Hello all,
I would like to swap my TH350 with an automatic overdrive transmission for better highway cruising RPM's. I have a mild 455 that powers my 1970 Cutlass Supreme with a 3.42 gear. Just wondering what everyone's opinion and advice is on the matter. Reliability, cost, pro/cons, etc. The three that I would like comments on are the following. Please forgive me if this has already been discussed in a another thread. Please add the link if so.
4L80E
700-R4
200-4R

Thanks in advance for any advice you would like to share!

 

If you scroll down towards the bottom of this page there are a few threads related to your question. I personally are from the camp of "if it ain't broke..." For the amount of miles that these old cars are driven, I see no reason to change your setup. The T350 will last a long time behind a mild 455 as long as it's beaten like a rented mule. It will take many years to recoup your investment costs based on fuel mileage.

 

Kevin is it the 3100 rpm at 70 thats bothering you or the mileage ? or both ?

Off the top of my head a factory high performance 200-4R would be the most direct fit that can handle your power production. GNXs share your exact performance. While hitting their 200-4Rs with 400 lb-ft net at 3900 rpm. Thats its real rating, they were in fact underrated from the factory. And people have pushed them and the like much harder with no issue...

Assuming your tires are factory height which is 27 inches. If you go with a 200-4R your engine will be turning 2100 rpm at 70 mph. If your like me over 50 and becoming less and less noise tolerant. When my car is taching 3000 rpm it now feels like my car is stuck in second. Its not, it's just so loud that it bothers me if cruising at that speed, it fills my head.

If you are still going to the track I would think the 4L80E will slow you down the most. As well as seemingly needing the most done to your present set-up to work correctly.

"The 4L80E is based on the TH400 internals, so it's strong, BUT, it's also much larger and heavier. The driveshaft needs to be shortened. The crossmember needs to move further back than even the TH400 location. That raises the issue of custom e-brake cables, since they hang off the crossmember. The floorpan will need to be cut and reshaped to fit (or at least smacked soundly with a large hammer). Of course you'll need the Chevy-to-BOP adapter plate. And yes, a stand-alone computer is also required." Joe Padavano Oct 26, 2011 post # 5 of https://classicoldsmobile.com/forums...2-455-a-41309/

 

These cars were designed to run all day long at freeway speeds (70MPH when they were new) without OD. You're going to spend upwards of $3K to do this, no matter which trans you pick, since neither the 200-4R nor the 700R4 will live behind a 455 in stock form. If you MUST have OD, get a 4L80E.

 

Don't forget that Gear Vendors is an option.

https://gearvendors.com/index.html

 

Absolutely Joe, and I completely agree. Been driving these same type of cars for 40 years. Going back to driving my dads 1970 Coronet on my permit in 1985.

With that said my tolerance has changed. Or I just became an old man early ... Maybe it's that my senses have been slightly blurred by driving far newer cars here and there that cruise on the highway at sub 2000 rpm. And my mind now tells me that the 69 is working hard at 3000 rpm.

 

I have several old cars. My snub nosed van has a 4.11. I have had it to 70, but I spoke with the Lord first, and it wasn't for long (either the conversation or the time at speed.) I have a Monte Carlo with a SBC 4 barrel 350 and a 2.73. One H/O has a 3.23 and a 455, and the other has a 3.08 and 455. I live in the midwest where I may go a couple hundred miles on a road trip to a car show. I like flooring it as much as any other.

I am of the opinion that 2.73 and 3.08 are ideal highway gears. 3.91 and 4.11 are truck and dragway gears. 3.23 and 3.3 may be the best all around gears. 3.42 seems to be like a street brawler gear to me, like a compromise to drive it to the track, and to do ok at the track, and it may do well at neither.

My recommendation is for OP to change his rear to a 3.23 if possible.

I do prefer driving my SBC Monte Carlo over the 72 H/O in terms of road tripping.

