Team Chevelle banner
Cancel
Create thread New Garage Forums

Muncie M20 question

Jump to Latest
1 - 19 of 19 Posts
J

Jakes_69Chevelle

· Registered
Joined
·
119 Posts
Discussion starter · #1 ·
Hey Guys!

So I pulled my muncie today on my Chevelle project. Not as easy as I remember working at the Exxon when I was a kid with a lift and good old fashion muscle. I pulled the trans again 30 years later but this time on a creeper.... :(

I think the trans is an M20 - 10 spline input shaft, 2 groove rings, 27 spline output shaft, trans tag 3952659WB. Case 3925661 POR28A.

After I pulled the trans, I was inspecting things and noticed I could grab the input shaft and move it up and down, and side to side. Should an input shaft have that much play??? Or is the bearing definitely bad?

Also, I was hearing a noise as well. could a bad input shaft bearing make sounds similar to a rod knock?

Thanks in advance for your expert advice!
 
#2 ·
Sounds like you answered your question. The input shaft shouldn't have much play at all. Your front bearing is most likely toast.
 
#3 ·
Jakes_69Chevelle said:
I think the trans is an M20 - 10 spline input shaft, 2 groove rings, 27 spline output shaft, trans tag 3952659WB. Case 3925661 POR28A.
Click to expand...
:cool: Yes, that's an M-20 as indicated by the "A" in the Date Code.
 
#4 ·
A lot of times a knocking sound is a broken or chipped gear tooth.

A little up and down play is normal to the Munce input shaft. The pilot bearing helps regulate this play as does a set of needle type bearings on the inside of the input shaft. It seems like a lot of play because the end of the input shaft is so far from the bearing. Been looking for an actual number but can't seem to find one. If you put the rear yoke in the trans or hold the output shaft to one side some of that play will go away. If the input shaft hits the inside of the bearing retainer then you definitely have too much play.

Unlike more modern transmissions, the Muncie uses a ball bearing type front bearing so more play there as opposed to a roller bearing in the newer transmissions that inherently have less play and require tighter tolerances, hence the use of a bearing type pilot bearing instead of a bushing that is recommended for Muncie use.

A bearing will usually make a whirling griding type noise that may change in frequency as opposed to a clunking rod knock type of noise which may be caused by a broken gear or tooth. There's also gear chatter from slop in the gear clearances but the frequency is usually higher and noise comes and goes with various loadings.

From your description of the noises, I'd send that trans in for a check-up or have an experienced trans builder look it over. You may be able to detect issues just by pulling the shifter cover and inspecting the gears on your own.
 
#5 · (Edited)
Not trying to downplay Al's advice as it is sound. However changing the front bearing is as easy as it gets. You could try a new bea ring and see if that fixes your issue. Can always take it to a trans guy if new input bearing doesn't take care of the issue.
Two things that will help with trans remove and install. First is getting the car as high off the floor as possible and second is a Harbor Freight trans jack. Very often found on Craigslist. Even if have to buy new think they are less than $100.00

Like this. Maybe Black Friday sale?
www.harborfreight.com/450-lbs-low-lift-transmission-jack-61232.html
 
#6 ·
Discussion starter · #10 ·
Thanks guys for the replies! I haven't pulled the side cover yet but will be inspecting the gears, syncro's, forks, sliders, etc. when I do. I think that input shaft comes damn close to the side of the bearing retainer when I move it around so I'm definitely gonna replace the bearing. Also, I need to pull the tail shaft and replace the bushing since it chewed up my yoke. Other than that I'm hoping just gaskets and seals. The trans never gave me any problems.

Thanks for the idea on the trans jack!! I was seriously saying to myself, how the @#&! am I going to get that back in?!?!? This car is up about 24 inches off the ground, and I was considering retrofitting one of my floor jack to support the trans... but it looks like Harbor Freight to the rescue again!! Thanks for the idea.

So the more I consider my setup.... I not sure I'm happy with it. I have an original 12 bolt KK rear with the 4.10, Muncie M20 wide ratio and soon to be Mark Jones 467. I cancelled the Tremec due to funds and was hoping to use the Muncie. Weekend cruiser, no racing but will definitely peel-off some rubber when i get the urge :)

What do you guys think of this setup??
 
#11 ·
Check out the play in this M22. Then click on the youtube logo on the player and read the comment and note who made it. The comment was made by one of the best Muncie builders in the US. Most here know him. Paul of 5speeds.com Also note the advice that inserting the drive shaft yoke will tighten up the play and the pilot bearing will mitigate the rest. Just found this, figured I'd post it so you didn't think I was just blowing smoke.


"GearBoxVideo
1 year ago
"They all float like that. It's normal. When the driveshaft yoke is in the unit it will tighten up more. Also if you apply a downward pressure on the output shaft you will see the input will not move. The yoke when installed will tighten it up and then the input pilots on the crankshaft."

