The ST300 in my 64 has always worked pretty good. I recently wired in a kickdown switch since the original switch was missing. Made the car even more fun to drive. After settling on swapping in a 200R4, I couldn't bring myself to do it. The ST300 only had one real problem: screaming at 2800 rpm on the freeway at 65 to 70 mph.

So I bought a Gear Vendors OD/UD unit. After installation and a few test drives...man what a difference. It's probably a few hundred dollars more than swapping in a 200R4. Installation is pretty simple and involves removing the original tailshaft housing and installing a new one with an extension. I did it without pulling the trans. I did pull the crossmember though. And I did have to hammer the snot out of the trans tunnel just underneath the back seat (can't see it).

Besides the overdrive benefit, the unit can attach to any trans they make an extension/adapter for. So I can pull it if I want to IF I ever sell the 64. Their customer service was great. I needed a new speedo gear to adjust mine and after calling and giving info to them, they mailed another gear and housing. This thing rocks. The ST300 is now a 4 speed auto with 4th being a 24% overdrive (or something like that). Spend good money once....

 

HA ha, screaming at 2800... now thats funny. Thats not really a high RPM and these cars can do that all day long. On a side note, the GV units are extremely well built and can handle a lot of abuse.

 

Does GV unit works on 2:56 and 3:08 gears?

 

As long as your engine has enough power and does not lug at low rpms.

 

Why did you not add a GV to a T350 or a T400 and have a 6 speed automatic?

2800 rpm is anything but screaming at highway speeds. It is your car but this seems like money poorly spent to me. You can drive from Seattle to Miami and back at 2800 rpm and hurt nothing.

The ST300 is a boring 2 speed and I am amazed that you did not toss it on the parts pile. Pick up a cheap T350 and add the GV to it then you'll really have something.

 

Splitting gears on these transmissions is worthless. Why do you need a gear ratio between first and second, or between second and third? Modern small engines with very narrow toque peaks might need this. An Olds V8 does not. The time lost during shifting more than negates any minuscule acceleration improvement.

 

A stock 64 290 hp 330 is hardly a powerhouse and gear splitting would be advantageous. The main purpose of the GV is the OD and its ability to handle real power. The gear splitting is just a bonus.

 

I think that's cool that you went with a GV unit. I've always heard good things about their products and their customer service. Provide us pics if you get a chance.

 

Personally I would rather have a steeper first gear, which is why the TH350 would be a better choice (and the 200-4R is even better). The 2.52 first vs. the 1.76 first in the Junkaway makes a phenomenal difference. Do you really need a 1.97 gear between first and second in the TH350? You wouldn't use it around town, and on the track the shifting delay would kill quarter mile times.

The big advantage of five and six speed manual transmissions or the 200-4R is not just the OD, it's the much wider ratio from first to the 1:1 gear. If you have any kind of torque curve, that wide ratio makes for great off the line performance while using reasonable (mid-three ratio) rear axle gears. I can't understand why people pay a premium for M21s, for example. I'd much rather have a 2.52 first in the M20. For that matter, I'm actually on the lookout for one of the Super T10s with the 2.82 first.

 

To answer questions, I have an open 3.08 rear end and the GV unit works great. There are several options for ratios and GV will send you another speedo gear and housing if you need a correction. Free of charge. Just send the other one back.

The GV unit, to me, had several advantages over anything else. First, my ST300 works fine but I wanted an overdrive gear so cruising from LA to Oregon wouldn't be a chore for the engine or trans. I'm aware engines can run all day at 2800 and have no issues. I believe, however, that tired seals, rings and bearings will fail sooner under prolonged stress. The 330 in my car is original as is the trans. I like it that way. I've built a lot of cars and now I stay mostly stock. I'm in no hurry to pull the engine or trans. The OD nurses the car along at a little better MPG. I like that, too.

Putting in a GV was as simple as removing the tail shaft housing, installing the adapter and GV, unit, connecting some electrical stuff, and getting a shorter driveshaft.

I don't know if the TH's need a new driveshaft with the swap, but I also didn't have to install other brackets under the hood or modify my console shifter to work with a new pattern. In doing my math, adding up the cost of a 200R4, associated TV cable and brackets, slip yoke, shifter plate, cable, etc...it was marginally less than the GV unit. And the GV seems like alot less work. Even a BOP TH350 will cost a couple of hundres bucks, plus a rebuild. Local shops here want $600 to $800 to rebuild a trans.

I don't race this car and for daily driving, the GV unit was a HUGE improvement. Another advantage of the GV unit is the manual mode that lets you hold first gear with an auto-shift to 1st Over that's so fast you miss it if you blink. But you can hold 1st Over as long as you like, then manually shift to second. If i decided to drag race this car, 1st and 1st Over are all i would probably need. Maybe second gear. Maybe.

Another thing. Every time I called GV with a question, I was told, "Don't worry. You won't break it." And if I change rear end gears. GV will send me another speedo gear. Now I want one for the Saginaw 4 speed in my Chevelle.

Will post pics at some point.
Up next, Holley Sniper EFI.

 

I have gear vendor in my Chevelle. TH400. Yes, you will need shorter drive shaft. I went with a Denny's Driveshaft. The GV .78 OD helps but not that much. And like was said in earlier post, the gear splitting function may help RVs but not in Chevelle (with my driving anyway). I went with the button on the shifter. I think the best combo or the max combo with TH400 would be 3.73 rear. My TH400/4.10/GV is ok, but still high 3100 RPM at 70/75 mph. Stays strong in the power band, but the 4L65E combo might be better - or Tremec TK600!!

 

GV & 3.55 gears yields a 2.77 final drive ratio....silky smooth purr.


Of course no where in this thread has there been any discussion of tire size. Going from a 26" tall tire to a 28" tall tire will knock the RPM down another 150 RPM (approximately).

 

Running a GV with 3:73 gears 28" tall tire

3,000 rpm = 80 mph
With out GV 3,000 = 60 mph

Strictly used as OD no other benefit.

1/4 mile car & cruiser

 

I have a GV, 3.90 rear gear and im very pleased with the final 3.04 ratio. I also bought the 442 shifter ball with the switch, i only use it in 3rd. It is a very firm shift when it goes into OD.