Muncie transmission speedometer gear fitting "bullet" question

[Stephen B.]

There's a rubber seal inside of the transmission speedometer gear bullet. Is there a way to replace the rubber seal inside of the bullet? I ordered a seal that looks like it's for the outside of the bullet. It's part number 3869910. Thanks

[Jim D.]

Re: Muncie transmission speedometer gear fitting "bullet" question

Are you looking for the seal on the right? Almost any auto parts store should have either one.

[Stephen B.]

Re: Muncie transmission speedometer gear fitting "bullet" question

I both of these seals. There's a rubber seat inside of the bullets that is similar to the seal on the left in terms of construction but thicker.

[Jim D.]

Re: Muncie transmission speedometer gear fitting "bullet" question

Can you post a picture? Those are the only two seals I've ever seen used and the one on the right wasn't added until very late 65.

[Joe L.]

Re: Muncie transmission speedometer gear fitting "bullet" question

There's a rubber seal inside of the transmission speedometer gear bullet. Is there a way to replace the rubber seal inside of the bullet? I ordered a seal that looks like it's for the outside of the bullet. It's part number 3869910. Thanks

Stephen-----


Seal GM #3869910 is the one shown on the right side in the photo. It installs INSIDE the fitting ("bullet"). The old seal must be pried out and the new one pressed in, pressing only on the frame of the seal. The seal on the left in the photo is the o-ring type seal that installs in the groove on the OUTSIDE of the fitting. It is currently GM #10054241. There are no other seals involved.

[Stephen B.]

Re: Muncie transmission speedometer gear fitting "bullet" question

Thank Joe and every one else. I also looked at an old Street Rodder article on the matter and realized that I had not pried the metal ring of the old seal out. Duhhh!!!! lol. My bad. Thanks for everyone's help.

[Richard G.]

Re: Muncie transmission speedometer gear fitting "bullet" question

Another issue is the plastic gear that gets worn where the seal contacts the gear's shaft. I can't tell you how many seals have been replaced without fixing the leak because of the worn gear shaft. The gear has spiral grooves to return any oil to the inside of the transmission. The continuous groove at the end will appear as being part of the spiral groves, it is not. Being manufactured of nylon the seal surface does not last long. Their are two method of repairing the leak with a worn gear.
1) Replace the gear with a new one, all the used ones are also worn.
2) Use the aftermarket seal that relocates the sealing surface further out on the gear to an unworn area.
Both work well. It may also be possible to not seat the replacement seal all the way back against the housing and in essence have the same situation as the after market seal. I am not sure this works as well as it might because the area left behind the seal can hold oil.
The aftermarket is designed to avoid this pocket. I suggest one of the first two repairs.
This seal is the same one used in many of the GM automatics. The aftermarket seal (with the relocated lip) should be available at almost any automatic repair shop. They are easier to change as their is no press fit. Just a small C clip that retains them.
You didn't indicate the year. Possible their are steel gear in some of the early stuff. If that's the case forget the above notes at they would not wear like the nylon gears.
Rick

[Joe L.]

Re: Muncie transmission speedometer gear fitting "bullet" question

Another issue is the plastic gear that gets worn where the seal contacts the gear's shaft. I can't tell you how many seals have been replaced without fixing the leak because of the worn gear shaft. The gear has spiral grooves to return any oil to the inside of the transmission. The continuous groove at the end will appear as being part of the spiral groves, it is not. Being manufactured of nylon the seal surface does not last long. Their are two method of repairing the leak with a worn gear.
1) Replace the gear with a new one, all the used ones are also worn.
2) Use the aftermarket seal that relocates the sealing surface further out on the gear to an unworn area.
Both work well. It may also be possible to not seat the replacement seal all the way back against the housing and in essence have the same situation as the after market seal. I am not sure this works as well as it might because the area left behind the seal can hold oil.
The aftermarket is designed to avoid this pocket. I suggest one of the first two repairs.
This seal is the same one used in many of the GM automatics. The aftermarket seal (with the relocated lip) should be available at almost any automatic repair shop. They are easier to change as their is no press fit. Just a small C clip that retains them.
You didn't indicate the year. Possible their are steel gear in some of the early stuff. If that's the case forget the above notes at they would not wear like the nylon gears.
Rick

Rick------


Yes, it's always best to replace the driven gear when the seal is replaced. The 19-22 tooth gears which cover the vast majority of 1961-1981 applications (except THM 400) are still available from GM for a very modest price. Earlier applications used mostly nylon gears, too, but with a longer shank. These are not available from GM but are easily available in the aftermarket. Very numerically low (e.g 2.73:1) and numerically high (e.g. 4.88:1) often used steel driven gears.

[Stephen B.]

Re: Muncie transmission speedometer gear fitting "bullet" question

I appreciate everyone's input.