Rebuilding.. TH350 or TH400?

[PFenstermaker]

Hey everyone.
Grew up on GM muscle cars, then got into the diesel world for awhile.
I picked up my '75 C10 a little bit ago on a trade, it ran great for about a year, and then spun a rod bearing.
Hoping to finish a modest engine rebuild in 6 months or so as money comes in, but I think I'm going to tackle the trans first while the truck's apart, it's had some slip in it.
I'm hoping to get 350-400 lb.ft. out of the motor when it's out back together. The truck is my weekend driver/work truck, to keep the hard miles off of my 01 Tahoe. I probabaly just drive it 65% of the time, but also do tow 1000-4000 lbs. on a fairly regular basis, short trips in no hurry.
The motor will be built to have a little fun, but not at the expense of it's usability.

I guess first, I've just assumed a 2x4 '75 C10 had the TH350 in it. How to confirm?
And second, do I rebuild a TH350 right, or should I switch to the TH400 or something else? On a pretty limited budget, and not too worried about fuel economy or speed for this truck.

Thanks!
- Paul

 

[1987 GMC Jimmy]

Hey everyone.
Grew up on GM muscle cars, then got into the diesel world for awhile.
I picked up my '75 C10 a little bit ago on a trade, it ran great for about a year, and then spun a rod bearing.
Hoping to finish a modest engine rebuild in 6 months or so as money comes in, but I think I'm going to tackle the trans first while the truck's apart, it's had some slip in it.
I'm hoping to get 350-400 lb.ft. out of the motor when it's out back together. The truck is my weekend driver/work truck, to keep the hard miles off of my 01 Tahoe. I probabaly just drive it 65% of the time, but also do tow 1000-4000 lbs. on a fairly regular basis, short trips in no hurry.
The motor will be built to have a little fun, but not at the expense of it's usability.

I guess first, I've just assumed a 2x4 '75 C10 had the TH350 in it. How to confirm?
And second, do I rebuild a TH350 right, or should I switch to the TH400 or something else? On a pretty limited budget, and not too worried about fuel economy or speed for this truck.

Thanks!
- Paul

To check and see what transmission you got from the factory, I'd cite the RPO sticker in your glovebox if you still have it. If not, there are sometimes ways to procure a build sheet on your truck. Sometimes not. If you're just asking which transmission you have now, I'd just look up TH350 and TH400 pans on Google and see which is yours. Sorry, I just wasn't completely sure if you were asking what you were supposed to have in it or what you already had in it. Either option works well for what your needs and expectations are. I will say that a TH350 would have to be built to match the 400, but if it were me, I'd just keep whichever transmission is in your truck and rebuild it/build it up as needed to keep your crossmember location, driveshaft length, output spline number, etc. all the same. That'll be a big money saver right there. Also, if you want someone to rebuild it for you, you'd save a good little chunk of dough by doing the R&R yourself if that's something that you had the time to tackle.

 

[74 Shortbed]

I guess first, I've just assumed a 2x4 '75 C10 had the TH350 in it. How to confirm?

Easiest way is crawl under the truck and look at the pan..

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[PFenstermaker]

TH350 confirmed

Awesome, thank you guys.
It is a TH350. So. Rebuild that? Or fond a TH400 to rebuild if I'll be towing pretty often?

 

[74 Shortbed]

Keep it simple and save time and money, just do a heavy duty rebuild to suit and you'll be just fine, I've done a ton of towing with a TH350 with no issues..

 

[RangRayy]

keep the TH350 pretty strong transmissions. my '87 has one in that used to tow a fifth wheel camper from Missouri through the hills of Tennessee down to Florida with no problems twice a year. granted now that I have the truck it doesn't see much towing anymore but would put it up against anything.

 

[Rusty Nail]

Add a shift kit ($50) and and auxiliary transmission cooler, ($50) - (as big is possible) to extend transmission life and aide in worry-free towing and fun.

 

[crazy4offroad]

Sorry, I'm feeling lazy, but most of the mods in this post would be great upgrades for higher horsepower demands and towing, but I would leave the #2 and 3 check balls in place for smoother shifts...
http://www.gmsquarebody.com/forum/showthread.php?p=167270&highlight=dual-feed#post167270

Edit: Here's a thread with a bunch of tips
http://www.gmsquarebody.com/forum/showthread.php?t=14404

 

[PFenstermaker]

Ok, TH350 rebuild it is.
I appreciate it, guys.

 

[PFenstermaker]

Torque Converter?

Hey guys, next step..
From my understanding, I can do a torque converter for either a TH350 or TH400 to pair with my TH350, depending on which flywheel I have. How to figure that out? Any other issues or reasons not to go with the TH400 one? Seems like a no brainer to go with the heavuer duty option..

Thanks
- Paul

 

[Honky Kong jr]

Count the teeth 153 small pattern 168 large if 168 check for 6 holes with 3 holes out further the the other 3 dual pattern. As stated in last thread.