Differential

[Ray K.]

While checking the lube level in the differential housing of my '83 (RQB 3420), I noticed a rusty steel tag attached to one of the bolts. Wire-brushing brought up the number "4.10". The previous owner had told me the rear was an original Studebaker rear with 3.42 gears. I jacked up one wheel in order to count the ratio (ie, number of drive shaft revolutions for 2 turns of one rear wheel, assuming an open rear), but the free wheel wouldn't turn (trans in neutral, brake off). So, assuming a Twin-Traction rear, I jacked up both rear wheels, but neither wheel would turn, in either direction. I started the car in neutral, shifted into drive, and both wheels ran forward, with no obvious indications of dragging brakes. I put it back into neutral and turned the engine off, but I still could not turn the rear wheels by hand. The driveshaft was also locked.

Four questions:

1. Is this situation normal, or is there something wrong with my car?

2. Did Studebaker offer 4.10 gears (or 3.42, for that matter)?

3. How do I tell if this is a genuine Studebaker rear?

4. What differences between the Twin-Traction and open rear can be observed through the filler plug hole?

[adamderosa]

Ray-

1. This does not seem normal; you should be able to turn the wheels by hand. It sounds like the brakes are dragging.

2. I do believe that Studebaker did offer a 4.10 gearset, along with 3.73. 3.55. 3.31 and 3.08 (I think) but I don't recall a 3.42.

3. Not sure how to identify the axle as a "Studebaker" axle, but the shape of the differential cover can at least identify it as a Dana axle. (Studebaker used axles made by Dana)

4. I don't think you can see enough through the oil fill plug to identify it a TT. But, if you can get the wheels freed, if you turn one wheel by hand (with both wheels off of the ground) and the other wheel turns in the opposit direction, you have an open diff. If the other wheel turns in the same direction, you have a TT.

[WayneC]

I can only give you a partial answer, I don't know enough to fully answer...

The expert on Avanti II through 1984 is Dan Booth at Nostalgic Motorcars in Wixom MI, 248-349-4884 mon-thurs 10am to 4:30pm eastern

The original Stude differentials, came only in these ratios, according to the parts manual:

3.07

3.31

3.54

3.73

4.09

4.55

Stude didn't make their own differentials, they used "Dana 44's" in Avanti

(Dana Corp, or Dana Spicer, is/was a parts supplier to the automobile makers and aftermarket).

I believe that all early Avanti II cars (at least up through '71) came with "Twin Traction" (also called posi, or

"Power Lok"), in either 3.31 or 3.54 ratios, but I don't know for certain whether that continued up through

your '83 model. I have an '80 that seems to have a high rear end ratio, but I never tried to find out the ratio,

and the spec/order sheet that came with the car does not mention it.

I'm surprised you weren't able to rotate the driveshaft with the wheels off the ground, but it's possible

the wheels need a strong resistance force to "unlock" (free) the axle shafts.

It's also possible that you need to rotate both rear wheels simultaneously; if that doesn't work, I'd suggest

marking the driveshaft and a tire and either:

1) have someone in the drivers seat put the tranny in low gear and apply the brakes lightly (to keep revs

down) and count driveshaft revs for one or more tire revolutions with the wheels off the ground, or

2) have someone move the car forward very slowly (brakes applied) while you watch from down at street

level to count how many times the driveshaft turns when the tire turns one or more full turns... get

creative and tie a weighted piece of brightly colored yarn to the driveshaft so you can see it flop down

each rev, or attach something that makes a noise each rev (as kids we used a playing card to make

a motor sound against the bicycle spokes)

You might also be able to estimate the ratio mathmatically if you have cruise control or a steady foot...

you could use freeway markers to determine what rpm is required to achieve exactly a timed one-minute mile.... an actual 60 miles/hr... on a level stretch and use the approx rolling diameter of your rear tire size to estimate how many turns the tires make in one mile, then divide that into the rpm to get a ratio (I'm assuming your tranny has a 1:1 ratio in drive... no overdrive... so engine rpm equals driveshaft rpm). For example, a 205/75-15 tire turns about 770 revs per mile, so if you needed to run at 3150 rpm to cover a mile in exactly one minute, then 3150/770 = 4.09 ratio; 2872 rpm is a 3.73 ratio, 2725 rpm is a 3:54 ratio, etc... not exact, but probably close enough to determine which stock ratio you most likely have. If you run 215/70-15 tires, the magic number to use in the calculations is 775 revs/mile, 225/60-15 is 812 revs/mile, etc. Caveat: I haven't tried it, this is purely theoretical.

Edited March 5, 2008 by WayneC

[Ray K.]

Thanks Adam & Wayne. Your responses have been most helpful (and thorough!)

Ray

[billsr2]

Do I have a Dana 44 Power Lock?

Poke your index finger in the filler hole.

Does it go no farther than the first knuckel?

Power lock

Does it go in farther?

Peg leg,One wheel wonder,Easy spin.

[Ray K.]

In that case, it's a Power Lock.

Ray

[Ray K.]

I figured why my Avanti wheels were locking up while the car was on jack stands. For safety's sake, I had placed the jackstands under the frame members on either side. This allowed the differential to "hang" on the leaf springs. As a result, the driveshaft lowered and came into contact with the exhaust pipe that goes to the left muffler, effectively binding the driveshaft (and the wheels) from turning. Placing a floor jack under the differential center housing and raising it just enough to allow the driveshaft to clear the exhaust pipe made it possible to turn the wheels and count the ratio.

The differential is definitely Twin-Traction, as both wheels turn in the same direction. A chalk mark on the driveshaft turned exactly 3 revolutions in approximately 325 degrees of wheel rotation. The axle ratio is therefore approximately (360/325) x 3 = 3.32. This is consistent with the 3.31 ratio known to have been used. The differential housing cover also has the same pattern as that for Dana, which I was able to find on the Web ( http://www.nationwideparts.com/differentials.htm )