M21 Trans down shifting problem

[Jeffro]

I have a 70 LT1 with 78K miles on it. To my knowledge, the M21 transmission has never been rebuilt.

I was having trouble getting the car into 2nd when shifting down from third. Last week a similar problem arose when shifting into 1st from 2nd as well.

I think this is evidence that the problem is getting worse.

Any advise would be helpful.

Jeff

 

[sscam69]

Can you give a better description of the problem?

Is there clanking when you shift?

Does it just get stuck?

What do you have to do to get it in gear (i.e. shift to differen gear and then back)?

 

[Mako]

Before pointing at the tranny, adjust the clutch to ensure your getting complete release.

If that's a no fix, re-adjust the shifter linkage as well and just because, change the tranny fluid.

Only if none of that work fixes the issue would I start to get suspicious about the tranny synchro's.

Good luck!
Mako

 

[cruzer99]

I agree with Mako......Try the cluch first.

 

[Jeffro]

Thanks for the information. I'll start with the cluch this weekend.

 

[Mako]

Thanks for the information. I'll start with the cluch this weekend.

Just following up - did the clutch adjustments fix the down shifting glitch?

CYa!
Mako

 

[mvftw]

I've got a 90K mile ST-10 that has Not been rebuilt. When it's cold (first shift of the day) it doesn't go into 2nd clean, I go into 3rd. Also getting out of reverse when cold is also tuff. After the first shift it all seems fine. I'm going to do a fluild change first. What fluild/weight do you suggest...name brand 75w-90 or 75w-140?

 

[Mako]

I've got a 90K mile ST-10 that has Not been rebuilt. When it's cold (first shift of the day) it doesn't go into 2nd clean, I go into 3rd. Also getting out of reverse when cold is also tuff. After the first shift it all seems fine. I'm going to do a fluild change first. What fluild/weight do you suggest...name brand 75w-90 or 75w-140?

What ever fluid is called for in your owners manual is what you should use. Don't trust the parts counter guys, get exactly what is in the manual. Sta-Lube makes a quality fluid, but it can be a pia to find.

The only other alternative is a synthetic fluid from Redline or Mobile. Expensive but they can be just the thing for some transmissions.

http://www.redlineoil.com/ Call them up and get a recommendation for your specific application. I don't have Mobil's www handy.

Good luck!
Mako

 

[Gunther]

Hi
Now where we at this, my 68 M21 close ratio also has a problem.
Downshifting from 3rd into 2nd is only possible, if I just first hit into 1rst , not completetly, but just a touch and straight back into 2nd. No bad noise or so, just doesn't want to engage .
All other shifting is ok.
Synchros ?
I have already changed the oil.
Thanks Gu nther