Wade Mahaffey

very nicely explained by DZAUTO. I too have a 62 with a 4:10 ratio. I am looking to change out the 3rd member for a complete 3:55 posi. Hopefully I can find one at Carlisle

MikeM

Thanks for what?

The GM term for the part the ring gear bolts to is caseThe GM term for the housing that encloses the case is the carrier.

If GM lit describes it any differently, I'm not aware of it. In the case of this post, confusion of which is which could cost many dollars and lot's of confusion.

I showed a picture of what was what, way back. Guess I wasted my time?

wmf62

Mike
nah, anytime I can get your blood circulating a little faster is well worth the effort...
Bill

Dreaming60’s

Thank you guys. As usual, this forum came through and I understand now. I did have some semantics issues at 1st, but it was explained so clearly, it's hard not to understand it now. At least my shop owner was correct in wanting to check it out (good to know as it builds confidence in him), he wasn't sure if it was possible to change from a 4:11 to 3:55 by just swapping gears, which, you can't do. You have to go from a 4 series carrier to a 3 series carrier to get the 3:55 ratio he recommends.

He thought new gears would be around $300, plus another $600 if a new carrier was needed, I wonder if he is close on these guesstimates? He never mentioned locating a used carrier, which looks like it might save quite a bit of money.

Will I feel a big performance difference going from the 4:11 to 3:55? Seat of the pants or actual? I don't street race the car, but it's nice to feel the performance when you step into it and by today's standards, even with the 327/300, M-21 trans and 4:11 in the car now, it doesn't feel any faster than my Honda Ridge Line or Touareg diesel, to be honest.

Butch

wmf62

going from a 4.11 to a 3.55 is definitely going to be a change to the seat of your pants, but the 3.55 will be easier on your wallet (and the engine) if you do a lot of long distance highway speed driving.

personally, I would look for a complete "good' used 3.55 'pumpkin' fully assembled and just swap the units out. your mechanic should be able to do a tooth pattern check to see if it is set up right. if you just want to 'drive' then a non-positraction rearend will be significantly cheaper than a positraction one

another $$$$ option is a new transmission with overdrive and keep the 4.11

Bill

MikeM

If you have a close ratio (M 21) you'll be waiting a lot longer for that thing to "come on the pipe" if you change to a 3.55 rear gear.

A close ratio and 4.11 is suited for a SHP engine. A wide ratio (M 20) and 3.36 rear gear is a nice combnation for a 327/300.i

MikeM

I don't get excited real easily!

How are you liking your brand new $15 rear view mirror you spent all day trying to twist the price down? There is another word for it but I got a speeding ticker for using that word a few years ago. Seems some Canadian was offended by it.

SW Vette

Hold on, now. You don't need to change the carrier (which could be described as the "housing") at all, just the case. Save the 4.11 case if you ever want to swap back later, maybe when you drop in the Tremec 5 speed

3.55's require a lot more finesse off the line than a 4.11, which some guys have trouble with, so they need the higher ratio. Otherwise life is much easier with a 3.55, especially if you want to cruise farther than to the local TasteeFreez. It really is a good compromise between the short and tall diff ratios.

Up till '66 all Muncies were called M20 and the factory decided based on which engine option was ordered whether to put a close or wide ratio gearset in. 327/300 got the wide set, perfectly compatible with 3.55.

Westlotorn

I've been around and worked on hobby cars my whole life, rebuilt 6 or 7 rear differentials and just today learned proper terminology. Good discussion guys.

wmf62

Mike
ya know, I can't remember whether I still have it or not....; but I still know why i had to have it, I remember stumbling and falling against the 'old' one and breaking the head off....

and I do remember the hospitality y'all extended to me in spite of my 'negotiating' skills at Kissimmee; miss seeing and talking to ya and drinking your beer...

Bill

Dreaming60’s

Thanks for the info. I came up with the M21 because on the internet (great place for information and misinformation) my case casting number on this transmission was supposedly used on 64-65 C-2's and if it had a Patent Number instead of Patent Pending cast on the case, it was a 1965 Muncie with 7/8" shaft and 2:20 ratio 1st gear. I just assume it meant it was a M-21. Thanks for the clarification I do appreciate it.
Butch

Jackfit

3:70 to 3:36.....very happy but....

You know, I did the same thing, but here is what happened. Yes on long trips I got 16-17 mpg....better than the 14 with the 3;70 at highway speeds.

However, around town, I found that I stayed in 1 , 2, 3rd much longer , enjoying more speed from each gear....result...same around town gas milage from the 3:36 as the 3:70. 11-12 mpg

Much more comfortable with it (3:36) at 70-90 mph that I usually drive when on highways.. My M-20 with the 3:70 was great...lots of acceleration to 110......

