1BadDime

iTrader: (26)

Can anyone explain the differences between a turbo400 and a turbo350 transmission?? weight, ability to handle power, efficiency, etc. etc.

I can't seem to find anything really in depth about the difference between these two transmissions.

seadoo

not sure about weight, the T350 is lighter... but the T400 handles more in stock form, than the T350, but both can be built to handle the same power... T350 is more efficient.
T350 has a 2.52 1st, 1.52 2nd BUT most aftermarket ones use a 2.75 first gear.

the T400 has a 2.48 1st and a 1.48 2nd

chris718

the mechanical components are very similar between the 2 in function and principles of operation.the main difference i find is that the planetary geartrain of the 350 is very prone to failure in hp applications over 500 especially with n20 turbo or schargers.i have built several that have worked at 700 hp but we are at the materials structural limitations above 500.with the th 400 the geartrain is good to well over 1500 horsepower .both units are plagued with roller clutch and outer race failures .these are easily addressed with upgraded parts.i designed a th400 sprag assembly that has been tested at over 1800 horsepower wiothout fail.this same sprag has also been adapted by me for use in the th350 and will way beyond the planetary geartrains crumbling point.input shafts usually snap in the center with a 350 with a high powered engine althought the last 3 years of production 350 units were usually equipt with a stronger input shaft from the factory.it is very shiny in apperance and used a teflon lube seal on the input shaft.this seal can never be found in an overhaul kit either so if you find one dont remove it.the components in the 350 are lighter as well but at the cost of compromises in geartrain strength.the slight increase in reduction with the 350 over the 400 is rarely of any benefit unless the 350 is being used in a mechanically safe operating environment where the use of the heavier 400 is not necessary to reduce mechanical failures.i did a write up on team cheveele a few days ago on the 350 .here it is .it may help you out if you decide to build it yourself. Tech Team Join Date: Jan 2005
Location: new york city
Posts: 132


Re: Mods "required" to make a th350 last with 500hp

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Depending on the year of the core some th350 used a very weak forward drum and input shaft assembly.The problem is the shaft is too hard and snaps or the drum strips out.Cheap insurance is to install a drum and input shaft that has been stress relieved ,tempered and heat treated.The intermediate sprag outer race failure is very common and can be aggravated by a valve body without proper 2nd gear clutch pack accumuation designed into it.Cheap insurance is to install a 40 element direct drum and sprag assembly.The 40 element is stronger than all others including b&m,tci,bte etc. 34 element setup. And in the event of a 40 element sprag failure(ive yet to see one) the sprag is replaced with a 35.00 item and not the $125.00 job they will try to sell you.I dont believe in the softened outer race commercially available with anything over 350 horsepower and a valve body of unknown origin or improper calibration.Clutch selection should be 5 forward frictions with stock lining,3 intermediate frictions with stock lining and 5 directfrictions with red linind. It may be necessary to machine the direct clutch piston to install 5 friction plates.This is done on a machinist or brake lathe.Dual feed the direct clutch by removing the middle ring from the stator support and installing a plug in the pump face of the case in the reverse circuit.Use a stock seperator plate and valve body with all 4 ballchecks installed,drill the 2 clutch feeds in the plate to .110",plug the third accumulator hole in the valve body casting (dont remove the spring or you risk breaking off the band lug when manual shifting),install a hi rate pressure regulator spring and a screen filter.Locate the 350 lockup front and rear planets as they have needle bearing assemblies instead of thrust washers to free up horsepower.Machine the low reverse roller clutch inner race .140"shorter and install a a500 converter bearing in place of the plastic washer.Drill an .060" air bleed in the ineer area of the reverse piston to reduce bindup on manual 1/2 upshifts.Install an oversize direct drum bushing in the drum to better stabilize it on the support and reduce wobbling.If you want later wide open throttle upshifts without losing part throttle passing gear install a special light 700r4 governer from an 86 to 88 9ci coded Caprice police car . The late 4l60e low reverse steels with turbulator holes can be installed in the low reverse section to reduce clutch drag at high rpm and the resulting power absorbtion they cause as well as installing the larger 4l60 low reverse sprag assembly .The early 70s sunshells are much thicker and tougher than the late wimpy ones so try to find one if you can. They are usually .210"thick.That should be all you need.If you are intersed in any of the specialty drum and shafts or anything else for the rebuild check out our listings on the site.
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www.ckperformance.com christoforos kokkonis gm transmission specialist.engineering and design of the finest street,strip,drag race automatics,custom ratio planetary gears

408WS6

iTrader: (1)

Finally....someone who knows what the hell they are talking about.

Thanks for the information.....