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Discussion Starter #1
I have an M-21 in a '69 that jumps out of all gears while coasting. Under load or normal driving, it works fine. However, if I back off the gas while coming up to a stop sign, or coast down hill, the tranny jumps out of gear. The shifter is set-up properly, and appears to be moving the shift levers full throw. Any suggestions ?

[This message has been edited by BlackCamaros (edited 03-17-2001).]
 

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The teeth on the syncro slider and the mating teeth on the gear are worn out. The only fix I know of for this is to replace the gear and slider. If it is 4th gear you are talking about, some people have been able to put a shim between the gear and front main bearing and make it work a little longer.

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'69 RS/SS396 pro street
427/4spd/9"
 

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Did it just start doing it or did you just get the tranny. People used to take the dogs out of Muncies to make them shift better but they will not stay in gear when you let off the throttle.Take a look sometimes really bad forks and sliders will cause the problem but I think big gear heads idea is probably right it is just worn out.
 

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Discussion Starter #4
I guess I should have given the whole history behind this transmission. I purchased the tranny in 1985. I had it in the car a number of times, but took it back out because it kept locking up in fourth gear. Everytime I pulled it apart, I found the clutch dogs popped out and jamming the slider, as if the slider were moving forward too far. I replaced the clutch dogs and the front bearing, and still had the problem. I took it to a guy that used to own a transmission shop, and he ended up puttting a used input shaft and used synchros in it. The tranny sat under the bench up until two years ago, when I put it back into the car. It hasn't locked up, but it pops out of all gears during a coast condition. It does not shift as smoothly as I think it should, so I was thinking about replacing the synchros. I am also running synthetic gear lube.

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'69 Camaro, M-21, 4.11 Posi.
 

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The whole story makes a difference it sounds like someone has put some early parts in a later trans they are different. The sliders and dogs are different and will cause your problem.
 

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I have read in multiple places that you are not supposed to run synthetic lube in Muncie 4 speeds. Apparently the synthetics lubricate so well that the synchros don't grab the gears as well as when conventional lube is used. I know that RedLine, and maybe Amsoil too, make a synthetic lube that is supposedly compatible with manual trannys, but I don't anybody who has run it in their Muncie.

-Marc
 

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I am using Amsoil 75W90 in my Muncie with no problems. Do you think the guy that rebuilt the trans may have used Borg Warner T-10 sliders in it? They have a different groove cut in them for the dogs to locate in. Maybe he used T-10 dogs. I was going to say that a shift fork may be bent, but if it is doing it in all gears it must be something else.

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'69 RS/SS396 pro street
427/4spd/9"
 

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Discussion Starter #8
I looked through all my receipts, but could not find the one for the tranny repair. I do remember that the repair was for replacing the synchros and input shaft with used ones, and a new gasket set. Total bill for the repair was 125 dollars. As for the T-10 sliders, I really don't know if they are or they aren't. I know they haven't been replaced since I've had the transmission, but prior to my purchasing it, I don't know. As for the synthetic oil, I used Mystic 75W90, which may be unique to my area ( Janesville, Wi.) As for the oils compatability with a muncie, I guess I have no information regarding that. This is the first time I've used synthetic oil in anything, so I don't have a lot of experience in that area. It sounds like the easiest thing to try at this point is to change the oil. What do you guys think ? ? ?

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'69 Camaro, M-21, 4.11 Posi.
 

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Discussion Starter #10
At this point, it would be the cheapest and easiest route to take. This problem has baffled me for quite a while, because it does it in all gears, and without fail, every time I back off the gas. I've gone through the shifter( Hurst Competition Plus), replaced the tranny shifter arms, changed the shifter rod bushings numerous times, and checked the dead stops on the shifter a number of times. At this point, I'm open for suggestions.

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'69 Camaro/M-21/4.11
 

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I don't think oil will help. What I ment was the 1964 and 1965 Muncies used narrower sliders and shorter dogs. There is one other thing people used to take the sheetmetal dogs and gring down the edge to make it shift better that can cause the dogs popping out and binding problem you had
 

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I got it backwards it has been 20 years since I did a small shaft Muncie the later ones have narrower sliders does yours have a 7/8 cluster shaft?
 

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Discussion Starter #13
No, it has a 1". From the serial numbers I read off the case and tailhousing, I have the following:
Main case : 1966-1967
Tailhousing: 1963-1965
So, this may have been something thrown together. In any case, I did receive an e-mail from someone that stated, without a doubt, that the synchro solders were garbage. Big gear head stated the same thing back on 3-17. I haven't pulled the tranny apart yet, but at least I have a good starting point. Thanks everyone for the help and input.

Joel


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'69 Camaro/M-21/4.11
 
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