Do I have a TH350 or TH400 .....


OSUCowboy27
06-05-2006, 01:51 PM
in my 1977 3/4 ton Chevy Suburban Trailer Towing Special, 350 ci, 2wd. This vehicle was built to pull so I am thinking it is the TH400 but I always thought itwas the TH350. How can you tell the difference? Both have 13 bolt pans.

BTW, it has 4.10 gears and 115000 miles on it and can do 140 mph. It has slightly larger tires than stock to help get better mileage but it only gets 14 mpg when pulling or not.

2000CAYukon
06-05-2006, 08:19 PM
in my 1977 3/4 ton Chevy Suburban Trailer Towing Special, 350 ci, 2wd. This vehicle was built to pull so I am thinking it is the TH400 but I always thought itwas the TH350. How can you tell the difference? Both have 13 bolt pans.

BTW, it has 4.10 gears and 115000 miles on it and can do 140 mph. It has slightly larger tires than stock to help get better mileage but it only gets 14 mpg when pulling or not.

What shape is your tranny oil pan? The Turbo 350 is mostly square but with one corner cut off. The 400 pan is very different than the 350 pan.

//2000CAYukon

MT-2500
06-05-2006, 09:58 PM
in my 1977 3/4 ton Chevy Suburban Trailer Towing Special, 350 ci, 2wd. This vehicle was built to pull so I am thinking it is the TH400 but I always thought itwas the TH350. How can you tell the difference? Both have 13 bolt pans.

BTW, it has 4.10 gears and 115000 miles on it and can do 140 mph. It has slightly larger tires than stock to help get better mileage but it only gets 14 mpg when pulling or not.

Also have a look at the shape of them tires at 140 MPH.
Unless you have tires built for that speed you are in danger of blow out.
MT

idmetro
06-06-2006, 10:04 AM
Here's a link to a page in the LMC truck catalog showing th shape of the pans on the different transmissions.
http://www.lmctruck.com/icatalog/csb/0012.html

OSUCowboy27
06-06-2006, 03:22 PM
Thanks guys, it is a TH350. Should I replace it with a TH400 or stick with the TH350. I inherited this vehicle from someone that did regular maintenance except for the trans. He never changed the fluid and did lots of pulling. I changed it at 85000 a few years back but the damage was done. It does not slip but the shifts are weak and erratic. It has a trans cooler seperate from the radiator which probably helped it not crap out sooner.

MT-2500
06-06-2006, 04:07 PM
Thanks guys, it is a TH350. Should I replace it with a TH400 or stick with the TH350. I inherited this vehicle from someone that did regular maintenance except for the trans. He never changed the fluid and did lots of pulling. I changed it at 85000 a few years back but the damage was done. It does not slip but the shifts are weak and erratic. It has a trans cooler seperate from the radiator which probably helped it not crap out sooner.

Change the filter and fluid and adjust the TV cable and modjulater valve to get a better firmer shift and see what it does.
Also a good running engine helps on a good trans shift.
MT

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