trans swap 82 915 into 74

PacificP · PacificP's Garage

can i swap a 82 sc trans 915 in place of the 74 915 as a replacement?
is everything the same?

Tom '74 911 · 08-11-2011, 12:10 PM

Quote:

Originally Posted by PacificP

can i swap a 82 sc trans 915 in place of the 74 915 as a replacement?
is everything the same?

The output flanges on the trans. are different than stock '74 flanges and thus won't mate w/your CVs and the '82 915 will also have an electric speedo, not a mechanical like a stock '74 915. Other than that, it will bolt in.

Tom

Flat6pac · 08-11-2011, 12:12 PM

The axle shafts are different and wont match. You will need late 85 or 86 drive flanges on the trans to partially match the CV joints.
If you have aluminum trailing arms then you can use the half shafts and stub axles that match the trans which are 77 to early 85.
Bruce

Matt Monson · 08-11-2011, 02:26 PM

It's probably cheaper to have your '74 rebuilt using the good parts out of the SC gearbox than to try and make it work in there. You'll need someone who can set up a ring and pinion, so you'll want to go to a professional and not attempt to DIY.

Peter Zimmermann · 08-11-2011, 04:22 PM

Plus, you will experience a difference in performance changing from your 7:31 ring and pinion ('74 915) to an 8:31 ring and pinion ('82 915). If you want to do the conversion as a vehicle update you will also have to budget for all of the clutch release parts because '77 and later cars are completely different from the '74.

PacificP · PacificP's Garage

thanks guys, i think ill have the 74 rebuilt.
has anyone had a tranny rebuilt by tom at mobile works west, how is it running now, he has very good prices on rebuilt 915s
feedback appreciated. thanks again
dave

Peter Zimmermann · 08-12-2011, 07:38 AM

I don't know who Mobile Works West is, but be very cautious of an up-front estimate that's too cheap. I can safely tell you that prices for replacement parts are off the chart. It is impossible to give you an estimate without more facts regarding the car. How many miles (documented?) are on the car? Has the car been used to commute, or for DEs, or a mix of the two? What kind of trans oil has been used, and are regular oil changes documented? What are your immediate problems with the trans?

PacificP · PacificP's Garage

hi pete,
we are exchanging transmissions with a cost of around 1,700. i pick up the new tranny and drop off the old one as a core. i just had a new motor installed, 1st from standaning still is not posible, the car will not shift into 3rd from 2nd, there are lima bean size pieces of gear on the magnetic plug. i think it is a goner. i bought the car not running and got the promise that the tranny was "just fine, no problem at all."

Marc Bixen · Marc Bixen's Garage

Sounds too inexpensive if it's a rebuild, that's a reasonable price for a used, not rebuilt trans. Especially with your return trans virtually unusable for core value.At todays parts prices even discounted you'll easily put $2,000 plus in parts in the trans. ALL 915's have a lot of miles on them and if you plan to upgrade an early box i.e. later, stronger hubs and new sliders, update 1st gear dogs, figuring an early 915, your looking at a LARGE bill. Heck look at the price of bearings.
Great points on the stubs, speedo etc. Tom74 911.

Matt Monson · 08-12-2011, 02:02 PM

I'd never give a guaranteed core exchange on a tranny in the condition yours is in. When I was still building these, we charged a $1000 core charge up front contingent on 3 major things:
1. The case was uncracked everywhere.
2. The ring and pinion was good.
3. The mainshaft and all gears were good.

We would then disassemble and inspect the gearbox within 72 hours of receipt. If all was fine, then the customer would immediately get a check. If there was damage, it was prorated according to replacement cost. Not every customer got any money back. Parts can easily cost more than the sum of the whole. Gears are like $250 each. A mainshaft is $400. A ring and pinion is $750. A maincase is $400. A tailcone is $200. etc.

If the case was broken and the ring and pinion was bad, that's over $1000.At that point, if the customer wanted to pay the return shipping they could have their gearbox back (not reassembled and we'd eat the teardown labor). Or they could "donate" it to us for scrap.