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TH350 vs TH400

S

srscout

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Dec 3, 2005
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utah
Hey All---- I am considering swapping out my SM465/205 in my crawler for a Automatic with a 203/205 Doubler. I already have a TH350 with a 203 range box bolted to it and several 27 spline 205's. I have a good friend who is a machinist so converting one of the 27 spline cases to 32spline is not a big deal.

So my question is this. Should I stick with the TH350 and 203 I already have? Or is it worth it strength wise to ditch the TH350 and try to find a TH400 with a matching 203? My rig runs a Chev V8 and is on 35's right now, but I am considering moving to 37's.
 
good light built th350 will hold up just fine .

my first truck had a built 400sbc / th350 with allision convertor - transtar reman kit - and no yoyo shift improver kit with a 205 on the back .

she did real good with 38" swampers on 1tons and 4.10 gears . lots of mud and snow abuse for me back in the day .

i have read over the years its 20-25hp loss going th400 over th350 for the internal parasitic loss.

i say get the trans built with good kit like transtar master reman kit and a no yoyo shift improver kit and good 4x4 style convertor and be good this way . and a th350 is shorter than a th400 is length is required for rear drive shaft to fit . granted only 2" or so . . .

@Greg Ducato is our trans guru guy he can get you dialed in real good on best bang for the buck .
 
Tried em all and went to standard doubler for good. Th400 is a power sucking hot box whereas the th350 wasn't near as bad. No strength issue with the 350 especially on such small tires and low doubler gearing.
 
Thanks for the info. I was kind of hoping that I could use the TH350 as in a lot of scrounging I haven't been able to round up a 400/203 combo yet. I talked to Steve Watson at EJS in Moab and after our talk I think that is where I will order my kit from. Working on narrowing the FF Dana 60 rear right now (going to try to keep it street legal if I can) so I guess the doubler will come next. The SM465 has been great, I'm just curious to try an automatic as Ive never had one in a serious 4X4.
 
Another related question. I have read that when figuring crawl ratio for an automatic you can basically double the calculated number and get a pretty realistic idea of what you will end up with vs a standard. Am I understanding this correctly? Or is this just not the case?
 
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