# help muncie 4 speed destroyed



## mbspeed (Sep 25, 2012)

Hi All ..I was out flogging my 67 GTO its got a 455 maybe 500 HP not to sure any how....I need some info/help... looks like a gear or some internal part of my Muncie shot hole through the case so I am looking into a new 4 speed don't have the $$$ now to have a 5/6 trim/TKO conversion the 4 speed was a m20 wide ratio . it could have been worn because got a gear grind going into 4 all the time ..would a m20 or m21 rebuild be a waist of money I know m22 is stronger witch 4 speed has the best off the line power I have 3.55 rear diff will a super T 10 fit with no mods any info would help :nonod:


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## geeteeohguy (Feb 2, 2008)

Super T-10 is not as strong as a Muncie. A Ford Toploader is stronger, as is the original base Dearborn 3 speed that came in these cars. It's also made by Ford. Muncies can be made stronger by iron midplates, upgraded parts, etc. Not cheap. For a 3.55 gear in the rear end, you want to stick with the wider ratio M20 for the best performance off the line. Stating the obvious: if you have a 500HP 455 powered '67 GTO, you will have to park it until you have the $$$ to properly replace the transmission. Cheaping out will cost you more $$$ long term, as cheap/worn units will become the 'fusible link' in your drivetrain! There are several very reputable and reasonable Muncie guys out there. All you need to do is find the one that best suits your needs. The cheapest way to deal with 500 HP is simply bolting in a TH400 automatic. Bulletproof, and stronger than a manual gearbox. About half the cost, too. But also about half the fun of rowing your own!!! I'd keep it a stickshift, personally.


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## ALKYGTO (Mar 29, 2010)

Agreed ^ Also remember that the M21 and M20 have a 10 spline input shaft and the M22 and TKO have 26 splines (more splines = more strength) so you will have to change your clutch disc but not the pressure plate if it is in good shape.

I agree also on keeping it a stick. :thumbsup:


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## mbspeed (Sep 25, 2012)

geeteeohguy said:


> Super T-10 is not as strong as a Muncie. A Ford Toploader is stronger, as is the original base Dearborn 3 speed that came in these cars. It's also made by Ford. Muncies can be made stronger by iron midplates, upgraded parts, etc. Not cheap. For a 3.55 gear in the rear end, you want to stick with the wider ratio M20 for the best performance off the line. Stating the obvious: if you have a 500HP 455 powered '67 GTO, you will have to park it until you have the $$$ to properly replace the transmission. Cheaping out will cost you more $$$ long term, as cheap/worn units will become the 'fusible link' in your drivetrain! There are several very reputable and reasonable Muncie guys out there. All you need to do is find the one that best suits your needs. The cheapest way to deal with 500 HP is simply bolting in a TH400 automatic. Bulletproof, and stronger than a manual gearbox. About half the cost, too. But also about half the fun of rowing your own!!! I'd keep it a stickshift, personally.


hum....TH 400 this car was made with a TH 400 I did a conversion I have never destroyed a manual the TH 400 blew up few times already .... I always believed/ think auto trans are weak.......manuals are better:wink2:


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## mbspeed (Sep 25, 2012)

ALKYGTO said:


> Agreed ^ Also remember that the M21 and M20 have a 10 spline input shaft and the M22 and TKO have 26 splines (more splines = more strength) so you will have to change your clutch disc but not the pressure plate if it is in good shape.
> 
> I agree also on keeping it a stick. :thumbsup:


Me too ....manual all the way ..I don't think I destroyed the case I saw all gear oil on floor and shifter was jammed ...when I got under car today cleaned off all dirt/oil case is ok may need an over haul just looks like lost a seal but it does have a problem going into 4 th gear before all this happened will always grind in 4th atriot:


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## PontiacJim (Dec 29, 2012)

Agree with all others. You may have 500HP, but a whole heck of a lot more torque. The Muncie M-20 & M-21 is not really strong enough at these HP & Torque levels. The Muncie M-22 Rockcrusher was designed for drag racing & road racing. It has a straighter cut angled gears which give it a "whine" and harder alloy gears.

