The Stovebolt Site Forums The Shop Area The HiPo Shop TH400 shifting problems.

I finally got to the point in my '49 build and attempted to drive it with a TH400 which I bought a couple of years ago from a guy who said that it had very recently been professionally rebuilt.
I don't know how long it had been sitting in his shed before I bought it. It had fluid in it which looks new.
The problem I am having is it won't shift through the forward gears automatically or manually.
It stays in one gear which is either 1st or 2nd gear (not sure which).
It functions in reverse just fine.
I have removed the governor and it looks like it just came out of the box, new. The valve moves freely when the counter weights are moved outward.
I put a Mighty-vac on the vacuum modulator and it holds vacuum.
Where should I look next?
Flush the transmission?
Remove the vacuum modulator to look for problems?
Drop the pan, remove the valve body to inspect for gummed up valves?
I want to exhaust all options short of transmission removal.
Carl

Grab the driveshaft and turn it, while watching the governor. It should turn. It's possible the gear isn't meshing with the output shaft for some reason.

If you remove the valve body, be careful- - - -the gaskets are easy to damage, and there are several check balls that will try to fall out and roll away if you don't hold the valve body perfectly level as you lower it.

I just remembered another possible problem. There's a snap ring about the middle of the transmission case that can jump out of place the first time a 1-2 shift is made, if it happens to get mixed up with another, similar-sized ring during reassembly. After that, the trans will not upshift out of 1st. speed. One ring has a tapered face- - - -the other one is square-cut. If the tapered ring is installed in the case instead of where it belongs, it won't stay put.

Please don't ask me how I know that- - - -or why it took two tries for the lesson to stick!
LOL!
Jerry

Thanks Jerry!!!
Stand by for some "good" stories...
Maybe I will find those tiny ball bearings that fell out of that fishing reel I took apart 3 years ago when I look for the ones that are going to fall out when I drop the valve body.
Carl

I really doubt that you've got a valve body problem. The snap ring thing brought back a whole bunch of bad memories, and there's absolutely no way to confirm it without tearing down about half the rotating assembly and at least one clutch pack.
Jerry

One other thing that I noticed while test driving it on both occasions was that when I moved the shifter from Drive to 2nd in an attempt to make it down shift, it made a sound similar to what a bad u-joint sounds like just before it comes apart, except nowhere near as loud, if that makes any sense. Kind of a rumbling of parts which did not want to cooperate. It would go away soon after moving the lever back to drive. (The u-joints are tight by the way.)

Those are exactly the symptoms that displaced clutch pack creates. it will freewheel like it's in neutral and rattle a little, and when the RPM catches up, it will pull again. Drop the transmission and open it up!
Jerry

Thanks Jerry, although I am not happy about it. I was hoping for an easy fix. I have completely rebuilt a Buick Super Turbine 300 years ago by following the step-by-step instructions the Factory Service manual years ago, so I am not totally green about digging in.

So I pulled the oil pan and while I found no marbles, boulders nor did it look like a snow globe, the bolt which someone chose to use to hold the filter in place was 1/4" too long and the filter was flopping around and it was not held tight to the pickup tube at all.
What effect will that have?

It's been a while since I've had a 400 apart, but I seem to remember the filter being able to "float" a little on a single retaining bolt. The siphon tube section of the filter that plugs into the case has a sleeve-shaped rubber seal with ridges on it, so the filer doesn't have to be rigidly held into place. The 350 filter is held on by two screws, and is attached tight to the valve body. Not so with the 400 for some reason.

Jerry

Yes, TH400 (later ones) the filter would float just slightly on the bolt.

You're building pressure to move, so the pump is getting fluid.

I too have mixed up the tapered snap ring with another. As jerry says, time to open it up.

