PRNDL

I just visited my vette at the shop today (should be all finished by now). In addition to replacing the clutch, when the trans was out they replaced the pinion seal. This should stop the trans from leaking. They were able to find a GM part locally. I was wondering what the part # was so I could find out availability and price online..... and grit my teeth at my mechanic's price! We were also discussing the lack of drain plug on my trans. I know there is not supposed to be one on my 1968 M21. Apparently, there is a place for a drain plug in the transmission casting. It is also my understanding that the M22 trans does have a drain plug. Does anyone know what years/models have a drain plug and which do not? Thanks, MJ

Rowdy Rat

This sounds like a Joe Lucia question to me...

Quote:

We were also discussing the lack of drain plug on my trans. I know there is not supposed to be one on my 1968 M21. Apparently, there is a place for a drain plug in the transmission casting. It is also my understanding that the M22 trans does have a drain plug. Does anyone know what years/models have a drain plug and which do not? Thanks, MJ

MJ, you are correct in that your 1968 M-21 (nor an M-20) should not have a second plug in the casting although, as you mentioned, the casting does have the raised area in the casting like the M-22 where a plug can be added. As you mentioned, the L-88 DID have this second plug.

The second plug began to be added to all four speed manual transmissions in late 1969... I have seen a couple of original October 1969 cars that have the second plug.

Good luck with your car!

Regards,

Stan Falenski

Joe Lucia

"MNJack"------

You mention that they replaced the "pinion seal" and then "that should stop the trans from leaking". The pinion seal is the seal located on the "snout" of the differential carrier assembly and is not related to the transmission, at all. In any event, I'll give you the part numbers for both the transmission extention housing rear seal and the differential pinion seal. These are:

trans extension housing seal-------GM #8673526 (all 63-70 Muncie transmissions)---GM list= $10.95/each

pinion seal---------------------------------GM #3924031 (all 65-79 Corvette)----GM list= $11.65/each

As far as drain plugs go, during the 65-69 period, only M-22 model Muncie 4-speeds were originally equipped with a drain plug. Beginning in 1970 with the introduction of the "661" main case, all Muncies got the drain plug. It is very possible, as Stan mentioned, that very late 69s also received the "661" main cases and, consequently, the drain plug. For most Chevrolet car lines (except Corvette and Camaro), the 1970 model year began in the fall of 1969. So, the "661" main case may have been the only one in production by the fall of 1969. My original owner, mid-September 1969 built Corvette has the "660" main case and does not have the drain plug. However, later build 69s (which were built through December) may use the "661" case.

Larry B.

I have an October '69 with the original M-20. It has a drain plug.

GTR1999

When I rebuilt my 69 M-20 20 years ago I drilled and tapped a 1/8" pipe plug in the bottom of the case. It didn't cause any problems and I don't care about the car being "correct", it works that's all I'm interested in.
Gary

PRNDL

Joe (and everyone else), thanks for the responses. My trans is an M20, not M21,another senior moment.... I know it doesnt make any difference about the drain plug info.

Now, before I have an apoplectic seizure.... I will just ask him again exactly what that GM NOS part was that he replaced..., and get the part #from him since they got it from GM (a local dealer?) Most of it is a steel rod (cylinder) about 4 or 5 inches long. They showed me the old one - it was a little bumpy. The new one was smooth. They told me it cost a lot more than $11.65..... a whole lot more!! :mad I hate being so clueless about this stuff... but I'm learning. MJ

74vetteman

Sounds like they replaced the yoke, which probably costs ~100 bucks.

Joe Lucia

"MNJack" and "Vetteman74"-----


Yes, I agree. Based upon the description it does sound like the rear transmission yoke was replaced. And, that's a whole 'nuther story as far as cost goes. The 1968 manual transmission yoke is GM #3868728 and it's an expensive piece. It currently GM lists for $189.35, although aftermarket versions MAY be available for less.

If your old one was "bumpy", you DEFINITELY needed a new one, too. However, if the old one was this worn, I hope that your mechanic also replaced the transmission tail shaft bushing. This is a rather inexpensive part, but it requires quite a bit of labor to replace, since the transmission must be removed and partially disassembled. The yoke, on the other hand, is an expensive part, but a snap to replace.

The tailshaft bushing should ALWAYS be replaced if the yoke is worn. Otherwise, the new yoke might suffer a " short but exciting life", which is not something that you want to have happen with a $200 part that might not even be available in the not-too-distant future.

Anyway, the tailshaft bushing for your car is GM #6260048 and currently GM lists for $2.85/each.

PRNDL

Thanks again for the replies. I have been surfing the net searching for pics, and sure enough, it's a transmission yoke, or "slip yoke" ?? Why would he call it a "pinion seal" ? I dont think I imagined that! I am paying GM list price. I will ask him about the tailshaft bushing. MJ

Gordonm

I replaced my tailshaft this winter along with the bushing. The bushing being worn allowed the tailshaft to wobble a little. This combination wore both out. Replaced both and no more leaks or vibration.