PDA

View Full Version : OT Anyone have experience with TH400?



Fasttrack
02-21-2006, 06:02 PM
I bought an old '77 chevy pickup a little while ago. It has a junkyard 400 and a junkyard 400 turbo trans in it. There is a holley 4-barrel carb w/ electric choke, one of the street legal models, but besides that i dont know specifics. Anyway, the kickdown solenoid isn't hooked up to anything. Just wondering where/how i should hook that up. There are no sensors, power wires, etc that i can find going to the gas pedal and there is only one coming off of the carb, it looks like it may be for the electric choke. The interior looks like its been guted and inexpertly reassembled, so some wires may be missing; the real trouble is almost nothing is stock so the wiring digrams don't help at all.

Dawai
02-21-2006, 06:26 PM
Them transmissions soak up 50hp.

Yeah, my last one had a rod coming up to shift it down. Actually a pressure feedback connector isn't it? controls the pressure feedback to the main valve body.

Seems it is not good to have them loose. Other than that? what else is it? that is the simplest engine, wiring on the market.

The carb electric choke usually hooks to a toggle switch inside the cab.

They made a adjustable modulator valve with a setscrew, diddling with that screw changes shift points.

I had one of them behind my "magic" chevy motor for a bit. (59 impala sedan delivery) I'd nail it and it'd blow the dipstick out of the transmission. I worked on it for a couple weeks. It'd only do it in burnouts, no other time.
Turns out, a vent tube on top of the transmission was bent flat. as I was putting the motor in I shook it to line up the pins. Yep, 300lb tattooed gorilla strikes again.
That old panel would launch so hard, Heavy, it was, but it got good traction. I had a toolbox behind the seat, I caught a glimpse of it as it went through the curved hatch glass and onto the roadway. I picked up wrenches for about ten minutes. I bondo'ed the glass frame flat and replaced it with flat cut glass.

torker
02-21-2006, 06:46 PM
A TH400 actually has an electric switch for the kickdown. It is sometimes mounted on the carb linkage (in several different places) or can be mounted under the gas pedal (most common)
The modulator controls shift points on the 400 til WOT then the detent system takes over and actuates the electric kickdown.
The reason for this is because there isn't enough vacuum at WOT to operate the heavier 400 components.
WOT shifts without the kickdown hooked up will cause the clutches to slip and they will wearout before you want them to.
If I remember right there are aftermarket kits that replace the GM electric switch.
Russ

torker
02-21-2006, 06:50 PM
Hey...or you can install a manual shift valve body kit! And you can kick it down yourself...whenever you want http://bbs.homeshopmachinist.net//biggrin.gif
Russ

Sharpshootermb
02-21-2006, 06:55 PM
Torker is correct. Several of the older GM cars had a self adjusting electric slide switch mounted to the accelerator pedal bracket. I know that my 68 GTO had it there as well as my parents old 69 Olds. To find one should not be difficult.

CCWKen
02-21-2006, 07:00 PM
The TH400 is basically a beefed up 350. It doesn't use a solenoid for kick-down--It uses a cable off the carb linkage. In fact, all the TH series use a cable. Only the E-series and up use electronic control. If there's a horizontal pigtail lead (or connector) by the shift linkage, that's the backup light switch lead.

If there's a pigtail (or connector) on the left side top above the pan, the trans could be a 350C, 200-4R or a 700-R4. The pan on the 700's are square, all the others are irregular. The 200 will also have "Metric" stamped into the pan.

Fasttrack
02-21-2006, 07:31 PM
"Hey...or you can install a manual shift valve body kit! And you can kick it down yourself...whenever you want
Russ "

http://bbs.homeshopmachinist.net//biggrin.gif I seriously considered it, but decided to get it street legal and reliable first, then start messing with cool stuff like trans shift improvers or manual valvebodies. I think that'd be alot of fun, although probably not the most practical!

I'll have to do some more poking around apparenlty, from what i saw online the TH-400 did have an electric kickdown, and i assumed that the connector i was looking at was for the kick down solenoid...a 700-R4 huh? Shoot the pan isn't square but that would have been a nice surprise to find that under there instead. I'd really like that extra overdrive gear.

Fasttrack
02-21-2006, 07:35 PM
"The TH400 is basically a beefed up 350. It doesn't use a solenoid for kick-down--It uses a cable off the carb linkage. In fact, all the TH series use a cable. Only the E-series and up use electronic control. If there's a horizontal pigtail lead (or connector) by the shift linkage, that's the backup light switch lead."

Are you sure about that? I'm just wondering because B&M offers an electric kickdown switch for swapping a TH-400 for a TH-350 or 700R4 - "B&M kickdown switch kits are perfect for use when swapping out a TH350 or TH700R4 for a TH400." I knew before i bought the truck that TH-400 are enormously popular for racing trans (obviously after being rebuilt by TCI or etc), seems like it should be easy to find parts for.

