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G80 locker, a few questions for those who have modded one.

This may be a dumb question (I am new to Volvo), but can you just pull the cover off and drill several holes into the weight?

You would not need to weld, or pull the axle shafts out and disassemble the diff, I would think that would raise the unlock speed.


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.
 
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.

is it possible that when the car shifts (auto) or the drivers shift (stick) this unloads the diff for a moment allowing it to unlock?
 
is it possible that when the car shifts (auto) or the drivers shift (stick) this unloads the diff for a moment allowing it to unlock?

Yes, as soon as power delivery stops, it should unlock. An auto never stops delivering power when it shifts. It's in one gear, then, the next by grabbing the next planetary gear. That's the beauty of an auto for drag racing.
 
Mine has stayed locked for as much as 300 feet of normal straight driving after regaining traction, then surprised me with as wild and noisy next corner.

I can come to a stop with a rear wheel airborne, and brakes locked idling in D is enough to keep it locked.

It does work on ice.

I think it is supposed to need to ramp the other way to unlock.
 
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.

Yeah.. but too many ppl have this issue, including me.. also some ppl say once and for all the G80 schould behave like this.. so.. whos got the right once and for all?

I dont want to piss you off... just want to clarify whats going on..


To grep your explanation.. what could be wrong with my diff? And ! Could it be possible that this ramping sometimes is reached while drifting when playing with the throttle to stabilize it?
 
Transitioning from drive to coast will unlock it.
You can weaken the holdback springs against the small weights to engage lock easier. This will doubtless increase wear, but possibly reduce shock, as there will be less time to build differential rotation. When it comes down to it, you will still ave a unit that is by its nature unsuited to any sort of performance driving, on or off road. I'm not hating, used gently , it is damn good for not getting stuck in a near stock vehicle, especially at PnP prices.
 
Transitioning from drive to coast will unlock it.
You can weaken the holdback springs against the small weights to engage lock easier. This will doubtless increase wear, but possibly reduce shock, as there will be less time to build differential rotation. When it comes down to it, you will still ave a unit that is by its nature unsuited to any sort of performance driving, on or off road. I'm not hating, used gently , it is damn good for not getting stuck in a near stock vehicle, especially at PnP prices.

Mine has lived for quite awhile behind a 400whp 16v motor. It just recently nuked the locking mechanism but seems to me that its a reasonably good part fore even moderately powered volvos.
 
so 2? years with stock wheelwells? How much time on slicks? Your car weighs how many hundred pounds less than a fully dressed 940?
But really what I take issue with is the way engagement requires substantial wheelspin, then just shocks the other tire loose.
 
Well the G80 was the first mod on the car. 3 years of performance only driving. I have a dozen or so 1.6-1.7 60' time slips on slicks and have slid the car around streets of willow, Adams kart track, let several people co-drive it at Davis auto-x the last two years and constant street abuse. We will see how long g80#2 lasts at this power level.

My full weight 245 has had one for ~5 years. Not nearly the power of the 242 but plenty of torque and huge loads. I have had this car/diff offroad in Baja with 1000lb of gear in the back (diff doing its thing hours on end), flat towed my 242 to the track, launched boats (slick launch ramps definitely make use of the locker). The g80 is still holding up fine. Makes the car so much more useful and for a minimal investment.

There are better diffs out there, they just cost a hell of a lot more than the $30~50 a moded g80 does. Bang for the buck is pretty damn good.
 
Transitioning from drive to coast will unlock it.

it just pisses me off that it unlocks while drifting.. so.. you do think it comes from playing with throttle? Mh.. normally when im in a drift the tires are spinning, sometimes faster/slower but never stop.. so there shouldtn be a transition between driving and coasting...

Naahh...
 
The one in my truck might be 25 years old. My contact patches are as much as a foot wide, and nice gear oil cost more than the axle I put it in. I don't go out of my way to thrash on it, and it hasn't broke yet. I have no regrets, it's a whole lot better than an open diff.

Maddog, could it be your tires are still sliding because you are going sideways and your wheel speed is momentarily less than ground speed?
But you are going over 25, so it won't lock up again.
 
I disagree, there is no disengagement function or speed.
If it comes unlocked while under load, it is broken.


I don't know about easier life, less heat load, but it engages with a ferocious bang every time, and can scramble the splines on the clutch plates, especially if you have more power and/or grip than stock.
Or maybe a bowl of this;
261672450.jpg


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.

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.

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.

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?

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?

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.
 
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:lol:

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.
 
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.
 
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.
 


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?
 
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