Mainly spinning 1 tire...

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7milesout

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Guys - I took the Scamp to the strip. Just to gather data (don't ask ... it is s-l-o-w (carb & exhaust issues)). But on the line, it would spin the right rear. I could feather it and make a difference ... but I don't wanna (feather it)!

I called the previous owner, he claims it has a limited-slip in it. Feels more like an unlimited slip. :D He said to approach the start line with the car aimed right, and then turn sharp left at a few feet before the line to align the car straight down the track. He described that doing this does something in the rear diff that helps both tires pull equally. I can see what he's talking about.

And while that may work ... I don't want to have to do that. 20 years ago, I watched him do that (in this car when he owned it) when we went to the Mopar Nationals, and to be honest, it looked ... ridiculous.

The car has an 8.75 rear end. What I would like some guidance on, is what should I be looking to do with this rear diff? I've heard of Trac-Loc but don't know anything about it. I don't want the clicking around the corners either. It's not a dragster. It's is 90% street. I just want both tires to pull evenly from a dead stop. That's all I'm after.
 
If a burnout won't lock it up there's something wrong
 
Jack it up in neutral, turn the rear wheels, they should both spin the same direction,(if limited slip/ Sure Grip) or if something is broke you will hear and feel it. If it is an open rear, one wheel will turn one way, the other will turn opposite direction or not at all. This will basically be a quick check, but it sounds to me like you have an 8 3/4 open rear, they are out there.
 
I'm not doing burnouts just yet. The brakes need to be gone through. They get the job done, but need TLC. I'll get to it. Until then, I'm not power-braking that sucker. Drums all around too.

Is the pumpkin strong enough to be the jack point?
 
Yes, roll your floor jack right under the rear and lift it up. It will balance well under the pumpkin.
 
I'll *try* to check it out tonight. But will be late, got stuff to do. Will reply back in here, and go from there.

Thanks!!!


7milesout
 
My bet is you have a open differential. Or a very worn out SG. Your going to have to pull the third member to know exactly what you have.
 
Yeah, those ole SG's, they wear out. What's an SG ... and will I need to pull the 4th member too? :lol:
 
It's the Mopar term for dual traction unit or Posi, Third member is the center section that is removable in the rear end. SG = Sure Grip
 
You can pull the center section and remove the SG unit and rebuild it! There are 2 different styles, the old Spicer clutch style, and the newer Auburn cone style, both are rebuildable, but the Auburn style needs the cone machines and shimmed, the clutch style just requires new clutches and steels!

Identify what you have and we can help you through this!!
 
You could call it a "Posi" but it would be sacrilege as "Positraction" was GM's Limited Slip Differential.
 
I'll stick to SG. Anything will better than the SS (Sure Slip ... or Sure Spin) that's in it now. Thanks for you help. I'll try to get to it tonight. I'm needing to jog the rear end out of the way anyway. I'll let the tires down on my auto dollies ... I won't try to roll it on the jack.
 
7milesout said:
I'll stick to SG. Anything will better than the SS (Sure Slip ... or Sure Spin) that's in it now. Thanks for you help. I'll try to get to it tonight. I'm needing to jog the rear end out of the way anyway. I'll let the tires down on my auto dollies ... I won't try to roll it on the jack.
Click to expand...
remove axles first lol
 
SGBARRACUDA said:
My bet is you have a open differential. Or a very worn out SG.
Click to expand...

Go ahead and go to the cash window, you're a winner! They spin different directions. Tell me this, if it were a really worn out SG, would they spin different directions? Or make noise. It makes no noise. I'm guessing it just an open diff as it drives just fine around town, absolutely no noise or nothing odd.

If you guys wouldn't mind pointing me to some directions on how to remove the 3rd member, i will do that and confirm.

In the end, i would like to keep the same ratio because at my goal speed it will run across the line at 5,400 rpm. That's about perfect. Even if the wheels spin different directions, can I still spin the wheel one rev and count the turns of the driveshaft to determine the ratio?

Thanks for your help guys. There a lot of things I have done, a few things I'm good at, but there's a whole ton of stuff I have NEVER been exposed to. Differentials is one of them. Your advice is much appreciated.


7milesout
 
Pulling the unit is easy enough, but maybe you should line up the parts to go in it first! You could rebuild a seperate center section on the bench and just swap it out! At least score the SG unit first if you plan on using your entire center and just adding the SG!

The procedure for pulling it out is basically this!!....

Jack it up, remove the rear wheels and put it on jack stands! Scoot under and take the driveshaft off the rear yoke!

Go to the passenger side of the car and remove the drum, you will see a collar around the axle center that is a giant collar nut that adjusts the axle end play! There is a locking tang under one of the nuts, remove that and turn the collar to release the preload on the axles, then take the rest of the nuts off and pull the axle out about 6" at most!

Go to the drivers side and remove the drum, then remove the nuts holding the axle in and pull that axle out about 6"! Now go under the car and remove the bolts holding the center section in, but leave the top 2 nuts on, but loose! Tap a screwdriver or small pry bar into the gap between the housing and center at the bottom, to release the seal and allow the fluid to escape into a waiting pan!

Remove the top 2 nuts when the fluid has drained out and remove the center with a hydraulic jack underneath it to lower it down!! Bada boom, it's out!
 
An open differential will spin both, or either wheel under the right circumstances. Sounds like you need a sure grip unit.
 
Also look on the side of the third member (drivers side, on the front nose) and look for the case number and see what the last three numbers are. Should be 741, 742,489. This will tell what case your starting with.
 
What's the difference in the SureGrip and TrueTrac? And is one better than the other?
 
Sure Grip is a Mopar term. Truetrac is a aftermarket product by Eaton Detroit. I like the Detroit locker if money is no object.
 
I heard lots of noise and driveability issues with the Detroit locker. And of course, money is an object. The car was given to me. I would like to keep it as free as possible.

Are you saying that the Sure Grip and the TrueTrac are basically one in the same, aside from the name?
 
Two different animals Mopar built two types the early model 68 and older uses friction clutches. The newer cone style uses a inference fit between splined cones and the case halves. Detroit locker uses These Eaton Detroit Truetrac differentials use a patented design of parallel-axis planetary helix gears to provide a quiet, automatic splitting of torque. The detroit locker will cost you about 550.00, a good clutch type SG will run 300-400 with new clutches.
 
Let me see if I understand this. 2 Types are:

  1. Mopar SureGrip
    • Type 1: The early model 68, cone style / interference fit ...
    • Type 2: Friction clutch based.
    • Type 2 cost is $300 - $400
  2. Detroit Locker
    • Implementing the Eaton "Truetrac," and all that entails.
    • ~$550
Am I understanding this correctly?
 
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