 

3.42 to 3.23 is less than a 6% difference in RPMs

 

I won't/don't sweat 3k plus cruise speeds. I've held nearly 4k for hours and hours before.

 

But we're talking about feelings, Joe. Feelings aren't logical. Some people think a few hundred rpm matters.

 

So, my purpose in the OD transmission is to help the 455 live as long as possible. Hours at time at 3100-3400 RPM at ~70MPH will take quite a bit of life off of the engine. Thanks for information thus far from everyone. Keep it coming!

Looks like the gear vendors price is $3,195.00 now. Ouch!

I was thinking that no transmission tunnel modifications were required for the 4L80E. My brother has 1970 Chevelle that has a 4L80E in it and I am pretty sure he did not have to modify the transmission tunnel.

 

[QUOTE=1970CutlassSupreme455;1620852]So, my purpose in the OD transmission is to help the 455 live as long as possible. Hours at time at 3100-3400 RPM at ~70MPH will take quite a bit of life off of the engine. /QUOTE]


No, it won't. Huge misconception thats been parroted over and over again.

 

No, it won't. Re-read post #4.

Keep in mind the GV price is parts only. Unless you can DIY the whole project, you can expect to be into it for twice that before you're done. I would budget similarly for any OD transmission swap -- three grand for a decently-built unit and then the same again to fit it properly.

Your car, your project to prioritize. Myself, I love the sound an Olds V-8 makes cruising at 3200 RPM (which is, conveniently enough, also the engine's torque peak -- when I nudge the throttle at speed without kicking it down, it's like a giant hand pushing me forward). If I want low revs and fuel economy on the freeway, I have a Honda CR-V.

 

How expensive are those other options? For a 4L80E you'd need a controller to interface with the computer. For a 2004R you'd need hardened parts to withstand the torque of a mild 455. For a 700-R4 you'd need an adapter plate.

 

I priced a 4L80E in April of 2023 from TCI and here is their cost:

Trans: $4,400
Saturday night special Converter: $800
Controller: $795
Trans Adapter: $85
TPS sensor for carb: $185

Grand total of $6265 and will still need a new crossmember and driveshaft.

 

And that doesn't get it installed. Are you capable of doing that yourself?

 

Yes, I could do the work. I think this option is the most expensive like Olds64 stated.

 

I've wrestled this demon a few times. First, everyone that says "no modifications needed" should add a disclaimer (or you should imply) that it only applies to your car. Second, determine your wildest anticipated antics. ALWAYS overbuild to avoid doubling back. Third, is cost feasibility.
A TH350/400/Gear Vendors is a very cost effective option, but may require tunnel modifications.

 

Another 4L80E option: pull a part or marketplace. Try to find one with a warranty, or fresh fluid, or ideally one still in a vehicle. If the unit is greasy/oily with radish fluid, it’s probably worth rolling the dice. Drop the pan, if the pan isn’t full of debris, then it’s worth a chance.

The nice thing about a 4L80 is unless your making 800hp, a fairly cheap shift kit is all that needed.

If you shop carefully, I’m confident you could do a 4L80 swap for 2500 bucks.

 

I wouldn't buy any used transmission if I found radish fluid in the pan.

 

$2500 with the computer?

 

Mail ordering a 4l80e is a waste. They are so common any builder can rebuild one with their eyes closed. Last one I had done on a bench build was $900 without the converter. That was before covid though.. there is nothing wrong with TCI

 

You can drive it all day long at those RPMs and the 455 will outlast you.

 

You can use this search engine to find a transmission in a salvage yard near you.

http://www.car-part.com/

 

I will say that I was originally skeptical of car-part.com, but I've used them a couple of times now to find unobtanimum parts for my 1988 Firenza wagon. Both times I was able to find what I needed at a reasonable price.

 

Good to hear that it worked for you Joe.

I was able to find a core 7.3l IDIT engine (from a 92 F350) in a salvage yard in Ft. Worth, TX a few years ago. I think the key is that if you want to find an older part, you have to expand the search area.

