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Discussion Starter · #1 ·
A few years ago I bought a cheap Muncie (M20) and rebuilt it, placing it behind my 396...

It has never seemed to shift real smooth, especially seeming to hang up a little going into second and third...

I adjusted the shifter and finally replaced it (Hurst Comp Plus), put all new bearings and synchros, dogs, spring retainers, one slider, etc in the trans, little engagement teeth (next to synchros) look good, and I just recently replaced the clutch and a new roller pilot bearing...

But I still have the problem with it not shifting smoothly. It will shift without much effort, but sometimes I will miss a shift because of it... It doesn't pop out of gear.

Just recently I noticed that it grinds a little going into fourth (unless your shift takes about 1+ seconds (slower than my grandma shifts). At a stop light in gear, its fine, and the pedal has to come up pretty high to engage, so I think the clutch is adjusted properly, and even if I put in in neutral, it will easily go into gear when running...

I did have a problem when rebuilding, the 2nd and 3rd gears wouldn't come off the main shaft(even tried a press, but not to much pressure...).

Any ideas what to check next???


I have a few M21s lying around, and I am thinking of trying one of these...

Any opinion of running the M21 with 3.42 rear gears??? Will the 2.20 first gear be adequate???


Thanks for any help/advise



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"Once you go RAT, you never go back..."
TC #1366
Tony
1966 SS L78 coupe
1966 SS convertible
1965 Impala convertible
1 wife that has drawn the line...
 

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Dumb question, but is the clutch disengaging all the way?
Did you put the new slider on 1-2 or 3-4?



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<A HREF="http://nacs.net/~drunion/First_Page.html/
69" TARGET=_blank>http://nacs.net/~drunion/First_Page.html/
69</A> Chevelle
454 .030 10.5:1
373 posi
M21 4spd.
12.63 E.T.
License Plate: NTHE 12S


"Fire all your guns at once and
Explode into space."
Steppenwolf "Born to be Wild"
 

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Discussion Starter · #3 ·
Yeah, the clutch does disengage all the way. When I am at a stoplight, it does not try to creep, no smell of burning slipping clutch (in gear/clutch disengaged), and if I put it in neutral, there is no problem getting back into gear. Also goes into reverse smoothly...

I seem to recall replacing the 3-4 (front?) slider only...

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"Once you go RAT, you never go back..."
TC #1366
Tony
1966 SS L78 coupe
1966 SS convertible
1965 Impala convertible
1 wife that has drawn the line...
 

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Are you using synthetic gear lube??
Second and third gear should have slid right off without any problem.

Im sure DZ auto will tell you exactly what it is. Looking forward to his reply.
 

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Sometimes the sleeve under first gear can get stuck on the main shaft. you should be able to get 3rd off with a press. Back to the problem try dialing in the bellhousing even if it is a stocker. With a roller pilot everything must be straight or the input shaft will bind and cause 4th gear not to shift correctly.
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by Mike Feudo:
Sometimes the sleeve under first gear can get stuck on the main shaft. you should be able to get 3rd off with a press. Back to the problem try dialing in the bellhousing even if it is a stocker. With a roller pilot everything must be straight or the input shaft will bind and cause 4th gear not to shift correctly.
<HR></BLOCKQUOTE>

Mike,

I have a question about this...I rebuilt my BW Super T-10 about March or so, and put it in my '66. Stock clutch/flywheel/bellhousing, as well as a GM roller pilot bearing. I had a good rebuilt M-21 behind it before I put my ST-10 in it, and it ran fine for more than 1000 miles.

Anyway, to make a long story short, after about 700 miles or so, my ST-10 locked in fourth gear. Went around and around trying to find what it was (Shifter poorly adjusted, or stuck, broken shift fork, etc.) Finally pulled the trans and tore it down, to find that the input shaft and mainshaft had 'welded' themselves together.


What had happened was that all of the roller bearings in between the two shafts had come out, and broken, and locked the shafts together. Also did some pretty good work on the washers between the case and counter gear. Also did a number on all of the needle bearings inside the counter gear.

Could all of this have been caused by a poorly aligned bellhousing and a roller pilot bearing??



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Nick Pratt,

TC #1442

Proud owner of a 66 Malibu -
355, four speed, 3.08 pegleg

14.94 @ 93.75 (Needs work, I know)

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Discussion Starter · #7 ·
Come to think of it, I don't ever remember aligning the bellhousing...

