Hi all,

In my quest to throw even more money at my '69 vert restoration, I've been considering replacing the original Muncie 4 speed with the TKX 5-Speed. I really like the fact that with .68 top gear, you can drop those freeway cruising RPMs down pretty considerably - around 32%, which is significant. Anyone here done this conversion on a C3, and if so:

How do you like it compared to the M20 or M21?
Was the installation direct-bolt in as they say, and without tunnel modifications?

Research is telling me it is not a direct bolt, although no cutting seems to be necessary
Doesn't look like you can use the original driveshaft. Researching this, it looks like you have to shorten the driveshaft by about 2.5"
Input shaft is fine spline as opposed to the course spline, so you have to use a late C3 Corvette clutch
The Yoke needed is a 31 spline, so you cannot use the OEM 27 spline yoke.
What if you want to maintain mechanical linkage? Any issues? - If I end up doing this conversion, I'd prefer to not convert to hydraulic clutch.

I'll be running a SBC stroker rated at about 425/450tq, and these are supposed to be rated at 600 ft lbs.

I'd love to get input from anyone who has done this conversion.

 

I have a TKX in my 79, I had mine professionally installed, the only "modification" they did was make a removable section of the welded in cross member. I also kept the original linkage. I absolutely LOVE it, Its a great comfortable highway cruiser now. The only issue that I had was a little drive shaft rub in the tunnel when hard cornering, I took it back and they did a slight adjustment (only took about 30 minutes) and its been perfect ever since.

 

I did my conversion in 2006 to TKO600, with .68 overdrive. Absolutely a great upgrade. I have 3:70 rear ratio. From 4 th to 5 th gear, rpm drops about 1,000.
- I purchased a Kit. Included driveshaft, speedo cable, and all necessary hardware to install.
- Purchased only clutch disc, used my existing pressure plate.
- Used my existing clutch linkage.
- No cutting of anything required.
- It IS a direct bolt in.

I've had no issues at all with the transmission since installed. BE SURE to index the bell housing.!!

A friend has a TKO 600 installed in his '74, stroker 383, best run, on engine dyno, was 502 hp. He has had it on the track a few times, best at 11.91.

I had not heard of anyone not liking the upgrade to a 5-speed.

 

What ratio are you running in the differential?

 

3.55

 

I did the swap to a TKO-600 about 7 or 10 years ago. It's pretty much the same as putting in a factory 4-speed except as you noted the input shaft and the output shaft. No big deal buying the correct clutch. The output yoke was a little more problematic. I ended up getting a yoke for a different u-joint (don't remember the numbers) and had to get a conversion u-joint. I used the trans mount bracket from an '82 and it lined up perfectly. You can use all factory parts for the clutch linkage. I recommend making your own frame bracket for the Z-bar. The ones that are available, expecially the bolt on bracket are very flimsy. I bought a bolt on bracket and used it for a pattern to make my own. Yes you have to adjust the dirveshaft length but that's just a matter of taking the measurement and finding a machine sopt to do the work.
If I were doing it over, I might consider the .72 or .81 overdrive. The drop to the .68 overdrive is substantial. It's more of a 4-speed with overdrive than a 5-speed trans. It works great for highway cruising economy, but you don't drive it like a true 5-speed. Adding the 5th gear makes all the difference. The car is now a joy on the highway. Before, it was just a pain.

 

Can you reply if your headers are stainless or if they are silver ceramic coated? Thanks

I had my 68 crossmember sectioned as shown in the second photo. A really great mod to make tranny install/removal much easier.

My TKO-500 with a 3.73:1 nicely drops engine revs when cruising on the freeway. Like the TKO shift...very neat and crisp. Seems like you can just about do the shifting with your wrist.

Bought my TKO-500 as a kit...included the drive shaft and hardware. I think I had to buy the clutch disk separately. Had it installed by J&D Corvette in Bellflower, Ca. They did the cross member modification also.

 

I agree with Drwet about the OD ratio. Your 3.55 gears should pair up nicely with the least amount of overdrive. I found my cammed solid lifter stroker engine was not thrilled to run around at 1800 RPM at cruise. I'm going to post some results at some time in the future once I drop in my L-46 and see how it runs with that combination.

 

This is excellent information, fellas. Much appreciate the input. Yeah, if I do this, I tend to agree about the 4 speed with an overdrive comment. With a .68 5th gear it is a real drop, like 900 RPM drop in RPM from 1:1. I did something similar (and even more extreme) in an old 911 with a built SBC mated to a (Porsche) 915 5-speed transaxle some years back, and decided to drop in a .59 5th gear (replacing the original .82), and the drop was way too big.

The big cammed 355 didn't like loafing along at 1900 RPM at 70 MPH on the freeway. Dropping down to 4th gear at the same speed brought you to about approx 3200 RPM - too much of a jump. .72 wide for the wide ratio or .81 for the close ratio set up would be better as a true 5 speed.

What I don't like about these kits is the fact that Tremec recommends you cut the rear cross member and make it removable for easier servicing. If I recall correctly, for automatic to 5-speed conversions, that's a non-issue because the cross member is already removable for servicing of the TH400 from the factory.

Mine is a 4-speed car, so it does not have the removable cross member, and I don't relish hacking at a perfectly good frame (which I just replaced BTW) to accommodate a 2.5" longer transmission. I'm guessing if you don't do that, then you have to remove the engine and transmission as a unit for clutch servicing.

Meh - Ferrari makes you lower the entire rear subframe (motor, trans/driveline/suspension) to change the timing belt on the older models. Makes engine/trans removal for clutch servicing on a Corvette seem easy, and which doesn't need to be done nearly as often. How frequently does one change a clutch anyway - not too often.

 

headman ceramic headers

 

I have done about a dozen of these swaps. Most of them were automatic frames but a few were 4 speed frames. Yes it is way easier to do it with a removeable X member but it can be done without cutting the frame. Just a lot less room to install the bellhousing and clutch. If you want to keep your frame original it can be done. Also much easier on a lift. On jack stands your room is even less. That being said it is one of the best upgrades on a C3 you can do.

 

A 383 stroker with 425 hp is probably going to have plenty of TQ at 1800-2000 and should cruise just fine in O.D. For others doing this, if you have a cammed engine I suggest practice cruising along at 1600 to 2500 rpm, and see how low your engine likes to go during cruise. At some point it will begin to "trailer hitch" or balk at you.

Then you will know your lowest reasonable cruise rpm and can gear things accordingly. I seriously doubt you can get these old school carb'd engines to cruise at 1500 rpm like a new fuel injected LS engine.

This attachment will help you play with gear ratios the cheap way: in a spreeadsheet!

My buddy george did not like his TKX / 3.70 gearset because he felt caught in between gears at his common 45-55 mph back road speeds. So he went 411 and is perfectly happy. He is in 5th at 55. I am doing the opposite and going 323s. I will never use 5th except on the 70+mph turnpike.

 

Do you remember were that clutch rod setup came from?
Thanks

 

I know a fellow selling a complete bolt-in Richmond 6 speed package. Includes driveshaft, Long shifter with custom mount to position it in console etc. It fits in trans tunnel without cutting.

Gear ratios: 3.28/2.13/1.57/1.24/1.00/.76.

He ran it for about 5K miles behind his street smallblock. He's going twin turbo now and will install a race style trans...hence the removal of this one.

He opened it up and sent parts to Liberty for inspection (all good) but replaced synchro's anyway.

He's asking $3500 for it all.

JIM

 

Tremec is now shipping all 3 versions of the TKX:

And I believe the heim jointed style clutch linkage in post #2 is from Speed Direct.