My 700r4 bit the dust and left me with only first. Instead of rebuilding it myself or paying some outrageous price to have it rebuilt I want to put a th 350 into it. I was wondering how this would affect the driveability of the car on the highway. My main questions would be what would the rpms be like driving on the highway and maybe a guess as to what the gas mileage would be like with a 305 tpi. Any information about the swap would be great. I already went to summit and found the hardware but do I need a new driveshaft, or any other misc. parts? Thanks for the info

 

what rear axle ratio do you have ?

driveshaft same as long as you get a th350 with 9" tail

find them in 73-up 2wd trucks burbs blazers

good luck

 

I have 2.73 gears right now but i may go up to a 3.23 rear so I am not with the air plane gears they gave me stock

 

imho you would be plenty fine with 3.23 and 1:1 final ratio

you should go use an rpm calculator like at randysringandpinion.com and enter your info so you can see what rpm youll be runnning



good luck

 

thanks for the advice. I have one more question, one of my friends just offered me a 200 trans. he said that it is out of a buick grand national. is this the truth or is he just lieing, and would it bolt up to my engine, also would it be worth the swap is it strong enough to handle some power any advice on that tranny would be appreciated. thanks for your time

 

yes 200c wa sin alot of different cars over the years,

dont get it, its junk

plus its the wrong length for your car, you would need a 3" longer driveshaft

plus it may not even bolt up behind your engine

dpeending on what it was bolted to and what engine you have

it will safely handle the power of a weak 4cyl at best lol


ive had many of these trannies and many bad stories

one story in which cost me 700 bucks extra during a trip to oklahoma and back

i wouldnt trust a 200c around my driveway let alone around a block or farther


total junk



good luck

 

You're going to hate your car with 1:1 final drive after being used to O/D. Prepare to lose probably 3-5 mpg as well, with no lockup and no o/d. I just bought a 1987 305 TPI complete, immaculate engine w/ all accessories, with rebuilt 700R4. This whole lot cost $110, even including shift cables, manifolds w/ smog lines, etc. A 700R4 should not cost much to replace with a used one.

 

Buick GN's have 200R4's in them, which is a 4speed AOD. A 200C 3 speed auto & is found on the low power drive trains of the late 70's & early 80's & it is weak. We repaired hundreds under warranty back in the day when they were new.

 

Through the 60's and 70's millions on cars and trucks had a TH350 and they're still driving up and down the highways. Hard to compare trucks though because they normally have a 28" tall wheel while most cars have a 26" tall wheel. The taller wheel can get away with a deeper diff gear.

The only disadvantage with the TH350 is not having an OD. All the OD will do is bring your cruising rpm down a bit which will increase your fuel mileage slightly. Unless you go with a real aggressive diff gear like 4.10 - 4.56, you won't notice much of a difference. For lots of highway driving I don't think I'd even suggest a 3.73 gear with a short 26" tall tire but it depends on what your final fuel mileage is going to be. My truck currently gets around 10 mpg and it doesn't bother me. 4L80E tranny, 4.10 gears, 28" tall tires and 4600 pounds.

The 700R4 became a perfect street tranny. With highway gears in the diff like the 2.73's, the 700R4 offers a very low first gear to help get off the line quicker to compensate for the highway gears and the OD brings the rpms down even lower for fuel mileage.

 

Well, I did the swap on my 89 IROC and I still have the 2.7x series gears (stock in the B/W 9 bolt). My stock 700R4 also ate it and left me with only 0-4500rpm in first (everything else was slip). I got a rebuilt TH350 out of a truck, re-used the stock driveshaft. I have a different rearend with better gearing but after driving the TH350 on the freeway I decided to leave these stock ones in. I would consider it a drastic change at highway cruzing compared to the 700R4, but everyone has their own opinion. Cruzing RPM's went up over 1000rpm @ 60mph and MPG went down the tubes. Its great at the track but crappy on the freeway. Now I drive everywhere at 45-50mph. hahaha

 

yeah going from say 2.73 to say 3.42 would be a drastic change

dont forget tire height and other factors

imho 3.42 and no overdrive is fine

but 3.73 with shorter tires and no overdrive is more than most ppl like

but wont hurt anything

its all personal preference really
how much highway driving you do, etc,



good luck