901 to 915 transmission swap

TargaNick · Post by **TargaNick** » Sat Dec 02, 2006 8:13 pm

Hey guys I need some help.

I just picked up a 71 911T with a bad transmission. I have sitting in the garage a 915 transmission with full linkage and mounts that works very well. would this be a fairly direct swap? Or is there minor body modifcations to make it fit? What all is involved?
Thanks for your help guys
Looking forward to getting this car on the road.

Barry · Post by **Barry** » Sat Dec 02, 2006 8:31 pm

I've not done this, but I gather that you may need to beat the gearbox tunnel out a bit towards the front. As far as I'm aware, the mounts are O.K.

Not sure about the clutch, but got a feeling that it will need changing to the 915 type. The gear selector is different, as the lock-out is in a different place. Also I've got a feeling that the driveshafts are a different length. My last 911 had a 911 box, but was built for a 915 box, which I subsequently put back in. In my case the driveshafts turned out to be tight on the 911 box, and fine on the 915: so you may find that you can get away with these. Also the actual gearlinkage shaft did fit between the boxes.

May come down to a bit of sucking and seeing to a degree ....

Nevertheless I'm sure that there are others that have had to do the same operation that may be able to confirm some of the above

.

davidppp · Post by **davidppp** » Sat Dec 02, 2006 9:46 pm

Barry is spot-on.

The clutch is different..but 915 clutches are cheap enuff.

The cable and cable outer is different of course: and there is a small difference in the pedal ratio which does not matter much.

Some do some do not need minor panel bashing in the tunnel between seats.

And depending on the year of the 915, the output flanges and speedo drive may need sorting..a mag case mech drive is favourite..

Or, probably better all round, just get another 911 box..keep it stock.

The 911 box gearchange is better, and the box lighter.

Old 911's are immediately suspect when fitted with the wrong bits..

I have one ready to swop you for the bust one..PM if interested.
I'd also buy the bust box and old clutch bits..

Kind regards
David

Alan @ CanfordClassics · Sat Dec 02, 2006 10:41 pm

Hi,

In case it helps PM me and I will call if it helps, (bit stuck on time right now). I have done several of these and if I can help with some info let me know.

Alan

TargaNick · Post by **TargaNick** » Sun Dec 03, 2006 12:58 am

Thanks for your fast responses.
Sounds like its possible then...I plan on pulling the tranny out of the car in a week so this will give me a idea of what parts to purchase. The old box I would love to keep its just a matter of figuring out what is wrong and its seems like parts alone are expensive for a 901 compared to a 915.

The 901 box worked for a little and then all of a sudden I can't get any gears and it makes a weird chunk chunk chunk sound like metal on metal when the clutch is fully depressed. Also I found fine bits of metal under the tranny which was worrying.

Anyway thanks again for your guy's input.
(As far as swapping with another tranny I live in the states so it may be difficult, as i know most of you guys live in the UK)

Barry · Post by **Barry** » Sun Dec 03, 2006 6:52 pm

Ah ha

.

That being the case, I would drop the transmission looking for a clutch problem. Sounds to me as though the clutch release mechanism has failed. This would then mean that you are doing the equivelent of trying to get it into gear without pressing the clutch down.

At the very least, well worth dropping the engine/box unit out, and splitting them before you commit to anything further. You may in luck, and not have to disturb the actual gearbox.

BTW, I agree with David: my personal veiw is that the 901 / 911 box is much nicer than the 915 in terms of shift. I've never looked inside either, but it feels as though the 915 is having to shift bigger, meatier bits around when you shift gear (that's all professional gearbox talk, that is

).

Look foward to an update

.

Gilbert '71 T · Post by **Gilbert '71 T** » Fri Dec 08, 2006 6:26 pm

Barry wrote:BTW, I agree with David: my personal veiw is that the 901 / 911 box is much nicer than the 915 in terms of shift. I've never looked inside either, but it feels as though the 915 is having to shift bigger, meatier bits around when you shift gear (that's all professional gearbox talk, that is ).

great comparison Barry, very true though, I converted my 911T to a '72 Mag cased 915, it does feel stronger, but the shift pattern and 'feel' of the 70-71 911 was far superior

. I do miss it, but if I need a 901 fix I'll drive my 914

Quite agree with Barry as well, it does sound more like a clutch problem rather than gearbox problem.

