Author Topic: TH-350 slips in all 3 gears.  (Read 912 times)

Offline Stewart G Griffin

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TH-350 slips in all 3 gears.
« on: December 26, 2019, 12:14:50 PM »
1) This just started Saturday or Sunday.

The only thing out of the ordinary was that i did some "acceleration tests" let's just say, on Friday----where the pedal was mashed all the way to the floor.  i did notice that the kickdown cable was disconnected from the throttle arm.  i can't confirm that the "acceleration tests" caused this or  not.

i am not strongly suggesting that this is the cause of  the problem, but curious as to whether it may be?

2) So, on saturday morning or so, upon  acceleration from stops, it started shudder/slipping where it was  more of a slight  pulsating slip.  i decided it must be low on fluid so i added  half  a bottle.   It then immediately became worse to where it is now----slipping in all forward gears.   Not slipping bad, but noticeable----like i have a 4000 stall converter or something.   If cruising at light throttle, it doesn't seem to slip.  Only when you go 1/2 throttle or more, or up a hill.


3) Fluid level has been checked, the right way, to be good.

4) Linkage checked to be adjusted  good.

5) Vac modulator checked out good.

6) Reverse is good, although it  now goes into reverse REAL HARD.   Like waaay too hard.  This just started yesterday.
Since reverse is good,  this proves the converter is not the problem?

This is the new, about a yr old ATI reman that i was/am so proud of.  i can't believe it's failing now?   i want to believe that i must have done something wrong?

Go.

Offline JohnnyPopper

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Re: TH-350 slips in all 3 gears.
« Reply #1 on: December 26, 2019, 01:03:24 PM »
How many miles since the rebuild? Is it whining at all when it get to operating temp?

Maybe time for service: trans flush solvent, then filter and fluid.

Whenever I suspect any issues with any of my vehicles trans I instinctively service them.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Stewart G Griffin

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Re: TH-350 slips in all 3 gears.
« Reply #2 on: December 26, 2019, 05:23:19 PM »
No more than 12,500 since rebuild.   No whinning at all.

Offline VileZambonie

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Re: TH-350 slips in all 3 gears.
« Reply #3 on: December 27, 2019, 08:49:11 AM »
You might want to drop the pan and check to ensure the filter is in tact, look for debris in the pan and check the valve body bolts. Otherwise, sounds like it gave up the ghost from what you describe. Time to upgrade.
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Offline Stewart G Griffin

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Re: TH-350 slips in all 3 gears.
« Reply #4 on: December 27, 2019, 11:53:20 AM »
You might want to drop the pan and check to ensure the filter is in tact, look for debris in the pan and check the valve body bolts. Otherwise, sounds like it gave up the ghost from what you describe. Time to upgrade.

When you say check the bolts----to see if they are tight?

Giving up the ghost is an unfortunate possibility, but i'm refusing to believe it for now;   

1)The trans has worked great for a whole year and 1/2 just up until last friday or so-----it just gave up like that, after working without a hitch?   i never drove it low on fluid, or at least not REALLY low.

2) i still think ATI is a great company, probably the best trans company.   Anyone can make a mistake, but i feel it's unlikely as it did last for so long.

3) i understand the advantages of the 2004r and 700r/460LE and overdrive and ultimately admit they are  better.   But i would like to stick with the TH-350 as i'm  most familiar  with it at this point.

i am hoping to think i did something wrong, which would still suck, but at least i would still have confidence in the product.

Do you feel the kickdown "valve"/mechanism being stuck on the "on" position may have something to with it?    The only think i can see/think that was changed was that i did see the cable connection popped off the throttle arm.  Also, recently and after the "acceleration test," the throttle stuck briefly.  So, maybe that action was so severe that it even messed up the alignment  of the throttle plates and pivot?

Also occasionally when i pumped the pedal all the way down to start, the throttle would hang up on high rpm (even though choke was working fine).   In this case, i would press the pedal as "enthusiastically" as the acceleration tests, but i would go all the way down to the floor.

Offline VileZambonie

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Re: TH-350 slips in all 3 gears.
« Reply #5 on: December 27, 2019, 06:45:01 PM »
Yes. The detent cable being disconnected will not cause it to slip like a 700R4 which uses a throttle valve cable. If all you did "wrong" was drive it like it was meant to be driven, then it was a weak rebuild or something new failed. I don't get the logic of keeping a TH350 because you are used to it but anyway, contact your rebuilder and let them know it failed.
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Offline JohnnyPopper

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Re: TH-350 slips in all 3 gears.
« Reply #6 on: December 28, 2019, 06:12:52 PM »
Go with his first recommendation and drop the pan, see what is inside.
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline Stewart G Griffin

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Re: TH-350 slips in all 3 gears.
« Reply #7 on: January 01, 2020, 11:48:41 AM »
i'm going to go ahead with dropping the pan, but i want to run a few things by everyone:

  This is going to be long, but it might hold the key to the problem?

1) i hear heat is bad for a trans.   In fact, some people say the worst thing.
a) Will running a trans "a little" low, but low to the point where there's any slipping, cause more heat in an of itself?   Or, at least heat to the point where it's bad for the trans?    i would think this is like running a radiator " a little" low?

b) i noticed that the previous trans(also a th-350)  ALSO FAILED in the exact same way---slipping a little only in forward gears, then gradually more and more.....reverse was fine  AND ALSO FAILED IN APPROXIMATELY THE SAME TIME FRAME.

c) Both transes failed the exact same way in approximately the same time frame----18 months AFTER the installation of the 4.3 v-6.
Why is the 4.3 possibly significant?

Both v-8's i had in the truck had dual exhaust no crossover.   Just two pipes running from the manifolds to the back of the truck.  This went on for about 8 years no problems.

