Th400 going bad?

[2INSANE]

Right after I did the 6.5 Optimizer Swap the Th400 has been acting up.

From park to drive in order to get the transmission to engage, I have to rev up the motor.

Sometimes when in first or second gear, the transmission acts like it slips out of gear into neutral and then goes back into gear while driving.

Could this be a vacuum issue or clutches going out?

 

[Barrman]

Vacuum will not have any effect on reverse or 1st gear. If they don't work from a stand still then it is an internal transmission issue.

 

[chevymike]

I am sure you have checked this but low fluid level will cause those types of symptoms. If not that, then internal issue.

 

[ezgn]

Right after I did the 6.5 Optimizer Swap the Th400 has been acting up.

From park to drive in order to get the transmission to engage, I have to rev up the motor.

Sometimes when in first or second gear, the transmission acts like it slips out of gear into neutral and then goes back into gear while driving.

Could this be a vacuum issue or clutches going out?

I had a similar problem with my M1008. turned out that the pickup tube on the transmission filter was backing out and not making a good seal. As you know the transmission filter moves up and down. I removed the bolt holding the filter, installed a longer spacer on the bolt to keep the filter from moving, and placed a washer on the head of the bolt that holds the filter. problem solved.

 

[2INSANE]

Thanks for the reply’s gentlemen! Could a bad torque converter cause these symptoms?

 

[ezgn]

Thanks for the reply’s gentlemen! Could a bad torque converter cause these symptoms?

Strange noises and vibration may go along with your symptoms if torque converter is going out.

 

[ezgn]

How long have you been operating your vehicle with the present torque converter before you started having trouble. Is your torque converter stall speed matched to the gears your running.

 

[LT67]

Thanks for the reply’s gentlemen! Could a bad torque converter cause these symptoms?

Yes...

 

[cucvrus]

Just a brief word on this transmission issue. I NEVER trust a used 35+ year old transmission. If I am building a reliable vehicle and want it to be my way to work not my work on every weekend truck. I do all the rebuilding up front. I have every TH400 from a CUCV rebuilt going forward. I found many have bad seals and burnt clutch packs. Many have never been apart and they are just waiting to destroy them selves internally. Getting them rebuilt before they self destruct is cost effective and keeps everything in place and reliable. Do it right the first time and drive on. Good Luck.

 

[2INSANE]

How long have you been operating your vehicle with the present torque converter before you started having trouble. Is your torque converter stall speed matched to the gears your running.

The torque converter is the OEM Cucv that was mated to the OEM th400 and 6.2 diesel. I did not have any problems until I did the 6.5 swap. I read the stalls for the 6.5 vs 6.2 is different?

 

[Ferroequinologist]

I just moved my CUCV out of the shed and up to the garage, she's next on the rotation for being made serviceable.

Haven't checked fluids or anything yet, (moved it around midnight) but it needed to be reved up to move in 1st and reverse. If I took my foot off the gas it would die like the torque converter stayed locked up.

Hoping it is just low on fluid, as the truck ran beautifully when she was on the road last (2 years or so)

Hate the idea of pulling the transmission, but I need it reliable so I might bite the bullet and have it done. What's the average cost?

 

[cucvrus]

That looks like a railroad truck. I pay anywhere between $700-$1,000 for having one gone over before it self destructs. I have had a few apart myself. Just like everything else I ever thought I could rebuild there is more to it then throwing a kit in it. If everything is not set up properly you can expect to revisit it again. I have always done the job of removing and installing and left the shop do the rebuild work. The friend with the transmission shop has the correct tools and warrants the work he does. The best warranty is one I never have to use. Replace the torque converter. No questions it is old and tired. Good Luck. I hope that helps get you back on the road for a long time.

 

[WWRD99]

So this started right after the motor swap?...any chance you bent the gear selector bar going to the trans? I'd check the rooster to make sure it's in the actual gear in the trans coordinated with the shifter on the column...unhook it from the trans and set it up while in nuetral...gotta make sure the shift valve is adjusted right...could be dumping line pressure if it's off a bit.

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[ezgn]

The torque converter is the OEM Cucv that was mated to the OEM th400 and 6.2 diesel. I did not have any problems until I did the 6.5 swap. I read the stalls for the 6.5 vs 6.2 is different?

A difference in the cam can make a difference in the stall speed of the torque converter going from a 6.2 to a 6.5.

 

[ezgn]

A difference in the cam can make a difference in the stall speed of the torque converter going from a 6.2 to a 6.5.

If the transmission was working like it should until the motor swap I think I would hesitate on a transmission overhaul. If it is not broken don't fix it.

 

[Ferroequinologist]

That looks like a railroad truck. I pay anywhere between $700-$1,000 for having one gone over before it self destructs. I have had a few apart myself. Just like everything else I ever thought I could rebuild there is more to it then throwing a kit in it. If everything is not set up properly you can expect to revisit it again. I have always done the job of removing and installing and left the shop do the rebuild work. they have the correct tolls and warrant the work they do. the best warranty is one I never have to use. Replace the torque converter. No questions it is old and tired. Good Luck. I hope that helps,

Yes, built for the Fort Stewart railroad by adding hydraulic hyrail gear and the inset wheels.

Guess I will budget getting it done. I need this truck to be a daily driver soon. Thanks for the advice.

 

[2INSANE]

I guess it really does not mater if it does not work because I’ll be doing a built 700r4 soon

 

[porkysplace]

I just moved my CUCV out of the shed and up to the garage, she's next on the rotation for being made serviceable.

Haven't checked fluids or anything yet, (moved it around midnight) but it needed to be reved up to move in 1st and reverse. If I took my foot off the gas it would die like the torque converter stayed locked up.

Hoping it is just low on fluid, as the truck ran beautifully when she was on the road last (2 years or so)

Hate the idea of pulling the transmission, but I need it reliable so I might bite the bullet and have it done. What's the average cost?

TH400 bench rebuild here in michigan $300-400 .

 

[WWRD99]

I guess it really does not mater if it does not work because I’ll be doing a built 700r4 soon

Do they have an output shaft to fit the stock tcase? I've done one for a np203...I was thinking of doing a 4L80E for my 1 ton truck but haven't looked into it yet.

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[DeadParrot]

To answer the original question: low fluid, loose filter, IIRC - the filter has a tube with o-ring, a bad o ring can cause poor fluid pickup, plugged filter.

I agree with cucvrus. If you have the motor out, take the trans to a shop for inspection and at the least, seal and filter replacement. I did that during a motor swap on a 75 C10 27 years ago. Haven't had any issues with that transmission since the swap. That C10 is used far more as a pickup then a passenger vehicle.