CCWKen
02-21-2006, 07:51 PM
Forgot to mention:

If you get a book for the 77, it will have the wiring diagrams in it. They didn't change much for different engines. IIRC, the electric choke power is taken off the alternator voltage sense lead. It can just as well be powered off any ignition-on circuit.

Is the solenoid you're referring to on the carb? It may be an anti-diesel solenoid. These hold the throttle open as the idle adjustment and shut off with the ignition. This allows the throttle to close past idle position and reduce key-off dieseling. Some designs used these to increase idle speed when the A/C was on. These were usually long with a "bolt head" that rested against the throttle linkage. The bolt head provided idle adjustment.

More specifics about the solenoid might help.

CCWKen
02-21-2006, 07:58 PM
There could be aftermarket kits for kick-down that eliminate the need for a cable. It would have to include a throttle position sensor/switch and a solenoid on the transmission to replace the cable.

The kits I've seen handle the converter lockup control on the TH series, not gear changes.

Fasttrack
02-21-2006, 08:01 PM
CCWKen-
I'll have to look for a repair manual. Thanks for the info about the electric choke, i'll have to wire that up. It still starts on the first turn even when its cold, you just have to pump the heck out of the pedal http://bbs.homeshopmachinist.net//wink.gif The "solenoid" i was refering sounds exactly like the backup light switch you described; i assumed it was the kickdown solenoid because all of the information i could find online said that the TH-400 (this is really the Turbo 400 before GM renamed thier trans lines - i dont know if this might change anything?) had an electric kick down with a sensor wired to a solenoid by the shift linkage. Regardless i know the kick down is hooked up because there are no cables or etc, going to the trans except the gear select linkage. I guess theres an easy way to find out what it is though...either test conductivity between a ground and the connector which is a sure way to get run over, or just check the back-up lights http://bbs.homeshopmachinist.net//smile.gif

Fasttrack
02-21-2006, 08:17 PM
Actually the Th-400 does, in fact, have an electric kickdown. According to a sales rep at GM, "There is a slide switch which mounts on the bracket which holds the gas pedal. It is mounted so that it is actuated when the gas pedal is beyond about 2/3 of its travel. The switch has two wires: one (pinkish) goes to the ignition terminal on the fuse block. The other (yellow) goes to the terminal on the transmission.[TH-400]"
Also, from Novak Conversions, "If you are trying to determine the TH400 from another in a vehicle, a fast way to tell is to look at the kick down mechanism. The TH400 uses an electrical slide switch, which is controlled by the throttle linkage. The TH350 uses a mechanical cable kick-down mechanism that is attached to the throttle linkage."
I guess i'll have to buy a conversion kit with the sensor and etc...dang http://bbs.homeshopmachinist.net//smile.gif I was really hoping it would be neccessary.

Boomer
02-21-2006, 08:21 PM
My vo-tech instructor said the
th-400 was the best A/T ever. One reason was that there was no critical timing between band release and clutch engagement. There was never a situation where a transmission element was being held by a band while a clutch was trying to turn it. They never fought themselves.
IIRC the kick-down solenoid dumped the hydraulic pressure for the direct (high-reverse)clutch and as such you were then in second.
In 65 and 66 the 400 had an electrically operated variable pitch stator and are/were highly prized by the racing crowd.
Bruce

Fasttrack
02-21-2006, 08:28 PM
"My vo-tech instructor said the
th-400 was the best A/T ever. One reason was that there was no critical timing between band release and clutch engagement. There was never a situation where a transmission element was being held by a band while a clutch was trying to turn it. They never fought themselves.
IIRC the kick-down solenoid dumped the hydraulic pressure for the direct (high-reverse)clutch and as such you were then in second.
In 65 and 66 the 400 had an electrically operated variable pitch stator and are/were highly prized by the racing crowd.
Bruce "

Thanks for passing that along! I've always heard they were great A/T trannys, and all the hi-po places have them as first picks above 350's, 700R4's, powerglides, and all the fords and chrysler products. I didnt know why though! I'm really pretty excited about restoring this old truck! I just want to make sure i dont half-ass anything because the guy i bought it from pretty much did everything half-assed. Its really a shame.

CCWKen
02-21-2006, 09:32 PM
Yep, you're absolutely right. I had to go drag out an old trany book and look. I was thinking of the 350C/375C. The 400 does indeed have a detent solenoid. It triggers the 3-2, 2-1 shift based on a throttle position switch. (Range override by governor)

My mistake, sorry.

