1974 911 Two Fourth Gears

[Chickenstrips]

I am getting close to buying a 1974 911 and something the seller says is puzzling to me. He strikes me as exceedingly honest, but not really very well informed or mechanical. One of the problems he describes is that he brought it to a Porsche shop to fix a “scratching 5th gear”. Later he discovered that “the mechanic must have just installed a another 4th gear where the 5th is supposed to be” because “when he shifts into 5th it’s at the exact same rpm as 4th gear”. Is this even possible? Any theories? Thanks

[SIMI BOB]

I"m a firm believer in the saying "If it can happen, it will".
Bob B

[catelluseng]

Yes, it is possible. The gear sets are mechanically interchangeable, 3 4 and 5.

[gled49]

4th and 5th gears are not interchangeable, completely different. But there are gear ratios that are the same for 4th & 5th. That would be very unusual. 74 4th gear is RP, 27:25 and 5th TL, 29:21. There is a special ratio 5th gear 27:25.

[Chickenstrips]

OK so my hope that he had to be wrong, and I don't need a tranny rebuild right out of the gates is still somewhat possible. Sounds like the only way he could be right is if somehow the mechanic put in the very unusual special ratio 5th gear 27:25. Going from 1.08 to 1.38 ought to be noticeable though if that's not it. And BTW it has not run in years so no test drive to see if he is right. Will buy if I can either way. thanks!

[Theunz]

Put the rear of the car on jack stands and make a chalk mark on one of the tires. Now put the car in 4th and turn the engine by hand exactly one revolution and note the position of the mark. Do the same in 5th gear if the mark ends up in a different spot the ratios are different (5th should go further). If not limited slip raise just one side.

[Chickenstrips]

Put the rear of the car on jack stands and make a chalk mark on one of the tires. Now put the car in 4th and turn the engine by hand exactly one revolution and note the position of the mark. Do the same in 5th gear if the mark ends up in a different spot the ratios are different (5th should go further). If not limited slip raise just one side.

Now that’s a good idea! Thanks

[Jon B]

Your previous thread, on the same subject...

https://www.early911sregistry.org/fo...-Two-4th-Gears

Jon B.
Vista, CA

[Chickenstrips]

Your previous thread, on the same subject...

https://www.early911sregistry.org/fo...-Two-4th-Gears

Jon B.
Vista, CA

Apologies. I am getting a running start on early senility. The transaction went cold and I kind of forgot about it. And it doesn’t take much for me to forget. Ask my wife, can never remember what movies I have seen or names. What car do I have?

[silverc4s]

Seem to recall in a Paul Frere" Porsche Book some years back, he was discussing Porsches early endurance runs where they used 901 transmission with identical ratios in 4 th and 5 th space, and used alternate ones each fuel stop to minimize gram wear at continuous top speed. It was at Monza or some such high speed oval..