anybody swapped a 350 trans in a nbs?
11-28-2010, 10:04 PM
#3
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A decent built 350 will work just fine in a truck. So will a 400. 400's are a longer, from what I rem are geared diff.. Also takes a little more power to turn the 400.. Not 100% but think they will bolt to the ls block.. You will prob have to use a spacer of some sort on the flex plate.. Great trans if your going racing. If not and your looking for strength, go to a 4l80e.. Will take about the same amount of work to get it to fit...
11-28-2010, 10:06 PM
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Actually I had this bookmarked.. This should tell you all you ever want to know...
Next common weakness to both is the direct drum apply area.
Since the direct drum is used to apply 3rd and reverse the direct apply piston is split in half.
So each gear only gets half the piston area in stock form.
This weakness even shows up behind stock motors.
Reverse is not a problem because we are not usually giving the trans full engine torque in reverse (LOL).. it also has the planets taking load off the direct clutuch because of the gear reduction, torque multiplication, as well as it not being a shifted gear. You put it in reverse and all the clutches are applied. No shifting to cause a clutch to slip as it goes to the next gear.
So if you are one of the weird ones using reverse for full engine torque (WTF are ya doing?) you'll probably not burn the directs up.
However going from 2nd to 3rd at WOT behind a stout powerplant taxes the direct clutches.
The TH350 has a lighter direct drum to have to spin up from zero rpm to engine rpm. Slight advantage but not much.
We fix the direct clutch failures by using both halves of the piston to apply in 3rd gear.
Several ways to go about this.
On a TH350 almost all "shift kits", valve body reprogramming kits, etc.. accomplish this.
If you've installed one you probably remember the "fluid transfer plate" that sandwiches between the valve body sperator plate, and the support plate to the front of the valve body. Just a plate with a passage cut into it to let fluid get to both sides of the direct piston in 3rd.
The lip seal on the middle, dividing the piston can also be omitted, and then a passage plugged to acomplish the same thing.
On a TH400 the only valve body kit that I'm aware of that "dual feeds" the direct clutches is the Transgo Reprogramming kit.
It has a patented sandwiched seperator plate that does the same thing as all the TH350 kits.
It can also be modded internally same as the Th350 to accomplish the same effect.
I prefer to use the TransGo kit on a TH400 because in my opinion it preserves the integrity of the fluid circuits.
On a TH350 either way will do fine.
I personally don't care for the gasket that is required in the TH350 VB kits.
Next common weakness to both is the direct drum apply area.
Since the direct drum is used to apply 3rd and reverse the direct apply piston is split in half.
So each gear only gets half the piston area in stock form.
This weakness even shows up behind stock motors.
Reverse is not a problem because we are not usually giving the trans full engine torque in reverse (LOL).. it also has the planets taking load off the direct clutuch because of the gear reduction, torque multiplication, as well as it not being a shifted gear. You put it in reverse and all the clutches are applied. No shifting to cause a clutch to slip as it goes to the next gear.
So if you are one of the weird ones using reverse for full engine torque (WTF are ya doing?) you'll probably not burn the directs up.
However going from 2nd to 3rd at WOT behind a stout powerplant taxes the direct clutches.
The TH350 has a lighter direct drum to have to spin up from zero rpm to engine rpm. Slight advantage but not much.
We fix the direct clutch failures by using both halves of the piston to apply in 3rd gear.
Several ways to go about this.
On a TH350 almost all "shift kits", valve body reprogramming kits, etc.. accomplish this.
If you've installed one you probably remember the "fluid transfer plate" that sandwiches between the valve body sperator plate, and the support plate to the front of the valve body. Just a plate with a passage cut into it to let fluid get to both sides of the direct piston in 3rd.
The lip seal on the middle, dividing the piston can also be omitted, and then a passage plugged to acomplish the same thing.
On a TH400 the only valve body kit that I'm aware of that "dual feeds" the direct clutches is the Transgo Reprogramming kit.
It has a patented sandwiched seperator plate that does the same thing as all the TH350 kits.
It can also be modded internally same as the Th350 to accomplish the same effect.
I prefer to use the TransGo kit on a TH400 because in my opinion it preserves the integrity of the fluid circuits.
On a TH350 either way will do fine.
I personally don't care for the gasket that is required in the TH350 VB kits.
11-28-2010, 10:07 PM
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Now for other strengths, weakness's, etc..
The TH400 has a very rigid center support placed in the center of the trans.
it is actually bolted to the case.
It provides support for the reaction carrier, low sprag, and direct drum, as well as the sun shaft.
