Muncie M20 Rebuild Advice

[Mark P.]

I am restoring the chassis on my 65 Coupe and wanted to have someone go through the transmission. The car has about 115K Miles on it. It is a 300HP model. I drove the car for a year before I took it apart in 2011 and the transmission seemed fine.

Any advice on what to expect when the rebuilder goes through it ? What parts are usually changed ?

Any special experience or tools required ?

How can I get the case cleaned ? I was planning to try Aluminum Naval Jelly, diluted Muriatic Acid or Wheel Cleaner.

Thanks,

Mark

[Gary R.]

Re: Muncie M20 Rebuild Advice

Mark
If it wasn't whining, popping out of gear, or leaking you may be in good shape and maybe this is something you might want to tackle. Its is very doable and I have the front glad nut wrench if you decide to try it. Look for oil leaks at the countershaft front bore, pull the side cover and look at the gears and small teeth on each gear and syncro.

[Richard G.]

Re: Muncie M20 Rebuild Advice

Mark;
I have had good luck with soda blasting aluminum parts.
Castings come out looking like they were just cast.
Here is a picture of a headlight gearbox I cleaned by soda blasting it.



I used a Harbor Freight model, I thing it sold for $90 and $40 for the soda.
Don't blast on the grass, it will die if too much is left there.
I still haven't told my wife why the grass is brown in one area of the back yard.....

If you decide to rebuild it you might want to clean it with soda blasting before is is disassembled.
You could tape up the input shaft and use the drive-line yolk in the tail-shaft.

If you decide to just reseal it soda blast it and then pull the side cover and re-seal the shifting shafts and replace the cover gasket.
Don't forget to seal the side cover bolts if they are through taped.
To replace the output shaft seal use a large screwdriver to collapse the side of the seal then pry it out.
Remember the red stuff, on the seal OD, is a glue and a sealant. Makes them difficult to pull without collapsing it first.
There is no seal on the input shaft so you would be good to go.

Some times the transmissions like to leak from the counter shaft pin. To determine if it is not going to be an issue pull the transmission and leave the oil in it. Clean and then support it off the ground and let is set there for a couple warm days and see if it leaks from the shaft. Sometimes the counter shaft gets put in from the wrong direction and it will enlarge the shaft bore in the case and cause the leak. Best to know before hand it this is going to be an issue.
These gearboxes and anything could have happened in their long life. Close attention to detail is required to keep the bottom of your car oil free.
Rick

Rick

[Mark P.]

Re: Muncie M20 Rebuild Advice

Should this side cover pin be tight ? It can be pushed in with a finger. Should I just seal from the inside with black RTV to prevent leaks ? Any other way to tighten this up ?

[Richard G.]

Re: Muncie M20 Rebuild Advice

It appears the head of the pin is broken off?
It will require replacement if it is.

Here is what it should look like.



Search eBay for "SIDE COVER SCISSOR PINS & E CLIPS"
You can purchase one for $10 and $4.95 shipping.

If the replacement wobbles you can Loctite it in.
Rick

[Mark P.]

Re: Muncie M20 Rebuild Advice

Thanks Richard - I will check the pin versus the EBAY listing and if damaged then I will replace it. I will also use Loctite Blue if it isn't snug.

[Mark P.]

Re: Muncie M20 Rebuild Advice

I believe the pin was an early design without the large head like in the photo above from the EBAY listing. I decided to replace the cover. My rebuilder had one with the right casting number and a solid pin. Other than this pin and the bushing needed for the countershaft bore, all the parts not included in the standard rebuild kit were in very good condition. I went with the torque lock sliders. The rebuilder will test everything with my linkage and shifter installed on the bench to make sure everything works well.