[boater bill]

My 70 M-20 has started a bad habit of popping out of 4th gear when braking, not coasting or braking in the other gears. I had rebuilt the trans with new bearings and syncros about 5K miles ago. I opened it up for inspection when I installed it last year and again when I put in the 461 6 months ago. No power shifting with the 461 to preserve the Muncie best I can. 11" clutch and diaphram pressure plate.
Hurst Comp plus shifter with end stops fully backed out. I put in a real short 3/4 shifter lever on the trans to make sure I had full travel, but still pops out of gear when braking about half of the time. I am not looking forward to dropping the trans to r&r syncros and maybe input gear.

Is there any thing else that I should look into before dropping it out?

[ponjohn]

What about a shifter adjustment?

I recall putting a 3/16 drill bit in the shifter to align all the rods.

[Ollie]

I always thought Popping out of 4 th was a symption of bad syncros too, You state the transmission was rebuilt 5 K ago with new syncros and bearings. Was the cluster gear shaft replaced? Maybe the shaft has some wear causing the trans to jump out of 4th.

[boater bill]

The cluster gear shaft had no grooves or taper and I replaced the needkle bearings when I rebuilt it. I use the 3/16" L tool that came with the shifter to align the shifter and am using the aluminum bushings for the rods to not have any slack.

[jmt455]

Couple of other ideas...

I went through similar aggravation and the problem went away after replacing the yoke; it was worn.

Also, make sure the output shaft isn't bottoming out on a burr or ridge in the yoke splines.

[HWYSTR455]

Would be surprised how many main shafts are bent, and that's a big cause of jumping out of 4th. Check the yoke as mentioned too, and the bearing in the tailshaft housing.

Call SK Speed, talk to Brian. He will school you on what the possible causes are, and provide valuable info to boot.

.

[stevep]

Put the shifter in 4th gear and disconnect the 3/4 rod from the 3/4 lever and see if you can push the 3/4 lever further into 4th. If so, your shifter stops need adjusting because you are not getting full throw.

[HWYSTR455]

I called a buddy and he says it's the blockers and blocker rings. Also said there are ones that are torque blockers, and found these:

http://www.dandltransmission.com/slider.html

mentioned to make sure the blocker synchro keys are in place and the rings.

He said that too much input shaft play can do it too, or a toast pilot. Said to check the front bearing cover for excessive wear.

In extreme cases, the intermediate plate area that retains the bearing gets worn, and allow the bearing to move around.

Main shaft was lower on the list, but he said he's seen that too. Over 450 ft lbs is where you see more of that. He said if you don't know the history of the trans, or it has a lot of miles (main shaft), replace it. They're like $100. He said same with the intermediate plate.

Completely toast forks will do it too, but that's pretty obvious.

Here's an exploded diagram, look at the second pic, #15, #89 & #91 items.

http://www.tbtrans.com/muncie_4_speed.htm#diagram

.

[boater bill]

Thanks HWYSTR, that is what I was afraid of. I'm thinking of installing new torque lock slider, keys and syncro assembly on the 3/4 and check everything else out while there. I might also replace the mid plate for a steel one since I am now operating about 500 Ft/pounds versus the Cammers 250.

[Half-Inch Stud]

Yea, I had a M21 HD that would bump out of 4th. Always put fault to the 3 tabs, MAYBE the blocking ring, now I see the input shaft (pilot bearing) theories showing up. In all scenarios, the trans has to get pulled.

Except for the shift-rod alignment comment: wonder if that holds any probability of success.

[HWYSTR455]

Yeah, you're right at the line with 500 ft lbs. When I had a stout 455 in the 'bird, had to go through the m20 every 3 years or so. Wish they had super cases back then! Consider moneying up for one of those, will make a bunch of headaches go away, especially if it's an older case. Does it weep a little out of the countershaft pin bore in the front of the case? Don't even think twice, do the midplate, especially if it's an aluminum one. And do both blockers/sliders if you're doing one.

It's all starting to come back to me now, remembering my munchie woes. Close inspection is key on a rebuild, and clean, just like an engine assembly. I never liked the way they shifted with synthetic lube either.

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[HWYSTR455]

Originally Posted by Half-Inch Stud

Yea, I had a M21 HD that would bump out of 4th. Always put fault to the 3 tabs, MAYBE the blocking ring, now I see the input shaft (pilot bearing) theories showing up. In all scenarios, the trans has to get pulled.

Except for the shift-rod alignment comment: wonder if that holds any probability of success.

I never had any luck with the roller pilots. Some are just plain cheaply made, and fail quick (roller pins). Then there are the ones that are open to one side, and you have to pack (ball bearings). Too much and you were doing a clutch. Too little and you would eat it up. And you had to make sure the input wasn't chewed up at all too, and fit the bearing. As well as super-perfect bellhousing alignment. So I went back to brass. I've seen where some force the trans into place and pop the brass ones too. That's not good. And some cranks get worn out and won't hold a brass. That's not good either! But still, I prefer the original style, they work fine, and are easier to install properly. Fail less too.

.

[Skip Fix]

A couple fo simple things I had do the same-tranny bolts to the bellhousing had loosened. Another car the pilot bearing was worn and caused it to jump out-found that when we pulled tranny to check it and replacing it fixed that one.

[boater bill]

I had a new pilot bearing installed when the 461 was built.
I just got off the phone with the local Muncie Guru, Jet boat Bill, and will be heading over there later today. He felt certain the sliders are the problem. He has the Torque lock sliders in stock and a steel midplate as well.

[HWYSTR455]

Yup, sounds like he's on the same page as the guy I spoke with, sliders/blockers/keys. Nice he has them in stock! Midplate, sure that's a good choice. Good luck, and let us know yoru results! Close the loop on the thread sowhen others search they get results.

.

[geeteeohguy]

I had the same problem with the M20 in my '65 about 20 years ago. The trans was rebuilt 10 years before that. It turned out to be nothing more than a worn out front driveshaft yoke and corresponding worn out tailshaft bearing. It was an easy fix, and it's still fine to this day. I'd check out the driveshaft and yoke first. Super easy to do.

[GTO Dan]

Originally Posted by HWYSTR455

Call SK Speed, talk to Brian. He will school you on what the possible causes are, and provide valuable info to boot.

.

Better hurry...Brian of SK Speed is retiring.

[HWYSTR455]

Originally Posted by GTO Dan

Better hurry...Brian of SK Speed is retiring.

Wow, hadn't heard! He deserves it though! Incredible, his contributions to hot rodding and all.

.

[boater bill]

I just left Jet Boat Bill's shop after giving him a test drive. He agrees it is most likely the sliders and keys the way it is acting. He will do a total refresh and Torque lock sliders next week.

Thanks for the input guys.

[boater bill]

Update

Had an allergic reaction to the chemo the first part of November and then the holidays. So I just was able to pull the transmission today and drop it off. The input gear was too worn to use behind the 461, so we made a deal. Jet Boat Bill had a used, less than 1000 miles, complete set of gears for a 10 spline input M-22. He is going to install the Italian Rockcrusher gears with torque lock sliders, new USA bearings and synchros for just a bit more than I was looking at for a rebuild and 4th gear. The first grear going to 2.20 shouldnt be a problem with my 3.23's and the amount of torque I have across the board.

He will have it done tomorrow and getting my friends ready to help with the Muncie bench press.

I feel better about having the rockcrusher behind the Beast 461 for sure.