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Since first owned my car ran with a 4:11 rear. While great for everything short of freeway cruising, there was always that feel of needing an extra gear at speed. 3000 rpm at roughly 60 mph was getting old.
A 3:08 pumpkin was purchased. The 3:08 diff resided in a garage corner for some time. Around 2013 the pumpkins were switched out, 4:11 to 3:08.
Going from 4:11 to 3:08 really worked out well. Now going 70 mph at 2700 rpm is a treat.
If not for already having the 3:08 on hand a Tremec 5 speed would probably have been in the cards to replace the M/20. The Muncie in the car has been rebuilt, but should it wear out or blow up a TKX would likely replace it with the 4:11 diff back in the car.
John
I'm always interested in this conversion and why people do it. What results are they expecting or what issues they are trying to resolve. Cost versus benefit. Dennis
All the fun of the original car with the additional ability to cruise at 70mph spinning 2,000 rpm quietly.
My reasons for opening this topic in the 1st place.
I have a 67 coupe std 327/350 with over 300k miles (3:70 rear) It is in excellent shape but given the miles and the years…not a matching numbers car. (back in those days matching numbers weren’t considered important!) I bought it 50 yrs ago and it was my only car for 14 years. It is on it’s 4th rebuild with one replacement. I performed a frame off in 2017 replacing the frame (live in Northeast) and blasting, painting, or replacing every part I touched. All new rubber, bearings, etc.
I heard a loud metallic bang while driving 70 mph back in mid 80’s. Following that incident I have been trying to find source of a high speed vibration. Since that time I have replaced clutch and pressure plate (multiple times), rear end, all wheel bearings, rebuilt trans twice, balanced drive shaft and axle shafts (twice w new b-joints), replaced bell housing, flywheel. I still have a lesser vibration than original, starting around 50mph. If I put car in neutral at that speed or push in the clutch, the vibration goes away. I should also mention I have replaced all 4 tires multiple times durning that period. I am now considering replacing trans with Tremec tkx which will replace drive shaft as well. Note engine runs smoothly and has physically been replaced, and then more recently been rebuilt durning that period.
I have done runout tests on flywheel, input shaft movement on trans and all are acceptable. Drive line is also within specs.
My interest in going to 5 speed is lower rpms at highway speeds and eliminating vibration while keeping car looking stock.
I have a 3.3 rearend in my Hemi/Vette and last year added the Tremec 5 spd. I really like it. The first four gear are close ratio, which I like, and then the 5th speed. 2000 rpm at 70 mph.
Removing the gas tank and reading what was
left of the spec sheet attached I found that the
original engine was an L79. I bought the car in 1971 ($2400) and at that time it was a 327/300! The car had a checkered past I assumed!!! During those days it was just a used car and no research or checking of vin’s was normally done. During the frame-off I rebuilt it to a L79 which obviously required a new harmonic balancer
I have had no luck finding this topic on the forum. I can’t seem to search and find c2 transmission topics. Can you direct me how to search for older discussions on this topic? I always seem to get results from all forums when trying to target search c1/c2 forum? Not sure how to find this data! tks? jb
You can also use Google to search the forum. Just type your search terms appended with "site:corvetteforum.com" (at the Google site or toolbar of course)
An example would be: "C2 mild cam lifters site:corvetteforum.com"
As others have said it is a personal preference.
For me I have always liked the sound and performance of these old engines at highway speeds with a variety of different engines and gear ratios. I hate side pipes and prefer a quite exhaust. Having said this a BB with 4.11 gears at 85 mph will wear on me after a while. However, I have three vehicles that I split my annual driving with. A 1965 & 1966 Corvettes and a 72 El Camino. I drive 15k miles or less a year now. When I am done with the Two Corvettes the 65 will be a Blueprint 396 500 h.p. with a wide ratio 4 speed and will keep the current 3.36 gears unless I feel the need for 3.70s. The L72 will have 4.11s with the close ratio 4 speed. For the amount I’d time I will spend on the freeway at 85 mph I will be fine with any of these vehicles and will enjoy the power that comes with them and see absolutely no reason for an extra gear. I will seldom see much above 100 mph unless it is a 1/4 mile blast once in a while, I no longer chase top end like I did in my youth. Everyone has to decide what makes them happy but what I have described above is as they were back in the day and all of it satisfies me just fine. If I were driving just one car daily and a lot of highway mile it would be a different story but I will never live long enough to wear out any of these engines and this is what many of you may also want consider. Ask yourself how many freeway miles you are going to put on your car annually?
I have a Muncie 4 spd close ratio with a 4:11 rear and it is just silly. I can start off in second with no problems and go right to fourth. I need a 3:70 of lower but I can live with what I've got unless someone wants to swap with me. 80 mph for my car is about 4500 rpm. I mostly cruise around the countryside at 60 mph or less so I can live with it. It really goes in first and second gear. Almost rocket-like.
Last edited by inspectorudy; 09-09-2021 at 11:32 PM.
I have more pressing fish to fry with this car presently, but a change in gear ratios is on my to-do list. The reason is the same as why I don't tool around town in first, second, or third gear at a steady 3,800 RPM. With a T-10, 3.70 and side exhaust, I can't stand highway driving for more than a couple of minutes, even with ear plugs. Sure, the engine can take it. But the driver can't. While I haven't dismissed the idea of swapping in a different R&P, I think it'll be the T-10 that comes out and gets sold.
I have a Muncie 4 spd close ratio with a 4:11 rear and it is just silly. I can start off in second with no problems and go right to fourth. I need a 3:70 of lower but I can live with what I've got unless someone wants to swap with me. 80 mph for my car is about 4500 rpm. I mostly cruise around the countryside at 60 mph or less so I can live with it. It really goes in first and second gear. Almost rocket-like.
Sounds familiar. My car had 4:11's too. With wide ratio trans, first gear wasn't needed in normal driving. Mainly a cruise car now with occasional speed runs, the RPM's at freeway speed finally got too old......3:08's in the rear now. Short of an OD trans, with good low end torque the 3:08/M20 is a good combination for a road car.
John
Same here. It’s not about cost/benefit calculations or payback period. If that were the criteria we wouldn’t even own these old toys - we’d be driving an econo box of some type.
What this is about is making our toy be the way we want it to be to suit our personal needs and preferences.
Cost is irrelevant. Either one has the funds to indulge themselves or one doesn’t
I have a Muncie 4 spd close ratio with a 4:11 rear and it is just silly. I can start off in second with no problems and go right to fourth. I need a 3:70 of lower but I can live with what I've got unless someone wants to swap with me. 80 mph for my car is about 4500 rpm. I mostly cruise around the countryside at 60 mph or less so I can live with it. It really goes in first and second gear. Almost rocket-like.
This is how mine is. BBC 4:11 - close ratio. I can start out in 1st wind it up a little and go straight to 3rd, no lag. Then 4th for around town. It’s just stupid on the freeway, but as you say, it’s a rocket if you get after it!
07-22-2021, 03:01 PM
