to rotate mine 2x to rotate the driveshaft about 3 3/4 turns. I take that makes mine an open diff, right?

What else do I now know about it?
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Old 06-14-2021, 08:59 AM   #2
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G80 diffs act like open diffs until you spin them fast enough. I think it needs about 100 rpm difference between the sides to engage.
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Old 06-14-2021, 05:31 PM   #3
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On the locker you'd have to give that one wheel a rather hard spin to make the locker engage.
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Old 06-14-2021, 05:32 PM   #4
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Quote:
Originally Posted by dalek View Post
Threads like https://forums.turbobricks.com/showthread.php?t=358061 made me become more interested in my diff. Because my car is a 91 turbo, I thought it had a 3.73:1 LSD, but since the sticker that goes in the rear axle is just a mirror, I needed another way to find out.

https://www.turbobricks.com/mods.php?content=art0014 states "Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs." I had to rotate mine 2x to rotate the driveshaft about 3 3/4 turns. I take that makes mine an open diff, right?

What else do I now know about it?
All your test did was show that your ratio is 3.73:1.
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Old 06-15-2021, 07:51 AM   #5
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Quote:
Originally Posted by JohnMc View Post
G80 diffs act like open diffs until you spin them fast enough. I think it needs about 100 rpm difference between the sides to engage.
How can I know if mine is a G80 without popping its cover open? According to http://forums.turbobricks.com/showthread.php?t=28125 cover has to come out.

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All your test did was show that your ratio is 3.73:1.
That is still more than I knew before. I also noticed when I was doing that if I spun a wheel hard enough the other would spin backwards, otherwise it would not spin at all.

The things that amuse me...

Last edited by dalek; 06-15-2021 at 08:24 AM..
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Old 06-15-2021, 08:31 AM   #6
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Pull the cover and change the oil at the same time
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Old 06-15-2021, 09:21 AM   #7
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I usually just try to do burnouts on dusty turns with the windows down

By this method seems my 91 is locking and my 90 is open

This is the super advanced tech method
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Old 06-15-2021, 09:26 AM   #8
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You can engage a G80 by hand spinning one side while on stands, I promise.

Any kind of minor loss of traction will engage it.

Major losses in traction will bypass it if the RPM rises fast enough. Unless modified. Unless you live somewhere with ice and drive in those conditions, mod is mandatory IMO. Weld a blob, don't cut it off.

But if it is open, that's only one step away from a 3.73 MIG welded 2-wheel drive non-diff

My 2c.
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Old 06-15-2021, 10:35 AM   #9
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I had a 91 740 turbo and it had the g80. By 92 all 7/9 models had the g80.
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Old 06-15-2021, 12:47 PM   #10
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Quote:
Originally Posted by dalek View Post
How can I know if mine is a G80 without popping its cover open? According to http://forums.turbobricks.com/showthread.php?t=28125 cover has to come out.



That is still more than I knew before. I also noticed when I was doing that if I spun a wheel hard enough the other would spin backwards, otherwise it would not spin at all.

The things that amuse me...
Take a floor jack and put it under the passenger side rear trailing arm. Jack the car up until the right rear tire is about 1" off the ground. Make sure your jack is pointed in the direction the car will travel and that the jack pad and wheels are clearing the rear tire. Jump in the car, start it up and put it in drive with your foot on the brake. While idling in gear ease off of the brake pedal. If you have a G80 the wheel will turn anywhere from 3-10 turns and then the G80 will lock and the car will start to move forward. Put it in reverse and it will do the same thing. If you want to see how good the clutches are you can power brake it while stepping on the gas. If the clutches are good it will do a burn out with the tire on the ground. You don't hold the brake pedal down hard. Just enough so that the front wheels don't want to move. If you do the last step, be careful. I always test G80s this way after selling one that had wimpy clutches in it without knowing that fact.
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Old 06-15-2021, 12:59 PM   #11
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It's not that hard to ge4t it to engage. Jack up one wheel, leave it in gear (or park if it's an auto), and spin the wheel by hand. Get it going fairly well, not scary fast or anything, and if it's a G80 it will engage and stop turning until you let it back off slightly.

BTW, I've tested the junkyard G80 in my 245 like this, it seems to work perfectly fine, and I can't turn it by hand once it's engaged, but it only loosely locks up on the road. On dry pavement it will still happily spin an inside wheel in a corner, takes a bit of rain to get the outside wheel to spin as well. I guess the clutches are a bit worn in it.
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Old 06-15-2021, 01:11 PM   #12
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Quote:
Originally Posted by JohnMc View Post
It's not that hard to ge4t it to engage. Jack up one wheel, leave it in gear (or park if it's an auto), and spin the wheel by hand. Get it going fairly well, not scary fast or anything, and if it's a G80 it will engage and stop turning until you let it back off slightly.

