Is my G80 working right?

stebob · January 27, 2004

Sorry if any of you saw this exact thing on another forum, I copy and pasted it here since I've nothing over there. Any thoughts is most welcome!

I have the G80 rear end. The other night on my road, (long country road) I stopped and just hammered the gas. My right wheel tire immed. lit up and spun very quickly. Now, I could feel and hear a clunk and could tell my left tire was trying to kick in, but never really did. I let off of it because my tire would have never quit spinning if I didn't. Stopped and did it again, same results. I went back and looked at the mark. It was deep black and went on for about 60'. I could see lighter marks for the left tire only a foot or so in lenth, a few feet more same thing, then after that no other marks from the left tire. Is my G80 working correctly? Did my right rear light up so quickly and spun too quickly for the G80 to grab? I'm worried about my rear end now...

However, in the rain, both tires will spin. Also, now that we have snow on the ground, both tires spin there too and kick the rear end out. What do you guys think?

Ben · January 27, 2004

Yes, it's working right.

Centrifagul weights spin out and throw the switch to locker. 100 rpm differential between left and right...but will NOT if the differential over certain amount.

Grenades the locker if locker switch thrown in over certain speed.

What you almost did was grenade your locker. Best to let off of the throttle when the centrifagul weights are about to throw the lever.

If you like to hot rod, better consider different type of locker. Maybe ARB or Electric so you can switch it on when going to nail the throttle.

JayMan · January 28, 2004

Yes, it's working right.

Centrifagul weights spin out and throw the switch to locker. 100 rpm differential between left and right...but will NOT if the differential over certain amount.

Grenades the locker if locker switch thrown in over certain speed.

What you almost did was grenade your locker. Best to let off of the throttle when the centrifagul weights are about to throw the lever.

If you like to hot rod, better consider different type of locker. Maybe ARB or Electric so you can switch it on when going to nail the throttle.

This is the weak point of the RPO G80 locker. If you keep pretending you're a muscle car driver and keep pulling that stunt, if your G80 isn't trashed already, it soon will be.

Remember the G80 "GovLok" was designed primarily to work at rest or at very low speeds. The design of the "locker" is actually the clutch plates from a limited slip differential, but the plates are engaged by mechanical force, not a preload spring.

When there is a difference in wheel speed - about 100 RPM on these trucks - that allows the flyweight/governor assembly to rotate. The weights beyond a certain rotational speed flip out (Centrifugal force) the catch on the drive cam, which drives the clutches together: this is known as "self engergizing." With the case at rotation, both wheels receive equal torque and work together.

There is also a safety feature: beyond a certain case speed, about 25 MPH, the entire flyweight/governor assembly is pushed against a small spring, and finally trips past that spring. Once locked out in that position, the cam can't be engaged to drive the clutch plates together.

This is important if you're going uphill at highway speeds and one wheel is on ice and the other is on the dry center part of the road. Otherwise, the truck could go sideways at highway speed. I had that happen once in my old Ford one ton with the locker, and I actually DID s*** myself. It was scary.

Yeah, there are some weak points to this design, but if you drive it as it was intended, it holds up well.

You really notice the difference when one wheel is on dry land and the other is on ice, or if one wheel is in the air. You have all the advantages of a true locker without the harsh CLANK CLANK CLANK business of going around corners. Don't get me wrong, the Detroit Locker is a bulletproof design and I had one in a 1985 2WD Ford F-350 chassis cab, but that noise drove me bonkers.

Remember a limited slip or "posi" has the clutch plates, but they're biased with the preload spring between them. Some designs have a large "S" spring, the Eaton Posi has a circular case with 4 smaller springs. With more input torque, the springs help compress the clutch plates and eventually both wheels receive close to equal torque.

Like with a muscle car, the more you floor it, the more the input torque is biased to both wheels. You can use stronger preload springs to bias earlier and stronger, but that's detrimental to normal driving: more heat, more wear, and chatter around corners.

For your G80 if you want to do a more sane test, try this: on cement or pavement in your driveway, jack up the right rear wheel and put a jackstand under the axle tube. Go into the truck and fire up.

Make sure the 4WD selector is in 2HI, put the truck in D, and VERY GENTLY step on the gas. At slightly above idle, like 800-900 RPM max, the G80 should engage very smoothly and quickly, and the left rear wheel (The one still on the ground) should try to drive the truck off the jackstand.

If you get a jerking/slipping/jerkng sensation, then something is very wrong. Either the fluid is old and all the LS additives are used up, or the flyweight assembly parts are damaged.

Drain the axle through a screened funnel to see if any chunks are in there. Next, pry the sheet metal cover off the axle and see if any chunks are stuck to the magnets. Beyond that, unless you're good at working on axles, better see a pro. Try adding a tube or two of LS additive, refill with something like Mobil 1 Gear Lube, and see if it comes back to life.

If you want to horse around, put in a regular Limited Slip. Those things bias according to input torque, though they're pretty useless offroad and especially if one wheel is on ice and one wheel is on dry road. They do appear quite resistant to "pedal to the metal fatigue" though.