When you've seperated the engine/box have a look at whch pivot you have. In diagram 1 - numbers 5,6,7,11, are apparently prone to failure, but i believe they are from the earlier 901 boxes.

A good thing to do would be to replace them with number 5 in this diagram.

The thing is with these cars, you never know what's been replaced by who over the years, and both pivot types are compatible, so you could have either.

I hope it's something simple for you & good luck.

p.s. just edited as I'd put the same diagram twice before

TargaNick · Post by **TargaNick** » Mon Jan 15, 2007 3:31 am

Ok, so I dropped the engine and found that the clutch fork pivot bolt was hand tight and very loose. I found that there where also 3 washers on the bolt instead of one so i am assuming the flywheel was refaced. I bought a new bolt, spring, and washer from porsche. The only problem is the washer I got is concave on one side and the other is flat. Which order and which way does the washer face? I am assuming since one side is concave it needs to go a certain way. Which way?
Thanks guys
If this description is bad i can get pics.
Thanks again

TargaNick · Post by **TargaNick** » Thu Jan 18, 2007 12:59 am

Can anyone help me?
Its the last thing i have to do before the engine goes back in.
Thanks guys

Gary71 · Post by **Gary71** » Thu Jan 18, 2007 8:01 am

I don't know the answer directly, but post up some pics showing the installation and I'll try to make a reasonable suggestion!

As long as the spring washer has a surface to react against on it's largest diameter then within reason it shouldn't matter which way around it goes.

Barry · Post by **Barry** » Thu Jan 18, 2007 10:24 am

When you say a concave washer, is it very concaved, or nearly flat? I'venot got a pearl of wisdom for this, BTW, just thought it might give a clue ...

Perhaps if you could put some pics up, as Gary says, between us, we could probably come up with the best way of assembling it

.

One thing that does occur though, is that even if you assemble the new parts correctly, you might find that they are no longer perfect for your set-up. I'd certainly do a dry-run, so to speak, by assembling everything (clutch parts, gearbox back on to engine), and try the clutch lever to make sure it's behaving about right: it'll be very stiff to operate though. That way you can check to see that the clutch is releasing O.K., or visa-versa.

TargaNick · Post by **TargaNick** » Thu Jan 18, 2007 10:00 pm

Alright for time issues i have some pictures someone else posted, but it is the same setup as mine I just need an idea of order. I also have a basic thin washer that i have to add because my flywheel was refaced which
I am not sure where i should put that. So to clear that up I have 1. the spring washer 2. the concial washer and 3. basic flat washer all on the pivot bolt.

Thanks for your help guys
i love this forum!!!

Gilbert '71 T · Post by **Gilbert '71 T** » Thu Jan 18, 2007 10:06 pm

I 'thought' that the washer in question was supposed to be convex, finger spring against the gearbox, the flat part of the washer against the finger spring and the convex part against/into the fork (to enable it to pivot) then the bolt through the fork and into the gearbox housing.

If you've got a convex washer I'm wondering if you've been given the wrong one

?

As Gary & Barry say

, if you can get some pictures up or email them to me if you like, I'll put them up for you.

I'm sure we'll get to the bottom of this.
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TargaNick · Post by **TargaNick** » Thu Jan 18, 2007 10:29 pm

911-116-743-01-M100
This is the part number for that convex washer.
I believe it is the correct one, just not sure what i should do with the basic washer i have. Should I put it after the convex one? or before it in relation to the fork? I do agree with you that the convex part should be next to the fork...I would just like to make things accurate...or at least the way Porsche intended.
Thanks guys

Gilbert '71 T · Post by **Gilbert '71 T** » Thu Jan 18, 2007 10:56 pm

sorry I just said i wonder if you've got the convex washer...... i meant to say I thought concave might be the wrong one

.

so you have an extra washer as well as the convex one?