I have a 88 camaro with a 83 305/ 700r4. The engine has been fairly modded( camshaft, ported/polished heads, intake/ carb, and just about everything else) but the tranny is original. Sense I've done all the changes to the engine the tranny is going south. It's slipping in first and into second. I'm swapping it out one way or another but A friend of mine has a th400 in great shape for 100 bucks. I was planning on the th350 but now I'm thinking the other. What's the difference and what way would you guys go.

 

The TH400 is much stronger than the TH350. Not to say that the 350 is weak by any means. It is stronger than your 700R4 but it lacks a 4th gear. Unless you plan to make about 450+ hp then the TH350 is the way to go. The TH400 requires much more power to turn so you need an engine that makes enough power to overcome this.

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1991 Z28 - 350 TPI, T56, Centerforce Dual Friction clutch, ported plenum & runners, AFPR, Holley Annihilator ignition box and wires, Hooker shorty headers w/o AIR, no cats, Flowmaster muffler, homeade ram-air, SSM subframe connectors, Steve Spohn adjustable torque arm and T56 crossmember

 

yeah, but if that TH400 is in good shape for sure, and only $100, that's not too shabby. Just be careful i fyou are buying it from a friend. DOn't want to end the friendship, if you can help it. You COULD buy the 400, clean it up, sell it and then buy a nice 350, I suppose, but gain, buddy would get mad.

350 will usually last through most anything of 400 hp or less but a fully equiped TH400 WILL last through anything up to Waaaaaaaaaay more HP than 400.

In all honesty, you should just have your 700 rebuilt to keep the OD. You will miss it when it is gone unless you are a race/drag/fast driver ALL THE TIME. If you take highway trips regularly, you'll be bumming...

[This message has been edited by FastBroker (edited October 09, 2000).]

 

going from yer 700r4's deep 1st gear ratio to the 350 or 400's is gonna kill yer bottom.........400 takes alot to turn??????hmmm...... somebody slap me

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87GTA,350,Auto,MAF screens removed,K&N,modified air intake,ADSchip,3:73s,3inch cat back Flowmaster,TPS.54,Bosch Plat plugs,base timing 6BTDC,Bilstiens in the rear....,don't let yer meat loaf

 

It only takes about 20 more HP to turn a TH400 than a TH350.

Make sure the TH400 you're going to buy is really a TH400 and not a TH375. They look the same but the 400's u-joint yoke is different. The output shaft has a different spline count than the TH350/700R4's

It takes a bit more work to squeeze a TH400 into a third gen than it does a TH350. There just isn't a lot of space under the floor.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
LS6 Big Block buildup now in progress

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Best corrected ET: 11.163
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Member of the Calgary Drag Racing Association

 

ok you say it takes 20 more HP to turn the 400trans........i'd love to see your test data on this conclusion........hmm i wonder if the torque convertors are the same for these two transmissions...by golly they are.Must be a little guy who see's ya drive by with the THM 400 then ZAPS it with a 20 HP noogie.........

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87GTA,350,Auto,MAF screens removed,K&N,modified air intake,ADSchip,3:73s,3inch cat back Flowmaster,TPS.54,Bosch Plat plugs,base timing 6BTDC,Bilstiens in the rear....,don't let yer meat loaf

 

It DOES take more to turn the 400, has to do with the flow internally after the pump. More parasitic losses than the 350. Bigger stuff to move, I guess?!? Ask a tranny shop, they will concur...

 

Of the three trannys being talked about, the TH400 has the lowest number ratio 1st gear, TH700 the highest. It'll seem like you've lost more than 20 hp on takeoff from that alone.

If you want a feel for what it will be like cruising with a TH350 or TH400, leave your current tranny in "D" and drive it down the road for awhile. I doubt you'll like it.

The TH400 is shorter than the TH700, so a longer driveshaft is in order. TH350's are available with a 9" tailshaft that makes it the same overall length as the 700. But, with either 350 or 400, you'll have to do something to mount up the torque arm.

Stock TH400's also have a weak point called the intermediate sprag. An aftermarket 34-roller (I think, vs. 28 stock) piece should be used in any rebuild.

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82 Berlinetta, orig V-6 car. Rescued w/86 LG4/TH700R with all harnesses, sensors, ECM, etc. 2.73 open. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LB9 w/ZZ3 cam, exhaust, paint, etc.).
57 Bel Air, my 1st car. Currently 396 .030 over, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & shift kit, 3.08 10-bolt, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.

 

i am the walrus...Coo COO CHa COO

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87GTA,350,Auto,MAF screens removed,K&N,modified air intake,ADSchip,3:73s,3inch cat back Flowmaster,TPS.54,Bosch Plat plugs,base timing 6BTDC,Bilstiens in the rear....,don't let yer meat loaf

 

The majority of the losses in an auto trans result from the clutches that are not engaged. There are however many frictions in each clutch pack, all of which have to be forced to turn with respect to the steels (or vice-versa) whenever that clutch is disengaged. The parts are only a few thousandths apart when disengaged so they all rub against one another, creating plenty of frictional losses. The 400 has more, bigger clutches than the 350, so there's more friction.

Stephen's advice about the 375 is a good one. It's basically a 400 with a 350 output shaft. I actually had a guy who built trans's at a Chevy dealer try to sell me one of those once to go in my 74 454 Caprice convertible; when I told him I couldn't use it, he almost attacked me, until I made him go get a 400 yoke and try to put it on the tailshaft.

For as long as the 350 has been around, it's been common knowledge that any car will go faster with a 350 (rule of thumb .15 - .2) but the 350 won't last as long. Maybe as these are replaced by 700s and FWDs, that knowledge is being forgotten.

RP you're wrong about the TCs. The 350 uses an 11" with a small 3-bolt pattern, the 400 a 12" with a large 3- or 6-bolt pattern. Cars that came with 400s often had flex plates that didn't even have the smaller 3-bolt pattern on them. Other than that potential gotcha, the TCs are however totally interchangeable. In fact, the easiest and cheapest hop-up for a mostly stock big-block car always used to be to get a set of gears first, and then a 350 TC for it. After a set of 3.73.or 4.11 gears (which were usually replacing 3.08s), the 350 TC would knock at least another .1 off your 60' time with no other mods. Then we'd start working on the motor.

In any case JC to answer your original post before it got sidetracked, you don't need a 400 behind a 305. You don't even really need a 350. You need a well-built 700 and a trans cooler, make sure the lockup clutch works since whenever the TC is "slipping" it's heating up the fluid, and you should be in good shape. Get a good converter while you're at it; people speak very highly of the Performance Industries Vigilante. $100 is a great price for a 400, however it's going to cost you many times that to put it in. You could get it for free and still be money behind what a good 700 job will cost.

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"So many Mustangs, so little time..."

 

Thanks guys, looks like I'll be keeping the 700r4. It wasn't like I didn't like it to begin with. Just the slipping thing getting to me. If I get a new TC will that solve that problem? When I do that I think I'll be getting a shift kit from B&M as well. An while I'm at it, it sounds like I should get a corvette servo. What does that do anyhow? I've heard alot about them but I have no idea what they are or do? Any other ideas would be appreciated. Thanks JC