I think just changing the front bearing is a waste of time with your described condition without taking a look into the trans and checking the gears for damage. It's possible that the front bearing is missing a piece of the race and you may get rod knock noise. You'll see that if you pull off the front bearing retainer. Just want to help you avoid having to pull that trans again.

If you need direction in pulling the shifter cover or changing the retainer bearing just ask and we'll hook you up. Don't fall into the MaxCap bearing hoopla as I did. I built 3 Muncies with these and although they are still holding, next time out, they come out. Learn as you live sort of deal.

https://youtu.be/UhMz44y_EwY?t=412

Paul, hope you don't mind me posting your videos here.
 
#12 ·
Jakes_69Chevelle said:
Thanks guys for the replies! I haven't pulled the side cover yet but will be inspecting the gears, syncro's, forks, sliders, etc. when I do. I think that input shaft comes damn close to the side of the bearing retainer when I move it around so I'm definitely gonna replace the bearing. Also, I need to pull the tail shaft and replace the bushing since it chewed up my yoke. Other than that I'm hoping just gaskets and seals. The trans never gave me any problems.

Thanks for the idea on the trans jack!! I was seriously saying to myself, how the @#&! am I going to get that back in?!?!? This car is up about 24 inches off the ground, and I was considering retrofitting one of my floor jack to support the trans... but it looks like Harbor Freight to the rescue again!! Thanks for the idea.

So the more I consider my setup.... I not sure I'm happy with it. I have an original 12 bolt KK rear with the 4.10, Muncie M20 wide ratio and soon to be Mark Jones 467. I cancelled the Tremec due to funds and was hoping to use the Muncie. Weekend cruiser, no racing but will definitely peel-off some rubber when i get the urge :)

What do you guys think of this setup??
Click to expand...
A little high in the rear gear, but great to row through gears with. You might find a lower rear gear might make cruising a little more bearable. That engine should make plenty of torque. Gonna be hard to keep tires under it. I'd run it as is and enjoy the fun factor, then decide on an overdrive trans or rear gear change when funds become available. Sounds like you have a good plan for the trans...post if you need help.:thumbsup:
 
Discussion starter · #13 ·
Dutch - thank you for all the information, it's been great. Good point about the yoke, I'll check the movement with the yoke installed. GearBoxVideo - wow, I love the videos on YouTube, been watching them for a while!! I want to get the Muncie rebuild book as well.

Got the trans jack today LOL!! $99 less 20% discount code - out the door for $79.
 
Discussion starter · #14 ·
So I got the input shaft bearing out today and boy was that bearing retainer TIGHT! The bearing probably wasn't bad, there wasn't a lot of movement within the bearing parts. It seemed nice and tight.

It was a New Departure brand #41307B (maybe original??)

Anyway - Will the Timken #N1307L work as a replacement does anyone know? RockAuto lists it under the 1969 4-speed Muncie. I see a JAF brand as well for really cheap but that makes me a little nervous.

Happy Thanksgiving everyone!!
 
#15 · (Edited)
You missed this video. It doesn't pop up in a player because it's cued to the time mark where these bearings are discussed.

https://youtu.be/UhMz44y_EwY?t=412

This thread shows where I learned of my mistake falling for marketing hype of a "super Heavy duty or Max Capacity Bearing ".
https://www.chevelles.com/forums/33-transmission-driveline/1056657-muncie-input-shaft-bearing.html

I'll let you watch the video and decide for yourself which bearing to use. JAF is good to go as are all the major US brands.

Knowing what I now know, I would use the 8 bearing unit on the input shaft location instead of the 12 bearing Timken #N1307L in future builds.

I may even use a sealed bearing in that location but still researching that idea. I think I 'll need to mod the case with a vent if I go the route. Still undecided.
 

Attachments

#18 ·
Wheel/tire width

What is the widest tire and wheel comb that I can put under my stock 67 Chevelle? How wide would the 15” rim be and what inside spacing would the wheel have? I hope I asked this right. I just wanna get the widest tire under there that I can without modifying anything. Thanks in advance
 
#19 ·
Re: Wheel/tire width

Chevelle53 said:
What is the widest tire and wheel comb that I can put under my stock 67 Chevelle? How wide would the 15” rim be and what inside spacing would the wheel have? I hope I asked this right. I just wanna get the widest tire under there that I can without modifying anything. Thanks in advance
Click to expand...
(name?) You need to start a new thread in the 'Wheels and Tires' forum with this question - it has NOTHING to do with a Muncie M20. ;)

And - whatever happened with this, Jake?
 
1 - 19 of 19 Posts
About this Discussion
18 Replies
9 Participants
Last post:
davewho1
Team Chevelle
posts
5.3M
members
131K
Since
1998
A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more!
Full Forum Listing
Explore Our Forums
Bench Racing Performance Engine Chevelle Tech Body Shop