Well I'm phukd. Th400 lost 3rd

[da_raabi]

I've been having intermittent slipping in third for a while. It was usually a sign I was a little low on fluid (damn thing leaks from places you don't even want to know about). Well I think it finally went over the hill. Saturday it started slipping bad when I tried to get up to highway speed. Anything over cracked throttle would make third slip like crazy. Basically had to idle it up to speed so I wouldn't hold up traffic.

Got home, checked fluid and added a quart. Got in it today and could barely hold third at any speed or load. It was even slipping doing 20 around my neighborhood. Previously it would only slip when it was hot and low on fluid. Not it does it cold and full.

Reverse seems to work ok. 1-2 shifts are ok. 2-3 shifts were always very slippy and there was always a big lag/drop in RPM when going 2-3.

Am I phukd? I turned around and brought it home and parked it. I didn't want to lose 3rd completely and get stuck doing 30 on the interstate!

What now???

 

[74 Shortbed]

Hate to tell ya this, but it's time to tear it down before more harm is done..

 

[da_raabi]

Wonderful...

You must be registered for see images attach

 

[78C10BigTen]

Wonderful...

You must be registered for see images attach

Welcome to my world there!!!

 

[78C10BigTen]

And i feel your pain with tranmissions, my truck is on its 4th one in 2 years. Factory one had no 3rd when i bought it, the second one lost 3rd and had a slippy reverse and the third one completely lost all forward gears one morning without warning. I finally dug up a good one. Wasnt easy tryin to find a 9" tail 2wd th350 around here

 

[MikeB]

Found this basic explanation of how a TH400 works. Sounds like your problem is the direct drum's internal clutch discs are worn out.
----------------------------------
1st gear - forward clutch engages to drive the planetary gearset/all other clutches disengaged. One-way low roller sprag in the rear planetary holds the gearset to create a 2.48:1 ratio. In low 1 the rear band would also apply for extra holding power. At this point due to planetary action the forward drum rotates clockwise but the direct drum spins counter clockwise at this point.

2nd gear - forward clutch engaged. The intermediate clutch applies to stop the direct drum dead in it’s tracks. This creates a 1.48:1 ratio. The low roller sprag that was holding then is rendered useless as the carrier switches direction. So you still have only 1 holding member.

3rd gear - forward clutch engaged. The intermediate clutch disengages and the internal clutch of the direct drum engages making a solid unit…..1:1 ratio. At this point the guts of the tranny spin as a unit. There is no gear reduction therefore no holding member in use.

Reverse - forward clutch disengaged. Direct drum then engages and is driven off an outer hub of the forward clutch. Now we have a problem we need a holding member but now if you are following this at all you guessed it, the low roller clutch won’t hold it either. This is where the rear band engages to hold the carrier all on it’s own.

 

[da_raabi]

Yeah I dunno what I'm going to do. I'm exploring options.

--Rebuild TH400 myself - probably around $500+/- plus some tool rentals - never done it before so could be big waste
--Purchase rebuilt TH400 - $1000+
--Go manual - unknown cost, though likely lots when including clutch pedal assembly and longer driveshaft

This sucks.

 

[74 Shortbed]

Sounds like your problem is the direct drum's internal clutch discs are worn out.

That's why I said it's time to tear it down.

 

[74 Shortbed]

Yeah I dunno what I'm going to do. I'm exploring options.

--Rebuild TH400 myself - probably around $500+/- plus some tool rentals - never done it before so could be big waste
--Purchase rebuilt TH400 - $1000+
--Go manual - unknown cost, though likely lots when including clutch pedal assembly and longer driveshaft

This sucks.

More like $150 if you don't need hard parts. You can download the manual from B&M for their Transkits, it's a step by step with pics of disassembly/assembly, that's what I used to do my first tranny way back in the day, I was totally amazed at how simple them stupid things are, lol.

 

[1987 GMC Jimmy]

What about seeing how much a reputable transmission guy would do it for on the bench if you do the R&R yourself? That way you can mitigate your worry about rebuilding it and the cost for a new unit.

 

[Honky Kong jr]

Yeah I dunno what I'm going to do. I'm exploring options.

--Rebuild TH400 myself - probably around $500+/- plus some tool rentals - never done it before so could be big waste
--Purchase rebuilt TH400 - $1000+
--Go manual - unknown cost, though likely lots when including clutch pedal assembly and longer driveshaft

This sucks.

It’s a fixed yoke right? Your down in Texas or Arizona aren’t you?

 

[MikeB]

A couple years ago here in the Dallas, TX area, shops charged anywhere from $500 to $800 parts & labor to rebuild a TH350. It may have cost a little more for a TH400.

I was fortunate to have a friend who spent the 70s and 80s working as a GM trans tech, so we rebuilt mine in his garage. (I say "we" because my role was to look on in awe and hand him parts.)

He had an old overhaul kit laying around, but it was missing some parts. So I went to Transtar and spent $89 on more parts, including adjustable modulator, speedo drive gear, and T/C dust cover, and another $67 on a torque converter. BTW, Transtar is great place if you have one near you.

 

[da_raabi]

I'm in Florida, and yes it's a bolt-on yoke. I've been doing a bit of research on kits etc, and this is what I'm looking at:

B&M 20229 Rebuild kit (includes parts/steps for shift improvement so no shift kit needed) - $152.00
Fliter kit - $10.00
Flex Plate (mine was ground down by a junk starter) - $56.00
Torque Converter (dunno about this yet) - $104 - 160.00 depending on brand/stall
Cooler (also optional) - $52.00

This stuff ain't cheap, that's for sure. I can't find a $67 T/C anywhere!

 

[75Monza]

TC's are definitely not cheap...I opted for a Hughes XTM heavy duty towing on mine and it was around $300.

 

[Honky Kong jr]

I'm in Florida, and yes it's a bolt-on yoke. I've been doing a bit of research on kits etc, and this is what I'm looking at:

B&M 20229 Rebuild kit (includes parts/steps for shift improvement so no shift kit needed) - $152.00
Fliter kit - $10.00
Flex Plate (mine was ground down by a junk starter) - $56.00
Torque Converter (dunno about this yet) - $104 - 160.00 depending on brand/stall
Cooler (also optional) - $52.00

This stuff ain't cheap, that's for sure. I can't find a $67 T/C anywhere!

I’d leave the overpriced B&M **** right where it is but that’s me.https://www.summitracing.com/parts/...Hc6ALV_ly8hus363evet4lgJkMT2L2YxoCgxMQAvD_BwE
https://www.amazon.com/TH400-Transmission-Master-Rebuild-Level/dp/B010R0GN62