[oldman66gto]

Being new to this forum, and quite a few years since working on classic vehicles, brings the above question.

I bought a '66 GTO, which has a 428, with a newly rebuilt Muncie 4-spd, and it has a 3:55 rear. And as you guys know, it turns significant "RPM's" at speed.

Is it very difficult to change over from the Muncie to the Tremec?
I've checked into pricing, and it's not cheap. Especially if I get all that they recommend in their quote. This is gonna be a challenge for a 78 yr old

Would the Muncie be a desirable transmission to sell? Price??

I look forward to the response and advice from Y'all, as there seems to be tremendous knowledge & experience in this forum.

Thanks.
Allan

[Scarebird]

It is not a task for amateurs. To be honest given your age I would assess how long you plan to drive it and how you drive it.

If just running down for ice cream I would leave well alone - 3.55's are within my limit for final gearing.

If you put 5,000 or more miles a year on it I would change.

[tom s]

I’m 80 and it is the single thing I have done to one of my pontiac.Have had them in 3 fiff cars.The new one I don’t think you have to cut the floors.Use you bellhousing,you pressure plate and put a 26 spline disc in.I would buy the aftermarket trans X member.You drive shaft will need to be shortened and a trans input yoke.You will need a shifter handle and the one from you trans.If you stay with you clutch linkage and bell and pressure plate it will save you a lot of money.Tom

[george kujanski]

Rebuilt Muncies sell for the price range of around $1200 from what I have seen.

George

[Scarebird]

Tom, I was hoping you would chime in here - you are a superb example of a life lived well. Some age better than others - hence my hopefully non-judgemental comment on essentially being honest with one's goals and capabilities.

The sorta new TKX fits quite well in older stuff but not perfectly - trimming is required.

[b-man]

If you should decide to keep the Muncie 4-speed going to a little taller rear tire will take the edge off those 3.55 gears at highway speeds.

Going an inch or so taller would bring those 3.55s close to having swapped gears to a 3.36 or 3.31.

[krisr]

I just put 215/60's on my GTO and it turns 2400rpm at 60mph. I used to run 255/60 tires and it was less obviously, but it's not crazy rpm's. How low do you want the RPM? Mine is a 4 speed Muncie + 3.5 rear ratio.

[oldman66gto]

Originally Posted by oldman66gto

Being new to this forum, and quite a few years since working on classic vehicles, brings the above question.

I bought a '66 GTO, which has a 428, with a newly rebuilt Muncie 4-spd, and it has a 3:55 rear. And as you guys know, it turns significant "RPM's" at speed.

Is it very difficult to change over from the Muncie to the Tremec?
I've checked into pricing, and it's not cheap. Especially if I get all that they recommend in their quote. This is gonna be a challenge for a 78 yr old

Would the Muncie be a desirable transmission to sell? Price??

I look forward to the response and advice from Y'all, as there seems to be tremendous knowledge & experience in this forum.

Thanks.
Allan

As another option, what about changing the rear to a 3:36? Would having a new rear "set-up" and installed be less expensive than the Tremec swap?
Just trying to think about engine load when on the highway. I would like to take it from here in St. Augustine to maybe Gatlinburg. How hard it is that gonna be on the engine. Heck, I'm used to these new 6 spd & 8 spd "OD" transmission, and the engine turning 1600-1800 at 65 mph!

And another question regards value. I presume the Tremec would add a decent bit of value, whereas the 3:36 may reduce its' value & desirablity.
What's your opinions.

I'm not opposed to spending the money, but want to do whichever gives the best value, & will help the value most, when time comes to part with it. Which do you think a buyer would prefer?

It's a beautiful car, & in awesome condition, and I don't want to do something that would have a negative impact. If that makes sense!

Thanks again for your advice. This is a knowlegeable and wise group, and I appreciate the help.
Allan

[Scarebird]

Is this Muncie a M20 or 21?