I should have remembered that. I got a 400 in the old motorhome just itching to be transplanted.

jim davies
02-22-2006, 12:24 AM
Based on overhauling a few thousand TH400s and 350s, I can categorically state that the 400 is not a beefed up 350. For one thing, the 400, a Borg-Warner design, came out in '64. The TH350, a GM in-house [mainly Buick] design came out in '68.

Boomer's instructor is arguably correct about the 400 being the best ever. I dunno if it was the best, but it is very good. It lives on as the 4L80E. As for the shift timing, yes, this is true. The TH350 [and Ford's E4OD and 4R100] copy the idea of replacing a band with a clutch, an overunning clutch and an overun band. Complex, yes, but it gives a smoother shift. The overunning clutch, AKA sprag clutch is alway a weak link, however. Transgo sells an HD sprag for the TH400. [It's out of a 540 Allison]Some use a roller type that is not upgradeable. For the TH350, the weak part in the overunning clutch is the outer race, a scintered steel part. A real steel replacement is available.

All TH400s use electric detent. If you can't find a GM switch, just get a micro type switch and hook it to the carb linkage in such a way that the last few degrees of travel at WOT closes it. Use a fused power wire to it of course...can't remember what the amperage is, but you can check the resistance of the solenoid to make sure your switch will be safe.

Some early 400's had a second solenoid inside that looks like the detent solenoid. That is for the VP stator.

Dawai
02-22-2006, 09:19 AM
I can attest to the fact that the only automatics that lasted behind the "magic" 350 were the powerglide (slipper all the time) and the TH400. In a 64 elcamino you could hole the powerglide in low at 100+ (damn airplane gear)
The Th350's would break the overrun band loose inside the transmission breaking the castings.

Other than that? heat from headers make them last less. If you run headers, run a trans cooler.

The Iroc 5 speed was real fun, except I could not shift gears fast enough and it stayed in red. Got the valve springs in a 77 Monza spyder. This was a week after I nearly rear-ended the boss's viper. *my car looked like crapola to him, primed, ugly wheels. He laid me off for embarrassing him.

I got rid of that car, kept the motor. Motor was in 7 cars, tore most all them to crap. Rippling body panels like nobodys business. a 72 4bolt main orange 350.

Automatics make fast cars engines last longer. You don't really have time to shift.

AND: too bad the transmission expert is 1000 miles away.

chipkent
02-22-2006, 01:11 PM
I have a TH400 on my '40 Packard restomod. It has been great. No problems dealing with the high performance 469 cu.in. engine I have on it. When I put this engine into the Packard, I had to deal with the kickdown. The TH400 uses an electronic kickdown as mentioned above. The car the motor and trans came out of used a switch attached to the accelerator pedal to activate the kickdown selenoid. It looked terrible in the beautiful car I put the motor in. To make things look good, I installed a TH400 kickdown kit made by Lokar (and a nice accelerator pedal). It attaches to the side of the transmission and has a cable that hooks to the carb. It has worked great and is polished stainless and billet. I think it cost $50-$100. It was worth the money.

Mike Dooley
02-22-2006, 09:55 PM
I have a reverse pattern, manual valve body TH400 behind a 474cid Pontiac motor in a 67 Pontiac GTO door slammer drag car. This car weighs about 2700lbs (no driver)with the fiberglass, lexan and aluminum parts on a full tube chassis. It runs the quarter mile consistently in the mid 9 second range at about 142mph through the traps. This trans is equipped with a Hipster trans brake valve body which essentially locks the trans in reverse and low at the same time via an electric solenoid controlled by a microswitch on the shifter. Once stagged the pedal is matted and the stall converter holds the engine at 5,000 rpm with the trans brake engaged. At the last amber I let go of that switch and it releases the solenoid lunching the car into a wheelstand against the wheelie bar that carries out roughly 60 feet or to the 1-2 shift. That first 60 feet gets covered in about 1.3 seconds and by the 1/8th mile mark the car is exceeding 110mph. It's one helluva fun ride. My turbo 400 has been in that car for three seasons and the only maintenance it recieves is fresh fluid and a filter each season. The only other popular auto trans at the dragstrip is the powerglide. The turbo 400 is probably the single most reliable trans ever produced. The current 4L80E used by GM in many of it's trucks is the modern, electronically controlled, overdrive equivalent. As far as parasitic horsepower loss, the TH400 probably soaks up more than the TH350 or the Powerglide by maybe 6-10 HP but they are hard to beat for strength. A HD sprag, with good clutches and bands and it's race ready.

abn
02-23-2006, 04:19 PM
Anyone want a Haynes '97-'87 Chevy P/U manual? It aint factory and about it will tell you about an auto trans is go see a professional but they do come in handy for tune ups and junk.

