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TH350 troubles... Time for 200 4R/700R4?


Krobb2000

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Well... I'm in a little predicament.  Bought my Monte and was able to drive it a few weeks and then trans fluid starts puking out.  My wife said she can follow my trail all the way up the driveway to our house.  =]   The leak is coming from between the engine block and the trans.  My assumption is it is a seal or a pump or who knows.  Fluid starts pouring out as soon as the car starts up, doesn't need to be in gear.

So my predicament is do I repair the TH350 or just jump into the overdrive world.  I know OD would make it nicer on the freeway.

Anyway, what's the consensus on swapping?  200 4R or 700 R4?  the 200 looks easier to swap but costs a few more bucks?  I'm sure there is a thread somewhere in the archives that details the swap, but if any of my fellow FGMCC have some advice or links, I'd love to hear it.

Thanks in advance!

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Krobb2000. Sounds like the pump seal. A fairly easy and inexpensive fix. It is the seal for the torque converter. I would r&r the seal and enjoy the car while you make up your mind on which overdrive to use. Everyone has their favorite and their reasons why. With that being said, my vote is for the 200r4. A grand national unit or Monte SS. Better valve body and servos. I don't like the gear spread from 1st to 2nd in the 700r4. Again, my .02

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My TH400 leaks at the front seal too, I replaced it years ago and it still leaks, my transmission guy said the next time I replace it to also replace the bushing for the torque converter in the pump.

 

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2 hours ago, MC1of80 said:

Ian, also think about the torque converter. Most likely worn also, the hub. 

It is new, or at least it was 15 years ago :lol:

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22 minutes ago, Ian said:

It is new, or at least it was 15 years ago :lol:

The usual causes of a bad bushing is usually a bad hub on the torque converter. (Not centered or crooked) . If just the seal, a groove worn into the hub where the seal rides or like most of us, not using the car much and the seal drying out. 

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  • 4 months later...

I put in a 2004R from a '86 Monte SS in my 72. Paired it up with a 3:31 rear gear (my car is a cruiser and low highway RPM's were my goal). At 70 mph my car cruises around 2100 RPMS. A 3:42 or a 3:55 would work good with a 2004r as well. 

And by the way if anyone incorrectly tells you that a 2004R can't handle a lot of horsepower, show them this video. I had an egghead at Jeg's call my transmission "a grenade" when I called to order parts one time (been shopping at Summit ever since).

https://youtu.be/_DDswtLUhdM

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  • 2 weeks later...

Quick update, Had the front seal and bushing replaced.  Trans guy said the rest of the trans looked in good shape and clean.  Now I need some good weather and no salt on the Michigan roads for a few laps around town.  =]

Still contemplating the OD swap. 

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  • 6 months later...

I have a 72 with 350 4 barrel 350 turbo and 3:31 posi rear end. At 70 MPH And I’m running 3500 rpm’s. Would like to run less rpms. Contemplating a 2004R. Please make a recommendation on where to get complete changeover kit.

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I changed to a 200r4 because it is a direct fit which makes installation a breeze. The only modifications needed were the shifter detent plate, the shift cable and carb linkage. I cannot speak for the 700R4 guys but I really like the overdrive on the highway. I would recommend gears a little shorter than my 3.73's if you are looking for fuel economy. In hindsight I would have been happier with 3.55's but I let someone talk me into the 3.73's. Oh well, it works well and I am pretty happy with both the acceleration and fuel mileage.

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rpm's and gear ratio is calculated with tire diameter included. I have P275/60's(29" tall tire) with 3:42 gear at 70 mph I'm right on 2200rpm in overdrive. taller tire, less rpm's. I'm going with 3:73-4:10 gear next. I do like the OD when traveling,post-259-0-61935100-1474727657_thumb.jpg

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