JH57Z06

Replaced the diff in my 57 corvette with a posi-trac unit. This one is assumed to be a 'non posi-trac' unit. Car was manufactured in Nov '56.

Anyone know what they're worth?

mickatbp

Have a look on ebay - non posi units (at a guess - haven't looked for a while) go for $300ish some less some more. The ratio is the determining factor, 3.7, 3.36 seem to be the best sellers. Also depends on how you present it.

I've been thinking about putting a posi unit in mine also for some time but I live in Australia and they are H E A V Y. What ratio did you put in? have you driven it since? what made you do it? How happy are you with your car now? Did it make a big difference? How much did you pay for your posi unit ($500 seems to be a very good buy but I've seem them as high as $1100 fully reconditioned)? Have the results outwayed the cost? Did you need to shorten your axles - I've read that non-posi axles are longer than posi axles? Sorry lots of questions given that all you wanted was a sales price for your old unit.

Regards

Mick

JH57Z06

I think the old one is a 3.73 unit but not sure. Had it installed by a mechanic and he didn't say anything about having to cut the axles which, based on what you said, makes me think it was a posi unit. New one cost me $1300 from Just Differentials ([url]http://www.justdifferentials.com/), including shipping. I shopped around quite a bit so I think I paid a fair price. I haven't really stopped to think about whether it was worth it. I was told it needed to be rebuilt so I just went for it since I didn't think it was a posi. I have driven it about 300 miles since then, no problems except the high reving doing ~ 65 mph (3500 rpm). That's also contributed to my decision to buy a TREMEC 5 speed: .64:1 5th gear.

mickatbp

Sounds like it might be a 4.1 posi they've installed .... or maybe even higher. Can you send me a photo of the old unit (michael.stumpf@bigpond.com). iIf you can see the gears from the back it is an open diff, if it has like a spindle/spool type thing (clutch housing) then it is a posi. If it needs to be rebuilt (new clutch) then the price is less if the gears are chipped or worn .. less again. What was your RPM with the old diff at 65mph?

JH57Z06

Mike, I ordered a 3.55 if I recall correctly. I may be off some on the speed and rpm. My speedometer reads high, I think. I think my speed/rpm figure with the old unit was approx. 3750 rpm at 65 mph. I can send a photo but it will be a couple of days. It's buried in the garage and will take some time to uncover.

mickatbp

Okay . when you have time.