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Old 10-01-2022, 03:37 PM
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Default M21 trans question

I noticed that my shifter linkage was feeling a little sloppy the last time I drove the TA, so figured I’d take a look underneath. I had also noticed that I was leaking a little bit of gear oil. Here are some shots of what I found, as well as a couple of questions:
1. Does this leak look like it’s coming from the tail shaft or more like where the tail shaft and body connect? Or both?

2. Like the engine, this trans was rebuilt less than 5000 miles ago, but probably close to 10 years. How easy is it to replace these gaskets with trans in car?

3. If I have to remove the trans (I’m pulling the engine next month anyway to build a 4.00” stroker), what do you think of putting M22 gears into it? I love that rock crusher whine.

4. How can I determine if this is the original trans. I believe it is, but just to double check. Is there a VIN stamped on the case? I took a photo of what looked like that.







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Old 10-01-2022, 03:55 PM
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Also, I believe this little switch is a TCS switch. I have no idea. If it is functional or not, but I noticed that it has a single spade, whereas the cap on the wiring harness has spores for two spades. Is the switch incorrect or is the wiring harness wrong?





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Old 10-01-2022, 05:35 PM
DANTIP DANTIP is offline
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The partial VIN is visible but looks subdued. I believe connector is for an automatic transmission. The harness should have a single wire beside that one for the manual trans TCS switch.

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Old 10-01-2022, 05:53 PM
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1st. The case is leaking.
2. Rebuilding that case, well you need a lot of parts, basically All of them. Would be cost prohibitive unless you have a transmission guru buddy. M22 whine gets old... like the dronemaster exhaust.
3. Could be that switch is for reverse light on some models.

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Old 10-01-2022, 06:21 PM
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Thanks for feedback guys. Turns out the VIN number is correct, which I kind of expected. This is a relatively low-owner car (4) and Owner 3 was the one who really went through most everything to make sure it was correct. Technically it’s a 6 owner car but the guy I bought it from (on consignment from dealer) only had it a year and the dealer actually was the one to buy it from Owner 3, but he flipped it pretty quickly (even though he told Owner 3 he wouldn’t do that. Anyway…

I did some reading on the site. The single spade TCS is correct for a 4-speed (I believe this is original). All 70 RA III cars got the two-spade wiring harness, and the automatic cars got a two-spade TCS switch. Unfortunately, maybe due to leakage, that connector does really stay on the spade switch.

I wasn’t originally planning on going through the trans when I did the motor, but now it looks like I should plan for it. I have a good Muncie guy near me. He did the trans in my ‘70 Judge a few years back, as well as the M20 in my ‘67 GTO.

FB, now you got me thinking about the whine. I definitely hated that drone from the flowmasters on my Judge, so now I’m wondering if I just leave this one alone, and do a stock rebuild. I was thinking that the M22 gears would also offer some protection from the additional torque o expect the stroker motor to make. Isn’t that why they started putting them behind the 455 HO cars in ‘71?


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Old 10-01-2022, 08:43 PM
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I never get tired of the M22 whine. It's quiet in 4th gear anyway.

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Old 10-01-2022, 10:15 PM
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So, let’s say I was going to go the M22 helix gear route and money was no object. Would you:

a. Rebuild the original M21 with M22 gears?

b. Buy a professionally rebuilt M22 with passenger-side Speedo and stick the original M21 in storage?

c. Buy an AutoGear M23, which I understand is even beefier than an M22 and is a direct bolt in?




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Old 10-01-2022, 11:09 PM
Ramairnacho Ramairnacho is offline
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I have a 78 ta with a t 10 and 342 posi 400 which is stock quick I guess but screams on freeway. I'm at 3200 rpms at 70. I personally hate loud slow cars. Have you considered the 5 or 6 speed ? I'm 50 and most older guys like the drag races I like road race. You probably get longer life out of car with a 5 speed or 6 but I don't know. I m a rookie still. I guess you need to figure out what you use it for. If just cruise around town ect. Retain value leave it stock. Another thing is I would never stroke original block if that breaks you would loose a lot of value. I would find some other block to.stroke and store original, but that's me. I seen a 70 very nice ta sell for 34k with an ls engine and a barn find sell for 50k number matching.


Last edited by Ramairnacho; 10-01-2022 at 11:17 PM.
  #9  
Old 10-02-2022, 09:20 AM
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Leave the m21 alone and fix the leak. For the cost to modify it, then it won't have right numbers on it for what it is, be better to buy one. All the parts you need are Not readily available last time I looked. You'll need a drive shaft yoke update, both input and tail shafts etc.. its not just some straight cut gears inside

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Old 10-02-2022, 12:19 PM
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Default Tranny

I found some info in an old ram air catalog I haven't transmissionidentification I got this from a vendor in 92 at LA pontiac show. I wish be was still around. Company called precision pontiac.
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  #11  
Old 10-02-2022, 06:54 PM
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Thanks for the feedback guys. I honestly thought rebuilding my M21 into an M22 was just a matter of swapping out the gears. Now that I’ve spend the last day and a half under the car, it definitely needs a rebuild, and if the M22 conversion is that much more involved, I’m fine just having my M21 gone through. I definitely don’t want a 5 or 6-speed in this car. If it was a non-matching number car, I might consider that route, but I want to keep the Muncie 4-spd in it.

