Automatic differential v manual

[That]

How much of a difference does auto (3.58--1) rear gear ratio make in performance of fiat 124 with manual tranny and prev 3.90-1 rear gear. Tks

[jfrawley]

Acceleration is noticeably effected by the change in my car, but not so much that it becomes a slug or anything. Having said that, it's so much nicer at highway speeds that it's a swap I'm happy I made. It dropped my RPM's about 5-600.

Very happy,

[baltobernie]

"Noticeable" is the best word I can come up with. The car will accelerate more slowly in second and third gear. (First is already a stump-puller, so there's not much to see. First with the 3.58 is actually a lot more usable.) What's really noticeable is the 600 rpm drop in fifth, on the highway. We have two club members who have intentionally made this swap, and both are very pleased. Both, however, have 2-liter, well-running cars. I wouldn't try this without the extra torque of the big motor. You also need a custom speedo gear or conversion box to make your speedo/odo accurate with the 3.58 five-speed.

[vandor]

There is a 9% difference in the ratios, so one would have 9% less torque at the wheels and engine speed is reduced by 9% at any given speed.
If you are after the lower rpm on the highway then the new transmissions with the 0.80:1 fifth gear will give you nearly the same result (stock 5th gear is 0.88:1).

[toyfiats]

"Noticeable" is the best word I can come up with. The car will accelerate more slowly in second and third gear. (First is already a stump-puller, so there's not much to see. First with the 3.58 is actually a lot more usable.) What's really noticeable is the 600 rpm drop in fifth, on the highway. We have two club members who have intentionally made this swap, and both are very pleased. Both, however, have 2-liter, well-running cars. I wouldn't try this without the extra torque of the big motor. You also need a custom speedo gear or conversion box to make your speedo/odo accurate with the 3.58 five-speed.

I did it based on numerous recommendations, together with the thought that the Spider (FI 2L) would mainly be for long-distance touring with my wife. The reality is quite different, as I end up doing a lot of city driving. That said, I hated it. It felt like running with your shoe laces tied together. Having suffered in my youth with torqueless 1600 motors I loved the pull of the FI 2L. The 3.58 just took some of that magic away, and I went back to the stock 3.90

And yes, the speedometer will be off, but I spent $300 at Palo Alto Speedometer having them recalibrate the gauge in the car on their dyno. Said gauge is now for sale should someone be in a similar predicament and not want an inaccurate gauge.

[divace73]

thought I'd add my 0.2c worth here as I had a 3.4 ratio diff (from a late 132 auto) in my car along with a 2L FI and a 131 box.

On the freeway the car was great, I'd be doing 110kph in 5th and was just under 3000rpm but on the track wasn't so exciting nor was there much acceleration.



I now have a 3.9 (with ATB centre) and it is much more fun to drive but when I am in 5th I do still go for an extra gear. One of those electric overdrives would be good....

[131]

I went from a 3.58 to a 4.1 on my 131, while it gets off the line quicker, it revs its ring out on the highway, and 1st gear is almost unnecessary. I have a 3.4 that I intend fitting, although hopefully a supercharger will add some torque eventually.

[divace73]

I went from a 3.58 to a 4.1 on my 131, while it gets off the line quicker, it revs its ring out on the highway, and 1st gear is almost unnecessary. I have a 3.4 that I intend fitting, although hopefully a supercharger will add some torque eventually.

Hey mick, what made you go to a 4.1? I found the 3.9 to be a reasonable compromise, I do miss the 3.4 on the freeway.
I still have a spare 131 manual diff which I think is the 3.58 but don't think I'll use it now???

The 3.4 with the supercharger would be the treat...

[131]

Hey mick, what made you go to a 4.1? I found the 3.9 to be a reasonable compromise, I do miss the 3.4 on the freeway.
I still have a spare 131 manual diff which I think is the 3.58 but don't think I'll use it now???

The 3.4 with the supercharger would be the treat...

I bought a 131 parts car that had a 132 disc rearend in it, which turned out to be 4.1, I've got an Argenta rearend to put in. I still have to modify it to fit the discs and upper control arm mounts, as well as shorten the tailshaft.

[davery]

There is a 9% difference in the ratios, so one would have 9% less torque at the wheels and engine speed is reduced by 9% at any given speed.
If you are after the lower rpm on the highway then the new transmissions with the 0.80:1 fifth gear will give you nearly the same result (stock 5th gear is 0.88:1).

Did you ever have any luck finding someone to manufacture the .80:1 fifth gear to install in an existing transmission?

[vandor]

Not so far.

[davery]

Not so far.

That's too bad. I'm rebuilding the transmission this winter.

[BERGFIAT]

The new overdrive trans that Csaba is talking about is the best upgrade you can do to these cars. With a 3.90 rear and the new trans, you can actually venture past the city limits without getting buzz fatigue. I noticed that the Auto Ricambi version of the new trans uses the original shifter assembly and fits through the original cut out in the console? If that's the case, theirs would be far superior to the version I bought elsewhere which utilizes a modified John-Deere shifter.

[vandor]

Hi Berg,

> I noticed that the Auto Ricambi version of the new trans uses the original shifter assembly and fits through the original cut out in the console

Yes, exactly, the stock shifter extension bolts to it, so there is no need for a weird long shift lever.

[gm404]

Hi Berg,

> I noticed that the Auto Ricambi version of the new trans uses the original shifter assembly and fits through the original cut out in the console

Yes, exactly, the stock shifter extension bolts to it, so there is no need for a weird long shift lever.

Csaba, do you have a picture or link to that modified transmission?
I am thinking about to design a Lada 5 speed shifter conversion kit to fit the Spider. There is a shifter extension I could partially use.

This is the gearbox. The bellhousing must be swapped of course for Fiat.

What I intend is a stable enough console to be laser cut, bent in angles and screwed onto the studs that hold the rear cover. The original setup uses flimsy sheet metal on a customised rear cover and extra screws to the chassis behind the shifter, and I don't wan't to go that way.

The conversion option would mean for Spider to choose from 3 sets of stock gear ratios (input shaft with 17, 18 or 19 teeth, resulting the 5th to be 0.88, 0.82 or 0.775), and also ways to use race spec stuff like straight toothed gears, sequential shifter and even 6th speed. Speedo drive and oil level plug are by Lada always on the left side.

I only miss the distance how far back the gear lever should sit. If somebody has a stock Spider 5 speed sitting around, I miss the distance from the output flange's rear surface to center of the shifter.
Thanks, Gabor