I also have a
GM J-car '82-'92 Haynes Manual
Toyota Tercel '87-'94

If you want one of these, I'd much appreciate the courtesy of $3 in stamps each, anywhere in the USA, media mail.

Arcane
02-23-2006, 05:01 PM
Years ago I came across a chart that listed the parasitic loses of auto trannys and now the only two I can recall are the venerable powerglide @ 19 HP and the big old C6 which gobbled up 60HP. The 60 HP figure surprised the hell out of me because it was substantially more than the TH400.

abn
02-23-2006, 05:30 PM
What amazes me is that it can dissipate 60 HP worth of heat!!

Arcane
02-23-2006, 08:06 PM
Yeah, that`s what I thought too. That`s an awful lot of heat and since it was from an old magazine article (old by now) I suspect the numbers aren`t all that accurate, but I think the relative losses probably are.

Fasttrack
02-23-2006, 08:41 PM
"My mistake, sorry."

No biggie! thanks for replying so fast. BTW, i could use some more information on the electric choke and how to correctly wire it. I haven't looked real close at it, more important stuff chalked up on the board right now, but any info, if someone knows it off the top of thier head, would be great! Save me from having to search around on it.

Also does anyone have any specifics on making a kick down switch? Is the micro type switch something easily found at radio shack? I've got a picture of what it should be/do in my head but i'm reluctant to try it until i really know what i'm doing http://bbs.homeshopmachinist.net//wink.gif Otherwise i'll just do it the easy way and buy one!

Boomer
02-23-2006, 09:39 PM
Both the kickdown switch and the electric choke should get power when ignition is on.
The electric choke is simply a heating element that warms up the bi-metal coil that closes the choke valve when it's cold. Idealy this warms up at about the same rate as the engine and causes the choke valve to open (in conjuction with the vacumm choke pull-off). The heating coil is grounded inside the choke so only one wire is required.
The old manifold heat stove types were invariably cloged up or rusted off after a few years operation or worse yet exhaust leaked into the system and really messed things up.
If you use a Micro-switch (so named for the amount of force required to activate it, not it's physical size) for the kickdown you will find three connectors on it labeled com, no, & nc. The "hot" wire goes to the com (common) and the wire to the transmission goes to the no (normaly open). The nc (normaly closed) is not used and should be nipped off or well insulated because it is "hot" when the K/D is not on. The kickdown solenoid is grounded inside the A/T.

As stated earlier these should be fused and if this is original these should exist in the fuse block. Otherwise you should use an inline fuse holder. What amperage? I dunno.

It's been awhile and I may be wrong on some of this so if anyone has any corrections, go fo it.

Bruce


[This message has been edited by Boomer (edited 02-23-2006).]

CCWKen
02-23-2006, 10:05 PM
<font face="Verdana, Arial" size="2">been awhile and I may be wrong on some of this so if anyone has any corrections, go fo it.</font>

LOL... Bruce, did my ripping make you gun shy or something? http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//eek.gif

What you said sounds good to me. Sometimes the choke will have two pins though. They're usually marked +/-. As you say though if there's one pin, it's the positive lead. (Hot on "run")

Boomer
02-24-2006, 07:45 AM
<font face="Verdana, Arial" size="2">Originally posted by CCWKen:
LOL... Bruce, did my ripping make you gun shy or something? http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//eek.gif

</font>
Not sure where you're coming from but no, I've been out of the auto mechanic business since 76 and I may have a Chevy choke confused with a VW fastback. My generalizations may not cover specifics.

I've got two TH 400s "outback", 76 Chevy van/Honey R/V and a 66 Olds Delta with a VP stator...but I could be wrong :P

Bruce

torker
02-24-2006, 08:49 AM
Speaking of electric chokes. I've given up on the GM/Q-Jet system. It doesn't work very well.
Yesterday I got an electric choke from NAPA...made by Echlin by the look of it.
I think this will be a good setup.
The one they brought me in was the wrong one for my choke but it looks good. There is a heat sensor that bolts to the intake manifold and the actual bimetal spring is controlled by a relay setup through the sensor.
A friend of mine steered me onto this. He put one on his car a few years ago and claims it works very well.
We'll see I guess.
Russ

Fasttrack
02-24-2006, 03:28 PM
I got the all the wiring stuff down, really just wondering about the current or size of fuse to use. Also a couple of days ago i wired the choke to a positive lead off of the battery w/ a switch between just to see how the thing worked. Nothing happened :P I hope i didn't screw it up...i didn't want to leave the switch on for a very long time since i was affraid of something shorting, so maybe it should have been left on longer?
Thanks again for all the help!

Boomer
02-24-2006, 08:02 PM
It won't have any imediate effect, but after several minutes the choke should have less intrest in snapping shut.