Jack

Jack

59 navy

A friend and I checked out three car junk yards searching for a good 3.36 He noticed a differential showing a new gasket. (someone had been in there before) Looked inside and it was fully rebuilt. Cost was $75.00 and was an easy swap. Take a friend who knows what he's doing... 59 navy

DZAUTO

These rearends were last used in 64 full size Chevy pass cars.
The 3.36 was first introduced in 57 and the 3.08 was introduced in 59 (predominantly behind 348 engines). The 3.36 and 3.08 were MOST commonly found in 62-64 pass cars behind auto trannys.
Also, I have frequently found posi rears (some of them 3.08) in 64 plain jane cars. As a result, I have sometimes wondered if there was a big inventory of posi units which needed to be used and if so, maybe posi rears just got installed in random cars just to get them used up from the inventory, because in 65 the rearends were different on every model of Chevy.

GTOguy

The statement that up until '66 Muncies were all M20 is incorrect. The close ratio, 2.20 first gear M21 was available from the very inception in 1963. Agree that for the O.P., the best bet would be to swap the 4.11 third member for a 3.70 and leave the trans alone, or swap in a 2.52-2.56 M-20 and change out the third member for a 3.55 or 3.36. He can pick up a non-posi complete unit in the under $500 range if he hunts for it on line. Not an uncommon part at all.

Dreaming60’s

Thanks Jack! I'm putting a lot of thought in this (maybe too much) and I think I need to drive the car awhile with the 4:11. I've only driven it 150 miles or so (due to issues) and that isn't enough to make a decision like this. Gas mileage is of no concern whatsoever. Engine wear is a concern, but I drove a 1961 with a 4:11, back in 1970 for almost a year before having it changed. And it was my daily driver on highways at 70mph, for 50-60 miles a day. So, engine wear might not be an issue for me.

I had to wait a month to get the car into the local corvette guru shop on Monday. They gave me thumbs up on the body and frame, which is a blessing. Found out the car had 3 tail lights at one time in its life. which at one time in my life I thought was cool, but not anymore. They found a bunch silly bubba problems, that are easy to fix, so I'm a happy camper.

Whoever installed the Muncie, forgot to change the yoke or installed the incorrect yoke, so it doesn't go into the tail housing as far as it should (IIRC). They think this is causing the vibration in the drive line.

R/H KIngPin is shot, causing the front end to dive on turns. Seller had the front end aligned just before I bought it so they just tried to disguise this issue.

Fuel and Temp gauge had a loose ground screw/wire so the gauges work now.

Shift linkage was way out of adjustment causing the shifting problems.

Found out through this shop there is a local shop who can install a new Haartz soft top for about 1/3 the cost I've been quoted by national companies and they do it for all the vette owners in town and are highly recommended.

Although it won't even touch new paint. The car can color sanded and polished at a local corvette body shop for maybe $1000-1200 and it will look tons better. I will go this way 1st. in lieu of a $10-15K paint job.

So, all in all, it was a very good Corvette day.

Butch

Dreaming60’s

Thanks very much for this input. So, you think swapping to a 3:70 instead of the 3:55 would be enough of a drop in RPM at 70mph to make driving more enjoyable. Although I don't know what these numbers mean to me, I multiplied the 1st gear ratio times the various rear end ratios and came up with the following.................I just don't know what it means.

4:11 with the 2:20 muncie = 9.04 ratio
3:70 with the 2:20 muncie = 8.14 ratio
3:55 with the 2:20 muncie = 7.81 ratio

I'm sure this equals my 1st gear performance and ultimate speed in that gear, but not sure how to interpret it for real life application. I won't be launching the car from a stop and never believed in dumping the clutch for fear of breakage, but I do like zippy performance.

Butch

SW Vette

From the website muncie4speed.com:

All wide ratio transmissions are designated M20 and close ratio transmissions are designated M21 or M22 depending on the gear set. From 1963 to 1965 the close ratio M21 was ordered under the M20 RPO code and the factory decided whether to install a wide ratio M20 or close ratio M21 depending on the rear axle ratio specified. From 1966 on, the customer could decide the transmission selection.

http://www.muncie4speed.com/

We're both right

wmf62

for drivability, the rule of thumb is 1st gear times rer should be about 10; that's why the 4.11 makes sense.

my ss700 2.66 1st times my 3.36 = 8.94 and I can really tell the difference between the my6 3.09 times 3.36 = 10.3.

a lot will depend on the engine's low end torque... a 300hp is a reasonably good engine. but I recommend you live with the 4.11 a while..

Bill

Dreaming60’s

True words of wisdom and exactly what I'll do.

Thanks Bill and all.

Butch