There is an aftermarket maker of a new M-22's that offers both close & wide ratio gears. This trans is for big HP & Torque, but expensive. At this price, this is why I went with a TKO-600 5-speed having overdrive.
NEW Auto Gear Super Case Muncie M22 4-Speed Rock-Crusher 26/32spl Street/Strip. Last 2 Days of Summer Sale - Midwest Muncie | M22 Rockcrusher | Muncie 4 Speeds

All to often when you build a big HP & Torque engine, you need to beef up the drivetrain to handle the power. The engine will find the weak link in your drivetrain, ie your trans, rear-end, U-joints, etc.. Of course this adds to your budget.

I don't know if you are using wide/sticky tires, but keeping narrower tires on the back is a way of allowing the power to break the tires loose rather than grabbing and placing all the HP & Torque into the driveline and breaking something. It may not be what you want, but it may save your driveline until you can go with stronger parts. Once you put in the stronger trans, it could be the rear-end that lets go next. So eventually, that BIG Pontiac engine is going to make you buy all the heavy duty parts whether you want to or not.:thumbsup:


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## mbspeed (Sep 25, 2012)

PontiacJim said:


> Agree with all others. You may have 500HP, but a whole heck of a lot more torque. The Muncie M-20 & M-21 is not really strong enough at these HP & Torque levels. The Muncie M-22 Rockcrusher was designed for drag racing & road racing. It has a straighter cut angled gears which give it a "whine" and harder alloy gears.
> 
> There is an aftermarket maker of a new M-22's that offers both close & wide ratio gears. This trans is for big HP & Torque, but expensive. At this price, this is why I went with a TKO-600 5-speed having overdrive.
> NEW Auto Gear Super Case Muncie M22 4-Speed Rock-Crusher 26/32spl Street/Strip. Last 2 Days of Summer Sale - Midwest Muncie | M22 Rockcrusher | Muncie 4 Speeds
> ...


Got it ...I have 235/60/15 street tires also have a 3.23 posi 12 bolt out of a 69 chevelle in garage.. got it from same car the Muncie out of I was thinking the diff would be the first to fail when I got the 4 speed it was rebuilt but with all stock parts ....a 5 speed would be bset but prices are over $3000 got save up


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## PontiacJim (Dec 29, 2012)

mbspeed said:


> Got it ...I have 235/60/15 street tires also have a 3.23 posi 12 bolt out of a 69 chevelle in garage.. got it from same car the Muncie out of I was thinking the diff would be the first to fail when I got the 4 speed it was rebuilt but with all stock parts ....a 5 speed would be bset but prices are over $3000 got save up


OK. A 3.23 posi gear set is a bit stiff in my opinion. Now I know I am going to catch some flak on that statement, but... 

Think of it this way. Your engine builds a lot of pressure(power) through your driveline. If we were to _lock up your rear brakes_ and keep your wheels from turning to create *resistance*, the pressure(power) from your engine is going to break something in your driveline once you let out the clutch. Now if we let off of the brakes(resistance) slightly to allow your tires to turn a little, the car would roll forward when you let out the clutch, but it would take some pressure(power) to do so and if you applied more engine pressure(power) to make it move faster, you would again probably break something as you _over-powered_ the brakes(resistance) even though you were slowly moving forward. You could let off the brakes some more(less resistance), roll faster, but still _over-power_ the driveline again with wide open acceleration and break something.

