TH400 acting oddly

[DoubleDingo]

Metal flakes are catastrophic. Friction and steel powder, probably normal wear.

There were flakes but I have no idea what they're from. Thin, light, and didn't stay on the bottom of the pan. The fluid looked okay and smelled okay too.

The battery charged, so I added the atf I'd bought, 6 quarts, and it still wasn't on the stick. 12oz more from the container behind the seat. Not on the stick, but good solid shifts for lacking fluid.

Found a quart in the jeep and got fluid on the stick. Still low, but enough to test drive for two miles.

7 quarts, 12 ounces and still low. Will get two or three more quarts tomorrow.

 

[DoubleDingo]

Drove it around today while running errands. It needed one more quart to top it off. So a drain and fill is 8.5 quarts on this truck. With it at the proper level it is operating better but will still shudder sometimes in neutral and reverse. The pump will whine at high rpms when shifting manually from 1st gear. But taking off in drive it doesn't whine. So I'll start sourcing parts to rebuild it, not just re-seal it like Pop said to do.

So what is it that I would need to get to refresh the transmission? Assuming the steels are good. Seals, of course, what else? Pump? Torque converter?

 

[Matt69olds]

Don’t reuse the converter whatever crap that’s in the converter will get pumped into your fresh rebuild. If the transmission functions for the most part, chances are you could reuse the steel plates. They are dirt cheap to replace. Get a set of bushings, a front pump bearing from a TH350 trans, and .088-.106 front clutch snap ring from a 518/618 Chrysler trans. If you have all that on hand, unless something else is torn up inside that will probably cover the needed parts.

 

[DoubleDingo]

Don’t reuse the converter whatever crap that’s in the converter will get pumped into your fresh rebuild. If the transmission functions for the most part, chances are you could reuse the steel plates. They are dirt cheap to replace. Get a set of bushings, a front pump bearing from a TH350 trans, and .088-.106 front clutch snap ring from a 518/618 Chrysler trans. If you have all that on hand, unless something else is torn up inside that will probably cover the needed parts.

The unit is creeping up on 77k miles, so it's not old as far as miles, but is old as far as time. By the looks of the o-ring I replaced, I'm guessing every o-ring and seal in that thing is beyond it's useful life at this point. What would cause the pump to whine at higher rpm's? Low on fluid? Sucking air? Is the pick-up tube the only passage that fluid enters the pump from? With this thing sucking air for so long, would that cause additional damage to clutches, etc? I don't want to replace what I don't have to if it's still in good shape, but I also don't want to cheap out and have to redo it again later. Is the whine from the pump just because of that bearing?

So a kit from the place @HotRodPC posted up on Post #57, the converter, some bushings, a TH350 bearing for the pump, and a Chrysler clutch snap ring from your list, and a Transgo 1-2 Kit for durability? Does that sound about right?

 

[Matt69olds]

If your doing a complete overhaul, don’t bother with the TransGo kit. You can do everything the shift kit will do for a couple bucks when it’s completely apart. As for the whine, if the filter is plugged up or restricted, that could cause it. Kinked cooler lines, restricted trans cooler, without a autopsy it a educated guess. It’s common practice to use 2 O-rings on the filter tube, where it fits into the case.

 

[DoubleDingo]

If your doing a complete overhaul, don’t bother with the TransGo kit. You can do everything the shift kit will do for a couple bucks when it’s completely apart. As for the whine, if the filter is plugged up or restricted, that could cause it. Kinked cooler lines, restricted trans cooler, without a autopsy it a educated guess. It’s common practice to use 2 O-rings on the filter tube, where it fits into the case.

The filter is new, the one before it was replaced a month ago. The only reason I dropped the pan again was to check the o-ring for the pick-up tube. That o-ring was flattened out as shown in the photos in previous posts, and it now has two of them. Prior to adding the two o-rings, it had a whine when first started, and it would go away after about a minute. When I installed the two o-rings, upon the first start-up there was no whine whatsoever, and it will only whine if I rev it up in first gear, shift into second and rev it up before shifting into third, taking off in drive the rpm's don't get high enough and it doesn't whine at all. As I wrote that it makes me wonder if the filter kit I'm getting from carquest doesn't flow like it should. I can't get the purolator filter anymore, which sucks because it was the brass screen that @HotRodPC said was a good one. I would like to know how to modify the tranny to get the same results as the transgo kit. The cooler lines are all stock, same with the radiator. They may be partially blocked, that's possible, but the truck doesn't overheat at all, it runs steady at the first mark above the "C" on the gauge no matter how I drive it and it doesn't matter if it's 110* outside.

