I've been told that putting a shift kit in my TH350 will make it last longer behind my 396 and I don't really need a TH400. I've been under the reasoning that the 400 is built stronger to begin with and was meant to go behind BBCs.
TH350 vs TH400
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neither are as strong as a properly built powerglide. however i have built more than my fare share of 350s and 400s. the 350 has less moving parts inside and is generally stronger. i usually dont like shift kits, but if you get a name brand one with stronger clutch packs, then you will be good.
the newer 4L80Es are currently used in the trucks, including the 8.1L IIRC. if you can swing that it will be an awesome setup.
the newer 4L80Es are currently used in the trucks, including the 8.1L IIRC. if you can swing that it will be an awesome setup.
Their are a bunch of mods for both transmissions. The big things are choseing a good friction material, beefed up sprage(sp) and forced lube to the sprages(sp), beefed up gear set, best Tq/converter you can afford, fully welded band instead of just spot welds etc......It helps to install a pan with a drain bolt so youcan drain and refill transmission easily and freq.! Either trannie can be made to work very well your application.
Most of my experince is with beefing up older 700R4's!
Have things changed?? I thought the TH400 was the stronger trans.
Thats why they put them in motorhomes, trucks and certain Rolls Royce vehicles.
Have things changed?
Thats why they put them in motorhomes, trucks and certain Rolls Royce vehicles.
Have things changed?
Wouldn't it just be easier to get a 400 instead of building a 350? I guess you have to consider the lower 1st gear in the 350 as a plus. But its not that much. I always get the 200 4R & the 700 R4 mixed up as to what gearing they have. One's more evenly geared that the other as far as spread. I was considering on of these, but am looking at a GearVendors OD unit in the future
The TH400 is by far the stronger unit,always was.The TH350 needs a few mods to achieve the same durability as a stock 400.The powerslide in stock form was iffy but sometimes favored for use its compact size for use in smaller bodied or space limited vehicles,it needed a lot of heavy duty mods to live behind a BB but worked very well when built right.I personally would just mate a 400 to the BB especially if its been built a little.The answer to the original question is yes a shift kit will help extend transmission life by reducing the slippage that normally occurs between shifts,choosing the shift harshness and shift RPM range can be a PITA though.
The TH400 and TH475(trucks & motorhomes) is stronger than a TH350. However, the TH350 has a better 1st gear, is lighter, and can still be built to take a decent beating. My B&M equipped TH350 in my Malibu drag car has taken a beating.
400's did come behind big blocks. I don't think a TH350 ever came behind a BBC from the factory. Doesn't mean that they won't work well though. I'd just run your TH350 you have in it now. If it breaks, have it built to handle your power output.
A powerglide is not a good street transmission IMO. You need at least a 3 speed. Personally I won't go without an OD after having both a 2004R and 700R4 but thats cause my cars are all daily drivers. If yours is going to be a weekend cruiser it's not a big deal. A shift kit is cheap insurance, it will do nothing but increase the durability of the transmission while giving you firmer shifts. If your TH350 seems in good shape now I would add a good shift kit and a good cooler and hope for the best. You might get lucky for a while. If you end up needing a rebuild its up to you whether you want to go to a TH400. You will run faster with a TH350 since they don't have as much internal power loss as the TH400.
About the OD's, its the 2004R that has the best gear spacing. It has a taller first gear than the 700R4, but 2nd gear is spaced much closer to first. That along with less internal power loss in the 2004R means you usually run faster with it. Also O/D is 0.67 for better mileage compared to the 700R4's 0.76? or something like that.
About the OD's, its the 2004R that has the best gear spacing. It has a taller first gear than the 700R4, but 2nd gear is spaced much closer to first. That along with less internal power loss in the 2004R means you usually run faster with it. Also O/D is 0.67 for better mileage compared to the 700R4's 0.76? or something like that.
Big Block should equal TH400..
