(I am "housekeeping" on this site tonight. Better than Christmas shopping with Myrna. ANYTHING would be better than that, here on December 23. I can proudly say I finished, and started, my Christmas shopping today, before the unwashed masses hit the downtown malls. But I digress...)
I also was curious about this topic, and I seem to remember posting a similar question regarding swapping Katheryn McCoy's '72 GT tailshaft to her much better "Ohio" 1970 transmission. If I find that posting, I will merge them and answer my own question....
Well I do know that the transmissions in My '70 and '72 are identical so I would imagine that the 70 and 73 would be interchangable. I would first look at both get some measurements to be sure, can't help you any further than that though.
Ritter, I don't know the exact cutoff date, but the early trannys are a little different from the later ones. I *think* the cutoff was 1971, but am not sure...it's been a while since my dealings in Opel parts as a profession. Basic changes were a different tailshaft housing (early ones had a bolt-on pivot for the side shift selector arm, later ones were cast into the tailshaft). The speedo drive was angled 90 degrees on the older trannys too. Some very early trannys also had ALL small synchros (same as 3rd and 4th on all gears). Kinda rare though. There were also at least two styles of shift selector arms (on the right side).
I've never tried swapping early-to-late tailshafts or vice-versa, so I can't offer any advice as to how to do it or if it's even feasible. I know there are two distinct gaskets from early to late tailshafts, FWIW.
Rally Bob is more than likely correct, For all I know the Tranny in my '72 could be a '70 or '71 couldn't tell you for sure as I am not the original owner by far.
You might still be able to get the swap to work though it may mean swapping out more than just the tailshaft. But I haven't tried this before. I would still look at the two transmissions closely if nothing else Figure out which offers the most reliability and rebuild it then you will have a transmission that will last. Another thought: I believe there is a '71 or '73 (with good trans) in the junkyard here if it hasn't been crushed yet I could call Dick in the dirt (an affectionate name we gave the owner of the scrap yard) and find out, if that would help you out LMK (shipping might hurt)
Can a late model tranny tailshaft housing replace an early model right angle drive?
I have the answer to this, and it is NO! I found this out the hard way this weekend, when trying to merge Kathryn McCoy's '71 GT transmission (the later version with the speedo drive on the driver's side) with an early (pre-mid 1970) tranny with the speedo drive on the passenger side and the right angle adaptor. This early transmission was a "later" early model, in that it had different synchro rings on 3rd/4th gears compared to 1st/2nd gears.
But the answer is the same. The early speedo drive gear is in a different location on the main shaft, and therefore the speedo drive on the new tailshaft housing will NOT fit the older style mainshaft.
But the good news is that the rest of the components, such as the counter gear, synchro rings, main bearings and inner needle bearings ARE interchangeable, at least between the "later-early" version and the latest tranny. So it is possible to "merge" these two tranny versions and get one good one. Because that is what we did.
While the tailshaft of a later tranny won't work with the earlier mainshaft, you CAN use most of the parts interchangeably. You should be able to use the good internal parts from the '70 tranny to make the '73 tranny serviceable. It really isn't very hard to disassemble an Opel transmission, so long as you have a factory service manual and CAREFULLY follow the steps. The pictures are quite easy to see how it comes apart and goes back together, and the text is very understandable.
You need a few basic tools: a bench vice, a set of circlip pliers, a brass drift, and a 1/8 inch (decent quality) drift to remove the roll pins. To remove the internal synchro rings (2nd and 3rd gear) you need to press the gear clusters off the main shaft, but any machine shop should have a bearing press that can accomplish that. The manual will call for a few special tools, but a bit of common sense can get around them. For example, to remove the counter gear cluster, it calls for a special tool to drift out the internal shaft while retaining the internal needle bearings. But a brass drift of approximately the right length and diameter will do, and the needles can be re-loaded (24 per side) by packing them in grease. The detent spring plugs are supposed to be pulled with a special tool and slide hammer, but a blunt chisel and a few upwards-directed hits will pop them out.
If the '73 tranny won't shift properly anyway, try disassembling it to see what has gone wrong. Look for worn synchro rings; a worn ring will not leave an gap between it and the matching gear, if the cone has worn. It is hard to explain, but it will be easy to see what I mean. And look for obviously worn gear teeth and damaged bearings. Virtually all of the major bearings and seals are available from either a quality bearing and seal supply store, or from OGTS.