Muncie issue
 

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.

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.

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.

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

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.

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....

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.

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.

I agree, definitely an internal issue with the 3rd gear synchronizer assembly or the small teeth on the 3rd gear. Bill

I spoke to Paul Cangialosi yesterday and sent some pictures of the trans to him and he said the issue was the prior builder of the transmission used a locking third gear with a non locking slider. He also recommended hardened hubs, new sliders, and new shift forks. I’ll post some pictures when I revise receive the parts and start the tear down process.

Paul's an awesome guy,he's been a huge help over the years with parts for my M22s, and Top loaders,
and he was the only person in the country that was able to come up with a 6th gear set for my Richmond when I had all but lost hope.

I agree, he’s been extremely helpful in this entire process. Couldn’t ask for better or faster customer service. I called and sent some pictures to him, it was immediately diagnosed and he had all the parts in stock and shipped them the same day! I have received the parts and started the process. I must admit, I’ve never disassembled a transmission before so it was a little intimidating but with Paul’s help and his book on Muncie 4 speeds, it’s been a very straightforward process.

I was able to make some more progress on the Muncie this weekend. The main drive assembly is back in the case, new seals have been installed in the extension housing and it has been reinstalled. Only thing left now is installing the shifter shaft seals in the side cover and putting the new shift forks in and it will be ready for the shifter to go back on.

Before I pulled the trans, the clutch was starting to show it's age so it will be replaced with a fresh one from Hays. I'll have the pressure plate balanced with the flywheel after it's resurfaced. I had this done on the first clutch and it made a significant difference in the smoothness of the driveline.

Update:

The Muncie is now back together. I replaced all of the bushings and retainer springs with a kit from Paul, and the difference in how the parts fit together is night and day. There is no more slop in the rods/levers. I also realized since my trans has the stud type shifter shafts, I need the spacers Paul sells to take up the slop in the slots that locate them on the shafts, so I've got those on order.

I used the bread trick to get the pilot bearing out of the crankshaft, and then I cleaned it up so that it's ready for the oilite bushing to go in and reassembly. I've got the bushing in the freezer so hopefully when I install it, it will go in without damaging it. I found that the national bearings brand bushing part number PB-656-HD is non-magnetic as many in the parts store are and those can damage the input shaft due to the iron content.

Pressure plate and flywheel will be balanced this Thursday so hopefully I can get the car back together this upcoming weekend and test out my hard work! I think it will be a tremendous improvement from what I had before.

Never heard of using bread to push a bearing out. Must need half a loaf to get it compressed enough to create pressure. I always use chassis grease and an old input shaft for that. Probably messier to clean up than bread crumbs.

I think I used 3-4 pieces. It was much cleaner to deal with than grease for sure!

So, do you just beat the bread in with a rubber mallet? What is the procedure?

I tore the bread into small pieces and pushed as much in as I could by hand through the hole in the pilot bearing. Once I could get no more in there, I took a 10mm 3/8" drive socket, and a 6" extension, lined the socket up in the hole and hit the end of the extension with a hammer to compress the bread. I didn't have an old input shaft to use for this. I would then continue to add bread by hand after it was compressed and repeat the process until I got the bearing out. Took me about 15 minutes. I tried to use a pilot bearing removal tool, but after 5 tries and it not working, I went to the bread, haha.

https://youtu.be/Lbao3zkxV3c for reference

I never had any luck with the removal tool either. After thousands of heat cycles, those bearings seem like they are welded in. As you may have noticed, it took a lot of pressure to break it loose and then it would move with less force.

Yes, you are right. It did not want to move at first, but once it got the pressure on it from the bread being packed in there, it slowly worked its way out.

Wet paper works also

And bar soap.

Jason

Progress! My crossmember was looking pretty rough, so I wire wheeled it, and shot it with some primer and paint to clean it up. I was able to get the flywheel resurfaced and balanced with the pressure plate. I started putting it back together, but one of the tabs on the clutch fork was broken and I thought I was done for the day at that point, but since I'm only 20 minutes from Auto Metal Direct I was able to source a new one and get the transmission back in. They had a sweet 69 Camaro SS350 automatic in the lobby, so it was a good excuse to go!

Still have to get the reverse lights hooked up, shifter handle/console plate reinstalled, driveshaft in, exhaust reconnected, and plug the distributor back in and re-time the engine, but I'm getting close now!

