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Old 07-19-2011, 06:36 AM   #76
745 TurboGreasel
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Originally Posted by Turbeam View Post
This has not been my experience of the unit, but much of the difference in their operation may be down to the very different usage that they get between our cars.

In mine, it is certainly disengaging, but that is under cornering loads and with a manual transmission and up to 12" slicks. It may not be under such constant loading as with an auto, but that may also be because the speeds where slip begins to occur is already above the 25mph stock 'engagement/ disengagement' maximum speed, and if much below that speed a gear change would be needed before very long.

No doubt you will also be starting off from full throttle from 0mph onwards and not lifting off at all, where on a circuit the throttle could be rolled on and off or feathered to the suit available grip and cornering radius so the load fluctuates.
I'm more prone to stop, spin a wheel just enough to lock, then proceed over/through the obstacle, that way I avoid walking home

The first step for me then is still to increase the engagement speed a little by reduction of the big mass.


The ferocity of engagement is a valid point, but even so I believe the shock loading on the half shafts and across the diff forging itself is the real issue. The clutch friction plates will only see this very briefly until the force on the ramps locks it all up when there will be no significant further slip.
Last time I went shopping for one, I saw a couple with the clutch ears all twisted off.

It would be interesting to see if any of the shock load could be reduced by softening of the springs controlling the rotating weights to reduce the required half shaft speed difference that activates engagement?

I'm curious as to the cause of failure of the G80 in the photo. Was this diff already modified to allow engagement at higher speed.... it looks unmodifieed in the photo? Did it fail on initial engagement at low speed or when moving faster? I don't personally believe that either the G80's clutch packs or its ramps will be the weakest link in the chain.

I don't think I've seen any evidence of the ramps failing first. The one pictured is from a 4wd with knobby tires, one spins, then hooks up and the case fails, or it doesn't have the grip to fully lock, and the clutches burn.

The fracture of the main diff body forging looks like a material failure around the big mass pivot pin bores? I take it that it failed during actual lock-up?
it locks, or it dies trying, I think breakage once locked is rare.

If serious wheelspin was to occur on a high-output car running big slicks and a modified G80 at higher road speed and rpm, the shock torque load across the axle immediately as the diff locked could be huge. There might even be an argument for reducing the clutch pack friction area and introducing more slip during lock-up to try to 'soften' the engagement?
Seems to me there isn't enough clutch materiel to support prolonged slip Eaton makes nice clutch diffs, and this isn't one of them. If I got 1/4 second of slip, I bet my 7000 lb wagon wouldn't snap sideways half up the freeway onramp by my house every time it rains.

We can't really complain too much about a unit failing like that that if we are asking it to do much more than it was ever designed or intended to, but for some uses it could still be a useful and low cost option with only minor mods.
^True dat,but the inability to operate it smoothly is a heavy compromise.

I've been considering putting one in the front axle, but the Dana44 Ujoints aren't that great, and I'm not sure how bad the grab on the steering wheel would be when it locked.
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Old 07-19-2011, 01:23 PM   #77
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Originally Posted by 2manyturbos View Post
Once and for all, there is no unlock speed to a properly functioning G80. There is a speed above which it will not lock. Once locked, as long as increasing power is delivered to the G80, it will not unlock.
Sorry for the incorrect wording. I bought my first Volvo on Saturday.

If you just drill holes into the weight (so you don't have to pull the diff, or weld it), wouldn't that raise the speed at which the diff will still lock?

Maybe bump it up to 50 for example.
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Old 07-19-2011, 02:16 PM   #78
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Originally Posted by 940Orlando View Post
Sorry for the incorrect wording. I bought my first Volvo on Saturday.

If you just drill holes into the weight (so you don't have to pull the diff, or weld it), wouldn't that raise the speed at which the diff will still lock?

Maybe bump it up to 50 for example.
Yes, that is what the G80 mod article describes. The more weight you remove from the governor weights, the higher the speed at which the diff will still lock. My comment was not specifically directed at you. It was put there because post after post contained statements/comments about the weights being there to unlock the differential at 25 mph. That is not what they were intended to do. Even an unmodified G80 will stay locked at much higher speeds than 25 as long as the power is increased. I've had stock units stay locked up until at least 60 in turbo cars. I couldn't tell if it was still locked above 60 because the cars all ran out of power, no more spin, they hooked. The 740 we autocross with a modified G80 can be seen in videos at 70+ mph laying 2 black lines across the asphalt. It makes 300 hp. Plenty of power to keep the tires spinning. It's not the intent. I would like the car to put it all down, not spin. The stiff springs/shocks don't allow much weight transfer so spinning is just something we have to live with until the wheel wells are flared and wider wheel/tire combos can be run.
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Old 07-19-2011, 02:29 PM   #79
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Originally Posted by 745 TurboGreasel View Post


I've been considering putting one in the front axle, but the Dana44 Ujoints aren't that great, and I'm not sure how bad the grab on the steering wheel would be when it locked.
Ah,.... that one failed in the rear axle of a big 4X4 at low speed/ from rest. With big, large-diameter knobbly tyres there's probably even more of a shock load there when it engages than with slicks that are already rolling at speed but due to slippage have the necessary speed difference across the axle.