I did some searching on the Wild Wild World of Web and everyone is wondering about the odd arrangement for attaching the filter on a TH400. I agree that don't have a fluid pickup issue.
So I'm digging in tomorrow to yank her out.
I will need to cut the riveted-on crossmember to drop it out (I installed it with the engine attached from the engine bay before the cab was in place).
I guess I will fab a new one out of square tubing.
I will keep you posted.
BTW, its getting serious all up in my shop right now. I broke out my lucky Spongebob Squarepants shirt!

Be sure to take some measurements before you start cutting rivets. Sometimes the frame rails spread out a little with a crossmember gone, particularly if it happens to be the one that also reinforces the mounting points for the back of the front springs.
Jerry

Good point Jerry. Will do. And yes, it is the one which shares rivets with the front spring mount. I am leaving all of the rivets alone and just cutting out a big enough section of the center of the crossmember to have enough room to drop the transmission.

The square tubing idea is a good one- - - -welding plates on the ends of the tubing that can bolt into some of the existing rivet holes seems to be a good compromise between accessibility and frame reinforcement.
Jerry

After looking at it will napping under the truck, I decided to just cut the crossmember close to where the riveted section is, cut a piece of plate steel to weld on the end of that stub which drops down 2 inches. (I need more clearance anyway.)
I will then weld a similar plate to the end of the original crossmember which will extend upwards, parallel to the plate previously welded to the stub ends of the crossmember on the frame.
I can then drill holes through these plates for bolts to hold everything together.
Total cost of materials $0.00.

Carl,
We need some pictures of this project!

I opened the hornets nest today. The snap rings were in the correct places. The drum which the rear band rides on (these are the parts deepest in the case), has some bizarre marks on them. I am seeing some deep grooves in a spiral pattern on the outer surface where the wide bands contact.
I am wondering if someone originally installed the big snap rings wrong (as suggested by you gurus), ran it, blew out the wrong snap ring scoring the spiral pattern in the surface, then stupidly decided to put it back together the right way with all of that damage.
What kind of damage does one typically see when the wrong snap ring blows out?
What should I do now with the bad what-ever-that-drum-looking-thing-what-the-wide-band-goes-on?
Don't be too judgemental about my lack of proper names for these parts. Truth be told, I am really good at taking stuff apart...
I am not too bad at putting them back together.
My concern is I don't know what to look for exactly to determine what is toast and what is normal wear.
Carl

I would replace that drum and the band that goes around it. Also the sprag clutch that is between the drum and the center support might need replacing as well as the center support.

Check the planetary gears in the back of the drum as well for any damage.

All the scoring was done when that assembly moved forward and back and may have hidden damage in the other pieces behind it.

Hotrod Lincoln can speak much better than I can on what it might need, but look everything over close for damage.

The case which contains the planetary gears looks like it has been in a very bad house fire. Either that, or that part is case hardened. It is the color of a case hardened six shooter revolver.

Run down to your local transmission exchange place and toss some green on the counter. Leave your stuff with them and bring home your newly rebuilt TH400. Problem solved. Not as much fun as building your own but less stressful.

While you have it out put a 700r4 in it's place and have overdrive.

Depending on the gearing in the back he may not need the overdrive.

"The case which contains the planetary gears"- - - -would you by chance be referring to the "internal gear" the one with gear teeth on the inside diameter? If so, yes it should be a dark gray or black color. It's hardened to the same degree as the planet gears, so they don't wear each other out. I don't like your description of the drum the rear band rides on. That doesn't sound right. You've got something going on that's more severe than a simple incorrect arrangement of parts, so it's going to be necessary for someone who is very familiar with that transmission to do a full teardown and inspection, all the way to disassembly of the clutches, pistons and all, and an inspection of every seal. I'm going to need to refresh my memory on the power flow in 1st. and 2nd. gear to give you an educated guess about what's slipping and/or failing to engage. I strongly suspect your "rebuilder" has made some expensive errors during assembly unless the transmission was actually run and badly abused for a short time after it was rebuilt.
Jerry

I don't need overdrive with my 3.08 rear gears, and 30" tires. I also want to avoid having to undo a lot of mods in the mounts and/or shift linkage, nor cut the drive shaft again.