[OCMDGTO]

3.55 to 3.36 will be hardly noticeable. 3.23 to 3.50 in my car was only a 150rpm difference

[Gator67]

I run an M20 and 3.55 in my 67 GTO (462ci)...the car has been on many long trips over the years. In fact, a previous owner was in the Navy and drove it back and forth between California and Virginia several times. That said, interstate traffic seems to move a lot faster these days so I too am considering a 5-speed swap (TKX).

[tom s]

On change that I did in my 62 GP was to put a 3.42 first these ST-10 and a 2.68 in the back gave me what I wanted.EZ pull away from a stop sign and low RPM cruise on the highway.Would not be a good race change but for a solid cruise car it’s great.First car I did it in was a 63 421 GP so the 63 421 GP was a EZ choice.FWIW,Tom

[b-man]

If going to the trouble and expense of swapping rear end gears go at least to 3.23 and if highway driving is a priority then consider going to 3.08. This assumes a Muncie M20 with either the 2.52 (late) or 2.56 (early) first gear.

Keep in mind that in the city taking off in first with a 3.08 rear gear might involve slipping the clutch more than you’d like. Depending on how radical your cam is you might not want that 3.08 so help us out and let us know what cam you have or at least how it behaves.

You haven’t yet shared your rear tire size which is a very important part of the equation.

[oldman66gto]

Originally Posted by Scarebird

Is this Muncie a M20 or 21?

LOL!! At my age it's getting harder to remember the numbers.
BUT, itis not the "close ratio" transmission. Is that the "M-20"?

Allan

PS: Today is a travel day, so I may not be able to get back on. And great replies, Y'all are making this ol man think!

[Scarebird]

That would be great if it was a M20.

[geeteeohguy]

Originally Posted by OCMDGTO

3.55 to 3.36 will be hardly noticeable. 3.23 to 3.50 in my car was only a 150rpm difference

I swapped the 3.55 rear gear in my 4 speed '65 GTO for a set of 3.36 gears in 1990. My cruise speed went from 60 mph to 70 mph. To me, a big enough difference to be worth it.

For the OP: with the Muncie M-20 and the 428, I would source a 3.08 geared rear end and bolt it in and be done with it. Thousands cheaper than a 5 speed conversion, you get to keep your 4 speed and Hurst shifter, and the swap can be done in a day with no modifications other than changing the speedometer gear at the tailhousing.

[65madgoat]

Most will tell you swapping to a 5 speed (or 6 speed) is the best thing they ever did. I was doing it decades ago. But if you don't need OD for long freeway drives, may not be worth the $4500 or so as in addition to the trans for $3k, you know you'll need a new shifter ($300) and driveshaft, crossmember, and electrical parts for reverse lights and speedo part.

But I'd do it in a heartbeat. Easy since your car is already a stick. You only live once. Makes the car so much more enjoyable off the line and on the freeway.

[oldman66gto]

Scarebird

Hi, Yes Sir, it is an M-20
I can post the case number, tail shaft, side case numbers if needed?

[oldman66gto]

Originally Posted by Scarebird

That would be great if it was a M20.

Yes Sir, it is an M-20
I can get the case #, tail shaft #, side case # if needed!
Thanks.

[oldman66gto]

UPDATE:
The "TREMEC TKX" is installed.
The tri-power system is finished, shipped and now installed.
The new distributor is arriving Monda/Tuesday, and will be dropped in, and other minor things on my list completed.
OIl, filter, grease, lube check for squeaks, and spring seats, trailing arms, etc.
Start engine, check for leaks, check/set timing, check shifting of transmission.
Check/charge A/C
Make other adjustments as needed.
Check tire rub & fix. A different tire size I hope cures it
Road test and give me full report! Wash & wax, detail.
Still in Virginia, and going nuts having to wait 3 weeks to leave & get back to Florida.
Go see car, test drive write the dang check! $$$$$
Take car home to the garage....then drive, drive, & enjoy!!

Thanks for all the help and advice!

Allan