I wonder if it is the same kind of loading that could be distorting the friction disc ears during the short period where the are coming into play, just before the ramps have fully engaged? Has this ever been known to happen in tarmac use?

I don't quite understand the conditions where there might not be enough grip for the G80 to lock up..... unless grip levels were so low that both rear wheels were to spin, but with less than a 100rpm speed difference between them, frying the clutch packs??

Diff oil grade and type could also have an effect on the clutch packs if they are slipping excessively, in the same way as it would on bike wet multi-plate type clutches.

Even with part worn friction plates, the ramps should just ride up each other a little more for the same transmitted torque, so plate pressure should be unchanged. Any 'burning' friction plates might be the result of oil type or something else rather than overloading during lock-up?

At low speed, as long as the speed of one wheel exceeded that of the other by the required amount surely it would lock?

I'm really a bit surprised that these units are giving trouble in 4X4s though, I thought that was largely the market they were aimed at. This video makes much play on the use of the G80 in large 4X4s....

http://www.youtube.com/watch?v=AjymmXvBYsI

Maybe very big knobblies and enthusiastic throttle use are just too much for it? They seem to be more of a useful 'get you out of trouble' diff than a true 4X4 (or 4X2 even) performance one.

For road/ tarmac use, even with slicks and/or engagement speed mods, I'd like to think they might stay in one piece a little better?

Last edited by Turbeam; 07-19-2011 at 02:32 PM.. Reason: clarity
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Old 07-19-2011, 02:33 PM   #80
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No surprise. The 4X4 guys break anything and everything. For most Volvo car applications, I think the G80 will work well. Especially, a modified G80.
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Old 07-19-2011, 07:18 PM   #81
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The more weight you remove from the governor weights, the higher the speed at which the diff will still lock. My comment was not specifically directed at you. It was put there because post after post contained statements/comments about the weights being there to unlock the differential at 25 mph. That is not what they were intended to do. Even an unmodified G80 will stay locked at much higher speeds than 25 as long as the power is increased. I've had stock units stay locked up until at least 60 in turbo cars. I couldn't tell if it was still locked above 60 because the cars all ran out of power, no more spin, they hooked. The 740 we autocross with a modified G80 can be seen in videos at 70+ mph laying 2 black lines across the asphalt. It makes 300 hp. Plenty of power to keep the tires spinning. It's not the intent. I would like the car to put it all down, not spin. The stiff springs/shocks don't allow much weight transfer so spinning is just something we have to live with until the wheel wells are flared and wider wheel/tire combos can be run.

That is very interesting. In that case providing that enough torque is kept on the axle, the rotating weight that is responsible for lock-up in the forward direction must continue to hold the hook end of the big mass and prevent it from being able to move outwards under increasing centriufugal force at speeds above the normal 25mph cut-off speed?

If the big mass was able to move outwards the diff would disengage, so the back-cut on the hook and rotating weight must then keep them held together....

I for one didn't believe this would be the case, but it could be a useful feature of the differential if it is. Once my own G80 has been modified this should become more obvious, but for the moment noticeable inside wheel slip is only starting to happen at just above the stock unit maximum engagement speed under cornering, so there is no lock up.

Mostly I'm only aware of ANY lock-up when moving slowly on wet grass or mud on the way back to the car trailer!

I was of the belief that the G80 lock-up would cut out at speeds above 30kph, and to avoid push-on oversteer for the same reason as done on the Porsche 928 electronically controlled hydraulic unit.

See 2.00 mins in...

http://www.youtube.com/watch?v=_PoocIsiV2c

With the rear tyre sizes I usually run and only 1060kg of car to propel, I've never been aware of any lock-up being necessary at lower speeds on tarmac.... the rear of the car just squats, grips and bites and very rarely spin at all. I'd assumed I'd hear/ feel it lock on tarmac, as it IS noticeable as it locks on wet grass.....and very effective.

I might try to borrow some wheels with worn out/ skinny tyres just to see if I can keep the wheels locked and spinning above 25mph to test this out for myself.


The autocross video footage sounds like fun......
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Old 07-20-2011, 10:24 AM   #82
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That is very interesting. In that case providing that enough torque is kept on the axle, the rotating weight that is responsible for lock-up in the forward direction must continue to hold the hook end of the big mass and prevent it from being able to move outwards under increasing centriufugal force at speeds above the normal 25mph cut-off speed?

If the big mass was able to move outwards the diff would disengage, so the back-cut on the hook and rotating weight must then keep them held together....
...
this is what i keep saying ... Look at the angle of the contact plane with respect to the direction of action (pawl arc when weight swings out) and that of the rotating flyweights - The thing is not designed to "disengage" until the wheel that initially had traction has less traction than the one that initially slipped (engaging the lock-up). The pawl does not govern the disengagement, it only governs the engagement.

Last edited by kildea; 07-20-2011 at 10:37 AM..
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Old 12-03-2011, 06:39 PM   #83
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I know this has been beaten to death, but I have another question. Does anybody know just how much preload the diff is applying to the clutchpacks when'locked'?? Is it so much torque that the clutches will never slip?

