Hey guys, I could use some second and third opinions here.

So right now my 75 vette is running a 4 speed (super T10). I really need an overdrive transmission. I'd prefer a manual transmission like a 5 speed.

Does anyone here have experience installing a manual overdrive transmission in a C3? I'm just looking for ideas. I'm not a rich man, I don't have $200k just laying around and can't just install anything I want. I'm looking for cost effectiveness here.

 

I have a 77 model, Super T10 4 speed car. I've been driving it for well over 30 years. Seems to work just fine. In fact it's about the only part of the car that has never needed to be rebuilt.
So, it begs to ask the question why. Why do you need a 5 speed in place of the 4 speed? For slightly better fuel economy?
Just a guess.
Factor in just how much better your fuel economy will be. Then how many miles a year do you expect to drive this car.
How many years will it take for this conversion to pay for itself before you start saving dime one.
I have a few friends in the Corvette clubs I belong to who have done this. Yes they report better fuel economy, but by no means are they getting modern car type of fuel economy.

 

How much do you have to budget for this?

The (new) TKX is probably the most cost effective complete solution. You can piece together your own kit for less, maybe.

I think there are few threads on this Forum about it now, search for Tremec TKX. Here's a video to get you started (the poster is on this Forum). The bellhousing needs to be set up just-so.


But as @4-vettes pointed out, it will take a LONG time to see a return if you are just after MPG and trying to save gas.

 

What's your rearend gear ratio? It differs by engine and if an L48 should be 3.08:1 (AW); or L82 3.56:1 (AA), maybe that's an option. Look for the two-letter code on the differential case...bottom.

 

3:08 sounds like a rear gear for a automatic L48. Not a 4 speed. L48 base should be 3:36 base. And then they go lower from their. None the less. Changing the rear gear could also help slightly. but costly just the same. And going tall in the rear gear would take ALL the fun out of the car.

 

you can go from a 300 buck T5 from an 80's camaro and install it yourself all the way up to 6-8k complete setups. there is always a cheaper way. it is usually a suboptimal choice...

 

A good world class T5 from a late 80's camaro or firebird installed in a stock 75 should do the trick without
breaking the bank.......with the correct gears behind it. Put one in my 77 years ago with a 3.08 rear.
Changed them to 3.70 soon after.

 

i have one earmarked for my 75.

 

Well here's the thing, this vette is my daily driver. I've put 30k miles on it since I've rebuilt it. It's holding up well but I don't like it turning 2750 rpm while going down the highway. I get about 18 mph highway.
I would like the engine to last at least 100k miles but turning 2750 rpm at 70 mph I don't believe is good for the engine.

Keep in mind this isn't an all original car. As one guy pointed out, the 1975 L48 model came with a 3.08 rear and a TH400. I've rebuilt the engine and transmission. It's got a 880 small block with 062 heads with a 3 angle valve job, LS6 springs, flat top hypereutectic Pistons and a LT4 hot cam. The transmission is a 3.42 first gear ST10 with a cast iron T10 case.
I originally built the car to go within 10 miles of my place of employment but the housing market is hot in Fort Worth so I moved out of town to a place I could afford but that turned out to be about 95 miles. I want an overdrive gear so my gas mileage and engine longevity will increase.

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You're going to enjoy it DD.Good luck with it.

 

what is your budget, how much power does your motor have and how much modification do you want to deal with. If you have $3000 I would go with theTKX. It is a copy of the McLeod Muscle car 5speed and is good for 500hp/500ft/lbs. It will pretty much bolt in with no major mods other than the shifter area in your car and maybe a shift lever mod and shortening your driveshaft. I used the Muscle car 5 speed and Im really happy with it but it does limit how much power you can use. If max power isnt a problem then go with either of the 2. I found mine used and had it rebuilt by McLeod very inexpensively. You can find the McLeod 5 speeds and the TKO500 or 600 used now adays as well. A richmond 5 speed or a T56 may require tunnel mods due to width. If yo ugo with a T5 it has to be the T5 WC (world class) it is limited to 400 to 500 torque and it may require a rebuild with a shorter input shaft, a bell housing adapter and a input shaft bushing adapter depending on whata model you find anad what it came out of. None of them will bolt right in without a lot of other parts


