Won't stay in 3rd gear

ErikTande · July 18, 2017, 07:47 PM

My transmission won't stay in 3rd gear. It will shift into 3rd just fine if there is no load on the engine. As soon as there is any load, it downshifts into second.

Was working great previously (did 400 miles). Started the next day.

I checked the vacuum modulator on the passenger side of the transmission and replaced it along with the vacuum lines to it, no change.

What do I check next? Thanks!

Rickf1985 · July 18, 2017, 09:56 PM

Are the other vacuum lines that are hooked to the same port as the modulator all good and no leaking? If one of them has a bad leak it will drop the vacuum and force a downshift. Do you have a mechanical downshift linkage from the carburetor to the transmission on that unit? If so did the return spring break?

ErikTande · July 19, 2017, 10:24 AM

Quote
Are the other vacuum lines that are hooked to the same port as the modulator all good and no leaking?

Yep, even connected the modulator directly to the manifold to eliminate other lines. No change.

QuoteDo you have a mechanical downshift linkage from the carburetor to the transmission on that unit? If so did the return spring break?

Not sure, I'll take a picture of mine. Got a pic of what that linkage should look like?

Also, if it's not the modulator and not the downshift linkage, is there anything else that could cause it?

Thanks again! I appreciate the help!

Rickf1985 · July 19, 2017, 10:40 AM

The only other thing I can think of is the governor, been a long time since I had one of these apart. I have to run out and fight with Motor vehicle over my disabled tags for my car, this may take a while but I will check my manual when I get home. Governor is more RPM related and what you are describing sounds load related. The valve body controls all of it but it is all mechanical and something has to physically tell each valve to move.

ErikTande · July 19, 2017, 10:51 AM

Here's apic of the carb:

ErikTande · July 19, 2017, 10:57 AM

Could this be the issue? I assume I just drop the pan to check this?

https://youtu.be/5O-6RxPOrGg

legomybago · July 19, 2017, 12:20 PM

Might sound crazy, but make sure your clutch fan isn't froze up. People have mistaken transmissions that wont shift out of 1st or second gear or whatever due to what they "think" they are feeling or hearing....simple one to check off your list.

ErikTande · July 19, 2017, 12:45 PM

Yep, fan clutch is working

M & J · July 19, 2017, 01:12 PM

I see a cruise cable and the throttle cable. Not a kick down lever. On GMs it was a round bar with a long slot where it connected to the carb linkage. Anything on the other side of the carb?

Rickf1985 · July 19, 2017, 01:23 PM

Choke is on the other side. That video does not appear to be a 400, that is an electronic trans with a screwed on filter. I am thinking governor but let me get into my manual. They had issues with them but it has been so long since I dealt with them I don't remember.

Rickf1985 · July 19, 2017, 01:40 PM

Ok, When you put in the new modulator did you do any adjustment on it? Does it shift up as it should through all the gears but then drops back down or it will not shift into third under any load? It is sounding like you may have crap in the valve body, when was the last time you dropped the transmission pan?

ErikTande · July 19, 2017, 01:54 PM

It shifts fine, reverse works, shifts fine from 1 to 2, and it shifts into 3rd fine as long as there is no load on the engine (like going downhill). As soon as there is any load it shifts back down to second.

I've never dropped the transmission pan. Fluid is clean though. Is the valve body in the pan?

Rickf1985 · July 19, 2017, 04:38 PM

The valve body is bolted to the bottom of the transmission in the pan. I think it sounds like a modulator issue but you say you have replaced it and the vacuum lines so that only leaves the internals. You could pull the governor and see if it looks like it has come apart. Since it was working and then stopped it has to be something that either failed or clogged/jammed. The fact that it does shift up but right back under load tells me that the shift valve is moving but the modulator valve is not holding. There should be an allen screw inside of the modulator vacuum line fitting, if you pull the vacuum line off the screw is down in there. You can try adjusting that and see if it makes any difference. Turn it out one or two full turns and try it and note any difference. Write down everything. Especially the number of turns every time you adjust it. You want to be able to come back to the original setting if the changes do not work. Try 2 turns out and if that improves it try one more out. If it gets worse go back to the baseline and then go two turns in etc. This may give me an idea of what is going on................ or not. But worth a try and free. I think if this does not tell you anything then the next step would be to pull the governor.

You do not want to open the valve body unless you are confident of your abilities to get it all back together.

Check out the diagnosis chart on page 10, first one. http://shop.ukrtrans.biz/wp-content/uploads/catalogs/TH400.pdf

Here is a complete teardown of a 400, This is probably the easiest automatic transmission to rebuild. https://www.youtube.com/watch?v=_TMFibSiwVw

This is about the only picture I could find of the valve body parts thanks to Photobucket. There are a lot more to it than this though, that is why I caution about taking it apart. You can remove it from the transmission in one piece. https://www.pavementsucks.com/threads/turbo-400-valve-body.103510/

ErikTande · July 19, 2017, 06:08 PM

Ok, I'll try adjust the modulator first. If that doesn't do it, check the governor, right? Should I grab a gasket or rebuild kit before I take it off? Looks like the kit is under $10 at napa.

