THm 350 Vs 400 vs 700r4

[capriceowns]

I know the 700r4 has the bad 3-4 clutch failure, but what makes the thm 350 and 400 better?

with all the money im pouring into my enigne I'd hate to have my trans bite it/fail all the time so which of the 3 is best for 320+HP?

(and for who know about the caprice, Will the thm 350 or 400 bolt to my new 350? would I need a new driveshaft?)

[silicon212]

The TH400, for brute strength, wins here. However, they soak more power than the TH350 or 700R4 does - more rotating mass. The TH350 is not quite as strong as the TH400 is, but has less rotating weight and therefore soaks less power. Either of these is good if you're not into economy, my personal pick is a TH350 because I like the way it shifts.

The TH700R4 prior to 1986 is weak in the 3-4 clutch area, later ones are better but could be made better still. Best thing is to repack the 3-4 clutch to use 8 plates instead of 6 - this requires a replacement clutch piston which is thinner to provide clearance for the additional two plates.

The TH350 and 700R4 are pretty comparable, as far as torque handling capability is concerned. They can both be built to withstand far more torque than factory. The 700R4 also has a LOW 1st gear (3.06:1) vs. 2.52:1 (TH350) or 2.48:1 (TH400). This will certainly motivate a larger car such as a Caprice from a stop, but racers tend not to favor that too much due to the separation of gears. There is a replacement planetary set available for the 700R4 which makes 1st gear taller. Blue Bowtie has the lowdown on that.

[capriceowns]

Is the THM 350 only a 3 speed?

[silicon212]

Originally Posted by capriceowns

Is the THM 350 only a 3 speed?

Yes, so is the 400. Basically in the newer GM nomenclature using car weight,

TH350 = 3L60
700R4 = 4L60
TH400 = 3L80

[capriceowns]

I was looking at some on Jegs and Summit, and I can score a thm 350 for about 800$ that can handle 400hp. Which isnt a bad deal considering the work my trans needs.

But none of them have Lock up for the Torque converter. Is this something I should consider? what does lock up do? Idk if they have overdrive or not, neither site says anything bout it. Im assuming no cause its a older trans.

About my driveshaft to, Is the THM 350 the same length as my 700R4? Im probably gonna have to find a dif lenght driveshaft to fit right?

[silicon212]

The 700R4 is somewhere in the middle, size-wise, of a TH400 and a TH350 w/ medium output housing. You will have to get the proper driveshaft, but they are out there. The Caprice was available from '77 -'86 with a TH200/C or TH350/C - a driveshaft from these will fit yours with a TH350.

Lockup takes the torque converter slip out of the equation. Basically, if you're accelerating, the output shaft of the transmission will be slower than the engine RPM when in 3rd or direct - this speed is up to the stall speed of the converter. Therefore, if the converter has a performance stall speed of say, 2200RPM, then on a non-lockup converter, your engine could be turning 2200RPM higher than the direct-drive output of the transmission! Locking the torque converter, so the impeller and turbine run at the same speed, remove this slip and allow the engine to run at the same RPM as the transmission output shaft in direct. This does two things - it reduces wear on the engine and also saves fuel!

Lockup on the 3-speed transmissions, TH200C or TH350C (the C denotes lockup), is optional and is generally for CAFE requirements. On the overdrive transmissions, such as the 2004R or 700R4, lockup is mandatory. TCC failure is the leading cause of 3-4 failure on the TH700R4.

[jveik]

yeah old turbo350s hold up pretty good even when stock. my buddy had an 86 silverado with a 454 that had all the goodies, such as a racing cam, installed. he could be cruising along at 30 mph and just stomp it and loosen up the rear tires. he used a stock th350 in that sucker and it never gave him any trouble.

as for the th400... i had one in my truck before i dismantled it for restoration and it seemed to work very well. one time this stupid chick i was hanging out with (a blonde by the way lol) decided to throw the floorshifter up into reverse randomly to see what would happen. mind you i was going about 35 or 40 in the forward direction when she did this, and the tranny actually did shift into reverse and started spinning my rear tires backwards and everything, at least until i let off the gas a moment later and it killed the motor lol. didnt seem to really mess it up at all though and i was really surprised.

[Blue Bowtie]

They will all bolt to your new SBC 350, old 350, old 305, 283, 327, 400 SB, and even the 262 V-6. However, the rear trans mount is in a different location, so you'll have to deal with that on EITHER the 350 or 400. The rear mount on the 350 is closer than the 400, unless the car had a TH200-4R. The splines at the tailshaft may not match either, so plan on adjusting the driveshaft length with a TH350 and the yoke either way. And depending upon what was in the vehicle, you may have a modulator, TV cable, and/or kickdown cable to consider.

This might help:

http://www.maliburacing.com/auto_tranny_id.htm

[capriceowns]

So really all I need to do is find the right driveshaft for my THm 350 (just called a junkyard there looking for one) and a way to hook up the kickdown cable?

whats this about the rear trans mount?(is confused)

[silicon212]

I forgot to mention it, Blue Bowtie caught it - the TH200C/TH350 has a different mounting location than either the TH700R4 (about an inch) or the TH400/TH2004R (about 5 inches or so). You will want to make sure that you have the proper crossmember for your application. I found out the hard way that the TH350 and TH700R4 are off about an inch - when I swapped my TH2004R for a 700R4/4L60, I grabbed a crossmember for a TH350 thinking it would fit - well, it didn't, and so I had to modify it.

The proper crossmember for any of the aforementioned transmissions exist for the '77-'96 B-body, you just need to snag the right one.

[capriceowns]

Originally Posted by silicon212

I forgot to mention it, Blue Bowtie caught it - the TH200C/TH350 has a different mounting location than either the TH700R4 (about an inch) or the TH400/TH2004R (about 5 inches or so). You will want to make sure that you have the proper crossmember for your application. I found out the hard way that the TH350 and TH700R4 are off about an inch - when I swapped my TH2004R for a 700R4/4L60, I grabbed a crossmember for a TH350 thinking it would fit - well, it didn't, and so I had to modify it.

The proper crossmember for any of the aforementioned transmissions exist for the '77-'96 B-body, you just need to snag the right one.

Whew, thanks, I thought I had to make some special holes in my frame :P

The stock drivesgaft that came with the thm 350. How much power can those take before twisting?

my goal is 330-350HP and 380-400lbs torque.

[GreyGoose006]

if its not too late to change your mind, you should go with the 700 trans.
i have the th350 and its a real gas guzzler on the highway due to only having 3 gears and no overdrive. top speed is redlined at around 85-90.
you would be much better off with getting a 700 and rebuilding it with more clutches.
thats just my opinion tho.

[capriceowns]

Iwant to keep my 700r4 I still can I havent bought thje 350 yet.

But I havent been able to find a smaller piston for my 3-4, I did find the TCI beast sun shell silicon mentioned before on eBay.

Anyone know of were I can buy a smaller 3-4 piston ?

[GreyGoose006]

try summit racing or jegs. those kind of places will probly have what you need. if you do a search, someone did a very in depth explanation of this exact procedure in the caprice forum a while ago.
try looking there for info.

[capriceowns]

Tried both places(summit/jegs), no luck on the 3-4 piston.

anyone know were I could find one?