Muncie Transmission Countershaft to Case leak

[Eric D.]

Re: Muncie Transmission Countershaft to Case leak

Rich, I found an M-20 non-VIN P7B22 complete core...
Also found an M-21 non-VIN P7A04 complete core...

Thanks... Eric........... sorry about the Tom

[Richard M.]

Re: Muncie Transmission Countershaft to Case leak

Eric, Thanks. I will get in touch when there's time. That M21 may appear as a viable candidate. Thanks for checking.

Tom, You're scaring me.....about all of those rollers. All I can imagine is rollers all over the floor of my shop.

Peter, Yes, time is of the essence as I have much to do the next several weeks to prepare. I can now check this setback off the list.(and get ready for the next one)

Et al......Thanks for your ideas.

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Update. I did the final cavity fill with RTV, troweled it flat, covered with a small piece of waxed paper and reinstalled the unit last night. No leaks so far. After the dust settles we will decide on a case repair/replacement strategy.

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Also, After some research and measurements I learned something yesterday morning before re-installing this transmission. The speedometer Drive gear needed a look at as I needed to get a replacement speedometer "Driven Gear". I was worried after some reading that I may have to change the internal Drive gear.

The speedometer was way off on this car. I found a Large 8 tooth Drive gear in the unit(via the measure the gear width method= 0.610" width) and a Red Driven gear inside. This car previously had a 4.11:1 Posi(now 3.70), and stock 7.75x15 tires. My calculations from the calculator HERE , told me I had quite a error. The Red (small gear) is for a 3.56 ratio. No wonder the speedometer was way off. I had the speedometer calibrated at Bill Harrison's a while ago and it was not too far off when he dialed it in perfect.

In my research, since I have a "Large" drive gear, but now the 3.70 gear set resides in the differential case. My result says I need a Silver Driven (small gear). Would you agree with this?

It appears that if you have a 3.70:1 gear set, you can use either Large or Small Drive gear, and choose it's properly toothed mating driven gear, 22 teeth. I guess as luck would have it, on my side this time, either internal gear would have been usable for a 3.70:1 rear diff ratio as I could use either 22 tooth driven gear, Silver or Green, based on which Drive gear was installed. In my case, I don't have to tear into the tail housing to change the Drive Gear.

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Below is a text copy/paste of the St Louis calc page for future reference if their server goes down, which it did yesterday morning for a while.

From http://www.stl-vettes.com/65Vette/GearCalc.htm? Credits to GB Janssen for this great tool.

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[John H.]

Re: Muncie Transmission Countershaft to Case leak

Here's the current version of my Corvette Speedo Tech Sheet, from which the St. Louis calculator was developed (credit is also due to Joe Lucia and Wayne Midkiff).


CORVETTE SPEEDO GEAR TECH.doc

[Tom P.]

Re: Muncie Transmission Countershaft to Case leak

I have zero issues with the chart posted above by John.
I will only add a couple of things. First, the PLASTIC DRIVE gear which is mentioned for 68-70 Muncies. It is retained by a metal spring "P"shaped clip. When I rebuild one of these transmissions, BOTH that spring clip and plastic drive gear go straight to the garbage can and I replace them with the appropriate press on steel gear.
Also, there is (or was) a small 17 teeth driven gear available (purple-3987917) to be used with the large drive gear (3708144-.610 wide). This would be used for very high gear rearends such as a 2.73 or 3.08, depending on tire size. The 17 teeth gear is no longer available from GM, but within the past few days I've seen it available online from one of the big speedo vendors. I use this gear in the Richmond 5sp in my Cutlass with a 2.41 rear.

[Richard M.]

Re: Muncie Transmission Countershaft to Case leak

Here's the current version of my Corvette Speedo Tech Sheet, from which the St. Louis calculator was developed (credit is also due to Joe Lucia and Wayne Midkiff).
[ATTACH]67332[/ATTACH]

John,et al......

Thanks very much for this. It confirms my choice for the driven gear.

Rich

[Joe L.]

Re: Muncie Transmission Countershaft to Case leak

I have zero issues with the chart posted above by John.
I will only add a couple of things. First, the PLASTIC DRIVE gear which is mentioned for 68-70 Muncies. It is retained by a metal spring "P"shaped clip. When I rebuild one of these transmissions, BOTH that spring clip and plastic drive gear go straight to the garbage can and I replace them with the appropriate press on steel gear.
Also, there is (or was) a small 17 teeth driven gear available (purple-3987917) to be used with the large drive gear (3708144-.610 wide). This would be used for very high gear rearends such as a 2.73 or 3.08, depending on tire size. The 17 teeth gear is no longer available from GM, but within the past few days I've seen it available online from one of the big speedo vendors. I use this gear in the Richmond 5sp in my Cutlass with a 2.41 rear.

Tom------


The clip used with the 68-70 nylon drive gear is GM #1373122 which is still available from GM. The advantage of using the nylon drive gear and clip is that the clip ensures that the gear is perfectly positioned on the shaft with no guesswork or measuring. I never had a bit of trouble with the nylon drive gear in 200,000 miles and 35 years of operation. However, the nylon drive gear and clip can only be used on main shafts in 1968-70 Muncies.

By the way, I believe most THM automatic transmission applications use a nylon drive gear and I've never heard of any problems with these.

[Joe R.]

Re: Muncie Transmission Countershaft to Case leak

Just a note for you professional transmission builders. Using axle grease is a no/no for installing the needle bearings and spacers in the countershaft. Why? because it does not allow the transmission lubricant to do it's job as it seals out the lighter weight oil and sometimes causes the countershaft to fail. What do you use??? Vaseline is used by rebuilders as it melts almost immediately when hot and allows the transmission oil to do it's job. The tip of the week!
Merry Christmas and a Happy New Year!

JR

[Gary R.]

Re: Muncie Transmission Countershaft to Case leak

Joe is correct.

I like to use the trans "grease" either the green or red. It is pasty but melts once hot. It holds the rollers in place great, no dummy shaft needed using this product. NAPA sells it as Trans goo.

Have a safe and happy Xmas!

[Joe R.]

Re: Muncie Transmission Countershaft to Case leak

Joe is correct.

I like to use the trans "grease" either the green or red. It is pasty but melts once hot. It holds the rollers in place great, no dummy shaft needed using this product. NAPA sells it as Trans goo.

Have a safe and happy Xmas!

Thanks for the tip Gary,

I'm gonna drop by NAPA the first of the week and get me some of that "GOO".

And Tom Parsons is absolutely correct when he says to fix it right or pay for your mistakes later.

JR

[Gary R.]

Re: Muncie Transmission Countershaft to Case leak

Joe to be more precise, it is Dr Trannies AssembLEE Goo- green. They make a blue as well but the green is what I use and never had a problem.

http://www.summitracing.com/int/parts/lbg-19250/overview/