72 tranny rebuild ????

[tobluforu]

I’m about to start gathering parts for the rebuild of the tranny in my 72 which will take place next summer. It will make the process a lot less painful for me to start buying the parts now (slowly), so when it’s broken open I’m not staring at a huge bill.
This is the original tranny, and besides the fact that it takes a lot of effort to put it in first and second gear; tranny oil is splashing all over the clutch, and the whining in third and fourth gear, it’s really not that bad for being 38 yrs old.
Here’s what I have collected, and what I need help with is what I “should” replace no matter what when I’m in there. I know that it’s hard to tell what needs to be replaced until it’s cracked open, and this where it can get expensive, or it can actually be pretty inexpensive if only a certain amount of parts need replacing, so any help is much appreciated. Here’s the short list of what I have in my closet:
1. Gasket set.
2. Wevo’s Transmission Side Cover.
3. Wevo’s XT-032 Bearing Retainer Plate.
4. Wevo’s Guide Tube Upgrade.
5. Main shaft seal
6. Shift shaft seal
And that is it. So what I think I need to buy, remember I have never done this, is first and second gear synchro’s and dog teeth. What causes the whining in third and fourth gear?
No idea if I need to but sliders, etc. or is this something that needs to wait for the tranny to be cracked open.
Thanks for the help.

[Peter Zimmermann]

You should just save $3000, and not buy any parts until your trans is apart. You might look at it and decide to get yourself a rebuilt replacement from a quality source. The possibilities regarding what needs to be replaced are endless, but if the ring & pinion are bad your plans might go out the window.

[jcsjcs]

I just had my transmission rebuilt by Gary Fairbanks for significantly less than the parts would have cost me. He uses high quality used parts - and has a major stash. I was considering the rebuilt it myself route - but had an expert do the work AND I saved money.

The parts list was EXTENSIVE - he took into account my autocrossing - and the cost was unbelievably good - less than 2k - for 1st and 2nd syncrhos, 1st, 2nd, 3rd , 4th sliders, gasket set, 4th gear guide, and an unidentified plate that needed replacing.

Cost was less than 2k (a lot less....)! He is a amazing guy - and he let me help him take the transmission apart on the spot to see what was up before he started the work.

HIGHLY recommend!

[mmasse]

tobluforu,
Search the term "tranny" under my username, I did this before and got LOTS of help from falks in this forum.

Good luck with this!!

[Peter Zimmermann]

This is another good thread...

Getting Ready for 915 Rebuild - It's my turn.

[RWebb]

also consider buying a later trans. - you can do a few updates and have something alot better than a '72 (if you don't care about an under the car concours check)

[tobluforu]

Concourse, have you seen the pic of my bastard car under my user name?
In all honesty I'm a CSOB, but I do like the cool factor of putting something else in that is better as long as it's not going to cost me an arm and a leg (what is suggested)?
The threads posted are great, thanks and if I'm going to rebuild this tranny I guess I should hold off on buying any parts; start stuffing the piggy bank, that of course will be hidden from my wife.

[RWebb]

take a look at that 'best' tranny thread - it has a nice chart of trans. features

the '72 is about the worst 915 there is...

I would get a later unit that has your same R&P ratio; and also has the same speedo drive (mech. for you)

then you can do the side cover upgrade & IIRC the int. plate - strength in a trans. costs money how strong do ya wanna go?

I am using a '75 in my '73, but I have a hotrodded 3.L motor in it.

[Eagledriver]

Actually the 72 is one of the better 915s. I have one in my race car and am keeping it. These mag case 915s have a steel bearing retainer in the main case unlike the later aluminum cases. This means that you probably don't need the Wevo bearing retainer. You can update the input shaft seal but I didn't. I just replaced it when I had the tranny apart. The first one lasted many years so I don't expect to have to replace this one for many years. You just have to make sure you put it in right. Once you get it apart you can mix and match parts to get the best of all worlds, early case, later input shaft (stronger), later 1st/2nd slider, etc.

-Andy

[tobluforu]

And the score is:
72 tranny good=1
72 tranny bad=1
Hmmmm, any others?

[RWebb]

what Eagledriver said applies to all Mg trans.

I'd go for one that is easy to fix oil leaks onto the clutch ... & that is NOT the '72

read that thread so you'll know what's up

[Matt Monson]

Originally Posted by RWebb

what Eagledriver said applies to all Mg trans.

I'd go for one that is easy to fix oil leaks onto the clutch ... & that is NOT the '72

read that thread so you'll know what's up

This.

[tobluforu]

How does v e r t e x rebuild these for only 1800, granted you have to give over your tranny? Anyone bought one of those?
I see MM has some good deals..... Just kidding.

