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TH400 slipping in third gear

  
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TH400 slipping in third gear

 
69GTOby 69GTOby
Guru | Posts: 1118 | Joined: 02/09
Posted: 11/17/12
04:41 PM

Hello gang!  It has been a long time... too long!  I have been quite busy with life.  Anyway, for those of you who remember my cracked frame situation, I welded it and drove it around every now and then, but it has been down due to a slipping trans  Shocked

Reverse works great, it goes right in and does not slip.  It goes right into drive, too.  Under light load, in "D" it seems that the 1 to 2 shift may be a little delayed, but the 2 to 3 shift is almost nonexistent.  In "2" the 1 to 2 shift seems pretty normal, under light and medium load.  If you go out and floor it though, it will rev past 5000 and never shift unless you let off.  That goes for the 2 to 3 shift for sure, and maybe for the 1 to 2 shift as well.  I haven't driven it in a while so I am not entirely sure.

The fluid is at the proper level, is pretty red, and smells perfect.  There is an enormous leak underneath.  It is very hard to pinpoint crawling underneath it in the driveway.  Based on all this information, what do you guys think?  Is it time to yank it out, or are there some things I can try to recover it?  Oh, the filter and vacuum modulator are only a couple years old with few miles on them.  And there is no ATF in the vacuum hose, and it seems to drive the same with or without the kick switch plugged in.  Could it be the torque converter?  
****
1969 GTO resto in progress. '76 350+.060, #13 heads, 9.2:1 CR, Lunati cam, Edelbrock Performer, 750 Holley, HEI, Ram Air manifolds, 2 1/2" exhaust. TH400 trans w/shift kit and 2400 stall.  235/60/15 front, 275/60/15 rear on Rally II 15X7s.  GM 12 bolt posi with 3.73's.

waynep71222 waynep71222
Enthusiast | Posts: 391 | Joined: 04/12
Posted: 11/18/12
07:19 AM

external leaks are BAD...

it really sounds like either your filter tube is Broken...  the plastic tube that connects the filter and the pump or case...    that would cause the transmission pump to pull air in when you stomp on it.. instead of a solid stream of fluid.. remember.. it has to pull the fluid up from the pan almost a foot through a fine filter...

take a look at this article on rebuilding the TH400...   yes.. yours will have a different bolt pattern and probably a longer tail housing and output shaft. but other than that.. its the SAME...

http://www.superchevy.com/technical/engines_drivetrain/transmission/sucp_1006_th400_transmission_rebuild/viewall.html



and an excellent article on tips and tricks on rebuilding the th400...

http://www.fourwheeler.com/techarticles/drivetrain/129_1002_turbo_400_rebuilding_tips_and_tricks/


all of you with TH400s should bookmark these two articles and read them once in a while...

be sure to check the second and third picture in the tips and tricks article.. it shows the plastic filter tube that fails... causing the transmission to FAIL...  

idrivejunk idrivejunk
Addict | Posts: 5163 | Joined: 12/09
Posted: 11/18/12
08:09 AM

GTOby, anytime an automatic slips I call it rebuild time but thats just me and I'm a bodyman. I bet it drives a little better after some frame welding. Smile

My TH400 has a one piece washable brass filter (tube is made onto filter box) and I've not seen another like it. Maybe it goes with the deep pan. I just back flush it with solvent to clean the metal mesh brick inside, then dry and reinstall it. I guess maybe its an upgrade piece that eliminates that filter tube problem and is re-usable.  
idrivejunk

tuffnuff tuffnuff
Moderator | Posts: 2567 | Joined: 12/09
Posted: 11/18/12
12:56 PM

+1 Matt
Here is some reading, to understand the Turbos.

Read more: http://forums.carcraft.com/70/7959346/general-car-craft-discussion/th-350-and-th-400-automatics/#ixzz2CbTXGRnS

Smile  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

69GTOby 69GTOby
Guru | Posts: 1118 | Joined: 02/09
Posted: 11/23/12
11:51 AM

Thanks for the replies guys, and Happy Thanksgiving!  I will look at those articles this weekend since I will have plenty of time.

I bought a 400/TH400 combo a while back out of a '68 Catalina.  I have no idea of the condition of the trans other than it looks pretty good on the outside.  If I stick my finder in the dipstick tube hole, it comes out a little gray (clutch material?), but the fluid on the stick is a nice red color and just smells old.  The engine it was mated to was locked up from sitting and needs machining.

Should I put this trans in and see what happens?  Is there a good chance it will work, at least for a while so I can rebuild the other one?  
****
1969 GTO resto in progress. '76 350+.060, #13 heads, 9.2:1 CR, Lunati cam, Edelbrock Performer, 750 Holley, HEI, Ram Air manifolds, 2 1/2" exhaust. TH400 trans w/shift kit and 2400 stall.  235/60/15 front, 275/60/15 rear on Rally II 15X7s.  GM 12 bolt posi with 3.73's.