Nice to have a lift for this work. Brings back memories of bench pressing my M-22 back into my car laying on a cold concrete slab in my parents carport in the middle of winter with the ice cold wind blowing after changing out the clutch.

I'm sure many here have a similar experience from their teen years. Good times.

Your throwout bearing is sitting on the fork wrong.

That it is. Nothing like a piece of humble pie in the morning. Better to know that now that after the car is running. Thanks for pointing it out.

Yes it is. I’ve had to pull this one out before in my early 20s without a lift. After doing it with a lift this time, I’ll never go back to the old way haha.

And that starter bolt... can't believe that doesn't let the starter move and slip on the flywheel teeth.

That’s next on list. I was waiting to be flamed for it and I don’t mind. Honestly, I haven’t worked on the car much to amount to anything over the last ten years. Stupid stuff I did as a teen and in my early 20s which there is no excuse for. I do recall that the bolts that came with the starter were cheap and actually stripped their threads when torqued to the spec that the starter installation instructions indicated and in a time crunch back then to put it back together, I used the only starter bolts I could from the parts store. Now that I have my own shop instead of working out of my parents single car garage, I’m able to leave it and come back if I don’t the parts I need to put it back together correctly.

I will say though, in the time it’s been on there, I haven’t had a single issue with it.

@L72Chevelle, I got the throw out bearing orientation fixed this afternoon. Sucked taking it apart but glad you pointed it out and it’s fixed correctly now.

I was wondering what the story was about that bolt, seeing as how meticulous you have been with this transmission venture. Gotta admit, I've been there and done that too. Might be time to upgrade to the mid 90's GM mini starter with the offset bolt pattern. They are one of the best starters out there for clearance and avoiding heat soak.

Yeah, my car has the 153 tooth flywheel & 10.5" clutch so I have to use the inline bolt pattern. Maybe I will have better luck sourcing bolts for the mini-starter that's currently on it now. If not, it looks like the 90s LT1 Corvettes used a 153 tooth setup and bolts for those should be readily available.

I would recommend checking your drive shaft angles when you are finished with the transmission installation. That transmission mount is thicker than a stock mount and can cause problems with the drive shaft angle. You might have to adjust the pinion angle to compensate.

Thanks for the suggestion. However, I've been running this mount for about 15 years or so now and I have no vibration issues. I checked the pinion angle when I first converted the car to a four speed and had to use some shims from competition engineering to get the angle correct.

I got the car running again last night but I haven't taken it off of the lift yet. The clutch needs adjusting some more due to the tires still wanting to turn when the pedal is still fully depressed, but I have reverse and 4 forward gears so I consider that a win! I got a inspection plate cover ordered today for the bellhousing and the correct length starter bolts should be arriving any day now. Should be ready to drive soon!

Actually it isn't unusual for the tires to turn in this situation. I would drop it on the floor and see if you feel/sense any drag from rpm change. That will give you a feel for if it is difficult to get in gear and where the clutch starts to engage for further adjustment.

X-2 Give it an 1" of free play and if everything is good, you should be good to go. Bill

Good deal, thanks for the input gentlemen. I've learned a lot through this project!

I'm tackling the starter bolt situation now and I've read that the GM 12338064/Dorman 678-107 bolt is the solution for "mini" starters since the bolt has a 10mm shank and knurl for the starter, and a smaller 3/8" knurl for the block so that it locates correctly. I will say that the knurling on the new bolt definitely provides a much tighter fit on the starter but, it appears that the bolt is sticking too far out of the starter, especially the larger knurling that engages the starter. I ran one of the bolts up by hand through the starter, into the block, and it stopped about 1/4"-5/16" before the machined face of the starter would contact the block. I do not want to damage the block by using the wrong bolt. I took some pictures of the bolt as it is installed in the starter and various other dimensions. Have any of you guys ran into this? Ideas? Should I junk this starter and get a GM type mini starter for a early 90s Corvette? It had a 153 tooth flywheel like my car does.

*under head bolt length- 4.31"
*knurl diameter on bolt for starter- .398"
*knurl diameter on bolt for block- .371"
*distance from machined face of starter to end of knurl for block engagement- .378"
*thickness of starter flange- 3.110"