Eek !! Bought a new tranny - now what??

Wrecked944 · 06-12-2002, 05:09 PM

Okay, so it was an impulse purchase. I needed to repair or replace my existing stock 1980 915 tranny anyway since I recently destroyed the synchros in first gear rendering the car undrivable. So while planning the tranny rebuild, I stumbled across an unrebuilt "early" 915 tranny with the lower gear ratios and jumped on it. I also got a set of early axles and a new clutch cable to match. So before going in any deeper, I have three questions:

1) Is there a way to use my electronic speedo with this early tranny (conversion kit? Mcgyver Solution?) ? If not, then that's okay. I just wanted to make certain before buying more parts.

2) The PO cut a notch underneath the shift linkage. I understand this makes it possible to remove the tranny without dropping the engine. Is this true and if so: Is it wise? I intend to patch the hole before Fall regardless. But until then, is this a realistic way of swapping trannies? Again, if not, then okay, I just want to know if I really need to go dropping the engine. The less I muck around with the less I can brake.

3) Have I missed anything? Is this a scary project or is it sort of "plug and play"?

Thanks,

Doug E · 06-12-2002, 05:48 PM

Sorry I don't have any answers for you as I am not that experienced with tranny's but I love your "plug and play" comment!

Bill Douglas · 06-12-2002, 06:10 PM

Yep, if it's plug and play, I want one too...

Wrecked944 · 06-13-2002, 06:21 AM

Doug E - "love your "plug and play" comment!"

Well, this is what happens when computer geeks get hold of european sports cars !!

And ya know...I'm going to reveal some serious ignorance here...the tranny appears to be a bronzish color - not gray...I wonder if this puppy is made of magnesium...

Bill Douglas - "Yep, if it's plug and play, I want one too..."

If I can do it then it must be plug and play since I have very limited mechanical skills. So if I manage to succeed without leaving a trail of metal parts on the road, I'll gladly relate the tale including potential pitfalls.

Thanks,

john walker's workshop · 06-13-2002, 06:48 AM

the electric speedo can't be adapted. you'll have to decide whether to go early or late on the clutch cable and release fork/shaft/overcenter spring. due to the 7:31 final drive, you'll be wound pretty tight on the freeway, and mileage will suffer. the gearing will feel pretty close around town, though. then hopefully, after all the work to install an unknown condition trans, it will function properly. cost and effort-wise, it probably would have been better to fix the original one.

Jim Sims · 08:48 AM

1) The electronic speedometer depends on a pickup coil (the sender) mounted in close proximity to a circular array of permanent magnets on a disk attached to the ring gear of the differential. The pickup coil is mounted in a specially cast recess on the outside of the tranmission case. The OEM system is apparently rather sensitive to the coil position and orientation; even being "cocked" in the recess causes errors. So, even if you could find a magnet disk, somehow mount it on your differential ring gear (differential has to be partially diassambled to mount magnet disk) and somehow hold the pickup coil on the outside of the housing I doubt it would work correctly. In addition, the electronics at the gage would need to be modified to accomodate the different final drive ratio and tire/wheel size. You will likely need to get a mechanical speedometer (with the correct gears for your final drive ratio and tire/wheel size) and drive cable. It will not be an easy task to install the mechanical speedometer cable.

2) Hopefully the arms and cross-shaft that operate the clutch release bearing came with the used transmission. You will likely need to install a new clutch cable to match these parts. This may also require modifications at the pedal cluster up front.

3) Are you planning on rebuilding this used transmission and then installing it? What are the conditions of the synchros? Depending upon the year/model of the transmission you will likely have to upgrade the 1st/2nd gear dogteeth and operating sleeve if you rebuild.

4) I'm always amazed that people do things like cut notches in the transverse bulkhead the shifter rod passes through; that has got to adversely impact the torsion stiffness of the chassis! You can probably drop the tranny this way leaving the engine in but I think it's false economy. IMO you should repair the notch and drop the tranny the usual way with the engine.

5) My overall advice is to resell the used tranny and get one that better matches your car.

Cheers, Jim

Wrecked944 · 06-13-2002, 08:47 AM

Wow !! Thanks very much for the info. It is enormously important and will definitely alter my course. For starters, I shall split open the used tranny (per Jim Simms and John Walker's warnings) to inspect its condition before considering installation. It may have seemed like an obvious task to most of you, but I have to admit I hadn't considered it.

"Dammit Jim, I'm a programmer, not a mechanic."

Then an inspection of the clutch cable mechanism to see how big the differences are. If it is okay and I haven't yet gone running in panic, then a mechanical speedo seems necessary.

And fear not, I won't be throwing away the stock tranny. I have already replaced a number of (less important) parts on this car and have kept all of the originals for the NO (and as insurance against my own mistakes). Again, this idea came from this board because I would not have otherwise considered saving old parts.

Might just use the stock tranny for "medical experiments".

And don't underestimate how helpful it is for novices to receive your input. I really can't say enough good things about the generous members of this BBS.

Thanks again,

Early_S_Man · 06-13-2002, 09:43 AM

Janus ... I think "Plug and PRAY" is the more appropriate term regarding lil' Billy's software/hardware empire!!! Just try to get USB to function on Win 2000 ... but, since I don't NEED USB, who's complaining! I can handle a "crashless" Windows 2000 just fine!

Actually, the speedo is a relatively easy swap ... any model from '69 thru '74 will work and closely match the appearance, and are readily available on eBay for under $100! Even a 120 mph 914 speedo will work, and I recently got one for $26 including shipping ... it will go with my "Donohue-geared" 915 perfectly ... in the near future! You may lose 2 mpg on the highway, but the smiles from better performance easily offsets the additional revs! The 1974 RS 3.0 used the 7:31 r & p ... and NOBODY complained about its' 19 mpg! And I wouldn't complain about it getting worse gas mileage than my '91 Town Car, either!

And, if you need to get rid of the early 915, just let me know!

Jim Sims · 06-13-2002, 10:06 AM

Putting in the speedo gage will be easy; installing the speedo drive cable though the tunnel will be a PIA especially without an old one to tie the pull cable to. Time for the fishtape! Cheers, Jim