Rickf1985 · July 19, 2017, 08:28 PM

I don't know what kit you are talking about but if it is a governor kit then yes I would get it. There is a valve in there that may be stuck but keep in mind that all valves in an automatic trans are very close tolerance so no hammering or cranking on things. If you can't gently move stuff then sit back and rethink how to go about it, the bores are all aluminum and will score very easily. That would be bad. Since you have never had the pan down now would be a good time to do it. Get a filter and a gasket. Get the higher quality parts so you don't get the garbage gasket. I would get 7-8 quarts of fluid and ask if you can bring back any you don't use, that way you are not making extra trips if you run out. When you drop the pan you can expect to see a layer of black gunk on the bottom of the pan. This is normal as long as it is not a 1/4" thick. There is a magnet in there on the pan, pull it out and clean it off. Again, fuzzy is OK but pieces are not. I will pm you my e-mail so you can get in touch quicker if need be, I only check in here off and on.

Froggy1936 · July 19, 2017, 09:31 PM

Is ent there supposed to be a pin that goes into the modulator that acts upon the valve ? Frank

Rickf1985 · July 20, 2017, 09:16 AM

Yes, without it there would be mo upshifts so I am pretty sure it is there. The adjustments I asked him to make will verify it is there because it should change the shift points for the 1-2 and 2-3 shifts. We used to adjust the modulator as far as it would go and them grind a bit off of the pin. The more I think about it the more I am inclined to say the high/reverse clutches may be gone though. This was a common problem with the 400 it it was abused and it sounds like maybe the history of this unit is unknown.
Erik, you might want to get that pan down before going to much further and see what it looks like in there.

ErikTande · July 20, 2017, 06:35 PM

What am I looking for when I drop the pan other than visible chunks of metal or signs of damage?

I adjusted the valve out 2 full turns, I'll try driving it tomorrow, been too busy to test it out, been camping

Rickf1985 · July 21, 2017, 08:51 AM

It is normal to see a thin layer of dark material on the bottom of the pan, this is normal clutch wear. If it is the consistency of gunk then you have far to much and that means the clutches are history and that is your problem, a rebuild is the only solution. There is a magnet in there and it will have a thin layer of dark fuzz on it, any more than that is also a bad sign. metallic flakes would mean the clutches are completely gone and wearing into the steels and chunks, ....................... well, need I say any more?

ErikTande · July 24, 2017, 03:04 PM

Quote from: Rickf1985 on July 20, 2017, 09:16 AM
The more I think about it the more I am inclined to say the high/reverse clutches may be gone though. This was a common problem with the 400 it it was abused and it sounds like maybe the history of this unit is unknown.

This was the problem. Reverse went out shortly after I made my last post, so that confirmed it. Got it at a shop doing a transmission swap, should be back on the road today or tomorrow. Thanks for the help everyone!

Easternmost Winnebago · July 24, 2017, 06:02 PM

Hey Rick.. does it matter what position if any the modulator valve is set when i install my new one? i noticed it has a red dot painted on one side for a "reference" point? The old one doesn't have one but is pretty beat up from road debris etc. chipping a lot of the paint off. Thanks

Rickf1985 · July 24, 2017, 06:06 PM

Transmission "swap" is not a good thing! That means you are going to get a 400 in return for the 475 they are taking out. It will work but the original had stronger low end gears in it, same ratios but straight cut gears. A rebuild would have been much better but that is a problem with a lot of so called "transmission shops" nowadays. They don't know how to rebuild them, just how to swap them. With a rebuild you could have gotten a Trans-Go shift improver kit put in at the same time.

Rickf1985 · July 24, 2017, 06:30 PM

As long as the modulator slides in and seats it will be fine. You should get a new one with the replacement trans already installed.

ErikTande · July 27, 2017, 12:47 PM

Quote from: Rickf1985 on July 24, 2017, 06:06 PM
Transmission "swap" is not a good thing! That means you are going to get a 400 in return for the 475 they are taking out. It will work but the original had stronger low end gears in it, same ratios but straight cut gears. A rebuild would have been much better but that is a problem with a lot of so called "transmission shops" nowadays. They don't know how to rebuild them, just how to swap them. With a rebuild you could have gotten a Trans-Go shift improver kit put in at the same time.

Sorry, used the wrong word. It was a rebuild, not a swap. They did recommend the shift kit as well so we did that too. It was a very cool shop in New Ulm, MN called Riverside Transmission. They put up with all the questions I asked and had it done in no time. I dropped it off on Friday at 3pm and had it back Tuesday at 7am. $1700 out the door with a 1 year warranty. Not an expense I wanted to pay on my vacation but I'm happy it's done. I have 2 more roadtrips planned this year already so it's worth it.

Rickf1985 · July 27, 2017, 03:42 PM

A little steep considering you dropped it off but maybe I am behind the times or maybe there were hard parts that needed replacing. You may not even feel the shift kit due to the weight of the vehicle but it will bring the clutches in faster and tighter so they will not wear as much. Also increase the line pressure across the board. Did you get a new convertor? The old one is going to have residue left from the burnt out clutches. Not good to circulate that through the new trans. If you got a new convertor then the price is right.