(Note that i decided not the run the dust cover when i first got the truck because i figured why bother?)

However, when i started running the v-6, i decided to run the stock Y-pipe to get the thing running asap:




Notice how this Y-pipe runs directly under and close to the converter.  And i ran without the dust cover the whole time.   On top of this, i hear the hottest part in the trans is the converter to begin with?

Could this have caused the trans to overheat?
« Last Edit: January 01, 2020, 11:50:23 AM by Stewart G Griffin »

Offline Irish_Alley

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Re: TH-350 slips in all 3 gears.
« Reply #8 on: January 01, 2020, 12:52:27 PM »
nope. i think theres a lot of trucks running without the dust cover on with no issue. running low on fluid would cause the fluid more heat and heat will kill the trans fluid and that will in turn kill the trans. when you do get the problem sorted out i would have a trans temp gauge installed to keep an eye on the trans temp. if it starts to overheat then you stop the issue before it becomes any bigger
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Offline JohnnyPopper

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Re: TH-350 slips in all 3 gears.
« Reply #9 on: January 01, 2020, 06:33:09 PM »
If your oil is super heated it thins out to the point of slipping due to loss of pressure.

If it is radiator cooled, it would also raise your operating temp a few ticks.

Is the oil burned or red?

Pull the pan...We're dying to know!
1957 Apache 3100 235 Inline 6, 3 on the tree
1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
1980 C-10 under construction

Offline MIKE S

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Re: TH-350 slips in all 3 gears.
« Reply #10 on: January 01, 2020, 08:45:07 PM »
Was your original transmission rebuilt or did you replace it with a different rebuilt unit. If the original was rebuilt it probably has an inherent pressure loss. It could be a crack in a clutch piston that could have missed when rebuilt. These transmissions had a very narrow bushing  in the front drum which typically would not support the drum well and cause it to wear the surface of the stator support causing a pressure loss and burnt clutches. Later units had a wider bushing and an added support ring to keep this from happing. If the original was rebuilt I would have them take it apart and find out if the forward clutch is burnt. If it is I would have them look for a pressure loss. If they can’t find a reason I would get a different core and have it rebuilt.

Offline Stewart G Griffin

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Re: TH-350 slips in all 3 gears.
« Reply #11 on: January 04, 2020, 11:33:02 AM »
Was your original transmission rebuilt or did you replace it with a different rebuilt unit. If the original was rebuilt it probably has an inherent pressure loss. It could be a crack in a clutch piston that could have missed when rebuilt. These transmissions had a very narrow bushing  in the front drum which typically would not support the drum well and cause it to wear the surface of the stator support causing a pressure loss and burnt clutches. Later units had a wider bushing and an added support ring to keep this from happing. If the original was rebuilt I would have them take it apart and find out if the forward clutch is burnt. If it is I would have them look for a pressure loss. If they can’t find a reason I would get a different core and have it rebuilt.

Sorry.  Didn't have internet for a few days---maybe that's a good thing?

The original trans, TH-350C was original to the truck from 83.   i replaced it with reman TH-350 last ('18) summer.

As i said, the funny thing is BOTH transes failed in the exact same way in approximately the same amount of time (18 months) AFTER installing the 4.3 v-6.

Will do pressure testing in a few mins---want to wait for everyone in the neighbourhood to wake up so as not to cause further irritation.


Offline Stewart G Griffin

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Re: TH-350 slips in all 3 gears.
« Reply #12 on: January 05, 2020, 06:13:28 AM »
    Pressures:

    P = 120ish
    R= 210
    N= 120ish (note: that the rpm in neutral is about 1400 due to a separate, unrelated problem)
    D = 120 ish
    2= 120 ish
    1 = 120 ish

    Note, that i'm saying "ish" because i was real nervous and the gauge needle was not exactly steady, but the readings are very close/in the general ballpark. 120 could have been 110. The needle was very close to 120.
    RPM in gear is about 700, but the throttle may be open more than average as i have to have the idle RPM set higher than normal to avoid stalling out.

    Original readings from ATI when shipped out the door (released to me):
    Line pressure                                                cooler pressure (i don't know what this is)
    1st 120                                                          28
    2nd 120                                                         28
    3rd  91                                                           22

    Flow rate(?) 3.16 GPM

    So, again when moving it around to a better position on the driveway and then test driving it because it seemed like it might have been improving, i don't think it's slipping at low throttle when you accelerate----like maybe under 1100rpm. Only if you give it more than 1/4 throttle does it seem to slip. Also it doesn't seem to be slipping in 2nd or 3rd cruising unless you really add throttle.
     


Offline VileZambonie

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Re: TH-350 slips in all 3 gears.
« Reply #13 on: January 05, 2020, 08:17:00 AM »
Was there anything in the pan? Do you have a tachometer? Have you performed a stall speed test?
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Offline Stewart G Griffin

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Re: TH-350 slips in all 3 gears.
« Reply #14 on: January 05, 2020, 07:30:57 PM »
Was there anything in the pan? Do you have a tachometer? Have you performed a stall speed test?

   

    i haven't dropped the pan yet, but plan to.   Yes, i definitely have a tach.


2)   i did some more pressure testing because i wanted to see what it was doing, pressure-wise, while the slipping was going on:

    i think this time i let the engine warm up a little more and thus had lower rpms:

    P = 90
    R = 180
    N = 90
    D = 110
    2 = 110
    1 = 110

    The pressure does increase with more rpm/throttle even when slipping. While coasting or light throttle in D = 90.
    i also want to add that i'm about 130 ft above sea level.

    3) i REALLY didn't want to do a stall test----GM and ATI recommend against it, but i'm sort of glad that i did----because something funny happened-----after i did the stall test in drive, the slipping went away for a while.

    The converter stalls at about 1500 in both Drive and Reverse.