I guess I should try that...

Anybody know the proper procedure for aligning a Lakewood scattershield?

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"Once you go RAT, you never go back..."
TC #1366
Tony
1966 SS L78 coupe
1966 SS convertible
1965 Impala convertible
1 wife that has drawn the line...
 
G

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Here we go with some basic questions. You said 3rd and 2nd gear would not come off the main shaft. To get second off you need to remove the first gear spacer, it's a press fit, not sloppy but tight. You can heat the spacer and use the weight of second and the clutch hub to knock it off. Pound the mainshaft on a block of wood on the concrete floor, that should do the trick for second. Third not coming off is a little odd. You removed the big bawana snap ring? Also does the gear spin freely on the main shaft? If you did remove the snap ring, and the gear spins, do the same thing to get third off, pound the big end on the wood and the gear should drive it off.

Those roller pilot bearings are almost useless and very unforgiving. The roller are hard and any misalignment in the input will cause havoc.

The not smooth shift from 2 to 3 is almost always the shifter unless the sliders are junk or the shift forks are worn down. Forks start life about .362 measured at or near the tips and need replacing when the show signs of wear, serious wear. The sliders get nasty on the leading edge, the part that engages the brass and the gear. If you get a combination of a worn slider and a normally worn gear it may not shift smooth.

It has been my experience that 3rd gear is in an unknown location in the trans! More people miss third than any other gear, and they look like it.

Wally

[This message has been edited by Wally (edited 09-18-2001).]
 

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Wally has pretty well covered it. I really can't add anything. I agree 100% that PROBABLY (without having the tranny/shifter in front of me) the shifting difficulty is due to the shifter----------------that is, of course, if all is well INSIDE the tranny.

I'm done.

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Tom Parsons
 

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Discussion Starter · #10 ·
Wally, DZ and everyone else,

Thanks for the input...

As for the shifter, I have had two Hurst comp Plus, the current brand new, and have readjusted them each time I had the trans out and back in... I Know its not the shifter, I have never had a problem like this before with other trans, and many comp plus shifters...

The worn shift fork may be a possibility...

Wally, I am a little confused about the third gear "spinning" freely on the mainshaft... Isn't it splined to the mainshaft, therefore not able to spin??? I do remember removing all the snap rings, but there might have been a pressed on spacer. We didn't use heat, but when we tried to press it off, it didn't budge, and I was worried about putting too much pressure...

Does anyone have an opinion about switching to an M21 with 3.42 rear gears? I have two M21s and the M20 in the car. Both M21 have low miles on a rebuilds (supposedly).

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"Once you go RAT, you never go back..."
TC #1366
Tony
1966 SS L78 coupe
1966 SS convertible
1965 Impala convertible
1 wife that has drawn the line...
 

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The 1, 2 and 3 gears (and 4th for that matter), are NOT splined to the mainshaft. They all spin freely. It is the SLIDER, which is splined to the syncro hub, which is splined to the mainshaft, which, when the SLIDER is ENGAGED with the little teeth on each gear, it THEN becomes LOCKED to the main shaft. The input gear (shaft) is also 4th gear. It also spins freely until the 3-4 slider is engaged with it. If you have a side cover removed and have all the gears in the neutral position, turn the input shaft. You will notice that EVERYTHING inside the case is turning EXCEPT the mainshaft. That means that ALL the gears are spinning on the mainshaft.
Hope this helps to clarify things.

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Tom Parsons
 

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Tony,

As far as the M21/3.42 combo goes it will probably be marginal. GM's rule of thumb was M21 for 3.73 and lower (eg: 4.10, 4.56) and the M20 for 3.55 and higher (eg: 3.31, 3.07). If your engine has a lot of low end torque you may be satisfied but if it's lacking on low end you'll grow to dislike it very fast and it'll take a toll on your clutch.

Dave
 

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Discussion Starter · #13 ·
Makes perfect sense... If they were all splined to the main shaft, it would be locked in all gears...

Just been a while since I had one apart...

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"Once you go RAT, you never go back..."
TC #1366
Tony
1966 SS L78 coupe
1966 SS convertible
1965 Impala convertible
1 wife that has drawn the line...
 
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