My wife's '73 was leaking a huge amount of oil out of the speedo drive. I contacted McMark to try out his newly designed speedo drive.

As you can see, this drive was leaking quite a bit. Just sitting in the garage it would drain out a major spot just in a couple days.


Here is my core sitting next to the new unit. Notice the extra O-ring:


The swap was straight forward. The only difference I noticed from a regular speedo drive was a little persuasion required to very lightly tap the drive into position. I just used a small rubber mallet to accomplish this. I am confident that I did not pinch the O-rings, and it felt like a good solid seal. Once in place without the set screw in, I could not wiggle or move the drive from side to side at all.

A quick fill of the trans:


A quick wipedown to get rid of any oil:


Also put a strip of cardboard underneath the trans...I want to make sure this isn't going to leak.


I will snap another picture underneath in a couple days. I highly doubt that this will leak at all! Such a good idea IMO...I wonder why no one thought of this before!

Mark has a BIG BRAIN Looks good so far!

That's just what I am looking for ...

Where ? How much ?

The problem with the 914 speedo drive is that they used aluminum in a magnesium case. Different expansion rates means leaks. On the 911, Porsche used a brass speedo drive. Same expansion rate as magnesium. Change the drive for the brass one, and it doesn't leak.

But those suckers are hard to find. This should be a good alternative solution.

http://www.914world.com/bbs2/index.php?showtopic=103985

Thanx ! ...

It has been two days and no leaks! I drove it and got it nice and warm...not a drip!

Val put 160 miles on her car today...still not a drip! Looks as if this was my last leak to fix! Nice and dry under there now!

I crawled up under the car again today. It really seems like this mod worked very well. It is so nice not to have to wipe gear oil off of my garage floor anymore...(at least on her side of the garage).

Sorry to jack the thread, but do you know if a drive from a 911 Sporto would work in a 901?

It should.

I don't think there is any difference at all......

But the 911 angle drive won't work. It turns backwards for a 914....... BTDT.

Hello Sleepin,
Besides removing the set screw what else is needed to remove the speedo drive?? Do you have to remove the back plate of the trans to get the speedo drive out??
Thanks,
Jack

Nope, there is the single screw, then it just pulls out. Drain the transmission or raise the ass end a lot or you'll get a nice stinky gear oil shower.

Mark,
I just got onto this thread (did a search as soon as I diagnosed the source of the leak). I want to remove the speedo drive, but ... where the heck is the set screw?? (I have a side shifter, if that makes any difference).

10 o'clock in the picture below ...