Muncie issue

[Andy]

I’ve got an M20 Muncie in my 67 Camaro. I bought it completely rebuilt from a reputable builder and it’s got around 8-10k miles on it. It’s currently behind a 525 HP 406 small block. My problem is when I am in 3rd gear, and I decelerate while leaving the trans in gear, it pops out of gear. What would be causing this to happen? It’s very annoying and I want to fix it.

Thanks.

[Jimlt4383]

Originally Posted by Andy

I’ve got an M20 Muncie in my 67 Camaro. I bought it completely rebuilt from a reputable builder and it’s got around 8-10k miles on it. It’s currently behind a 525 HP 406 small block. My problem is when I am in 3rd gear, and I decelerate while leaving the trans in gear, it pops out of gear. What would be causing this to happen? It’s very annoying and I want to fix it.

Thanks.

Look for wear on the little gear teeth or slider teeth that slide on to them to engage 3rd gear. I usually replace the slider and gear at the same time. It's not that bad of a job.

[Too Many Projects]

I suggest inspecting the bushings on the ends of the 3-4 rod for any wear or abnormality. Check the fastener at the shift shaft for any wear or looseness that allows the arm to move on the shaft. Also, that the adjustment is still correct. Components seat in and can be off enough that the 3rd gear slider may not be traveling far enough to fully engage the keys in the hub in the detent in the slider to help keep it engaged. Do the simple stuff first before looking at an internal cause.

[Andy]

Thank you both for your feedback. I will put the car on the lift and begin the inspection process. I’ll post back with what I find.

[LT1vette]

Send it back to the builder.... Not a external problem, internal that should have been addressed on the rebuild..

[SuperNovaSS]

Andy,

Has this always been an issue or is it fairly new? I agree with Mitch. If it is not going all the way into gear then it could pop out on deceleration. Check bushings and the adjustment by putting a proper drill bit throug the neutral hole in the shifter and check your adjustments. If it’s a Hurst shifter, also be sure the detent limiter bolt is not too tight since limits how far the lever pushes the fork.

LT1Vette,

I disagree on sending it back to the builder. We don’t even know if this is a recent problem or it has been happening all along. Why do you say with certainty that it is an internal issue? After 10k miles, lots can happen. If this has been happening for 10k miles, then lots of damage could have happened simply from having things out of adjustment this long. If it is a recent issue, it could be very simple. Calling the builder to troubleshoot may be an option though.

Jason

[Andy]

Originally Posted by SuperNovaSS

Andy,

Has this always been an issue or is it fairly new? I agree with Mitch. If it is not going all the way into gear then it could pop out on deceleration. Check bushings and the adjustment by putting a proper drill bit throug the neutral hole in the shifter and check your adjustments. If it’s a Hurst shifter, also be sure the detent limiter bolt is not too tight since limits how far the lever pushes the fork.

LT1Vette,

I disagree on sending it back to the builder. We don’t even know if this is a recent problem or it has been happening all along. Why do you say with certainty that it is an internal issue? After 10k miles, lots can happen. If this has been happening for 10k miles, then lots of damage could have happened simply from having things out of adjustment this long. If it is a recent issue, it could be very simple. Calling the builder to troubleshoot may be an option though.

Jason

Jason,

I've noticed it the last couple of times I've drove the car over the past year or so and it's progressively gotten worse. I'm lucky to get a chance to drive it every 3 months due to my current schedule. My drive on Saturday wasn't really enjoyable because it continued to pop out of gear, much worse than before.

I have had to send the trans back to the builder once before, but that was due to an internal failure of 3rd gear. Several teeth broke off of it during a spirited drive,(no missed gears or powershifting) and was told it was replaced with a new one. This was around 7 years ago and has only had about 3-4 K miles put on it since then.

When I first put the trans in it, if I recall correctly, I used metal bushings on the linkage, something similar to this. https://www.speedwaymotors.com/Speed...et,408860.html The shifter (Hurst competition plus) was new, as was the linkage and shift levers. I did the adjustment on the shifter with the trans out of the car prior to first putting it in so that I could easily see everything. I'll go through and check the condition of the bushings, the linkage adjustment, stop adjustment and shift levers first before I pull the trans to check the internals.

Thanks for the feedback.

[LT1vette]

Originally Posted by SuperNovaSS

Andy,

Has this always been an issue or is it fairly new? I agree with Mitch. If it is not going all the way into gear then it could pop out on deceleration. Check bushings and the adjustment by putting a proper drill bit throug the neutral hole in the shifter and check your adjustments. If it’s a Hurst shifter, also be sure the detent limiter bolt is not too tight since limits how far the lever pushes the fork.

LT1Vette,

I disagree on sending it back to the builder. We don’t even know if this is a recent problem or it has been happening all along. Why do you say with certainty that it is an internal issue? After 10k miles, lots can happen. If this has been happening for 10k miles, then lots of damage could have happened simply from having things out of adjustment this long. If it is a recent issue, it could be very simple. Calling the builder to troubleshoot may be an option though.

Jason

I think you answered the question. The OP did not gives all the info at first to help us with the diagnosis. I thought it was a recent build within the year, he was driving the car quite regular and this problem had just popped up. If I follow the story right, the tranny was built a number of years ago. I would hope that this problem has not been ongoing for that reason.
I would call the builder before removal and see what he says, may be just an adjustment, jam nut has backed off causing the problem....

[Too Many Projects]

With the, more complete, history on this, I'm beginning to think it may well be an internal issue. Steel bushings and new shifter eliminate a few of the possibilities. Could still be a loose arm, stop bolt nut loose and allowing the bolt to work it's way down or linkage out of adjustment, but getting worse with time/wear and with the same 3rd gear issue from the past, just seems to lead me to the hub/slider assembly, or another gear problem, now with the engagement cogs.
Talking with the builder may give insight, if he can recall, or have a record of exactly what he did when the gear was replaced.

Pulling the side cover will give a visual of the gear cogs, but they are not the primary component of keeping the slider engaged. Yes good cogs that aren't all rounded and chipped do help, but the keys (dogs to many) in the hub have that task as well as the fork springs and levers in the cover. The keys are under tension from a large "C" spring under them and between the keys being worn from use and the springs occasionally breaking, they are the main reason for popping out of gear. Broken springs and worn levers in the cover can add to the problem.

If you do remove the trans and side cover, moving the slider to second gear should have a slight click sound and the keys pulling the slider into position the last slight bit. You'll probably have to move it a few times to get the syncro ring and gear cogs lined up perfectly to "feel" the keys engaging. If you don't feel/hear the same positive engagement going into 3rd, my bet would be on the hub/slider assembly being an used component that is now worn enough to not hold the slider in place tightly enough.

[RALLY]

Make sure linkage is adjusted properly. Engine off shift thru all gears and make sure they are all engaging. Get car jacked up and have someone watch underneath to see if the gears are engaging again and if possible have a extra person watch the linkage and listen to the engagement. You can feel that on the shifter and hear it too. Linkage adjustment maybe. If not pull tranny and have a good reputable trans guy who knows Muncie and Saginaw 4 speed trans well and go thru it. Good luck.