[tobluforu]

I checked that thread out and it looks like the latest year I can get, if I decide to find a used one, is a 75 based on the mechanical speedo drive?
I also found some threads on ****** and the hell with that!
Does anyone know of a shop that would have a rebuilt 75 tranny that would take my 72tranny as a core?
Now, lets say that I stick with the 72, when checking rennsport they state this:
The 915 transmission, unlike its cousin the 901, has 1st gear machined onto the mainshaft. This means that you must change the entire shaft when this gear is to be changed. Since this isn’t always cost effective to do, most folks simply change 2nd through 5th gears to achieve the desired spacing. There is a good selection of 915 gears now available on the aftermarket that allow you to build a custom gearbox for your exact application. Here is a real nice close-ratio street setup that has been very successful:

1st Gear 11/35 (stock)

2nd Gear 17/31

3rd Gear 21/31

4th Gear 24/27

5th Gear 27/24 or 28/24
Does anyone know how much these gears would cost and has anyone installed these on a street car? Something tells me that they are not cheap, like say around 700 per gear?
Thanks

[jcsjcs]

I have not hear such great things about ****** - but I did investigate how Gary Fairbanks can charge so little (based on a convo with him and Matt Monson at Guard Transmission).

Basically Gary has a major stock of great used parts and uses the best based on the job required. I saw his inventory and it is pretty impressive. He also did not skimp on parts when doing mine - anything that looked suspicious was replaced.

Not sure if he would sell you parts only.

Gary - (203) 866-2466

I pick up my transmission tomorrow.

He turned it around in 3 days - and that is all he does. Porsche Transmissions for 915 and 901. Not sure if he handles 944 - but he definitely is not interested in the new stuff.


Jonathan

[Matt Monson]

Originally Posted by tobluforu

Here is a real nice close-ratio street setup that has been very successful:

1st Gear 11/35 (stock)

2nd Gear 17/31

3rd Gear 21/31

4th Gear 24/27

5th Gear 27/24 or 28/24
Does anyone know how much these gears would cost and has anyone installed these on a street car? Something tells me that they are not cheap, like say around 700 per gear?
Thanks

Are you sure on that 2nd gear? That's not a toothcount that I am familiar with, and it's definitely not one that we manufacture. The other strange thing about it, is that as a decimal it's really close to the stock 2nd gear (1.833 versus 1.824). I don't know why anyone would spend $700+ to change a gear by 1/100th!!!

What I suspect that should be is 17:34 and it was just a mis-type on the ten key of either yourself or whoever published those numbers? A 2.00 second gear is a much better match for the other gears listed and very popular.

I would choose the 5th gear based on how much highway cruising versus tracking driving you do. The 28:24 will drop your rpms at 75mph by 200-300rpms (depending on wheel and tire size). The 27:24 will be quicker if you are tracking the car or doing any acceleration above 105mph.

[tobluforu]

All I did was cut and paste from their site, but I just went back and read another paragraph that states this setup would be best for a 3.2 motor. I think I will probably just open it up and see what needs to be done and go from there. I really don't need any special gearing as this is a street car, 2.7rs p/c's with solex cams and mfi. It would be cool to have a taller 1st gear (there was something about going 57mph in first in another car I had), but that's not going to happen.
Thanks.

[kenikh]

IMHO, the mag trannies are best as they don't shag the bearing races due to having steel races versus the later ally cases having the bearings sit diect in the ally case. This situuation is what leads to the uber dollar Wevo case fix.

There are some other minor case differences between mag and ally, but the benefits outweigh the negatives. I like your parts list and would use them all, including the intermediate plate, as it adds stiffness over the mag plate, even though the mag unit does have steel races.

One upgrade I'd suggest: use the later sliders, as they are stronger. They are notchier when cold, but are more robust. Also, consider the Wevo gateshifter, as nothing will ruin your day faster than a sloppy shift leaving you stuck between gears.

BTW, if you want fancy gear ratios, nothing touches Matt's new gears. Not cheap, but a good deal given what Carquip charges for inferior OEM/used gears. Hopefully you R&P is fine, but if it running on a 2.4T, the chances are very good.

[Peter Zimmermann]

Originally Posted by tobluforu

All I did was cut and paste from their site, but I just went back and read another paragraph that states this setup would be best for a 3.2 motor. I think I will probably just open it up and see what needs to be done and go from there. I really don't need any special gearing as this is a street car, 2.7rs p/c's with solex cams and mfi. It would be cool to have a taller 1st gear (there was something about going 57mph in first in another car I had), but that's not going to happen.
Thanks.

Not sure if you know about my Tutorial, but...

Porsche Wiki: Forum Categories

Click on "915" under "Page Tags" and you'll be at my 915 repair Tutorial. Enjoy!

[kenikh]

Originally Posted by Peter Zimmermann

Not sure if you know about my Tutorial, but...

Porsche Wiki: Forum Categories

Click on "915" under "Page Tags" and you'll be at my 915 repair Tutorial. Enjoy!

Great wiki! Once constructive comment: the pics are soooo small. Would be lovely to be able to blow them up and see the details.

Fantastic content!