BTW, I've tested the junkyard G80 in my 245 like this, it seems to work perfectly fine, and I can't turn it by hand once it's engaged, but it only loosely locks up on the road. On dry pavement it will still happily spin an inside wheel in a corner, takes a bit of rain to get the outside wheel to spin as well. I guess the clutches are a bit worn in it.
Your G80 is the one I'm referring to. It passed the manual lock test. I know I don't generate 300 lb*ft torque. After you installed that one and were underwhelmed at how it worked I've tested every one for how hard they lock. I've only tossed one since. That G80 would lock, yet, wouldn't even move the car. The clutches were that bad, or, something was stuck/broken inside.
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Old 06-15-2021, 02:46 PM   #13
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I got a lower mile one from a junkyard since then, but just haven't bothered to stick it in. With the turbo LS spinning the wheels, a better working G80 would probably just start breaking things. Better to leave it alone and get to do the Ford 8.8 swap when I want to, not when it demands it.
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Old 06-15-2021, 03:13 PM   #14
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Quote:
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I got a lower mile one from a junkyard since then, but just haven't bothered to stick it in. With the turbo LS spinning the wheels, a better working G80 would probably just start breaking things. Better to leave it alone and get to do the Ford 8.8 swap when I want to, not when it demands it.
Yep. Start getting that 8.8 ready now and be ahead of the demand. You know it's coming.
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Old 06-16-2021, 01:51 AM   #15
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Mine used to do two wheel skids every single time, but I was destroying some tyres the other night and for the first time found the thing one wheeling slightly - this is modified, so no excuses and consistent operation, skids were started foot in brake, full lock, full throttle until tyres spin, release brakes, and round she goes. But during some pendulum style movements I guess the traction generated was in excess of the clutch holding power and uh oh, it slipped a bit.

+1 for hand spin test, it's enough, not difficult, and no risk of damaging the under side falling off a jack. Wet grass under one wheel and tarmac under the other is easiest, though my 960 wagon failed that test, I don't think it had seen any wheel spin in 100,000km or more. Works now that I've owned it for a while
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Old 06-16-2021, 03:22 AM   #16
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Wet grass and tarmac broke one of my G80's. I wasn't testing it though, I pulled over on the shoulder for an ambulance
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Old 06-16-2021, 08:47 AM   #17
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It was on its last legs then. Josh from Yoshifab reckons it's fairly random. He had one last for years of abuse and another fail within the first week. If the little fly weights break, it's from fatigue. A typical operating scenario for a factory fitted G80 is a mild overpowering of one wheel from a sensible operator that causes barely enough speed differential to induce a lock and then, therefore, that amount of power is insufficient to spin both and the car proceeds to accelerate away. This saved my mrs driving a 940 wagon across a dangerous wet roundabout here one day, she put her foot down and the B234F started to slip the right rear and it actuated and she accelerated across the intersection and out of the way of the oncoming car that would have had to brake or hit her if she'd just spun up that wheel badly with an open diff. That's what they're for. Not what I do to them If you put your foot hard down on wet grass then you can actually MISS the actuation because the speed increases before the fly weight can spin out and the other fly weight is already out of the way. If you get it just right, it locks and you drift sideways down the road stressing the clutch packs to the max
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Old 06-16-2021, 11:33 AM   #18
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I've had pretty solid luck with jacking one side up, give the wheel a SHARP twist as fast as you can move it and you'll feel it catch very solidly. Also the G80's should have the half moon on the cover for the filter, where the open's won't.

Oh...then there's this...
http://forums.turbobricks.com/showthread.php?t=113713
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Old 07-11-2021, 11:30 AM   #19
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I will try the transmission-in-park/drive-while-other-wheel-on-the-ground method and see if I can get it to lock. I tried with both wheels in the air and in neutral and nothing. I will keep you posted.

About 8.8, I have been thinking on that (or Toyota one) at https://forums.turbobricks.com/showthread.php?t=360855.

Am I correct to assume only the G80 does not have a gasket?
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Old 07-11-2021, 05:08 PM   #20
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There should be a small white label hidden under lots of undercoating, it should be on the rear side of the left axle tube, use chemicals to remove the undercoating

There you should find a label with the ratio, and either 1031 or 1041 (G80 locking) that will tell you what you have is the axle is original to the car
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