 

[HotRodPC]

Drove it around today while running errands. It needed one more quart to top it off. So a drain and fill is 8.5 quarts on this truck. With it at the proper level it is operating better but will still shudder sometimes in neutral and reverse. The pump will whine at high rpms when shifting manually from 1st gear. But taking off in drive it doesn't whine. So I'll start sourcing parts to rebuild it, not just re-seal it like Pop said to do.

So what is it that I would need to get to refresh the transmission? Assuming the steels are good. Seals, of course, what else? Pump? Torque converter?

I'm beginning to wonder if you might not have a burnt or close to wore out Low/Reverse Band? I'd say the 2 O rings helped on picking up fluid quicker at start up and taking away a pause from garage shifts. But you mention Reverse shutter and whine manually shifting from 1st. Those are the 2 things that band does. Without it, you'd have no Reverse and manually selected 1st gear engine braking. Hence the reason it's called the Low/Reverse band. In D, first gear is made a different way so the band isn't used in D, just R and 1st. If it's not the band, it could also be the servo that operates that band. Maybe worn sealing ring on the servo piston or something of that nature. The good news, no major metal shavings in the pan so as of yet, nothing catastrophic has happened, and the other good news, that band is nothing that will leave you stranded. Worse case scenario, you might lose reverse at some point but D will work just fine.

 

[DoubleDingo]

That's somewhat good news. With it functioning pretty much like normal now, would it hold up until I can source the parts and rebuild it.

 

[HotRodPC]

That's somewhat good news. With it functioning pretty much like normal now, would it hold up until I can source the parts and rebuild it.

If it's just a band chatter, I'd sure think so. I think it would last quite awhile and as said, even if the band does go, all you're going to lose is R, and D will continue to work just fine so you're not going to be left stranded. Just make sure you park in a place where you don't need R, like up a slight slope or pull through so you're nosed out, but I say it's highly unlikely you'll lose R completely. I wouldn't be afraid to jump in it right now and drive it coast to coast but that's just me. I've done some weird **** having faith in vehicles that blew peoples mind because I just figured there isn't much I can fix or patch up to make it home at least.

What made me think of that, is you mention the shuttering in R. You ever heard of clutch chatter in a manual transmission? Just about the same principle. That band is scorched or worn and chattering on the drum. It all came to mind when you mentioned problem in R and in Low but D working fine. I do beleive the filter to be part of your problem and that could have been what allowed the band to get overheated. Especially since the first thing someone normally does when they start up a vehicle, is back up. So it's possible starting up, not quite picked up enough fluid yet, go into R and the band has been allowed to chatter long enough, and enough times that it's now scorched. This is all just a thought process of possibilities and I won't claim to be 100% right, but it does seem to reason. So do plan on replacing both bands on a rebuild. Alot of times bands don't need replaced but I'd for sure replace yours.

 

[Matt69olds]

Next thing to check is line pressure. Maybe you have a pressure regulator sticking, boost valve hanging up, modulator valve stuck, or some other reason for excessive line pressure. If you can’t find a brass filter, I can tell you where to get them, I don’t think the auto parts store can get them, try a trans shop?

 

[HotRodPC]

That's somewhat good news. With it functioning pretty much like normal now, would it hold up until I can source the parts and rebuild it.

If it's just a band chatter, I'd sure think so. I think it would last quite awhile and as said, even if the band does go, all you're going to lose is R, and D will continue to work just fine so you're not going to be left stranded. Just make sure you park in a place where you don't need R, like up a slight slope or pull through so you're nosed out, but I say it's highly unlikely you'll lose R completely. I wouldn't be afraid to jump in it right now and drive it coast to coast but that's just me. I've done some weird **** having faith in vehicles that blew peoples mind because I just figured there isn't much I can't fix or patch up to make it home at least.

What made me think of that, is you mention the shuttering in R. You ever heard of clutch chatter in a manual transmission? Just about the same principle. That band is scorched or worn and chattering on the drum. It all came to mind when you mentioned problem in R and in Low but D working fine. I do beleive the filter to be part of your problem and that could have been what allowed the band to get overheated. Especially since the first thing someone normally does when they start up a vehicle, is back up. So it's possible starting up, not quite picked up enough fluid yet, go into R and the band has been allowed to chatter long enough, and enough times that it's now scorched. This is all just a thought process of possibilities and I won't claim to be 100% right, but it does seem to reason. So do plan on replacing both bands on a rebuild. Alot of times bands don't need replaced but I'd for sure replace yours.

