Rear end swap 4.3 to 3.9 ratio?

[kensmith]

Any idea of cost and labor involved in swapping out my 4.3 rear gears for the 3.9 ratio in my 1978 124 spider?

[lanciahf]

No, But it might be easier to find a 3.90 rear and swap it out. If your car is pre 77 I think you will need the drive shaft and panhard rod.

[azruss]

I swapped a 71 rear end in my 80 FI. As stated already, will need the old style driveline and panhard rod. I would also recommend older springs as well to help get the ass out of the air.

[RoyBatty]

Look in the Vick catalog.
http://www.vickauto.com/newstore/index. ... ts_id=2038
If you have the correct style rear axle. They have a 3.9 pumpkin ready to plug into your rear housing.
So you would basically have to buy the 3.9 pumpkin assy. The guy at Vick said all clearances were preset for gear lash.
Remove both rear tire and brake assy's.
Remove the snap rings that retain both axles and slide the axles out.
Disconnect the drive shaft.
Drain the rear axle. This process could be done when you separate the pumpkin from the rear axle.
Remove the 4.1 pumpkin, possibly scrape sealant and gasket and cuss.
Install new gasket with the 3.9 pumpkin.
Reverse the rest of the process. And yes add lube.
I'm gonna guess a guy in his garage could do this in a few hours.

This mod is on my list of things to do.
And again, I'll offer my help if you like. I'm just under an hour down the road from you.

[kensmith]

I was checking the 4.3 VS 3.9 rear end ratio on a gear calculator and it will not substantially drop the RPM in 1st gear. So I don't see that spending almost $1,000 after tax and shipping would be worth the change. Seems the transmission gearing would be the way to go and I'm not going to do that as I am sure it would be very expensive and not sure there is anything available for transmission gearing. So on to the next project!

[RoyBatty]

I never looked at it as a benefit for use of first gear.
I am looking to drop the RPM's in cruise config on the highways.
Looks like about a 350 RPM drop from the 4.3 to the 3.9.

[kensmith]

I feel like a semi truck starting out in first gear. Going to second about half way through an intersection.

[fiat2000]

I had a 79 with the 4.3 rear end, i didnt even use 1st gear, i started in 2nd gear, 60 mph was 4200 rpm!!

[124ADDHE]

My 1981 spider (3.9 gear) cruises at 98kms (60mph) @ exactly 3500 rpm's with the 185/60 tires.