IMO if you did all the tricks to both trans as far as upgraded sprags, dual feeding directs, more clutch surface area, etc..
This is one of the key differences why a Th400 is stronger.
It simply holds the heavy internal rotating parts more stable, centered, and with more bushing surface area.
The TH350 does not have quite as much support internally and therefore is rougher on bushings and thrust materials.
Next,
the TH350 direct drum drives the sun shell.
The sun shell is about 6" outside diamter shaped somewhat like a bell with lugs that catch outer lugs on the direct drum.
The sun gear is attached to the sun shell by thin wire snap rings.
This shell gets loaded by the direct drum, the higher the loading, especially during shift, the harder this shell gets "cocked".
Since it is 6" diameter is has more of a tendecy to get side loaded, causing greater bushing wear, and is weaker by design than the TH400's sun shaft.
The TH400 sun shaft is about 1.5" diameter with splines that are driven by the center of the direct drum. So very little side loading. And any side loading is better controlled by the TH400's generous center support bushing, probably 3" of length compared to not quite an inch on a TH350 in stock form or a little less than 2" in modded form.
TH400 intermediate clutch pressure plate is held into the case by a snap ring, locking into a groove in the aluminum splines in the case.
Under extreme pressure this snap ring can beat the lugs out of the case.
There are fixes for this but the best thing to do is keep line pressure down to prevent this failure.
Excessive line pressure is rough on pump gears and housing, lip seals, drum to sealing ring surfaces, converter, and potentially the engine thrust bearing.
This should pretty well cover the basic difference between the 2 units and their strengths/weakness
The TH400 has a very rigid center support placed in the center of the trans.
it is actually bolted to the case.
It provides support for the reaction carrier, low sprag, and direct drum, as well as the sun shaft.
IMO if you did all the tricks to both trans as far as upgraded sprags, dual feeding directs, more clutch surface area, etc..
This is one of the key differences why a Th400 is stronger.
It simply holds the heavy internal rotating parts more stable, centered, and with more bushing surface area.
The TH350 does not have quite as much support internally and therefore is rougher on bushings and thrust materials.
Next,
the TH350 direct drum drives the sun shell.
The sun shell is about 6" outside diamter shaped somewhat like a bell with lugs that catch outer lugs on the direct drum.
The sun gear is attached to the sun shell by thin wire snap rings.
This shell gets loaded by the direct drum, the higher the loading, especially during shift, the harder this shell gets "cocked".
Since it is 6" diameter is has more of a tendecy to get side loaded, causing greater bushing wear, and is weaker by design than the TH400's sun shaft.
The TH400 sun shaft is about 1.5" diameter with splines that are driven by the center of the direct drum. So very little side loading. And any side loading is better controlled by the TH400's generous center support bushing, probably 3" of length compared to not quite an inch on a TH350 in stock form or a little less than 2" in modded form.
TH400 intermediate clutch pressure plate is held into the case by a snap ring, locking into a groove in the aluminum splines in the case.
Under extreme pressure this snap ring can beat the lugs out of the case.
There are fixes for this but the best thing to do is keep line pressure down to prevent this failure.
Excessive line pressure is rough on pump gears and housing, lip seals, drum to sealing ring surfaces, converter, and potentially the engine thrust bearing.
This should pretty well cover the basic difference between the 2 units and their strengths/weakness
11-30-2010, 05:39 PM
#7
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i ran a th350 behind a cammed lq9 and had 0 issues with it. worked flawless! it will bolt to the block minus the very top bolt and the one to the right of it. but no worries you will still have 5 bolts and two dowel pins holding the transmission to the block. as far as the converter goes a few companys actually make converters for this swap that bolt to the 4l60e flexplate and have the correct size pilot hub or you can get the 4l80e flexplate and adapter that comes sandwiched betwene it and the crank and bolt up a large pattern converter and the hub on the converter will slide right into the adapter. i have heard of people using the adapter with the 4l60e flexplate by instaling the flexplate sandwiched betwene the crank and adapter and elongating the converter mounting holes because they dont have the same pattern. close but not the same. i personaly dont like the last method but it will work. as far as length goes i know the "longtail" version th350 is really close to the same length so you can use the stock length drive shaft. although you will either need a th350 yoke or seal the small hole in the end of the 4l60e yoke as they are the same spline count and size. you may have to modify the transmission mount/crossmember and figure something out with the park neutral switch. but it should be a straight forward swap with either the th350 or th400. i sure hopes this makes sense to you. good luck with the swap if you decide to do it!
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