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Turbo 400 not shifting

18K views 20 replies 7 participants last post by  JeepHammer 
#1 ·
My 83 cj7 has a turbo 400 mated to an AMC 304ci V8 and it won't shift into 3rd gear. Seeing as how it only has 3 gears this is a problem. I think it's a vacuum leak but after I checked all the hoses all I can think that it might be is either the brake booster or the the part on the transmission where the vacuum line connects. Any ideas?
 
#4 ·
Also when you change your filter, change the "O" ring on the drivers side front corner of the tranny when U drop the pan. There is a pick up tube and it just pulls straight down. When this cracks "O-ring" it will shift weird and slip into gear. Mine did the same thing and a .50 cent "O" ring saved the day along w/a new shift module.
 
#6 ·
I believe what you refering to is the modulator. This is were the vaccume connects to. Cheque the vaccume line from the
manifold to the tranny.

Bill
 
#8 ·
One Quick Question,
When you stomped down on the throttle, did it go into 'Passing Gear', from 3rd to 2nd, or even 1st?

This is important, so think hard and let me know.

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Anyway, if it didn't want to shift UP before failing, then pull the vacuum line off the vacuum modulator and put a clean vacuum line on the modulator and (Suck) on that line to see if the diaphragm is busted or not.

Take the Governor cover off and take the governor out, see if it's got some crap stuck in it that is keeping it from working...

Make sure your 'Kick Down' switch on the throttle pedal is working.
Without electronic kick down, the high gear clutch drum won't live long, and that means a rebuild.

Also a good idea to take the pan off and see if there is a bunch of clutch material in the pan.... change filter/fluid while you are there.

With TH 400s, when high gear goes out (Direct) it's usually kick-down not working or it's the governor not letting you get an 'Up Shift'.

If it's Kick Down, then the direct drive clutch pack is shot and there is NOTHING you can do about it without rebuilding the transmission.
That's about $250 for materials, rebuild kit, ect. and it's a pain in the butt to get out and back in... that's the bad news.

The good news is these things are so simple a monkey could rebuild them.
Tons of rebuild manuals and books out there, and as long as you follow the steps in the books, you will be fine.

Crud in the governor or the spool valve just inside the vacuum modulator port can be cleaned out, but if you are getting pieces of clutch large enough to jam up those spool valves, then start saving for a rebuild.

If it's just a popped vacuum modulator around $25 and half an hour fixes the problem.
 
#10 ·
I think what JH wants you to do is, go drive it, easy on the gas, after it shifts to second gear, put the gas pedal to the floor. See if it shifts back down to first gear.

Bill
 
#11 ·
Does reverse work? The direct clutch is used in both reverse and high (3rd) gears.
Adjust the kick down switch by pulling the arm all the way back toward the throttle pedal or linkage. It is on a ratchet of sorts and this is how it is adjusted.
Next push the throttle pedal to the floor and this adjusts the kick down. The kick down opens a solenoid valve that bleeds governor pressure and that will prevent a 2-3 shift. Also the kick down solenoid can be bad. Easy fix. Just drop the pan remove two screws and replace.
BTW, Kick down switch is best adjusted with the engine off. HTH
 
#12 ·
Wrenches_00 said:
Does reverse work? The direct clutch is used in both reverse and high (3rd) gears.
Adjust the kick down switch by pulling the arm all the way back toward the throttle pedal or linkage. It is on a ratchet of sorts and this is how it is adjusted.
Next push the throttle pedal to the floor and this adjusts the kick down. The kick down opens a solenoid valve that bleeds governor pressure and that will prevent a 2-3 shift. Also the kick down solenoid can be bad. Easy fix. Just drop the pan remove two screws and replace.
BTW, Kick down switch is best adjusted with the engine off. HTH
If his TH400 is from "76" to "79" it doesn't use a TV cable. There's a elect. switch on the gas pedal. That works with WOT. Up shifts on my 400 work off vaccume. As far as I know.

Bill
 
#13 ·
You are correct. The 400 doesn't use a TV cable. I simply told him how to adjust the electric kick down switch.
Up shifts occur when governor pressure overcomes vacuum modulator pressure. Downshifts work opposite of this. Kick down occurs because the kick down solenoid bleeds off governor pressure so to assist the vacuum modulator.
A Power brake in reverse will test the direct clutch and rear band. If the engine revs to the stall speed and stays there then the clutch and band are good. If not then rebuild is in order.
 
#15 ·
Bigkuntree007 said:
I drove it. it does shift back into 1st gear but still doesn't go up to 3rd. I will have to try to test or adjust the kickdown
Because your Jeep didn't originally come with a 304 and TH400, do you have the switch that connects to the upper part of the pedal, inside the tub? I ask because mine isn't connected and shifts fine. Wrenches00 seems to know whats up. He can probably help you more than me. And Earl, welcome to Jeep forums.

Bill
 
#17 ·
OK, First off, What vehicle are you working on?

Second, when it WAS WORKING, what did it do when you stomped the throttle?
Did it shift down into 'Passing' gear?, From 3rd to 2nd, or is this a new install that isn't working correctly?

Third, Is this a fresh rebuild or tired, used transmission?

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No throttle valve on a TH 400, electric kick down solenoid.
If it's not hooked up or working, you labor the hell out of the direct drive clutch with low line pressure (Low engine rpm, lots of load, too tall of gear, recipe for burning the direct clutch up),

The two other things that can effect 3rd gear are, in order of importance,

Governor. half round 'Dome' cover over the governor, the governor will pull out of the transmission, kind of 'Un-Screws' as the drive gear comes off the transmission shaft teeth.
If that governor's plastic teeth are damaged, or if something is keeping the governor valve from passing fluid pressure (Like crap caught in the valve) you won't get an Up shift.

The next place I would look is the Vacuum Modulator Canister and it's spool valve just inside the transmission.
Some times that vacuum modulator will quit working and cuase odd issues,
Other times the spool valve the vacuum modulator works (just inside the case) will jam up and cause problems.

Vacuum pump or sucking on the diaphragm with a clean piece of tubing will tell you if the diaphram is ruptured and leaking,
Vacuum pump will tell you if it's working correctly,
And taking the spool valve out will tell you if it's jammed,
(Obviously, if it's jammed in the bore, THERE'S YOUR PROBLEM!)
They slide out pretty easy, so have a look to see if there are signs of burned clutch material stuck to it...

This REALLY isn't rocket science...
Like I said, there are DOZENS of those $20 rebuild manuals out there with trouble shooting sections, pictures, ect.
Picking one up would be a good idea,
Along with getting it to one of those $20 or Free inspection transmission shops where they have all the tools to do the proper testing and find EXACTLY what the issue is.
 
#19 ·
Sounds like a $20 trip to the local transmission shop is in order!

Love those $20 diagnostic testing deals!
They tell me EXACTLY what's wrong, then I go home and fix it instead of letting them sell me an entire rebuild!
 
#21 ·
It's NOT supposed to stay in 'High' Gear when you stop, or when you 'Stomp On It'.
Both cases it's supposed to down shift as you slow down, or as you stomp on the throttle kicking in 'Passing Gear' (Clutch Overrun)...

Not sure you came across with your issue very well, so if I misunderstood, excuse me...
 
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