The TH475 if he can find one should be run either with a HD oil cooler and synthetic fluids. The gear set in the TH475 is straight cut not helical cut and it shear's and heats the heck out of ATF. They are really strong though basicly a beefed up TH400 mostly used in Motorhomes!
The 400 IS stronger..i pounded one behind a 454 in a 4x4
for years and couldn't kill it.
i've messed around with alot of GM transmissions in my day
thers know way a 350 would have held up...
for years and couldn't kill it.
i've messed around with alot of GM transmissions in my day
thers know way a 350 would have held up...
I have been always told that a 400 will always absorb more horsepower through the driveline as well, meaning less hp at the rear wheel than a 350
I see nothing wrong with a th350 and don't recommend bigger transmissions until you break a few smaller ones first. Unless you are over 500hp, there is no need for the heavier and power robbing th400.
Any transmission can be made to handle almost any power level if there is enough time or money involved. When you break the th350, find a competent builder/upgrader. There are numerous aftermarket parts to address weaknesses.
If you don't have a shift kit, get it installed along with a cooler, quality ATF, and a remote ATF filter. If/when you break it, research your budget and whether the th400 is required at time.
Any transmission can be made to handle almost any power level if there is enough time or money involved. When you break the th350, find a competent builder/upgrader. There are numerous aftermarket parts to address weaknesses.
If you don't have a shift kit, get it installed along with a cooler, quality ATF, and a remote ATF filter. If/when you break it, research your budget and whether the th400 is required at time.
^ Agreed with him. Even the 2004R can be built to handle vehicles running in the 9's in the 1/4 mile.
^I'm with undummy and harley, the 400 has more weight and internal drag. Great for tow rigs and HD apps. Not so much for a sprightly hot rod. Depends on the weight of the vehicle, axle ratio, etc.
If you were doing a V8 swap into a S10 or other featherweight, (built) turbo 350 all the way. Chevelle is what, 4000 lbs? Middleweight, maybe?
This is all "armchair hotrodding" for me of course so you'll want a grain of salt with it...
If you were doing a V8 swap into a S10 or other featherweight, (built) turbo 350 all the way. Chevelle is what, 4000 lbs? Middleweight, maybe?
This is all "armchair hotrodding" for me of course so you'll want a grain of salt with it...
I think GM would disagree with that,the issue isn't so much HP as it is torque.Mouse motors can produce lots of HP and get the low ETs in light cars but the torque produced isn't anywhere near that of a comparable HP BB.Its the torque that will tear the guts out of a transmission and spit them all over the street.For drag racing lencodrive,Lenco CS1 CS2 and CS3 transmissions are used behind extreme motors.
Waiting for someone to mention that. Input torque and traction capabilities (output shaft resistance) are your determining factors for transmission longevity.
There are also a few different levels of transmission within each series. TH350s can have any different numbers of FWD clutches, same for a TH400. Generally, IMHO, a stock configuration TH350 gets iffy around the..............350 ft/lb mark. It gets better as you go to aftermarket planetaries, higher line pressure, aftermarket shift kits/valve bodies etc. I have seen properly built (with cherry picked stock parts) TH350s used behind mild bigblocks (396/402) and hold up as long as they aren't abused. A TH400 on the other hand can be built easily to handle about 500 ft/lbs of torque. Remember they came behind some mean Buick 455s that put out nearly 510 ft/lbs. A TH400 with the happy clutch drum, HD sprag, bumped line pressure, and decent valve body can live behind some monsters. You will often start twisting up some input or output shafts before you have any real internal damage.
It comes down to economics for me. You can build a TH350 to live behind a real bigblock, but to do it costs more money than getting a TH400 and doing a straight rebuild on it. A decent/mild 396/402 with oval ports will still put out ~425 ft/lb and that is pushing a generic 350 a bit. Remember also, a higher stall converter effects input torque as well.
If the wallet is thick enough a shop can darn near build any transmission to handle real power. It is just often cheaper to move up to a higher capacity stock unit rather than dump cash building a medium duty unit to take the abuse.
Just an opinion.
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