So part of what your transmission gearing, rear-end gearing, and tires do is build resistance while your engine wants to make pressure(power). This is why you try to match the transmission gearing(close ratio/wide ration/low first gearing) with the rear-end gears so that you minimize the amount of resistance going through your drivetrain as they meet up with the resistance of your wide sticky tires which are trying to grip the road and fight to hang on(Posi-traction increases resistance as you now have two tires, *more rubber*, trying to grip the road). If you had skinny tires, they would offer little resistance and go up in a real nice looooong smokey burn out.:thumbsup:

So, a 3.23 posi is part of this resistance as it takes more pressure(power) to turn it. A 3.55, 3.73, 3.90. 4.11 gear would take less pressure(power) to turn the gears with each higher gear taking less pressure(power) to turn. For example: It would be like starting in third gear(if you used 3.23's) versus starting in first gear(if you used 4.11's). The stiffer 3.23's have more resistance than if you used 4.11's. The benefit here is that with less resistance, the pressure(power & RPM's) can build up faster and accelerate your car quicker -and you get blistering 1/4 mile drag strip time.

Now you can use the 3.23 posi with your wide ratio Muncie, but the posi-traction is going to have both wide tires wanting to grip and develop a lot of resistance -which will put a lot of pressure into your Muncie and rear-end just like my beginning example where you put your brakes on. You have to make sure you have strong enough parts in the trans/rear-end to handle the power of your engine.

Also, the weight of the vehicle creates forward/rolling resistance, but I did not want to get to complicated.:wink2:

Hope I made this clear enough, however silly my examples may have seemed.


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## Midwest-Muncie (Oct 14, 2014)

MB Speed. Don't think about installing a boring :nonod:TH-400 that will suck away a lot of your 500HP. Don't think about a TKO-600 that will be a pain to install and never be able to power shift :banghead:!!! Isn't the TKO made in China now? I have a Super Duty M23 that will take on your 500HP and want more and the strongest 1st gear on the market. Also have the Super M22 with all the Super Duty parts. Either will be a direct replacement for your factory installed Muncie. You can use your shifter, cross member and drive shaft.:thumbsup: Midwestmuncie.com


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## Midwest-Muncie (Oct 14, 2014)

MB Speed. One more thing, make sure to think about the correct gear ratio for the rear gear ratio.
3.55 gear with 26" tire needs a M22w (wide ratio 2.56-1st, 1.75-2nd, 1.36-3rd) I have custom modular cluster gears to change 2nd and 3rd ratios, I would recommend 1.90-2nd gear with your torque monster.
3.23 gear with 26" tire needs a M22z (2.98-1st, 2.04-2nd, 1.46-3rd) I might recommend using the modular cluster again and going 2.22-2nd gear.


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## geeteeohguy (Feb 2, 2008)

Mbspeed, you probably pulled the front bearing retainer out of the case or cracked it. BTDT.....I like what Midwest-Muncie is saying. Pull out the unit, and have it upgraded with better parts. Win-win. Not a fan of the way TKO's shift, either.


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## 68Resto-mod (Nov 10, 2009)

MB

I worked with these folks when I re-built my wide ratio Muncie:

Medatronics Corporation's 5 Speed Home page!

They can make you a new HD Muncie the way you want it or send you a re-build kit so you can fix the one you have. But with 500 HP, you might just break it again. You should also go with 3:55 (at least) in the rear as per Pontiac Jim above .


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## Midwest-Muncie (Oct 14, 2014)

Don't waste your time trying to put heavy duty parts in a worn out factory main case. You will hurt it with the weak factory case. You need to go with a new super duty main case. I would recommend that we us the enlarged steel thrust button case to keep the gear deflection to zero.


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## mbspeed (Sep 25, 2012)

:bannana::smile2:


68Resto-mod said:


> MB
> 
> I worked with these folks when I re-built my wide ratio Muncie:
> 
> ...


I did it guys auto gear super case ....metal med plate auto gear tail shaft and super duty reuild kit we will see how all goes....if gears look got all winter to check things out make it bad to the ass :wink2: just got the GM 12 BOILT INCASE


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## PontiacJim (Dec 29, 2012)

Midwest-Muncie said:


> Don't waste your time trying to put heavy duty parts in a worn out factory main case. You will hurt it with the weak factory case. You need to go with a new super duty main case. I would recommend that we us the enlarged steel thrust button case to keep the gear deflection to zero.


Midwest-Muncie, appreciate your input on this forum. Looks like mbspeed made his choice.

