[grivera]

My 66 came with a Gear Vendors (GV) unit installed, 3.90 12 bolt posi from a 66 Chevelle, TCI TH350 (unsure on power rating)or converter - other than it’s red and looks like a Hughes. The prior owner didn’t want to alter the trans tunnel so instead added 1 inch bushings above the rubber frame to body mounts to clear the GV unit. This led to him removing the rag joint and going with a u-joint connection. He destroyed the lower steering column bushing in the process. I pulled the trans and GV unit yesterday to remove the “body lift” and installing a Borgeson steering gear with a rag joint.

I have a nice TH400 built by Hossler that used to be in my 69 bird before I went 4l80e. I will install the TH400 in the 66 Lemans and if I choose to reinstall the GV I will need the TH400 to GV adapter that’s about $1200 . And then I have to alter my trans tunnel either with a BFH or cutting/welding.

Or I can sell the GV and swap the rear gears to 3.45-3.55. My overall plan was to install 275/60 15 tires in the rear so about 28” tall. Use of the car will be mainly local and one or two times a year, three hour trips. I do want to visit the track periodically with this one.

Currently in process of upgrading the top end - 455 .030 over, 310 KRE D Ports, port matched Torker 2, 236/245 HR, 6.27/6.30 lift with 1.65 rockers, 850 DP, 1.75” Doug’s Headers, 3” exhaust all the way to tails, Flow Master 40 series mufflers.

Help me decide what to do re: the GV unit.

[tom s]

Sell it all and maybe a 200R?Tom

[Lemans64]

Engine probably won't be happy with the O/D unit unless your doing 80 mph. I run 255/70/15 (29 inch tall) and a 3.9 rear gear, 2700 at 65 mph. Have made a few long trips but don't
drive that fast for long distance. Ditch the Gear vendors and drive it for a while to see if you like it that way. Can alway go back if you keep it for a while.

[grivera]

Originally Posted by tom s

Sell it all and maybe a 200R?Tom

I’m not opposed to one of them - though I haven’t checked the going rate for one that handles a very stout build.

Lemans64 - what’s your engine build?

[Lemans64]

LOL, it's got a SBC 400. Solid roller motor, So maybe a little different than what yours may be. LOL.
It's a Canadian Pontiac engine. LOL. Engine likes 2500 cruising minimum.

[Half-Inch Stud]

Overdrive is needed for 400+ PMD and 70 mph higways. How you get OD will be the decisions made. Highway 2.56:1 posi rear gear is also a choice.

[64speed]

My first Pontiac had a complete 66 GTO driveline with 2.56. Even with that it would just roast the tires.

[Formulajones]

Gear vendors only have a .78 gear reduction so it's not a ton. With your 3.90 gear and a 28" tire, just going 65 is still 2400 rpm and that's figured with a locked converter which you don't have, so you could possibly add 200-300 rpm to that figure. So it's not like it's going to be loafing down the highway. And without a lockup it's not going to have the buck and kick syndrome at low rpm either. If you have trouble tuning around that then this setup really isn't a bad deal.

Me personally, you know me, I prefer the overdrive in the transmission. And to be honest you could easily loaf your combo down the highway at 2000 rpm if you wanted. I do much more radical combos that cruise fine at very low rpm. The key is fuel and timing and when and where you have the converter lock. That's the beauty of having an electronic control lockup, I can make it do what ever I want and tailor it specifically to the engine.

It's up to you really but since you already have it you may as well use it. If I had one laying around I'd probably throw it in something just because it's there and paid for, but since I don't, I typically just buy overdrive transmissions.

[b-man]

Bang on the tunnel and make clearance for the TH350/Gear Vendor combo like rhe previous installer should have done.

Zero dollars invested.

Or sell everything transmission related you have sitting there and put a 4L80E in it.

If you can do without overdrive put 3.07 gears in the 12-bolt and run your TH400. Play with different tires between 27” and 29” to get the rpm where it suits you best.

[grivera]

If I didn’t have to buy the TH400 adapter it would be an easier decision. Unrelated, but the GV phone rep I spoke to was pretty rude - like he wasn’t in the business of selling parts.