You might be better off finding a TH400 from a reputable rebuilder and see if he'll take yours as a core.

400's are usually extremely rugged, reliable transmissions- - - - -if- - - - - -and only if they're set up with the right assembly procedures and clearances, etc. They can be very unforgiving of sloppy assembly and inattention to details where clutch pack clearances and the corresponding movement of the clutch pistons is concerned. There are also a few places where a "selective thrust washer" (different thicknesses) needs to be fitted to keep the gear train from bouncing around and breaking stuff!
Jerry

So here is what I found after disassembling and cleaning this "rebuilt, ready to go transmission" (as stated by the seller).
1) Missing accumulation valve spring, seal, and retainer clip.
2) Intermediate check ball in the wrong spot in valve body.
3) 3 or 4 burnt steel clutch discs, 3 well worn steel clutch discs (the fiber discs appear to be brand new).
4) Bad lower roller clutch assembly (bearings fall out of the carrier).
5) Badly scored reaction drum, the one which the reverse band rides on (the reverse band looks like new).

I have a question about the main shaft fit on the rear internal ring gear. It is held in place by a snap ring. It seems to have a lot of play in it. How much, if any play is acceptable?
I received the ATSG TH400 repair manual yesterday and I am going to rebuild this boat anchor. The book is pretty thorough.
As far as the guy who I bought this transmission from, I am going to allow Karma to take care of him, if it hasn't already. There is an outside chance that we had no idea it was this bad, so he won't be "bothered" by me.
Carl

There are two end play specifications on the 400. The rear section which includes both planetary units and the sprag and roller clutches is positioned by the intermediate clutch hardware, which is locked into the case by the snap ring I was referring to earlier in this post. That end play is adjusted with a selective-thickness snap ring, which should cure any apparent slop in the output shaft. Once the front and rear clutch assemblies are installed, a thrust washer incorporated into the pump assembly sets end play for the front section.

This differs from the Turbo 200, which adjusts end play with a single thrust washer. The 400 was designed and built long before the baby chick engineering folks got involved in transmission design ("CHEEP- - - -CHEEP- - - - -CHEEP!")
Jerry

Know this probably is not the reason for your 400 problem but it was for my 400 and was fixed rather quickly after a thorough methodical search of the disturbed area. I had a guy do some drive line work to straighten up and properly set pinion and drive angles and replace my driveshaft. I took the vehicle out for a test run and it would not shift, I did not rev it past the point of ruining something. Limped back to the garage and explained what happened and after a lengthy search it was found that the vacume line running down to the front passenger side was not secure. Secured that line and everything was like it was before, just a simple vacume source, again hope this helps. Thanks HUGH

He checked the vacuum to the modulator before making his first post. This transmission was a victim of an assembly job by Mr. Bad Wrench.
Jerry

You said it, Jerry!
I have most of it all back together. I am waiting on a shift kit to replace whatever Mr.Bad Wrench put in it. I was thinking about just going with a stock valve body set up, but even if I found one, I wouldn't know for sure that it hadn't been monkeyed with.
The latest missing part that the dufus left out was the big spring in the reverse servo.

"DANGER, WILL ROBINSON!"

RUN, do not walk away from anything with "shift kit" in the name. If you leave the "F" out it's a better description. Most of the rear end failures, and an overwhelming majority of premature universal joint failures I've seen were on vehicles that also had a shift kit installed. If you absolutely must have a more positive shift, machine the front and rear clutch pack pistons and pressure plates to accommodate a couple more clutch plates, and leave the shift strategy the way the GM engineers designed it to be!
Jerry

I have had really good luck with Trans-go shift kits in the past. Dash 2 kits make sharp, consistent shifts under load, and smooth shifts under light load. Dash-3 were the all out racing, bust the windshield shift's. My T350 I have behind my 250ci has the dash-2 kit and hasn't broke anything in 17 years of driving, and it will chirp the tire going into second under full ( all 120 hp ) throttle!

