tranny swap?

fiater · Post by **fiater** » Tue Jan 31, 2006 3:53 am

I've always wanted to replace the 4-speed in my '74 124TC (orig. 1592, now 1800) with a 5-speed. The engine screams at 65mph. and gets poor mpg. Also the shifter's sloppy. I got the car with 37,000mi. from the sec. owner and he said it was always that way. The tranny doesn't have the extension on the tail like the spider does, so my question is; will a 131 or 124 sport coup tranny work? thanks

So Cal Mark · Post by **So Cal Mark** » Tue Jan 31, 2006 12:02 pm

I haven't seen that swap done, but if the length is different you'll have to address the driveshaft length. What you have to realize is that the 5th gear in a Spider isn't much of an overdrive. I believe it will only drop your rpm about 300 at 65mph. What rear end ratio does your car have?

Bluedog873 · Post by **Bluedog873** » Tue Jan 31, 2006 2:16 pm

Mark is right. The drop is only about 300 rpm. Believe me, it's not worth the time to change it over. 5th gear won't change gas mileage much if at all considering the car sucks down about the same amount of gas as my truck! Good luck though!

fiater · Post by **fiater** » Tue Jan 31, 2006 8:07 pm

Thanks for the replys guys. If the rpm drop's only 3-500, then what's the purpose of the 5-speed? The special was offered with a 4 or 5 speed or an automatic. I have no idea about rear ends or which one I have. The difference in trannys isn't in the case, it's in how the shifter mounts. The special shifter mounts to the top of the tranny. The spider shifter mounts to a horizontal extension, that mounts to the top of the tranny, which moves the shifter several inches toward the rear of the car If I tried to put one of my spare spider trannys into the special, I'd have to modify my floor. I know where there's a 131 tranny. I was hoping that it would fit in my special and I could kill two birds with one stone. The special shifter's so sloppy that it's like shifting a marshmallow! My spider shifter's very precise. The hwy. mpg for my special's 19-21. my spider gets 26-29mpg. Granted, the special's a little heavier, but not that much. thanks

So Cal Mark · Post by **So Cal Mark** » Tue Jan 31, 2006 10:17 pm

well, every little bit helps so maybe 300 rpm would be worth the trouble

fiater · Post by **fiater** » Wed Feb 01, 2006 1:13 am

that still leaves two questions.(1) How do I find out what rear end I have? If it's lower than my '80 spider parts car, and I can make the '80 work, It may be worth the swap, with or without a different tranny.
(2) Are the 131 or 124 sport coup trannys the same as the 124 spider?
The tranny and rear end aren't my highest priority, so I have time to find what I need(when I find out what I need) thanks again

bandit · Post by **bandit** » Wed Feb 01, 2006 1:33 am

The 124 coup and spider use the same tranny and rear ends
the 131 is different u need a 124 auto drive shaft from what
I've been told to use with the 131 tranny .
If you have a 74 rear end i believe you have a ratio in the
rear of 4:10s and the 1980 will have 3:90 that would be
a better jump to lower your rpm .

fiater · Post by **fiater** » Wed Feb 01, 2006 7:00 am

thanks for the reply bandit. The car will be running after I correct some fuel issues. I'm hoping a carb re-build will solve them. It's such a rare and cool car, that eventually I'd love to do the tranny and or rear end swap, or at least try to fix the sloppy shifter. thanks again

ventura ace · Post by **ventura ace** » Wed Feb 01, 2006 9:03 am

It's very easy to check the rear end ratio. Lift the rear end of the car, so that one rear wheel is off the ground. Chock the other rear wheel so that the car won't move, release the brake, and put the car in Neutral. Put reference marks (chalk, felt marker, etc.) at the rear pinion yoke where it joins the differential housing so you can count turns of the drive shaft. Also put reference marks on the rear tire and the floor, so you can count turns of the rear wheel. Rotate the rear wheel exactly 1 turn, and count turns of the drive shaft. Since only 1 wheel is turning, the result will be off by a factor of 2, so you will need to mutiply by 2.

If it is just slightly less than 2 turns, then you likely have a 3.9 rear end ratio. Slightly more than 2 turns would likely be a 4.1. Be precise in your counting, since there is also a 4.3 (2.15 turns), and a 3.58 (1.79 turns).

alvon
'70 Fiat spider (4.1 rear end ratio)
Ventura, CA

fiater · Post by **fiater** » Wed Feb 01, 2006 5:57 pm

thanks Ace,
I was thinking along those lines, but I didn't have the details worked out. You just made the job a little easier. My '80 parts car is still rolling (not running) so I can easily do your ck. This Sun. before the game, I might just ck. the Special, My '76 Spider and the parts car. Thanks again

bandit · Post by **bandit** » Thu Feb 02, 2006 10:52 pm

only the automatics came with 3:56 ratios and the 4:30 are real
early 124s but i think if you can find a automatic rear end that
would be the best setup for street driving .

Daniel

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