Imagine this - Say I cut 100% of the weight off of those flyweights, how much preload would be applied when locked? Is there any slip under normal use at all, or is it locked 100% of the time? At this point, it seems like it's a function of preload on those clutches, the condition of those clutches, and the fluid/friction modifiers used? Or is there also something else thats mechanically locking those clutches together?


What I'm wondering is, if I remove 100% of that flyweight, and then potentially attempt to measure breakaway torque, and from there start adding friction modifier to the point where the breakaway torque gets down to the level of a traditional track-oriented LSD diff (say in the ~40% lockup range), will it act like a traditional LSD at some point, or is there so much preload on those clutch packs that it's not possible?
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Old 12-03-2011, 08:38 PM   #84
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I know this has been beaten to death, but I have another question. Does anybody know just how much preload the diff is applying to the clutchpacks when'locked'?? Is it so much torque that the clutches will never slip?

Imagine this - Say I cut 100% of the weight off of those flyweights, how much preload would be applied when locked? Is there any slip under normal use at all, or is it locked 100% of the time? At this point, it seems like it's a function of preload on those clutches, the condition of those clutches, and the fluid/friction modifiers used? Or is there also something else thats mechanically locking those clutches together?


What I'm wondering is, if I remove 100% of that flyweight, and then potentially attempt to measure breakaway torque, and from there start adding friction modifier to the point where the breakaway torque gets down to the level of a traditional track-oriented LSD diff (say in the ~40% lockup range), will it act like a traditional LSD at some point, or is there so much preload on those clutch packs that it's not possible?
you may have slightly misunderstood what cutting off the weight does. it doesn't mean it's locked all the time. and when it does lock up, it doesn't act like a 100% locked diff. I'd say it drives like a low preload clutch diff.

it means it can BECOME locked at any speed. as opposed to with the weight, it will only BECOME locked at less than about 25mph. at ~25mph the weight would sling out and it wouldn't lock up at all once that happened.

both rear tires off the ground, with the weight cut off, spin one tire slowly and it's an open diff. give it a quick accelerating spin and you'll hear it lock, then both wheels spin together, the same direction.

I haven't measured breakaway torque. I'll see if I can try that tonight. it'll be an approximation since I don't have an easy way to spin a wheel from the center, just from one of the lugnuts.
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Old 12-03-2011, 09:09 PM   #85
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Ahh, nevermind then. Sounds like it's just as much of a waste of time as I'd thought it was before. Also sounds extremely dangerous, and not predictable at all. Thanks for clearing that up though!
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Old 12-04-2011, 01:52 PM   #86
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Could try shimming it for more breakaway torque. Last time I had one out, I didn't have time to play with shims before we had to put it together for the race. It works good, though (when it works). Ours broke and spit the shaft w/cut governor weight out of the carrier. Probably is a good idea to weld that piece in place.
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Old 12-11-2011, 05:50 PM   #87
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Hi. I have modified a G80 locker by cutting 100% of weight.Job done as shown in this thread http://turbobricks.com/mods.php?content=art0027. But my flyweight was smaller,the car is 940 from 1996 (different locker? weaker?).After no more than 100km the flyweight has been smashed into small pieces! It happens with normal, easy drive.After I removed cover the flyweight and the shaft were disintegrated. I really don't know whats happen?What went wrong? Or maybe this locker was just to weak? I deicided to weld it but I still want to have a limited diff so I'm looking for it. I found Gripper LSD locker but it's really expensive. So the question is: does anybody know is it possible to swap LSD diff from any other car without any difficult mods? Any suggest welcome.Thx
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Old 12-11-2011, 05:57 PM   #88
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Hi. I have modified a G80 locker by cutting 100% of weight.Job done as shown in this thread http://turbobricks.com/mods.php?content=art0027. But my flyweight was smaller,the car is 940 from 1996 (different locker? weaker?).After no more than 100km the flyweight has been smashed into small pieces! It happens with normal, easy drive.After I removed cover the flyweight and the shaft were disintegrated. I really don't know whats happen?What went wrong? Or maybe this locker was just to weak? I deicided to weld it but I still want to have a limited diff so I'm looking for it. I found Gripper LSD locker but it's really expensive. So the question is: does anybody know is it possible to swap LSD diff from any other car without any difficult mods? Any suggest welcome.Thx
I did a bunch of research on this, and the general consensus is that a Dana 30 LSD from trucks like Ford Ranger's and Ford Aerostar vans, etc., SHOULD be a bolt-in. Haven't ever confirmed it though.
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Old 12-11-2011, 09:48 PM   #89
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I did a bunch of research on this, and the general consensus is that a Dana 30 LSD from trucks like Ford Ranger's and Ford Aerostar vans, etc., SHOULD be a bolt-in. Haven't ever confirmed it though.
As long as the dana 30 LSD is from a 3.73+ ratio, it will work in a volvo 1030/1031/1041 axle. The dana axle uses a different carrier for 3.54 and numerically lower ratios, but the volvo doesn't...they're all 3.73+ carriers regardless of ratio.
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