Transmission question

[scotts72]

Hey guys have a question and looking for a solution. I have gotten my 68 driving but have found down here in Texas the stock 350 trans is not a good match, when you get on the road here you have to run 70 or 80 or you will get run over, at these speeds I am turning high rpms and the truck is screaming. I wanted to see if you all just deal with it or have changed the trans to something newer. Thanks for letting me pick your brains.

[Eddie H.]

Your choices are either going to an overdrive trans like a 700R4 (which is a pretty easy swap), or higher rear end gear ratio.

[mbradsher]

700R4 is a good swap not too hard to do. Just did it on my 72. still playing with the torque converter lock-up. Haven't found one that I like yet.

[Lee H]

That's a nice looking truck! I'm living with my 350THM until it goes out, then swapping to a 700R4. At 70 MPH I'm taching right at 3500.

[kwmech]

What rear axle ratio you running?

[scotts72]

I want to say the ratio is a 3.73 but I would need to check for sure. I wanted to ask because I am running into the trans leaking after sitting for awhile which is normal for older trans that hasn't been rebuilt. I just wanted to see before jumping into what was needed to do a conversion. My wheels and tires I guess are on the side burner for now. LOL

[leftybass209]

As stated, you have 2 options, overdrive trans or freeway flier rear gears. I have a 700r4 and love it. However, a 2004r and a 4l60, are also great overdrive choices with the 2004r having slightly more desirable gear ratios. The catch: if you do NOT have 3.42 gears or higher, your truck won't be in any hurry to accelerate off the line. I have 3.08 gears and it will move easily, don't get me wrong, it just feels underpowered. It also spins the gears at a real low rpm in overdrive.

[diceman50]

The 7004R is certainly a good transmission, but the first gear ratio is so low that it is almost useless unless you are hauling and/or towing heavy loads. The 200-4R has a better first gear for cruising in my opinion. (2.74 vs. 3.06) And it has the same .75 O.D. as the 7004R. Plus it is a close ratio transmission compared to the 700. Some might try to tell you that they aren't as strong as the 700 but I have seen them behind 600 horsepower Buick Grand Nationals with no problems. I have had both in my "Cruisers" and prefer the 200-4R. I recommend that you check them out before you make a decision.

Great looking truck!

[cdowns]

Those 200 trannys livin behind 600 hp grand nationals are $2500-$3000 setups not junkyard or local yokal places

[diceman50]

Originally Posted by cdowns

Those 200 trannys livin behind 600 hp grand nationals are $2500-$3000 setups not junkyard or local yokal places

Just an example. I don't think he needs one at that level and it has been my experience that you can build an equal quality transmission for about the same money. If your using junkyard stuff then use what you can find.

[Andy4639]

Since no one has mentioned it:

Gear vendor is another choice.

https://www.gearvendors.com/

[Z10]

I just made this swap earlier this year. Running a 700r4 from a 91 Corvette, 2400 rpm stall, 3:73 rear, and 30" tall tires. The engine is turning about 2000 RPM at 70mph.

I think you'll love the first gear, it will scoot off the line.

[mechanicalman]

Originally Posted by mbradsher

700R4 is a good swap not too hard to do. Just did it on my 72. still playing with the torque converter lock-up. Haven't found one that I like yet.

What part do you not like, the vacuum cut-out switch? Are you using a relay?

[outdoorsman310]

What size tires do you have? I have 265/75/16, I think they are 31". My rear is a 4.57 and i have a 350/350 it ran at 28/3500 on the highway. It removes carbon and you always have passing power!
A 700r4 would be a good option if you want overdrive. Make sure the kickdown cable is adjusted properly as it is very important.

[Tkmadone]

I just swapped a 2004r in for my TH400 and I love it. I have 3.54 gears and I now turn 2000 rpm at 70. I wired it up to lock the overdrive in 4th, which cost about $15 to do.

[Fitz]

Originally Posted by scotts72

Hey guys have a question and looking for a solution. I have gotten my 68 driving but have found down here in Texas the stock 350 trans is not a good match, when you get on the road here you have to run 70 or 80 or you will get run over, at these speeds I am turning high rpms and the truck is screaming. I wanted to see if you all just deal with it or have changed the trans to something newer. Thanks for letting me pick your brains.

Try an overdrive transmission like the 2004R or 700R4. I use a built turbo 400 backed by a Gear Vendors overdrive which gives about the same final drive ratio as the 700R4 but will take the torque of my big block which the 700R4 will not.