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GM Turbo 400 Tranny
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Supporting Member of Barthmobile.com 12/15
Picture of Pgh. Pirate
posted
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.


'92 Breakaway
Diesel Pusher, Cummins 190hp,
No Modifications
Allison AT542
Floor Plan 30-BS-11B
9205-3798-30BS11B
 
Posts: 178 | Location: Pittsburgh, PA | Member Since: 11-07-2014Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 3/11
Picture of Tom  and Julie
posted Hide Post
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.


1993 32' Regency Wide Body, 4 speed Allison Trans, Front Entry door, Diamond Plate aluminum roof &
1981 Euro 22' w Chevy 350 engine and TH 400 tranny
 
Posts: 1370 | Location: Houston Texas | Member Since: 12-19-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 2/16
Captain Doom
Picture of Rusty
posted Hide Post
I'd add SunCoast Diesel. f/k/a Sun Coast Converters for upgrades and stock rebuilds, as well as their upgraded torque converters.


Rusty


MilSpec AMG 6.5L TD 230HP; built-to-order by Peninsular Engines:  Hi-pop injectors, gear-driven camshaft, non-waste-gated, high-output turbo, 18:1 pistons.  Fuel economy increased by 15-20%, power, WOW!"StaRV II"

'94 28' Breakaway: MilSpec AMG 6.5L TD 230HP

Nelson and Chester, not-spoiled Golden Retrievers

Sometimes I think we're alone in the universe, and sometimes I think we're not.
In either case the idea is quite staggering.
- Arthur C. Clarke

It was a woman who drove me to drink, and I've been searching thirty years to find her and thank her - W. C. Fields
 
Posts: 8211 | Location: Brooker, FL, USA | Member Since: 09-08-2005Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 8/16
Picture of Kevin
posted Hide Post
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? hmm
 
Posts: 2625 | Location: Northeast , Ohio | Member Since: 07-29-2012Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/10
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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


I was taught to respect my elders but it is getting harder to find them!
 
Posts: 731 | Location: St. Charles, MO, USA | Member Since: 10-09-2003Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/15
Picture of Pgh. Pirate
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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.


'92 Breakaway
Diesel Pusher, Cummins 190hp,
No Modifications
Allison AT542
Floor Plan 30-BS-11B
9205-3798-30BS11B
 
Posts: 178 | Location: Pittsburgh, PA | Member Since: 11-07-2014Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 3/11
Picture of Tom  and Julie
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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.


1993 32' Regency Wide Body, 4 speed Allison Trans, Front Entry door, Diamond Plate aluminum roof &
1981 Euro 22' w Chevy 350 engine and TH 400 tranny
 
Posts: 1370 | Location: Houston Texas | Member Since: 12-19-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 8/16
Picture of Kevin
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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?
 
Posts: 2625 | Location: Northeast , Ohio | Member Since: 07-29-2012Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/15
Picture of Pgh. Pirate
posted Hide Post
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?


'92 Breakaway
Diesel Pusher, Cummins 190hp,
No Modifications
Allison AT542
Floor Plan 30-BS-11B
9205-3798-30BS11B
 
Posts: 178 | Location: Pittsburgh, PA | Member Since: 11-07-2014Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 3/11
Picture of Tom  and Julie
posted Hide Post
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.


1993 32' Regency Wide Body, 4 speed Allison Trans, Front Entry door, Diamond Plate aluminum roof &
1981 Euro 22' w Chevy 350 engine and TH 400 tranny
 
Posts: 1370 | Location: Houston Texas | Member Since: 12-19-2006Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 8/16
Picture of Kevin
posted Hide Post
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.
Does this transmission have a inside filter that could be changed before and after the flush?
 
Posts: 2625 | Location: Northeast , Ohio | Member Since: 07-29-2012Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 7/17
Picture of Steve VW
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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.


8607-3346-33TFPOB------9708-M0037-37MM-01
86 Regal SE 33 Tag axle--"98" Monarch 37
Chev P3(7) 454TBI--------Cummins 8.3 300 hp
400 hp fuel injected-------6 spd Allison, Spartan MM
 
Posts: 3252 | Location: Kalkaska, MI | Member Since: 02-04-2011Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 8/16
Picture of Kevin
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That VW guy is a GENIUS!
 
Posts: 2625 | Location: Northeast , Ohio | Member Since: 07-29-2012Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 12/15
Picture of Pgh. Pirate
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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.


'92 Breakaway
Diesel Pusher, Cummins 190hp,
No Modifications
Allison AT542
Floor Plan 30-BS-11B
9205-3798-30BS11B
 
Posts: 178 | Location: Pittsburgh, PA | Member Since: 11-07-2014Reply With QuoteReport This Post
Supporting Member of Barthmobile.com 7/17
Picture of Steve VW
posted Hide Post
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.


8607-3346-33TFPOB------9708-M0037-37MM-01
86 Regal SE 33 Tag axle--"98" Monarch 37
Chev P3(7) 454TBI--------Cummins 8.3 300 hp
400 hp fuel injected-------6 spd Allison, Spartan MM
 
Posts: 3252 | Location: Kalkaska, MI | Member Since: 02-04-2011Reply With QuoteReport This Post
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