HELP! Th350 to Which over drive tranny?

[Bhaynes702]

Help! I need overdrive! What is the best tranny to go with? This is my daily driver and the gas is killing me. What I have is

66 GMC step side short box
305 CID out of a 85 GM
600 CFM Holly carb
TH350 tranny
As far as the rear end no sure yet

I'm looking at putting a 700r4 in it and need to know the best way and cheapest way about it. I'm a little over budget at this point ( I married a accountant). There is no computer all old school stuff. Except for the candy apple paint your help would greatly be appreciated

[Captainfab]

There are many, many, many threads in the Engine and Drivetrain' section of this forum on how to properly setup the TV cable and the TCC lockup on the 700R4. The TV cable is probably the absolute most important part of a 700R4 installation. If not done correctly, you will burn up your trans in a short time.

As for the rest of the installation, it really is quite simple. Especilly since you already have an auto trans now.

[pestwagon]

I replaced my TH350 with a 200R4 by Bowtie Overdrives (guy in Los Angeles sold my his with low miles and torque convertor for 1100. Mileage went immediately from 9-10 to 15-16. With lock up engaged truck cruises 65-70 all day...

[padresag]

I take that it is a 305 sbc and not a 305 gmc(even though they were not in production in 86).
what mpg are you getting now and what is your rear axle ratio? you probably don't require a 600 carb
how deep is your foot in it?
ron

[PGSigns]

If you g with a 700 you will need to shorten the drive shaft. Also get the TV made easy kit from Bowtie overdrives. Shifter of your choice. One thing that may also help out is swapping the rear gear to a 308. Most these trucks have a 373 in them.
Jimmy

[Tx Firefighter]

Originally Posted by PGSigns

If you g with a 700 you will need to shorten the drive shaft. Also get the TV made easy kit from Bowtie overdrives. Shifter of your choice. One thing that may also help out is swapping the rear gear to a 308. Most these trucks have a 373 in them.
Jimmy

Shortening the driveshaft depends on which TH350 he currently has. If they used the Th350 out of the same donor truck as his 305 engine, he will be good to go as is. There are three lengths of Th350 trans, the 6 inch, 9 inch, and 12 inch. The 700r4 is the same length as the 9 inch Th350 and consequently no driveshaft mods needed at all. In the 80s trucks, the Th350s used were 9"ers. Only way to know is gonna be to climb under there and measure the tail housing.

[parrisc19844x4_468]

You may want to consider converting your th350 to a lock up, that may be an option. When I just had my rebuilt they offered me that for extra $50.
The tranny builder claimed these would give me 2-3 mpg more. I don't drive it much so was not a consideration for me.
Not sure what else would have to be done though, experts may know

[Dubnova]

I think a 200r4 is the same size as a 350 so it should bolt up.

[chevy_mike]

I personally like the 200 better then the 700 due to a better 1-2 gear spacing. I hate the big drop between 1st and 2nd on the 700. The 200 is like a t350 with an overdrive gear. Both need to be built up to handle any power as they both kind of sucked from the factory.

[NEWFISHER]

"" 600 CFM Holly carb ""---to big for your set up

"" As far as the rear end no sure yet ""---if it's 3:07 or 3:42 you will be unhappy with a 2004r or 700r4 conversion

[61_FL_Apache]

Originally Posted by NEWFISHER

"" 600 CFM Holly carb ""---to big for your set up

"" As far as the rear end no sure yet ""---if it's 3:07 or 3:42 you will be unhappy with a 2004r or 700r4 conversion

I agree with the carb comment above.. The PO of my truck had a 750 on my 305. I replaced that with a 500cfm Edelbrock and it has worked a lot better.

I don't know much about the 200R4, but I if your are looking at the 700's, the earlier years of them have less or no electronics on them. Maybe around the early 90's.

[NEWFISHER]

If you go 700r4 you want an MD8 case. This was the later style and had all of the internal upgrades. Bowtie overdrives is a great trans supply company with good answers to any questions.

[Bhaynes702]

The condition I purchased the truck in was raw ill try to load the picks the rearend I'm unsure on but the engine block numbers are for a 85 GM. I,m trying to make it a daily driver. I'm not putting my foot in it at all. I'll double check the length of the tranny in it.

Thanks for all your help

[Bhaynes702]

Pic when I got the truck no interior no wiring or steering gutted inside

[Bhaynes702]

This is now

[Jeff La]

Originally Posted by Bhaynes702

This is now

Man really nice stance, what size tires are you running???

[Bhaynes702]

Running P275/60R15 all away around.

[chevyrestoguy]

Measure the tailshaft length per Tx Firefighter's suggestion, and then you'll know what direction you need to go in. Not having to shorten your driveshaft will save you a couple of hundred dollars.

Keep the Holley 600 carb, it's not too big, you'll be just fine. People tend to forget that the factory Q-Jet that they put on the 305 SB back in '85 was 650 cfm. If you're looking for maximum fuel mileage with a carb, a Q-jet is a good choice. Just remember that when you crack the secondaries, that all goes out the window. Bowtie Overdrives makes a kit called "TV Made Easy", and it has all of the adapters you need to hook the TV cable to your Holley linkage. As mentioned earlier, the adjustment of the TV cable is critical. It's not hard to adjust, but just make sure you do it before you decide to take the truck for a test run after the transmission install. You can smoke a 700r4 quickly if you don't.