Differential

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Jeffrohotrod
Posts: 1
Joined: Sat Sep 01, 2018 9:31 am
TOA Membership Number: 0
Years Owned: 1980

Differential

Postby Jeffrohotrod » Sat Sep 01, 2018 9:38 am

Hello I'm new to the group. I just bought a 1980 toronado with a 350. When I bought it he said the differential was going out. I'm new to these cars and didnt even know they had diffs just thought it would be the cv joint. But now I have found out that is the shaft that the dr cv axle hooks up to that goes inside the diff is bad. Am I going to have to have the whole diff rebuilt or can I just fix where that shaft goes in and if so what would the part be called. Thanks

bcroe
Posts: 192
Joined: Thu Nov 15, 2012 12:25 pm
TOA Membership Number: 378
Years Owned: 79 Toronado or Eldorado

Re: Differential

Postby bcroe » Sat Sep 01, 2018 7:48 pm

I owned a couple 79 Toros, and in each case the final drive/differential failed
at around 100,000 miles. Also a Cutlass about that year. Teeth broke off the
gear and jammed into the other gear. I had read that the factory built some
bad metal process gears leading to this, so I had a junk yard spare ready for
the second one, an overnight job.

These final drives all interchange between 79-85 Toro, Riviera, and Eldorado,
seems like it would be far cheaper to just find a yard unit and bolt it in. BUT
there were quite a few different ratios, including 2.2, 2.41, 2.73, 2.95, or 3.15:1
depending on the engine and 3 or 4 speed trans. I am happy with the 350
engine and 2.73:1 ratio. If you get one with a different ratio, be sure to get
the speed cable gears from the trans to put in also, so your speedo is still right.
Bruce Roe

Otto Skorzeny
Posts: 962
Joined: Fri Feb 28, 2014 12:41 pm
TOA Membership Number: 0
Years Owned: 1966 Toronado

Re: Differential

Postby Otto Skorzeny » Sun Sep 02, 2018 6:24 am

Bruce, what is the reason for so many different gear ratios on the same car? Were there choices when new or did you just get whatever was in there?

The difference between 2.2:1 and 3.15:1 is quite significant.

I recently had a new rear end installed in my truck. The original 2.88:1 gears were no longer made so a 3.0:1 was installed. Just that small change cost me 2 mpg on the highway.

bcroe
Posts: 192
Joined: Thu Nov 15, 2012 12:25 pm
TOA Membership Number: 378
Years Owned: 79 Toronado or Eldorado

Differential

Postby bcroe » Sun Sep 02, 2018 10:28 am

Otto Skorzeny wrote:Bruce, what is the reason for so many different gear ratios on the same car? Were there choices when new or did you just get whatever was in there?

The difference between 2.2:1 and 3.15:1 is quite significant.

I recently had a new rear end installed in my truck. The original 2.88:1 gears were no longer made so a 3.0:1 was installed. Just that small change cost me 2 mpg on the highway.


As I said, engines included 5.7 diesel, 5.7, 6.0, 5.0, 4.5, 4.1, 4.1 V6, turbo 3.8, carb
or EFI, used with 4 speed lockup overdrive or 3 speed trans. I don't claim that is even
a complete list for 79-85, and certainly only some were available on a given brand and
year. Don't know if ratio was on the option list at all. I tried a 2.2, 2.41, and 2.73 on
my 79 FWD.

In 77 the General was putting 2.41:1 axles in V8 big cars to get the mileage up. It
worked but launch suffered. After trying some ratios, I concluded a switch pitch
transmission gave me back much of the launch while retaining the economy of a 2.41.
And the switch pitch added a bit of economy as well.

My 79 Eldo has a switch pitch 66 Toro TH425 transmission, with a 2.40:1 overall final
ratio. It also got rid of the failing later final drive. Bruce Roe


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