FWIW I tried the same sort of stunt on a gravel road when mine was brand new, but only giving it 1/3 pedal. Both rear tires appeared to spin an equal amount and the truck stepped out to the right. This week with a lot of snow/ice on the roads, at a stop sign both rear wheels appear to grab equally and the truck will step to the right if I don't ease off.

stebob · January 28, 2004

Great info.!! Thanks, guys. Yeah, that's something that I really don't do. I decided to that day for some reason... Well, I know what it can do and I won't be doing that anymore.

I'm going to jack it up like you said and see how it engages. I hope all is well with it. On another forum a guy told me that it sounds like my clutches are gone for it doing what it did, but from what you guys stated (and makes sense) it's working correctly other than my abusing it.

Thanks, again!

tmoreau · January 28, 2004

Goodness... the more I read about the G80 the more I'm glad I dont have it. Don't get me wrong, sounds like a great piece of equipment for its intended use its just that that dosent fit well with MY intended use.

Yesterday in the snow and once more this morning on a frosty/icy road I got my open diff to spin both wheels, in over 37k miles I have only had that happen about three times but dang did it feel good to have the back and step out like it should. Sigh.... I want a LOCKER!

robsawatsky · January 28, 2004

If your intended use is extreme launch traction, then a true limited-slip would be preferable to a locker like the G80.

I exercise my G80 quite regularly with the frequent rain showers around here that leave the middle of the road dry and the edges closer to the curbs wet. A right turn under those conditions leads to right-rear wheelspin rather easily. Definitely feel the locker engaging after a few momemts of wheelspin and then off we go. Somewhat different effect (step out) when both wheels are on the slippery stuff. A couple of weeks ago had a patch of snow/ice at the intersection on the residential street coming out of my area and you could definitely feel the lock-up causing some crow-hopping while trying to turn with both rear wheels initially slipping.

A lot better a getting going in the wet with no load in the bed than my old F150 was with no limited-slip of any sort.

tommyboyZ71 · January 30, 2004

And people wonder why I wont buy a used truck

AlanTDickey · January 31, 2004

Related question:

To test my locker, I drove on some new snow recently (less than an inch on the road), rolled to a stop, hit the pedal, and left two, equal length (about 10ft) spin marks before both rear tires caught traction and stopped spinning.

I also did the same thing with one rear tire on about 2 inches of snow and the other one on (almost) dry pavement. Both tires spun when I gunned the truck for a short period. Now, the tire on the pavement was on pavement that may have had with some reduced friction because of the weather (a slight glaze of moisture).

Question: Did I prove anything about my locker?

I know the conventional wisdom is that, to test the locker, you have to try to break traction when one tire is on ice and the other is on dry pavement. However, when following cars and trucks with open diffs drecently, I notice, that when they have both rear tires on the same snowy surface they always spin one tire and only one tire. When you see a car moving slowly in the snow, it always has one tire moving at the spead of the vehicle, and the other is spinning and throwing snow. Does the fact that I'm not doing that, but rather spinning both tires, mean that my locker is working properly? Or is there some other reason why I get both of my rear tires to spin on slippery surfaces???

Thanks in advance for any comments.

traxion · January 31, 2004

I was on gravel on a steep grade and was going in reverse (up the grade) and lightly jabbed the accelerator for a bout 6' the wheels spun the exact amount. Try doing that with a ford. Love that G80.

JayMan · January 31, 2004

Related question:
To test my locker, I drove on some new snow recently (less than an inch on the road), rolled to a stop, hit the pedal, and left two, equal length (about 10ft) spin marks before both rear tires caught traction and stopped spinning.

I also did the same thing with one rear tire on about 2 inches of snow and the other one on (almost) dry pavement. Both tires spun when I gunned the truck for a short period. Now, the tire on the pavement was on pavement that may have had with some reduced friction because of the weather (a slight glaze of moisture).

Question: Did I prove anything about my locker?

I know the conventional wisdom is that, to test the locker, you have to try to break traction when one tire is on ice and the other is on dry pavement. However, when following cars and trucks with open diffs drecently, I notice, that when they have both rear tires on the same snowy surface they always spin one tire and only one tire. When you see a car moving slowly in the snow, it always has one tire moving at the spead of the vehicle, and the other is spinning and throwing snow. Does the fact that I'm not doing that, but rather spinning both tires, mean that my locker is working properly? Or is there some other reason why I get both of my rear tires to spin on slippery surfaces???

Thanks in advance for any comments.

I would suggest your "test" with one wheel on snow and one wheel on almost-dry pavement proved your G80 is working properly. In an open-carrier rear, you would have sat there.

Like yesterday, I had to pull off the highway when I noticed an ambulance approaching. Once the ambulance and police car went by, I drove off. One wheel was on bone dry pavement and one wheel was on slippery snow and ice of the shoulder.

The G80 smoothly engaged and away I went. I stepped harder on the gas and the wheel on bone-dry pavement started to lightly squeal.

With a regular Limited Slip it would not have been that smooth, and there would have been a lot of wheelspin from the wheel on the shoulder before I moved. Or you might have to use the "parking brake trick" to get moving in such a situation, not with the G80.

On very poor traction surfaces, an open-carrier differential will appear to have both rear wheels spinning equally. All the power goes to the wheel with the least traction, so on snow/ice both can spin at the same time.