The disadvantage to all shi(f)t kits is on the downshifts, not the upshifts. On a 3-2 kickdown, the clutch that engages second speed gets locked in before the high clutch releases- - - - -with the transmission in two ratios at once, the driveshaft locks up momentarily and a tremendous amount of load goes onto the u joints and the cross pin in the rear end that holds the spider gears in place. I've seen rear end carriers with the pin hole slotted out 1/4" or more instead of being round. You guessed it- - - - -shift kit! If the vehicle always shifts 1-2-3 and stops, and NEVER gets a full-throttle kickdown, I guess it's OK to have an uncomfortable shift.

That tire chirp is fun to listen to, I'm sure- - - - -just be aware of what it really costs to hear it!
Jerry

This process of trying to fix a problem caused by a lummox has been frustrating. I was too eager to git-r-done and payed for the kit (special ordered) before running it by those who know. I have zero faith in the shift kit job which was done previously by the dufus and I have no idea where to find a stock valve body plate.
The kit which I ordered is not described as a neck snapping affair.
I will investigate further, the possibility of finding a stock plate and pay the restocking fee for the kit that I ordered.
I did however have a ball rebuilding this transmission. There is a lot going on in one of those babies.

Transgo offers the best shift kit out there and their kits usually allow you to choose the level of firmness you want.

Transtar is a company you should be able to get a new plate for the valve body, or a complete valve body ready to go.

Can't say I've ever had any issue with a shift kit that I've installed over the years. But a stock shifting TH400 works fine and will be trouble free forever almost with a little maintenance.

If you speak Noo Joisey yankee fluently, give FATSCO transmission parts a call. Once we get past the north/south language barrier, they are very good guys who really know their transmissions- - - -particularly the older ones like the Dual Range Hydramatic, cast iron Powerglides, etc. Google the shop name for a phone number, etc.
Jerry

I received the B&M shift kit today.
It came with a stock valve body separator plate and gaskets,
Pan gasket,
Detent switch metal gasket,
Pickup tube o-rings,
Two drill bits.
The instructions say that there are 3 options.
1) Street. -Drill holes in plate in 2 locations, remove 1-2 accumulator return spring, delete 3 of 6 check balls.
2) Heavy Duty. -Drill one hole in plate.
3) Stock. -install plate. (No other Modifications.)
I essentially payed $50.00 for a stock, unaltered by who-knows-who plate. I can live with that.
I now have the rebuilt-by-me transmission bolted up to the engine.
I will button up everything else tomorrow and give it a test drive.
Standby for updates!
Carl

Great! Now throw those drill bits and that instruction sheet in the nearest circular file, and do your best to forget you ever read about altering the plate!

There is a method that I've used to beef up automatic transmission clutch assemblies by machining them to accommodate a thicker stack of friction and steel plates, which has the effect of adding to the swept area of the clutch. It's the equivalent of installing a larger diameter clutch disc ahead of a manual transmission. Then, even with stock shift timing and no increase in line pressure, the clutch is able to carry much more load. I've done that mostly on rigs that tow heavy trailers, but it also works well on high-HP hot rods.
Jerry

Got the TH400 rebuilt and installed! Shifts just like it is supposed to. I did have a scare which had me second guessing my proficiency in transmission rebuilding ability however.
I had a noise during coasting when it downshifted from 3rd to 2nd which sounded just like a u-joint about to give out. I kept crawling under to shake the front end of the drive shaft to feel for play but never found any. I thought that I would have to take the transmission back out.
Should have wiggled the rear end sooner. Turns out that the pinion bearing in the rear end is horribly loose.
So now I need to find a Japanese six lug rear end with drum brakes which has a ratio in the low 3s at our local pick-n-pull.
The nice thing is that most of the 2000 and later Japanese vehicles have the rear end gear ratio on an easy to read sticker on the door jam.
Thank you for the help and moral support!
Carl