You need to decide if you want to stick with your manual clutch and go with a hydraulic clutch as well. I switched over and I have less issues with the hydraulic clutch. THe big thing you can do to help yourself out is cut your tranny crossmember out and make it removable. It makes life so much easier under he car

When you go to a 5 speed you definitely need to dial in your bellhousing to center the input shaft to the pilot bushing. THe 4 speeds allowed for significant deflection and you could bolt any 4 speed into any engine without any problems what-so-ever. I did it for years and never wore any input shaft bearings or pilot bushing out. YOu will do some damage to your bearings in a 5 speed if you dont do this. Its easy but you need to dial indicator and a magnetic base. Dont do it and you will end up with vibrations and bills.

https://shiftsst.com/blog/post/bellh...engine%20block.

 

it is not just how much power you have, it is how you apply it to the drivetrain. put a 4 banger iron duke in there and launch it hard enough and often enough and that T5 will be parts tinkling on the street behind you.

 

The world class T5 is the way to go in you're on a budget like me. Mine's been trouble free for the past 17 years. However, the days of the $300 trans is long gone. You could pay up to a grand for a good one. That being said, you could do it yourself for $1500 or less. The trans is only rated for 320 ft-lb, but mine's taken its share of abuse, guys have put them behind big blocks without blowing them up, and the Mustang guys have been thrashing them for decades.

 

I have the tkx 5 speed. Love it. I run it with my stock 3.73 rear. Gas efficiency is nice but I don’t drive it enough for that to be a big deal. I like the idea of keeping lower rpms for the longevity of my crate engine. It’s also nice to not sound like I’m in low gear when I’m just cruising.

 

Well guys. This guy has made one total post on this forum. this one. And according to his profile, he has been back to have a look. But no reply.
I'd say where done here.

 

Hey guys, I've been looking at all of your replies. I've also responded via Quick Reply to several of you. Just because I haven't put up another thread or responded with a general response yet doesn't mean I haven't been listening. I've been on this forum a total of 2 days.

For some of yall who are asking. The motor is putting out 450ftlb of torque. I have been looking at the T5 for a while. There is one for sale in Corsicana TX but I'm not sure if I can handle my torque if I throw a rebuild kit at it. Is there a way I can beef up a T5 to handle the torque?

 

Also something for you guys to know, the car did have an automatic TH400 but I replaced it with a 4speed. I am considering replacing the transmission because the 4 speed I had in mind was meant for a short cruise to work, not 95 miles one way.

Yes I do drive it daily, yes I do get groceries with it and no, I don't believe a car is meant to stay locked up in the garage for all it's life. It's a car, not simply a showpiece. It's taking 190 miles a day, it's never left me on the side of the road. It's meant to be driven. I would however like the engine RPMs to stay below 2k at 70mph.

 

My 2 cents based on your situation is make the investment into a 5 speed. My TKX around 3 or 4K from American Powertrain.

 

I'm in the T5 club, I put one in my 76. I had the trans rebuilt and upgraded. I've yet to drive the car but..I have the same setup in my 69 Z/28. I put a WC T5 in that for the same reason, the 3.73's just killed the car on the highway. After the swap I found 1st gear was useless so I pulled the 3.73's and replaced them with 3.08's. BINGO! 1st and 2nd gear in the T5 are pretty short so the car is still very sporty off the line and 5th gear just puts the motor to sleep on the highway. I see no reason the C3 with the exact same setup wouldn't be just as satisfying. I'm all for the WC T5 if you can find one. Oh-my son also has one in his 68 Chevelle-we're believers.
My C3 was originally an auto, I bought a conversion kit from COrvette Central, it came with the pedals, and linkage, was very complete and helpful. I found the correct bellhousing on local CL, bought a flywheel from Advance Auto and clutch kit from Summit.

 

Sorry to sound like a broken record about the T5. I loved mine for 13 years until these achy knees said 400 auto swap recently.

Both my conversions were big block c3's. An auto car and the one prior to that was from another 5 speed. Of all things..........a T50 was in the car.

No sticky tires or dropping the clutch at crazy revs, and they both performed flawlessly.