Alan '79 928

What year did Porsche change the gearing in the 5 speed? Is there a difference between a 1981 US MT and a 1979 MT? I think by '83 they had moved to longer gears, correct? Somebody please educate me.

Starting to think about a swap...

Alan
1979 auto

Scott M.

Alan;

77-82 use the 2.75 final gear ratio. 83 started the 2.36.
Not sure about the actual gears themselves but after vin#5000 in 1980 they switched from the G28/03 box to a G28/05 box.

Alan '79 928

Thanks Scott - I guess the next question is what are the differences between the G28/03 and the G28/05?

Alan

Scott M.

Alan;

G28/05 box has the following gears, ratios:

1st 17/44 3.601
2nd 22/39 2.4646
3rd 26/34 1.8194
4th 29/28 1.3433
5th 1.0000
rev 22/50 3.1621

Can't find my tech spec book for the 78/79 cars. You'll have to do some leg work on that.

John Veninger

The actual lenght of the G28/05 case is shorter. You need a different torquer tube to fit it in a 78/79 car.

hacker-pschorr

In a perfect world we would all have 3.09 gears.

FlyingDog

Some of us like to get decent highway milage.










Who am I kidding? My car got under 13mpg for the first 750 miles I had it and almost all of them were cruising on interstates.

Scott M.

But Matt, how long did it take you to do those 750 miles?? 2 hours??

I recently read an article about 911 turbo testing, somewhere in South Africa, they would use a tankful per hour.

Alan '79 928

Thanks for the info. My auto trans is shot and my mechanic has a full 1981 5 speed parts car. He is eager to rebuild and swap the whole drivetrain into my 1979. My car was at the transmission shop and they failed to fix it.

I know people caution against the swap but he doesn't think its that big a deal with a full donor car. I figure its going to cost around $3000 to get my auto trans working right (local shop or 928 intl rebuild) and if he agrees to do the swap for around that price I trust he will.

Does the whole idea sound crazy? Is he underestimating the job? He definitely knows 928s and has never let me down. What do you think? I think I'm gonna start a new thread for opinions on the swap.

Alan
1979 auto

Vilhuer

G28/03 and G28/05 have different input shafts. Clamp bolt groove is in in more forward position on 05 compared to gearbox mounting point making it necessary to swap TT also. Or new groove needs to be machined some 10mm forward on TT center shaft. 05 and later user 30mm shorter TT. Porsche wanted to move drive shaft joints to more straight angle and this could be accomplished easiest by shortening TT. Taking both TT and gearbox from donor should work fine.

John Veninger

Especially since his current car is an automatic!

Scott M.

Vilhuer;

Is there a difference in gear counts between the 03 and 05 boxes??

Vilhuer

Scott, quess you mean if different gears are shorter or longer between 03 and 05. 5th is obviously same as it's direct through the box and only differential is used. Also all other gears seem to be same and they even have same part numbers. All except input shaft are same parts.

Joe F

Scott,
My '83 Euro 5 sp has 2.73 ratio. According to spec sheet at 928 specialists, the '83 and '84 Euros had G28/07 box. I thought '84 was the year that got the new BW synchro system. My '83 still has the older style synchros. I'm so confused

Cheers,

Vilhuer

BW syncros came in '85 model year with introduction of G28/10 and /11.