Tranny questions, once again.

tobluforu · tobluforu's Garage

On my 72, which has the org tranny, is about to be put away for the winter, but I want to get a head start on the tranny-parts wise. I have posted before about this, but before I do anything I want to ask the pro's. Here's the issues: Hard at times to get into first and second, downshift to second can grind at times. Shifting into third, fourth and fifth is like butter, as well as reverse. Tranny has a whine in third and fifth gear only when it has a load. Tranny/ TO bearing makes noise until I press clutch in, then noise goes away which is strange as isn't this usually the opposite?. Clutch is about gone, tranny leaks fluid out of seal. Based on my description, should I even start to accumulate parts like dogteeth, synchros, etc. Or should I just hold off as the tranny/RP might be toast.
Thanks

Peter Zimmermann · 10-12-2010, 07:03 AM

Unless hyper-inflation hits before you take it apart, my advice is to wait until the pieces are on your workbench. For example, your "tranny/TOB noise" is most likely not the TOB (based on your symptom description), but is a noisy bearing inside the trans. That alone presents complications, because bearing failure can have any number of related problems. You really can't anticipate need until the unit is open.

Before you put the car away, is it possible to remove the trans and have a suitable (organized and warm) place to make some progress on the trans?

Grady Clay · 10-12-2010, 07:18 AM

Good set of questions.

The ‘whine’ may only be diagnosable when looking at the parts and may be related to the ‘TO bearing noise’ Peter notes.

I agree with using the winter to do this.
Think through also protecting the MFI and fuel system for storage.

The shifting issues are fairly predictable.

I like to use the non-angled 1-2 sliding sleeve and the 2nd gear dogs in place of the current parts for 1st gear. These may be difficult to find as they have been out of production for a long time. I am also fond of using used-but-good syncro rings.

The hub for 3-4 sliding sleeve was reinforced in ’76 and may be an appropriate update.

The “Dam Seal” mod is a must.
Input shaft seal Problem with 915 Mag case

Replacing the clutch release ‘fork’ with new (and carefully inspected) part is useful.

The shift pivot should be the ‘early’ (stronger) part but should be inspected and ensure firm attachment to the shift plate.

The WEVO bearing retainer is desirable.

If you suspect you need to replace the ring & pinion gear set, it is desirable to measure the existing pattern, position, backlash and preload before disturbing the settings. If you need a R&P, you will need to choose between your existing 7:31 ratio and the later (longer ratio but stronger) 8:31 ratio.

There is always some controversy about bearings. Some recommend replacing everything. Due to the high expense, perhaps only a few critical bearings may be in order. Part of this is what you find on inspection.

Since you have been into most everything, I suspect your mag castings don’t have any corrosion issues. Remember Tectyl coating.

Best,
Grady

tobluforu · tobluforu's Garage

Thanks guys. This was a Ca car until about 3 years go and has about 170k on the tranny, and from the outside looks pretty good (car does not get driven in the rain/snow). I have accumulated some parts from Wevo/etc which from what I have read should be replaced no mater what. I'll put a hold on everything else as it's the whine and the noise that goes away when I put the clutch in that has me worried based on other posts I have read. Now, let’s just say that when the tranny is cracked open and the results are that it needs more than just sliders, teeth, synchros, etc. I was thinking that maybe I should source out a 75 which has the 8:31 R/P, and the mechanical speedo, or is it hard finding these, and could be even more of an expense? Or heck, should I just find a 75 that has been rebuilt, pay the piper, crack it open and see how it looks?
Thanks again

Peter Zimmermann · 10-12-2010, 12:04 PM

Quote:

Originally Posted by tobluforu

I was thinking that maybe I should source out a 75 which has the 8:31 R/P, and the mechanical speedo, or is it hard finding these, and could be even more of an expense? Or heck, should I just find a 75 that has been rebuilt, pay the piper, crack it open and see how it looks?
Thanks again

That is certainly worth considering, because it will immediately take care of the ridiculous M/S seal issue. Be sure that you plot the gear ratios for your '72 trans, and the '75 trans, and compare the two so you will know what your performance changes will be up front. Also, consider a '74 unit (w/mech speedo and 7:31 R&P)!

tobluforu · tobluforu's Garage

Based on this thread and if I was too search out a 75 with an 8:31, how does one know if it has this R/P in it by looking at it from the outside?
Best Year for a 915 Transmission?
Also, I have seen trannies with different part numbers like 915/63, etc.. If I was looking for a tranny with a mechanical speedo, is there a certain part number I should be looking for? Sorry for the noob tranny questions.
Thanks again

Peter Zimmermann · 10-13-2010, 07:13 AM

Unless you know the actual history of a transmission, buying a "used" or "rebuilt" one can be a crap-shoot. That said, if you buy one from a legitimate guy who has parted out a legitimate car, you might be OK. But even then you might have to do synchros, etc., before the unit would be serviceable.

Using type numbers is the best place to start (the below info is a little fuzzy because a transmission built for a given year might have been put into the next year's car):
915/06 = 1974 7:31 with FIVE forward speeds
915/16 = 1974 7:31 with FOUR forward speeds
915/40 = 1975 8:31 with FIVE forward speeds
915/43 = 1975 (Euro) 7:31 with FIVE forward speeds
915/45 = 1975 8:31 with FOUR forward speeds
915/48 = 1975 (Euro) 7:31 with FOUR forward speeds

FWIW, I can't recall ever seeing a couple of the above trans models, but at least this list will help you to avoid a 4-speed!

(915/61 and higher numbers all have electronic speedo connections, as do 915/44 & 49 (1976) models, and 915/60 (1977 Euro) models.

tobluforu · tobluforu's Garage

Quote:

Originally Posted by Peter Zimmermann

Unless you know the actual history of a transmission, buying a "used" or "rebuilt" one can be a crap-shoot. That said, if you buy one from a legitimate guy who has parted out a legitimate car, you might be OK. But even then you might have to do synchros, etc., before the unit would be serviceable.

Using type numbers is the best place to start (the below info is a little fuzzy because a transmission built for a given year might have been put into the next year's car):
915/06 = 1974 7:31 with FIVE forward speeds
915/16 = 1974 7:31 with FOUR forward speeds
915/40 = 1975 8:31 with FIVE forward speeds
915/43 = 1975 (Euro) 7:31 with FIVE forward speeds
915/45 = 1975 8:31 with FOUR forward speeds
915/48 = 1975 (Euro) 7:31 with FOUR forward speeds

FWIW, I can't recall ever seeing a couple of the above trans models, but at least this list will help you to avoid a 4-speed!

(915/61 and higher numbers all have electronic speedo connections, as do 915/44 & 49 (1976) models, and 915/60 (1977 Euro) models.

Awesome, thanks.

tobluforu · tobluforu's Garage

One more question, ok maybe there will be more.... What would you do?
1). Take a chance and rebuild the 72 which really isn't something I want to do based on the above.
2). Buy a used 75 core which will be taking a chance on what is inside, even if I can find one and from I have read it will cost at least 750.
3). Buy a used/rebuilt 75 tranny from carquip/etc for around 3200.