[Formulajones]

I'd almost say my son could be interested in your gear vendor, since I just built a 350 turbo and installed it in his vega. That deal is supposed to be short lived because he ultimately wants to do a 4L60E in the car at some point next year, so I don't want to say for certain. The drives to Phoenix and other distances we go may have him move a little faster on deciding LOL

[grivera]

Any experience with the strength of a TCI Streetfighter TH350?

[Formulajones]

I had a street fighter turbo 400 back around 1988. I killed it after a couple years running it in my Chevelle when it still had a fairly stock 454 in it. It was losing second gear and when I tore it down the clutches were toast. It did have nice stuff in it with red altos etc.. but something wasn't setup in it correctly. They did help me with about a week worth of diagnosing when it stopped shifting hard in 2nd, checking line pressure and all the usual stuff, even changed the pump and valve body, so customer service was good right up to the point I told them it had to come out and completely gone through LOL. I still have that thing sitting on the shelf. Haven't bought another TCI product since. That's when I started building my own transmissions.

[HWYSTR455]

I did a TCI street fighter TH400 in the 90s, had to flush the heck out of it, the amount of crap that came out was so much it was like they had to have put crap in it, or so it seemed. But after the flushing, I got many years out of it. But that was a TH400, and it was in the 90s, so...

Hampton (at Vienna trans shop) went through it when I went to a 4L80e and it's in the 442 now.

I'm with B-Man, sell it all and go 4L80e. Hands down a better driving experience over a GV.

And 200s these days are a crap-shoot. Not to mention a built one is about the same cost as a 4L80e setup. You can talk about cost of a controller, but keep in mind, to do a 200 'right' you still need an MPH controller & vacuum switch, as well as a TV cable setup. You can do a delay lockup switch, but the MPH controller is a much better experience. (It sux when they 'hunt').

Jake Shoe and CK both recommend a 4L80e these days, and they were/are some of the best 200 builders in the country. There's no question if a 4L80e will take the punishment.


.

[chuckies76ta]

Originally Posted by grivera

If I didn’t have to buy the TH400 adapter it would be an easier decision. Unrelated, but the GV phone rep I spoke to was pretty rude - like he wasn’t in the business of selling parts.

I think you have your answer right there. I considered the GV unit years ago. I think there a great unit. personality now I would go with the 4L80E tranny if I was gonna change anything.

Having said that, Use your well built Th400. It will never let you down if done right. I would get your engine done and install the TH400. Install your 28" tires. Engine should be making around 550 H/P when done. Now drive the car around and find out where your engine likes to cruise at rpm on the highway/street.
Then change your rear gears to accommodate your combo for the highway/street of your liking. I'm thinking something around 3.08 gear. Maybe even lower numerically (2.73) will even be better. Your definitely gonna have to ditch the 3.90 gear. Only other thing will be a decent converter and install a cooler for the transmission. You can use these calculators to help you choose your rear gearing.

https://spicerparts.com/calculators/...rpm-calculator

I was just looking at your speed limits on interstates and local limits. anywhere from 35 mph to 70 mph. So your gonna want a rear gear to accommodate the interstate. Keep that in mind.

[chuckies76ta]

4L80E Transmission. Built of the TH400 platform. Awesome Transmission. Now you'll need a converter and controller. Your looking at $5000 easily. Yes/no? thoughts.

[ta man]

I would run the th400 and a 307 gear.

[HWYSTR455]

Not a straight-forward answer. In stock form, a 4L80e is rated at 700hp/80ftlbs, but that can be debated. IF you are buying a 4L80e, you probably want some mods, which pushes the cost up some.

A general rebuilt 4L80e can be had in the $1600-$2400 range, depending on converter. So cost varies.

Controllers, um, vary. But in general, are in the $500-$750 range.

Crossmembers also vary, and some of the more inexpensive ones not sure I would trust fitment, but are in the $100-$375 range.

.

[slowbird]

If performance is a concern 4L80 will cost you a little. 400 with the gv is the ticket if performance is the goal.

[OCMDGTO]

T400 all the way! Make sure your converter stalls in the high 3's and have fun. If it turns out you don't like the 3.90s drop down to 3.23s