 

Yes, if you shop carefully. I have a few friends who have made the swap, that’s about what they spent.

Last time I looked, the computer was 600ish bucks. Figure 500 for a good used transmission, that leaves lots of pocket change for all the little things that go into making the swap. Obviously, if the combination needs really fancy converter, the price will go up. But for a mild engine I’m betting a stock remanufactured converter would be adequate.

 

Agreed. If I found radishes in the fluid, it would be smart to just “lettuce” sit right there.

 

I had a Fastgate shifter, no way the column shifter would work, so price that in, free for me. $1500 for a low mile reman trans with the reman converter that flashes at 2100 rpm. The braided cooler lines $75 and $200 driveshaft from Amazon, the 96 to 05 Blazer was the application. Just needed the factory 1350 yoke with a 32 spline vs the supplied 27 spline yoke. The seller included the 32 spline yoke with my trans and it had a rear 1350 to 3R conversion joint, perfect with the Type O 12 bolt. I rigged up the emergency brake cables to work. The cheapest I have seen is $500 for a controller. For me it was the difference between a Terminator X and a X Max. Even with a new shifter, it would have squeezed in under $2500.

 

I purchased a flawless passenger door in the right color for my Tacoma back in the day and swapped it to avoid painting. Saved some few hundred. From that car-part site.

 

This has gone through my mind more than a few times. I have a 66 with a Gear Vender that I just installed. With more clear hindsight I should have gone with the 4L80E. I thought about the 2004-R quite a bit, but the lowering availability of parts and the TV cable bullshit turned me off. Like I said, hindsight, 4L80E with a manual valve body. I thought the Gear Vender would be simpler with the Tri-Power, but its really not.

 

Why do you think a 4L80e would have been easier with your carburetor setup? Does the Gear Vendors use a throttle/kickdown cable like the 2004R?

Running a manual valve body is a pretty drastic step. I considered putting a manual valve body in the C6 in my 86 F250 but instead had the metered vacuum orifice (VRV) rebuilt by the 1 online shop available.

 

I have a gear vender in my car, it’s been there a long time. I had a couple things going in my favor to justify buying it, number 1 was the fact it’s the ONLY thing I have ever successfully bid for on eBay, and number 2 back then the computers to run it was ridiculously more expensive than now.

Having said that, if I was looking for overdrive today, I’d go 4L80 without hesitation.

 

The Gear Vender is a tight fit in the 66. It requires a custom crossmember or the offset one I bought to make it work. Also a little tricky to get the pinion angles right.

 

You can leave a Gear Vendor in overdrive, correct, and essentially have a 3 speed with highway gearing?

 

So, essentially a six-speed sort of like the Columbia Dual-Ratio diffs of the 1930s, only upstream?

 

Correct

 

So, the transmission finally gave up this morning on the way to work. Its about to get towed to the house. I was WOT and shifted it into the 3rd and lost power through the transmission. No forward or reverse gears work. Luckily I was able to get into the parking at work. I am leaning toward a built 200-4R from extreme automatics. I have heard good things about this company and their 200-4R's. Remind me again what parts I will need? Will I need new crossmember and driveshaft and e-brake cable? Anything else? Reminder that the car currently has a TH350 in it with a mild 455.

Transmission
Converter
Crossmember?
Driveshaft?
E-brake cable?
Overdrive detent for the console shifter

 

Move the crossmember to the TH400 position, reuse the drive shaft and get TH400 emergency brake cables. Speedometer hook up is the same, will just need the right gear combo and get whatever lock up control appeals to you most. The 2004R is an easy swap in place of a short tail 350. Shiftworks for the shifter modifications, I believe and get a converter to match your current cam specs. About the lowest I have seen from a 2004R stock converter is 1900 rpm flash stall. Tell Extreme where you want WOT shifts, stock is 3000 rpm to low 4000 rpm for most stock 2004R trans, obviously needs modification, not hard, just trial and error. Good luck.

 

Th350