1960 Rear End Question

[Joe L.]

Re: 1960 Rear End Question

Check the length of the axles. Axles for the posi were shorter, but they may have left the posi axles in the car when they took out the posi carrier. I am still looking for that information. I have it somewhere.

Wayne------


According to GM, for 1960 the axles were the same.

[Terry D.]

Re: 1960 Rear End Question

How can you be sure the axle housing is original? Let's be honest unless you are or know the original owner that rear end could have changed several times, and I'm not talking about just the center section. Since you have to pull the axles anyway, be sure to check the axle bearings, etc.

[Pete P.]

Re: 1960 Rear End Question

Terry,
You're absolutely right; I'm not sure if the housing is original. The only thing I I know for sure, is that the housing has the vent tube on top and the " Limited Slip" tag on the filler plug. And, I wIill definitely check the axle bearings when I pull the axles.

Gary and I are still wondering if the wheel rotation I mentioned above is a good check to verify positraction

Pete

[Bill M.]

Re: 1960 Rear End Question

Gary and I are still wondering if the wheel rotation I mentioned above is a good check to verify positraction

Usually, wheels will turn in the same direction with posi.

The early posi (57-59) was a torque-lock design with no pre-load on the clutch pack and the wheels may turn in the opposite direction when hanging free because there is no torque applied to the posi and with no torque on the posi, there is no load applied to the clutch pack.

In 1960, Belleville washers were used to pre-load the clutch pack, and the hanging-free wheels will turn in the same direction with posi.

[Tom P.]

Re: 1960 Rear End Question

As old, and as knowledgeable, and as extensive of an information and technical base as NCRS has, I CANNOT believe that so far no one has really provided positive, definitive answers (most of the above seems to be somewhat guess work, or, word of mouth supposition)!

Let's start with the axle housing itself.
If it has the brackets for the radius rods (factory traction bars) on top of the axle tubes, between the U-bolts, and if it has a drain plug on the BOTTOM, CENTER of the housing, it is for a fact a 1959-1961 axle housing (1962 Vette and pass cars NO LONGER had a drain plug). Just because it has a round posi tag and a vent tube which goes over to the top of the housing DOES NOT mean the housing was originally a posi housing. WITH THE CENTER SECTION REMOVED, INSIDE the housing, the posi axle housings had an oil deflector welded to the top of the housing, PLUS, there was a round baffle (looks like a BIG washer) welded to each axle tube to limit oil slosh away from the differential during severe cornering.

Now, the differential case.
There were TWO, repeat, TWO posi cases during the 57-64 models: 3743833(57-61), 3789812(late 61-64). REMEMBER, this style rear was last used in Corvettes in 62, but continued in pass car service through the 64 model------------and was available in several ratios as a service replacement from the Chevy parts dept for a few years afterward (I personally have seen casting dates as late as 68).
With the exception of the VERY, VERY early 57 posi cases (Dec 56, Jan, Feb 57), ALLLLLLLLLLLLLLLLLLLLLL posi cases had a BIG P along side the casting number. The rears were built at two plants: Detroit Gear and Axle and Buffalo (NY) plants. The Detroit built rears had a THIN P and the Buffalo rears had a THICK P, as below.





Axles.
ONLY, ONLY, ONLY, ONLY 1957 Corvettes and pass cars----------------WITH POSI INSTALLED AT THE FACTORY--------------got 1/8in shorter (at the splined end) axles. The NON-posi 57 cars and ALLLLLLLLLLLLLLLLLLL 58-62 Corvettes used the SAME axles. Why did 58-62 models not get the shorter axles with posi??? BECAUSE they either had a spacer about .120in thick installed between the axle bearing and the end of the housing, OR, they received the thicker (about 1/8in thicker) RW607 series bearing which was a ball bearing. Cars built with posi received roller bearings.
Below is a comparison of 55-6, 57, 58-64 axle bearings. The 55-6 (left) were a smaller diameter, 57-62 were a larger diameter, but the 58-62 bearing is about 1/8in thicker than the 57 bearing.






Wheel rotation.
GENERALLY speaking, if a car has a NON-posi rear, with or without the transmission in gear, when one wheel is turned, the other wheel will turn in the opposite direction. But, if the tranny is in neutral, and there is no drag on the wheels (such as the brake shoes dragging on the drums), then when the driveshaft is turned, the wheels very well may turn the same direction (just as they would when going down the road).
If the car has a posi rear, and the clutches are in good condition, then BOTH wheels will (or should) turn the same direction. BUT, if the clutches are plum worn out, OR, as already mentioned above, the posi is an early (57-59) unit, the wheels MAY, repeat, MAY turn in opposite directions (with the tranny in neutral) because the 57-59 posi units had NO Belleville clutch plates to provide preload on the posi.

I'm quite sure I've left out a lot, but the above is the basics of posi vs non-posi rears in these early cars.

[Pete P.]

Re: 1960 Rear End Question

Tom,

Thank you very much for all the information you have provided.

I should have provided more information about my axle housing. My differential does not have the thin P, just P/N 3725899, H297, BB011. However, my axle housing does have the radius rods (traction bars) on each side above the U-bolts and also the drain plug on the bottom of the housing center section, along with the vent tube on top and posi tag. Then, based on what you mentioned, I have the correct 59-61 axle housing. I also know that I should have a 3743833 differential.

I realize that the TDB has tossed around this topic quite a bit, but it helps to get guidance from you gents on specific situations. I wasn't sure if I was getting into more than I bargained if I replace just the differential. Since the gaskets are leaking, it seemed like a good time to consider replacing the differential with the correct one.

Thanks again.

[Tom P.]

Re: 1960 Rear End Question

Pete,
Are you familiar with what is required to change out the center section?
Very honestly, it is quite easy. I USED to be able to change the center section in 45min.

[Pete P.]

Re: 1960 Rear End Question

Tom,

I believe that I know the overall process; drain rear end fluid, remove wheels and brake shoes, remove axle retainers and pull out axles, etc. Originally, I was concerned that I would have to change axles, causing the replacement of parts to multiply. At this point, I don't think I have a axle bearing problem.

[Tom P.]

Re: 1960 Rear End Question

To remove the axles and the center section----------YOU DO NOT NEED TO REMOVE THE BRAKE SHOES!!!!!!!!!

[Terry D.]

Re: 1960 Rear End Question

Pete
One thing that will make getting the axle retainers out is a half moon or gearwrench as it is called. If you have never seen one just google half moon wrench. It makes getting those nuts off much easier.

[Pete P.]

Re: 1960 Rear End Question

Tom - Thank you for the clarification on what I don't need to remove.

Terry - Thank you for the tooling tip.