Opontee Opontee
Guru | Posts: 1422 | Joined: 07/09
Posted: 11/23/12
03:18 PM

If you have the time and energy to do a swap, it probably wouldn't be a bad idea. Or you could get the tranny that is out rebuilt and then do a swap. Make sure they both have the same length tail housing. I know on some of the Cats, they come with a 9" long housing.  
OponteeOpontee
Anna Mae quit. Opontee

gtojack1366 gtojack1366
Guru | Posts: 1277 | Joined: 11/09
Posted: 11/23/12
04:09 PM

+2 you need the turbo 400 with the short tail housing 4" full size cars had a longer tail shaft housing .  

69GTOby 69GTOby
Guru | Posts: 1118 | Joined: 02/09
Posted: 11/24/12
08:01 AM

Oh okay, thanks guys.  Can the tail housings be swapped fairly easily?

I am considering a 4 speed swap, so if I can swap this one in and get the car driveable again that would be great.  Then, I can start looking into the 4 speed swap and consider that option.  
****
1969 GTO resto in progress. '76 350+.060, #13 heads, 9.2:1 CR, Lunati cam, Edelbrock Performer, 750 Holley, HEI, Ram Air manifolds, 2 1/2" exhaust. TH400 trans w/shift kit and 2400 stall.  235/60/15 front, 275/60/15 rear on Rally II 15X7s.  GM 12 bolt posi with 3.73's.

gtojack1366 gtojack1366
Guru | Posts: 1277 | Joined: 11/09
Posted: 11/24/12
08:18 AM

You can't swap the housings .The whole trans would have to be taken apart to change it .Because the output shaft is different .  

Brazil Brazil
Addict | Posts: 3963 | Joined: 06/09
Posted: 11/24/12
09:25 AM

A really good racing transmission dude would be my call. They can put in heavier duty parts and see where weak areas are. The two main things I run into on my TH400 were just simple things. I had to rig up the kickdown switch up on the carb because it didn't have the petal bracket. I really like it better that way because it's easy to adjust with the car running. Secondly, the internal end of the kickdown switch floats in transmission fluid and argues with the electrical circuit, thus, no kickdown. That is one part that just seems like a design flaw, and one of the reasons I tend to like a well built TH350 with a mechanical kickdown.  

69GTOby 69GTOby
Guru | Posts: 1118 | Joined: 02/09
Posted: 11/24/12
09:56 AM

I need to make a decision, lol.  I would love a 4 speed in it, but that will require lots of new parts and lots of down time.  I could take a stab at rebuilding the trans myself and risk wasting time and money since I have no experience working on transmissions, or I can have someone reputable rebuild it for me.  The latter is probably the best route I suppose.

While I do this, I'd like to change the TC.  I am thinking a 2400 stall or so would be good.  Can my TC be rebuilt with an increased stall somehow, or do I need to buy a new one?

Another thought...  overdrive would be really nice.  But, if I go through all of that work, I may as well do my 4 speed at that point.  
****
1969 GTO resto in progress. '76 350+.060, #13 heads, 9.2:1 CR, Lunati cam, Edelbrock Performer, 750 Holley, HEI, Ram Air manifolds, 2 1/2" exhaust. TH400 trans w/shift kit and 2400 stall.  235/60/15 front, 275/60/15 rear on Rally II 15X7s.  GM 12 bolt posi with 3.73's.

gtojack1366 gtojack1366
Guru | Posts: 1277 | Joined: 11/09
Posted: 11/24/12
02:29 PM

Trans rebuild kits are cheep if that's all you need if all the hard parts are good .But you have to know what your doing .If you don't know what your doing I would find a used one in a salvage yard .If your going to change to a 4 speed no need in buying a rebuilt trans .  

Formulajim Formulajim
Enthusiast | Posts: 379 | Joined: 02/09
Posted: 11/29/12
09:57 PM

It sounds to me like the governor gear just stripped. Pull the square cover off the left rear of case just ahead of tail housing pull out the governor the gear is plastic and likely bad. There is a HPP article about recalibrating your trans on a firebird that would show you pictures of what I'm talking about. Check that first before you get carried away for not! Jim  
Drive it before your dead!

Brazil Brazil
Addict | Posts: 3963 | Joined: 06/09
Posted: 11/30/12
01:19 PM

Dead on Jim. That's the main thing lowlife trans shops will screw you on.  

Poncho462 Poncho462
User | Posts: 103 | Joined: 01/12
Posted: 11/30/12
10:03 PM

If you gather the necessary pedal assy, clutch linkage(mechanical or hydraulic), a stick bellhousing, tranny and clutch assembly, and a possibly a different trans crossmember and verify everything you will need is on hand, the conversion can be done in a few man hours from 400 to any stick you choose.  I did that on my Firebird as part of a total teardown/refurbish, using a Richmond 5 speed, and by making sure in advance I had what I needed, I had very minimal problems.  

A few years ago, I helped a friend of mine do a full conversion of a 58 Chevy from powerglide to 4 speed in about 6 hours total, and we did it in a parking lot in the rain, so don't be too intimidated by the thought of the conversion, as long as you plan it carefully.  
"Wherever you go, there you are."..Buckaroo Banzai, 1984

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