Sure grip sometimes only spins one wheel, other times both

[68charger440]

My sure grip sometimes only spins one wheel when doing burnout, other times both tires burn.  Do I have to rebuild or is there a way to adjust the clutches or something to make them grip better?

[lukedukem]

Check the posi unit itself first.

1) Jack up both rear wheels, car in neutral. Spin one side. They should of course both spin the same direction, if not uh oh.

2) Jack up just ONE rear wheel. Try to spin the other. If it doesn't spin with just a little force, try harder. If you can make it spin somewhat easily, your posi is working, but not real well. if you can't spin it at all your posi unit is working decently.

I think its possible to spin just one wheel if the torque differential is high enough. If you put one wheel on decent pavement and the other on a very slick surface and mat the go pedal, you can get one to spin. Once you exceed the breakaway torque (the "grip" internally in the posi unit), that one can spin, and it takes a bit of backing off until you get the slippage to stop.  eventually the available torque will be less than the breakaway, or the clutches may heat and find friction, and things will grab. Put too much heat in it though, and it'll glaze like any other clutch, and that breakaway torque will be drastically reduced.

Try this. Go to a parking lot or whatever and try some low speed figure 8's. it will break the varnish loose on the clutches. worth a shot. maybe change the oil in it before.

luke

[68charger440]

Check the posi unit itself first.

1) Jack up both rear wheels, car in neutral. Spin one side. They should of course both spin the same direction, if not uh oh.

2) Jack up just ONE rear wheel. Try to spin the other. If it doesn't spin with just a little force, try harder. If you can make it spin somewhat easily, your posi is working, but not real well. if you can't spin it at all your posi unit is working decently.

I think its possible to spin just one wheel if the torque differential is high enough. If you put one wheel on decent pavement and the other on a very slick surface and mat the go pedal, you can get one to spin. Once you exceed the breakaway torque (the "grip" internally in the posi unit), that one can spin, and it takes a bit of backing off until you get the slippage to stop.  eventually the available torque will be less than the breakaway, or the clutches may heat and find friction, and things will grab. Put too much heat in it though, and it'll glaze like any other clutch, and that breakaway torque will be drastically reduced.

Try this. Go to a parking lot or whatever and try some low speed figure 8's. it will break the varnish loose on the clutches. worth a shot. maybe change the oil in it before.

luke

I'll give it a shot.

[Cooter]

She you say"burnouts", are you just nailing it from a stand still?

"Burnouts", by "power braking" car is hard on torque converters as well as Sure grips
not the best way to tell if Sure grip is working. Could be one rear brake is holding more than other..

If you punch it from a stand still, it should either spin both wheels, or hook both wheels.

[68charger440]

She you say"burnouts", are you just nailing it from a stand still?

"Burnouts", by "power braking" car is hard on torque converters as well as Sure grips
not the best way to tell if Sure grip is working. Could be one rear brake is holding more than other..

If you punch it from a stand still, it should either spin both wheels, or hook both wheels.

With my setup being a 500" stroker, 3:91 gears and street tires, I don't have to power brake it.  I just mash the pedal and get an easy 50 feet of rubber with no power braking, but it still sometimes leaves one line of rubber and other times two even though the pavement looks the same under both wheels.

[Cooter]

She you say"burnouts", are you just nailing it from a stand still?

"Burnouts", by "power braking" car is hard on torque converters as well as Sure grips
not the best way to tell if Sure grip is working. Could be one rear brake is holding more than other..

If you punch it from a stand still, it should either spin both wheels, or hook both wheels.

With my setup being a 500" stroker, 3:91 gears and street tires, I don't have to power brake it.  I just mash the pedal and get an easy 50 feet of rubber with no power braking, but it still sometimes leaves one line of rubber and other times two even though the pavement looks the same under both wheels.

Lemme guess...45 year old Sure grip unit?
All depends on which wheel has tge most traction. Contrary to popular belief, a limited slip means just that, limited slip. The ONLY WAY to insure BOTH wheels leave insane marks??

Spool.

[68charger440]

Yup, it is a 45 year old sure grip.  So should I not worry about it?  It just seems like it should do better than gripping 1/2 of the time.

[c00nhunterjoe]

Sounds worn out. Normal for a 40 year old unit. Replace it with a detroit tru-trac unit. Drives like an open, grips like a spool. You cant beat it.

[chargd72]

Sounds worn out. Normal for a 40 year old unit. Replace it with a detroit tru-trac unit. Drives like an open, grips like a spool. You cant beat it.

Agreed.  Just put one in my 8.75.  Works great and never have to worry about parts wearing out.  Right now Eaton is offering a 50$ rebate on them.