Most importantly, my Barth is fine.
Have an '85 Chevy pickup with a Turbo 400 tranny. I present the following query to our site members because I understand Barth utilized this tranny in some models.

The pickup is a clean mid-western vehicle with 82k original miles. The symptom I wish your input is as follows:

Immediately following a cold engine start the tranny performs as expected. Throughout local driving it continues to perform well for the first five miles or so. Much further and the symptom arises - REVERSE WILL NOT ENGAGE, even though it performs well in all other regards. Reverse will engage following a cool down (shut the engine down for roughly an hour and a half).Any thoughts?

Two regrets - I wish I knew more worthy of contributing and secondly, the size of my wife's calves from pushing on the front bumper.

The TH 400 is a three speed heavy duty tranny, used in lots of medium duty trucks. Your symptom is consistent with a sticking valve body, or fluid bypassing a valve. You have no choice but to rebuild it. When you do, have them magnaflux the solenoid and valve bores looking for cracks in the walls. Some will merely put in the soft parts and pistons but ignore the surfaces inside the valves. You can also get cracks in the steel faceplate between the valves and the transmission body. If they are knowledgeable like Monster Transmissions in Florida they will check. You can also send it to Monster and they will make it stronger and better than new.

I'd add SunCoast Diesel. f/k/a Sun Coast Converters for upgrades and stock rebuilds, as well as their upgraded torque converters.

quote:

You have no choice but to rebuild it.

Tom, Do you mean Pgh. Pirate would need to have the valve body rebuilt or the entire transmission rebuilt?

Rebuild the transmission and the torque converter. You don't want bad or contaminated fluid from the torque converter ruining a rebuild. I routinely changed the few quarts of fluid and filter on my T400s around every 30K miles along with the differential fluid. The total for the tc and trans is much more but the tc doesn't drain with the trans pan.
Tim

Thanks all for your thoughts. Any idea as to a price range I should expect to spend for rebuilding the tranny and tc? BTW, you guys are great.

If the valve body shows cracks they toss it. The soft parts are just gaskets and o rings. If the case is worn or the solenoid and valves scratched they try to hone them, but it is better to just get another core and do it right. My experience is the rebuilder will not warrant it unless you change the converter. If it has overheated the converter will be brown and then it's toast. Around Houston the bench price (no installation) is between $1600 and $2200. I would call Monster or the others Rusty suggested.

quote:

consistent with a sticking valve body

Tom,
If the valve body is sticking would it be worth a complete flush out and fill with a complete flush machine or using the transmission cooler lines?

Thanks for the response Tom, but not the repair cost estimates. Nice truck (factory 1ton, 6.2 diesel, loaded, all original) worth a whopping $5K, tops. I looked into a "crap shot" full blown tranny flush - $200. Thoughts?

During a rebuild the parts are cleaned with solvent that will dissolve gaskets and rubber parts. A flush uses mild detergents that will not solve cracks or leaks. Most likely it will make the problem constant rather than periodic. You might watch Craigslist for 400TH tranny's, and see if a used one might do you. For something you are going to take trips in you can try a flush, but a rebuild is the only good solution.

quote:

Originally posted by Tom and Julie:
you can try a flush,

I would try a flush first from what you have told us here Tom. Especially with only 82000 miles on the transmission.

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Does this transmission have a inside filter that could be changed before and after the flush?

The TH400 uses a regulated high pressure main fluid line to provide power to switch gears and engage clutches. The pump output pressure varies with engine input rpm, but the "line pressure" is regulated by a spring loaded bypass valve.

The main valve body of the trans diverts this line pressure to switch gears and engage clutches, depending on the gear selected, load, etc.

It appears that your reverse gear is not getting the pressure it needs to engage when warm. I suspect that as the trans warms up, the fluid thins out a bit and the regulated pressure drops a bit. Evidently reverse is most affected, maybe dirt in that circuit, etc.

If you find the right trans guy, you can drop the pan and play with some of the valves and shims, also clean out some valve seats. Not all can be accessed from below. As a last resort you could try shimming the main line pressure regulater for a higher pressure. Hot rod guys do it for harder shifts but it might be enough to nudge the reverse to working. Might get a few miles out of it.

Higher line pressure can cause crankshaft thrust bearing wear when overdone.

That VW guy is a GENIUS!

Hot/thinned fluid was a thought I had as well. Tranny fluids don't come in different weights (like motor oils) do they? I don't use the truck for travel, unless you consider my local Home Depot a resort destination. And that is why I am considering a cheap "fix" to alleviate the symptom.

(I truly hope this discussion may help a Barth/Turbo 400 owner.) As always, much appreciated.

On the driver side of the trans near the shifter there is a tap to measure pressure. It will vary quite a bit depending on which gear, etc. You can google normal pressure ranges and get an idea how yours compare.