As far as the stroker crank, I didn’t really think of that as being any different than swapping camshafts. Granted, I’d have to run different rods as well, but not sure why that would hurt the value of the car. Am I wrong? And as far as the crank letting go and taking the block with it, trust me, I’ve experienced first hand what happens when Pontiac cast rods reach their breaking point. I would think any forged crank/rods would be a welcome upgrade to any future buyer (not planning on selling the car, but we never know what tomorrow brings).

That said, I did finally get to drive my ‘67 GTO with its 400 today. That car has ported 670 heads (Gessler), an SD Perf. stump puller roller cam, and a carb done by one of Cliff’s disciples. Even though it’s only got am M20 and 3.55 rear, that think would absolutely destroy my stock RA III car. It feels even faster than it did all the years I ran a 428 in it.


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Old 10-03-2022, 12:52 AM
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Stroking a Pontiac 400 is a great idea if you are looking for more power. Upgrading the crank and rods is a smart move. But the longer stroke is not resolved by shorter rods, rather the pin placement in the pistons is where the difference is made up, so you need to get the correct pistons for the crank you buy. You may want to consider a complete rotating assembly from one of the Pontiac suppliers or even having them build your block, bad news is they are all very busy.

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Old 10-03-2022, 05:28 AM
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Is your driveshaft connected to the differential in that picture? If so, I think your driveshaft is too short. Slip yoke is hanging out a long way.

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Old 10-03-2022, 08:11 AM
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Quote:
Originally Posted by nas t eh View Post
Stroking a Pontiac 400 is a great idea if you are looking for more power. Upgrading the crank and rods is a smart move. But the longer stroke is not resolved by shorter rods, rather the pin placement in the pistons is where the difference is made up, so you need to get the correct pistons for the crank you buy. You may want to consider a complete rotating assembly from one of the Pontiac suppliers or even having them build your block, bad news is they are all very busy.

Thanks! I would definitely be looking at going with a whole rotating assembly from someone like Butler.


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Old 10-03-2022, 08:13 AM
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Quote:
Originally Posted by JSchmitz View Post
Is your driveshaft connected to the differential in that picture? If so, I think your driveshaft is too short. Slip yoke is hanging out a long way.

I didn’t even notice that. Thanks. The driveshaft is still attached to the differential. Ugh. Better to fix it now, once I pull the motor/trans out of the car, I guess.


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Old 10-03-2022, 11:53 AM
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Quote:
Originally Posted by racerboy View Post
I didn’t even notice that. Thanks. The driveshaft is still attached to the differential. Ugh. Better to fix it now, once I pull the motor/trans out of the car, I guess.


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No problem. I learned that lesson, the hard way, years ago. It wore the tailshaft bushing out because it was hanging out too far. Could also cause a leak.

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Old 10-04-2022, 12:15 PM
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Quote:
Originally Posted by JSchmitz View Post
No problem. I learned that lesson, the hard way, years ago. It wore the tailshaft bushing out because it was hanging out too far. Could also cause a leak.

Thanks again. Seems very strange to me, considering this car has original engine and transmission. Both have been rebuilt (back in 2011) so maybe the previous owner had the driveshaft done back then and somehow it got shortened.


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The frogs take up where they left off.
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Old 10-04-2022, 12:59 PM
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Might be that the car is off the ground and the rear suspension has relaxed enough to pull the yoke out of the transmission a little along with the perspective the picture is taken making it look worse than it is.?

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Old 10-04-2022, 03:41 PM
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Quote:
Originally Posted by nas t eh View Post
Might be that the car is off the ground and the rear suspension has relaxed enough to pull the yoke out of the transmission a little along with the perspective the picture is taken making it look worse than it is.?
Not sure if they all behave the same. On my car, the yoke goes in farther when it's lifted.

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Old 10-04-2022, 07:55 PM
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Quote:
Originally Posted by nas t eh View Post
Might be that the car is off the ground and the rear suspension has relaxed enough to pull the yoke out of the transmission a little along with the perspective the picture is taken making it look worse than it is.?

This car is on one of my parking lifts, as opposed to a service lift, so all 4 tires are on ‘solid ground’ so to speak. I didn’t want to use the device lift in my garage because I figured the car is going to be tied up for a while. I figure once I get the engine/trans out, I can just lift her out of the way for however long the rebuild takes.


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