Let's Talk Six Speeds
 

One of thee days I will need to replace the clutch in my '74, and I definitely want to go back with an overdrive while I have the trans out. The Richmond and Tremec are too damned expensive. What about the newer 'Vettes, Camaros, Mustangs with sixers? Viable alternative? I believe diesel trucks nowadays are also available with six speed manuals, would one of those be suitable for a performance car? I don't have a problem with fabricating a new trans mount.

Buying a used trans is real dicey no way to really know waht youre getting.
May seem steep up front but buying a new TKO with an entire kit is the way to go. Lots of variables with inut shaft length, FW/clutch type slaves or manual linkage pieces bellhousings etc

A few have taken old T5s from IROCs , S10s etc and made them work dont plan on putting any power behind one though

AS much as I hate to write it...if you want to play...you have to pay.

I can 'say' that if you use an early 6-speed out of a Camaro and it is ZF design...just be AWARE that they used a DUAL-MASS flywheel...which keeps the internal workings of the transmission QUIET. IF you use s single mass flywheel...you can have noise come out of the transmission ....even though I am sure some may have a fix for it...I have never torn into a ZF transmsiion to try any of the noise fixes I believe I have seen on the forum in the C4 section.

If you go that route...I would do my research in this before you put it in the car....because the dual mass flywheels are NOT being reproduced. Or at least the last time I needed one...they were not being made.

DUB

I looked at fitting a t56 out of a Commodore here in Aus (same box I believe as Camaro, GTO etc in US). They have no provision for cable operated speedo or mechanically operated clutch, so if you want to keep your original speedo you need an expensive box to convert the electrical signal to cable driven (can't remember exact cost, but in the hundreds of $), and you need to convert to hydraulic clutch. If coming from an auto then the numbers might be better, but by the time I bought the converter box and hydraulic clutch components the cost was almost the same as buying a new tko600 (and bolting it up with my original bellhousing and z bar clutch release assembly), and you had an unknown second hand gearbox. I bought a standard tko600, and just bought a few specific conversion items. This meant I had to cut and reweld the shifter to come through the console correctly, and open the hole in the floor larger and cover it with an aftermarket boot, but wasn't a lot of extra effort and saved me quite a bit of money (partially because I could buy the box locally and avoid the import taxes charged on anything over $1000) over importing a bolt in kit from the US, as well as avoiding the possible issues I've read about with the corvette specific shifter mechanisms. I still bought the shifter lever and console insert etc from Hurst to give the factory look.

I put in a used T56 from an LT1 Camaro and all the parts for the auto to manual swap were far less than a new transmission by itself. The guy had no reason to lie to me about the condition of the transmission, he sold it to me from his house.

Ah ok, only ls1 boxes here in Aus. Costs may be quite different too. I just had a look at my notes, I was looking at ~$1200AU on an unknown secondhand box, ~$1000AU on hydraulic clutch bits (could have done that a lot cheaper, but for the parts I wanted to use), and ~$600AU for an electronic to cable speedo drive converter. At that point, $3050AU for a brand new gearbox that would bolt up and use my existing speedo cable and bellhousing/clutch mechanism and didn't require the same amount of fabrication, fiddling, and potential problems, seemed like a good idea. Particularly given I wasn't that fussed between 5 or 6 gears, my main reason for the swap was increased strength for the stroker I'm building to put in front of it.

Have you considered having your gearbox converted to an overdrive 4th gear ? Don't know who does it for Chevy, but it is common over on the Mopar side. Would be a lot less expensive.

Just to clarify what I think you were trying to say.

C4 Corvettes use the ZF6. Some BMW also use a variation of it... but generally the ZF it is a noisey and difficult to get parts for trans. It's also very big, heavy and due to the C4 chassis/drive train design, has a weird trans mount attachment to the tail housing.

4th Gen Camaros use the T56... which is a Tremec mfgrd trans today and is what all the aftermarket companies modify to sell in their kits... However the early Camaro T56s are weaker and have a higher low gear ratio than the later T56s.
Will

I didn't consider the clutch. Maybe Gear Vendors OD would be the way to go...

What engine is in the car ? What is the power level ? Factory HP was pretty low in '74, so unless it's an LS4 big block I'd be comfortable with a World Class ('88 up I think) T5 from a TPI Iroc or Trans Am. No Blazer transmissions. F car only.

If you have a 383 or 406 (or a super hot 350/355) I'd go Gear Vendors I think...

It's a mild small block. I doubt I'll ever have much more than around 400 H.P. in the future. That said, I'm thinking more and more the Gear Vendors unit is the way to go.I remember reading about them long ago and really digging them, but the cost seemed very high. I'm older now and have a bit more money; they are still pricey but not out of reach.

I'll give you my .02

T5s are CHEAP to buy, cheap and relatively easy to rebuild, if your car was a stock L48 or L82 I'd say go that way, but I think 400 HP is asking for trouble.

EDIT: I thought I'd share a story about my cousin's '73 Silver L48 4 speed car. It had an M21 stock, 3.36 rear gears. He didn't like taking it to work on nice summer days because of the lack of OD and his hour + commute, so we hatched a plan. We bought an M20 and put those guts into the M21 case (for the numbers). Next, we found a 400 small block and a set of big valve (2.02/1.60) big chamber heads and pocket ported them and had a 3 angle valve job done. Bored block .030 and zero decked with 5.7 rods. KB hyper pistons (this car is a cruiser, not a racer). Put in Lingenfelter's biggest flat tappet TPI cam. Used an aluminum L82 intake (ported) and an 800cfm Q jet. 1.6 SS roller rockers. Compression was about 9.3:1 In this configuration, car was very nice to cruise (even swapping to a 3.08 rear), but cruise RPM still wasn't low enough. A few years later, we got hold of another 400 block, did the same short block work (lower compression pistons) and went with tweaked Vortec heads. Same cam, iron Scoggin Dickey dual plane intake (ported again). 1.6 roller rockers again. This time, we swapped the Muncie for a 2.64 geared Super T10 and put in 2.73 rear gears. NOW he's happy with it. This car has plenty of grunt from a stop and the cruise RPM is tolerable. Modern OD trannys are nice, but sometimes you can tweak it without OD and still come up with a fun to drive car. Engine is about 440 HP, 500+lb/ft torque. Even with 2.73 gears it scoots. NOT a drag racer mind you, but a fun street car.

That's what I'm thinking and I don't exactly plan to baby it...I know the GV is bulletproof.

They are stout! Lots of motorhomes came with them. They suck a little power but so what. Nice to have od in ea gear if you want it

High torque motor with a 2.6x first gear you wouldnt be slipping the clutch as much still got OD. Looked into that prior to doing a 6 spd thought it was too expensive looking back maybe not so much

I have been advocating numerically lower rear end gears for years or steep overdrives for moderately powered V8's, especially BB V8's with big lower rpm torque for street cars for years. These type of engines can easily overcome the steep rear end/OD ratios with zero issues, on the street. My 88 5.0 Mustang LX V8 (225 Net HP/325 torque) with a 5 speed and 2.73 gear in that lite car was a hoot! If a C3 has 450-500 Gross HP it is going to move pretty well regardless of the ratios, on the street.

Where exactly are You going to put the Gear Vendors OD in a C3? Keep in mind that most 5 speeds have the same spread from 1st to Top gear as a 6 speed. 5 speeds weigh less and are smaller in size and cost less. There is a reason why the TKO 500-600 is the most produced aftermarket trans for Hot Rods. There are other options as well.

I think the GV fits a C3, not a C2 though...