Maybe you could start a new thread titled "Build your Muncie to handle 500+ HP" and write a few words on your suggestions/recommendations and a link to your website? 

I don't think this is against forum rules?:confused We do get questions about manual trans conversions, both 4 & 5-speeds, as well as repair/noises questions on ocassion.

Just a suggestion.:thumbsup:


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## 666bbl (Apr 13, 2014)

Feel free to kick my thoughts in the stones, but I've been under the impression for decades that a Super T-10 is superior to the M-20/21. M-22, coin toss, again my opinion based on what I've seen and read for a long time. My list of OEM tough boxes from tough to wimp would read, Mopar A833, Ford iron box top loader, Super T-10 (including later aluminum case versions), M-22, M-20-21, Saginaw. So what else besides opinion and reading do I base this on? The number of welded ear Muncies that litter swap meets and used parts adds, days at the drag strip over many decades, street racing (but I'd never admit it!), and my personal experience with the 1st 3. Again, I'd be happy to learn the difference with genuine input from those who know. The Muncie was simply **** popular in early GM muscle and is now highly prized by the numbers/resto set, but I wouldn't hang a blue cape on it unless it was seriously built by an expert. Even then, the case becomes the weak link again. This does not include any number of aftermarket cases which improve the breed, speaking in terms of what the average hot rodder can get his hands on without too much $$$$ strain.


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## ibarbuckle (Feb 24, 2014)

Comparing Richmond ST-10 to stock Muncie's is a little bit of apples-to-oranges. Richmond has significantly improved the old Borg & Warner design (internally railed, new mid-bearing support, et.c.) Comparing similar year transmissions usually has Muncie out ahead. 

To reiterate some advice given already in this thread: expecting a stock transmission to handle 25% more torque than it was designed for is foolish. Look for a good 26 spline input, 32 spline tail trans and have it upgraded with later high-nickle gears, or pay for a new SM-20/21 or Richmond ST-10. 

Also, does anybody know why GM when to the T-10 in 1975?


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## geeteeohguy (Feb 2, 2008)

What ibarbuckle said. Year for year, the Muncie is stronger than the T-10. That's why the Corvette and GM cars upgraded to the Muncie in late '63. I ran a 1962 iron case T-10 in an old GTO I once had, and it was excellent, with nary a problem. I would only guess at the use of the T-10 after 1975.....but it would be that because the '75 on up cars had much less power than the earlier cars, the T-10 was adequate. But, from personal experience, I can say that the Muncie is certainly not the end-all strongest tranny out there.....far from it!


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## 666bbl (Apr 13, 2014)

Right on. Headers and traction bars on the average SS 396 Chevelle could shell Muncies like walnuts. Clearly we can't base this on driver input since there were a lot of guys who tried to play Ronnie Sox and lost with alarming frequency, but when the numbers show a trend? Racers I knew who had to row their own preferred the HEMI 4spd for all out durability in double duty cars, some strictly drag racers too. They're a very heavy trans too, HEMI or not. Maybe 50% or more in wieght. When I took mine out of my 383 car I wasn't ready for it and yelled for help to get it off my chest! My old Boss 302 shifted like butter at any RPM and never wimpered once. I'm putting a 75 ST-10 in my 65. Not going for numbers and balls out authenticity and this trans is in superb condition. I can't justify paying a grand or more for a good used Muncie that may be 1 high RPM shift from calling for a tow home. Many a Pontiac T/A with 4spds lasted a lot of miles and the shift quality is superior, but again that's my personal opinion. Can I break it? Freakin eh I could, but I think there's a lot more smiles per gallon in an average "day 2" build designed to enjoy bygone days rather than set a 1/4 mile record. I don't care if it goes mid 15s in the 1/4, but I do care that when I make some noise I can feel better about it. Just a bit more of where I'm coming from and I'm not alone. We did a home built "crash box" Muncie decades ago. Ground off every other tooth in the syncros and it worked like a charm. My buddy couldn't shift it silent but I could. I never told him I was taking the load off by lightly lifting my foot. My bad...


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