 

[DoubleDingo]

If it's just a band chatter, I'd sure think so. I think it would last quite awhile and as said, even if the band does go, all you're going to lose is R, and D will continue to work just fine so you're not going to be left stranded. Just make sure you park in a place where you don't need R, like up a slight slope or pull through so you're nosed out, but I say it's highly unlikely you'll lose R completely. I wouldn't be afraid to jump in it right now and drive it coast to coast but that's just me. I've done some weird **** having faith in vehicles that blew peoples mind because I just figured there isn't much I can fix or patch up to make it home at least.

What made me think of that, is you mention the shuttering in R. You ever heard of clutch chatter in a manual transmission? Just about the same principle. That band is scorched or worn and chattering on the drum. It all came to mind when you mentioned problem in R and in Low but D working fine. I do beleive the filter to be part of your problem and that could have been what allowed the band to get overheated. Especially since the first thing someone normally does when they start up a vehicle, is back up. So it's possible starting up, not quite picked up enough fluid yet, go into R and the band has been allowed to chatter long enough, and enough times that it's now scorched. This is all just a thought process of possibilities and I won't claim to be 100% right, but it does seem to reason. So do plan on replacing both bands on a rebuild. Alot of times bands don't need replaced but I'd for sure replace yours.

Yeah, good old clutch chatter in a manual vehicle, I can see that type of thing happening here. The way you explained it makes sense. If this thing was quietly sucking air for a long time, and I like to shift it manually about 1/3 of the time, that would explain things getting scorched due to lack of fluid. L works fine when I take off in L, it's just the R chatter.

I would drive it across the country too, I'm crazy like that. I basically did a 3,000 mile road test when I took Old Crusty from here to Texas and back in 2017. Tore off the top end, replaced the heads, the cam, did the cam break-in, fixed any leaks with short drives around town, changed the oil, loaded up, and headed out. It did great! Once we got to her parent's after three days of driving, I checked all the fluids front to back, and all were at the proper level, and no strange particles or colors in any of them. Three more days coming back, and not an issue to speak of.

 

[DoubleDingo]

Next thing to check is line pressure. Maybe you have a pressure regulator sticking, boost valve hanging up, modulator valve stuck, or some other reason for excessive line pressure. If you can’t find a brass filter, I can tell you where to get them, I don’t think the auto parts store can get them, try a trans shop?

Do I need to check the line pressures even if I am going to rebuild it? The modulator is new, and that didn't fix anything, but I didn't know it was sucking air when I replaced it either. I'll see if a transmission shop has a brass filter.

 

[Matt69olds]

It may be useful to know what the pressure is now, if nothing else just to give an idea one where to look for problems. How much do you know about the history of this truck? There are differences in pressure regulator valves. The later valves will interchange, but if you use a early valve in a later pump body, the pressure can go way high. I have interchange info taped to my garage wall. If someone has had their hands in it and mismatched parts that could be the reason for the whine

 

[DoubleDingo]

It may be useful to know what the pressure is now, if nothing else just to give an idea one where to look for problems. How much do you know about the history of this truck? There are differences in pressure regulator valves. The later valves will interchange, but if you use a early valve in a later pump body, the pressure can go way high. I have interchange info taped to my garage wall. If someone has had their hands in it and mismatched parts that could be the reason for the whine

I'll have to acquire a gauge before I rebuild to do the pressure check. This is a near 77 thousand mile truck and transmission, I am the third owner of the vehicle and it is an unmolested numbers matching vehicle, except for the vortec heads on the engine. Pretty sure I have been the only person to drop the pan on it and replace the filter and modulator valve. So we'll call this a bone stock, 1981 Turbo Hydromatic 400 transmission, with all stock internals, externals and gaskets and such, except for the o-rings I've replaced, and the filters, pan gaskets, and modulator, and new fluid. I appreciate your knowledge on the various parts and how to build these up, but all I am interested in is rebuilding a stock TH400 with the shift kit upgrade. Nothing fancy. I like reliable so I tend to stick to factory parts as much as possible.