Replacing the differential

[Redline]

I'll give them a call then. Maybe it's just a poor translation.

[vandor]

We now have the 3.90:1 third members in stock.

[Betis]

Someone told me that older rear diffs were more robust. Is there any truth to that?

[Betis]

Someone told me that older rear diffs were more robust. Is there any truth to that?

Anyone?

[azruss]

I just switched my early style (71) diffy to a 3.9. Very tricky getting the right lash and side bearing load without the special fiat tools. If you can find a good diffy in tact, then pulling the brakes and axles isn't a monumental job.

[MonitorSteve]

I’m mid differential replacement and I can not definatively tell what the torque specs are for the eight bolts that hold the pumpkin in are? The Haynes manual has torque specs for setting up pre load and the bearings. The pumpkin is referred to several times as the “Final Drive” but there are no torque specs.

Anyone have an idea on what these should be torqued to?

[blazingspider]

When I purchased a new differential from AR I was told to torque those bolts to 16 ft. lbs.

[blazingspider]

FYI.......the shop manual I have lists the torque spec for those same bolts at 33 ft. lbs. go figure!!

[MonitorSteve]

I found 33 lbs in the dark reaches of the net as well. Thanks much, I’m rolling already and I can’t believe how noisy it has been. The before and after is night and day.

[SanJoseSteve]

I recently replaced the 4.3 differential in my car, (1972 124 w/ 1600 motor) with a new 3.9 unit from AutoRicambi. It was easy….. (After burning $25 for the right angle snap ring pliers on Amazon.) Once the that was out of the way, my axle slid out with just a firm tug. My experience is that it drives great though initially I did manage to stall it in 1st gear 2-3 times until I re-calibrated my ear and left foot to the change. Previously I had changed from the 165-13 size tires to 185-13’s. I had also replaced my original transmission with a new Polski-Fiat unit with the taller 5th gear.

Driving on the highway at 70-75 mph is quite enjoyable. Sustained cruises at that speed had been quite manic. OK for a temporary burst of speed to pass someone, but I found it wearing after the 1st 10-15 minutes. Now I can hold that speed all day long and not feel like I’m about to get a face full of pistons at any moment. Holding ~50 and then ~70mph per the speedometer, the WAYZE App on my phone indicates 50 and 70 mph. Not bad……..

Steve (The Fiat driving) Ferrari

[nelsonj]

What RPM are you at at 70MPH? I'd love to be in the 3500 range instead of the 4500 I'm currently at.

[donm]

Is there a way to know which ratio you have? Is it stamped on the differential somewhere?

[SanJoseSteve]

I have a 3.9 rear differential and indeed do cruise 70mph at about 3,800 rpm. BUT.... I also have a Polski-Fiat 5 speed with the taller 5th gear. The size of my tires 185/13 and 1600 engine all factor into the equation too. I'd think it would be an even sweeter set up in a 2L car.

-Steve (The Fiat driving) Ferrari