Does the TH400 have a "Limp Mode"?

Steel Soldiers is supported by:

edpdx

Member
744
10
18
Location
Oregon
I have read several articles about transmissions that give out and render a maximum speed of 35MPH- to "Limp Home". The issue seems to be a shift solenoid.. Is this a thing with the 400?
 
Last edited:

cucvrus

Well-known member
8,584
1,259
113
Location
Jonestown Pennsylvania
You can limp any transmission home. You just take it easy and figure out the comfort zone and go from there. But per say there is no limp mode built into a TH400 transmission. I had a broken TH400 transmission on a CUCV plow truck and plowed snow for a day. The last thing that happened was no reverse. I plowed all day in forward. The entire top of the case was broken and only really leaked fluid when I put full power to it. Crazy. Also a transfer case broken in 1/2 and still had 2WD. That limp mode is built into newer vehicles as a safety precaution to get you out of traffic and to a safe place. Some people think to limp home. What if I am 900 miles from home and it goes out. The SOL mode kicks in and there I sit. At this point in time if your CUCV transmission has never been rebuilt by a competent transmission person I recommend doing so before you do more damage to the already tired and worn internal seals and parts. Just letting a jack do the work is not the same. Most vehicles at 35 + years require regular maintenance and doing it right the first time goes a long way to keep it reliable. Do it all at once and drive on a long time. Or not and just keep draining the wallet slowly. Good Luck and Be Safe. As I limp off to work in this great new pandemic fiasco.
 

Tow4

Well-known member
Steel Soldiers Supporter
1,846
62
48
Location
Orlando, FL
Sounds like something is keeping the transmission from upshifting. Back in the day, I had the down shift switch break with the rod stuck inside and the switch was on. That kept the TH400 from upshifting. I think CUCV's have a mechanical linkage for down shifting based on throttle position. I'd have to go look to be sure.
 

cucvrus

Well-known member
8,584
1,259
113
Location
Jonestown Pennsylvania
TH400 is vacuum shifted from throttle position and the VRV controlling the vacuum. The down shift is electric and controlled by an electric switch located directly above the throttle pedal in the cab. The Orange wire is attached mid ship of the transmission case on the left (drivers side). That is the only electrical connection on the transmission. The vacuum control modulator is located on the right front (passengers side of the TH 400 transmission. The VRV is controlled by 2 vacuum lines. Bottom being B back of engine and top being T to transmission. The rubber block means nothing and if cracked and broken can be discarded. New vacuum lines make a huge difference. The rubber block served 1 purpose to ease and correct the original assembly during the vehicle being built. Good Luck. Be Safe.
 

LastFbody

Member
126
9
18
Location
Milwaukee WI
Sorry to necro here a bit.

Cucvrus, you mentioned something about an electric switch near the pedal that causes the th400 to downshift that piqued my curiosity. Is there a proper name for that component? Mine might be broken based on how the truck doesn't like coming out of 3rd/2nd unless I'm slowing down significantly (under 25 for 3rd to 2nd) or almost completely stopping for 2nd to 1st. This is with a recently rebuilt 400 with a new vrv and hoses. A brief snowplowing career prior to my ownership killed the reverse/3rd band.
 

cruzer747

Active member
182
99
28
Location
California
Sorry to necro here a bit.

Cucvrus, you mentioned something about an electric switch near the pedal that causes the th400 to downshift that piqued my curiosity. Is there a proper name for that component? Mine might be broken based on how the truck doesn't like coming out of 3rd/2nd unless I'm slowing down significantly (under 25 for 3rd to 2nd) or almost completely stopping for 2nd to 1st. This is with a recently rebuilt 400 with a new vrv and hoses. A brief snowplowing career prior to my ownership killed the reverse/3rd band.
Does not sound like it is related to your downshifting problem. The switch cucvrus mentioned is the kickdown switch (attached to gas pedal) which downshifts when you floor it and tells the tranny to downshift and hold out the gear until higher rpms for maximum acceleration.

downshifting when rolling to a stop, I cant remember how my th400 used to act but I am pretty sure it is not designed to use the lower gears for slowing down, going down grades, etc... I could be wrong but I know some later transmissions do this (my new 700r4 for example is great for slow decents. Also the 4.56:1 helps too!)

also this thread may help you;
 

Curtisje

Active member
227
93
28
Location
Twentynine Palms, CA
Che
Sorry to necro here a bit.

Cucvrus, you mentioned something about an electric switch near the pedal that causes the th400 to downshift that piqued my curiosity. Is there a proper name for that component? Mine might be broken based on how the truck doesn't like coming out of 3rd/2nd unless I'm slowing down significantly (under 25 for 3rd to 2nd) or almost completely stopping for 2nd to 1st. This is with a recently rebuilt 400 with a new vrv and hoses. A brief snowplowing career prior to my ownership killed the reverse/3rd band.
Check to see if the red wire on the side of the tranny just above the pan is connected. If it has come lose this will be your problem. Happened to me a few times.
 

LastFbody

Member
126
9
18
Location
Milwaukee WI
Ah, I didn't word that very well. An example of what I was trying to say is if I'm going 40, then slow down to 27 or so to make a gentle curve, then get back on the throttle the truck stays in 3rd and bogs down instead of downshifting. In that situation I've been manually shifting to 2nd and going back to drive once I get back up to speed since my transmission doesn't kick down under load.
 

cruzer747

Active member
182
99
28
Location
California
Ah, I didn't word that very well. An example of what I was trying to say is if I'm going 40, then slow down to 27 or so to make a gentle curve, then get back on the throttle the truck stays in 3rd and bogs down instead of downshifting. In that situation I've been manually shifting to 2nd and going back to drive once I get back up to speed since my transmission doesn't kick down under load.
ahhh, mine did that unless I floored it (the switch only comes into play when pedal is floored, easy to crawl under the dash and check switch operation. ) Sounds like maybe time to do an adjustment of the vrv?
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks