Early trans from a 73E in later car? A few questions from a non mechanic...

wide911guy · 09-13-2007, 05:39 AM

I just bought a tranny from a dismantled 73E and since the box was already out of the car and engine locked up, no way to test anything other than placing the trans into all five gears with no issues while on the ground. Plans are street car with light track duty and stuffing a 3.6 into a SC...all action is very smooth while turning splined shaft, only left side turns but turning left side, the right side turns oposite direction so I guess no lim slip.
...so Im wondering if I should sell it and buy a later 915 or are these generally good trannys compared to later ones?

Is there anything I can test or look at to determine shape and condition of the inside of trans like opening a cover or remove a plate?? or should I just install it?

Also, can I use this trans with a carrera speedo since I already have the speedo? also need advice on 'how to' clean the outside of the box to make it look newer again?

Would serial numbers from the side or rear of the box help tell me what I have?

Thanks for the info, guys.

Dantilla · 09-13-2007, 06:03 AM

A 1973 tranny has a 7:31 ring & pinion. That's what I'm using in my 3.2 powered autocross car, but with a 3.6, you will want the stronger 8:31 from a later 915. The 7:31 gearing will be too low for a 3.6.

yel911 · yel911's Garage

Your speedometer won't work with the 73 transmission. From 77 (not sure...) on up, the speedometers are electronic, before that they were mechanical. I have a 74 that I did the 3.2 conversion, using my old tranny (with a replaced 8:31 ring/pinion) keeping the mechanical speedo. From what I've been told, the ring/pinion is the only valueable parts of that tranny. Check the threads about using a 915 to a 3.6 motor, it's not good. Too much torque.

wide911guy · 09-13-2007, 08:17 AM

Whats the 7:31 worth by itself? so the 7:31 is good for a 3.2 engine?
and then whats the whole trans worth if sold? can I verify its a 7:31 ring and pinion by serial numbers?

Doesnt that make it very quicker than the 8:31??

RWebb · RWebb's Garage

'76 on up for electro speedo.

I have a 7:31 with a 3.2 now and wouldn't say it is good - just more acceptable than with a 3.6L.

quicker?

wide911guy · 09-13-2007, 01:13 PM

Can anyone tell me what the difference is in driving a car with a 7:31 vs an 8:31 would be??

2.7RACER · 09-13-2007, 03:29 PM

I have a '76 2.7 set up for racing. I swapped my stock transaxle (8:31) early last year for a '72 (7:31) to gain more torque coming out of slower corners at the local track. Works very well. Much better acceleration and lower lap times.
The down side, at parking lot autocrosses, first gear hits the rev limiter much quicker. That is there are more times on a parking lot AX when I would do better with the stock gears.
Parking lots aren't for me anyway. Give me a real race track and real speeds.
If I was using the car on the street, which I don't often do, the revs would be 300 to 500 higher at highway speeds.
Conversely stop light to stop light accelleration is better. It will match or beat my 3.2 Carrera.
Top speed has been reduced from 145/150 mph to 125/130 mph.
Oh, the '72 drives a mechanical speedo, the '76 drives an electric speedo. So no speedo.
Would I do it again? My answer? The stock transaxle is for sale.

RWebb · RWebb's Garage

Quote:

Originally Posted by wide911guy

Can anyone tell me what the difference is in driving a car with a 7:31 vs an 8:31 would be??

former will have stump-puller 1st gear, etc. when used w/motor meant for the latter

Jack Olsen · 09-13-2007, 05:17 PM

My freshly-rebuilt 7:31 lasted about a year with a 3.6.

My 8:31 mag-case has lasted six years and is going strong.

wide911guy · 09:29 AM

How can I tell if its limited slip or not? (Someone told me to turn one flange and see if other side turn same way but this is not always the case, right?) What do I look for if its an open box inside cover? Thanks again.