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TH-350 slipping in first...mostly......

Wow. i didn't know these modulators could be adjusted. Yes, they do have screws in them. It might take a few days to report back as i took the battery out of the truck to put in another car (so if the truck couldn't get running right again i would have transportation). The car is now in the shop with it's own issues............ (newer gm fwd-----need i say more....?)
 
Ok, was able to try it with the modulator adjusted 3 screws in. No noticeable change. The trans might be shifting a little firmer, but it's difficult to tell as i was using real gentle throttle for fear of damaging the trans. At any rate the original problem is still there.

1) i noticed that if i just let the truck move under idle, there doesn't seem to be any slipping. It will even go up hills in idle. Only when you give it a little throttle does it seem to slip. The generally applies in all 3 gears.

a) One of the other unrelated problems i was having was that i'm having difficulty idling without stalling out. When you put it in gear, the trans still engages enough(apparently) to stall out. So, it doesn't feel like it's slipping in this case.

So maybe the clutch packs, forward drum etc. (note: you'll have to forgive as i know nothing about transes) are not worn and maybe the piston thing that the modulator controls is sticky in the trans?


2) a few mins ago i put the trans in D and it took a few secs to engage, but after 1-2 secs, it did engage and was able to move forward on idle only.
 
You could put a pressure gauge on the trans and see if you have line pressure rise with throttle opening ( you should). I think at this point a pan inspection is needed to see if the filter is on tight and what kind, if any, debris is in the pan. One more thing, when you say "slipping" can you actually see rpm going way up or hear the engine rpm increasing noticeably with throttle?
 
Ok, i'm waiting for the gauge to come. i noticed the test port has a 7/16" plug? Will this need any sealant when it's plugged back in after testing?
One good point is that this port seems to have good access----no exhaust or crossmembers in the way.

2) Yes, i can see rpms climb with the tach, and hear the engine correspondingly. i've had this combo, 4.3, b+m traveler conv, th-350 for about a yr+1/2, so yes, i can tell something is definitely slipping either the conv or trans, most likely trans.

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:

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Notice how this Y-pipe runs directly under and close to the converter. And i ran without the dusk 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?
 
No way will that cause it to overheat. Way to much airflow and way to much space between the two. I don't run a dust cover and have a y-pipe with zero issues.
 
I agree that the pipe is not the issue. Are you using a kickdown cable on this trans that is hooked up and functioning? Have you verified that your dipstick and tube are correct for this application?
 
Greg Ducato said:
I agree that the pipe is not the issue. Are you using a kickdown cable on this trans that is hooked up and functioning? Have you verified that your dipstick and tube are correct for this application?
Click to expand...


The kickdown is hooked up, but i'm not sure if it's functioning----i don't notice it downshifting. i rarely floor it anyways. i did take the cable off at the trans to verify that the hook thing is in fact, moving and not stuck.

i used the same dipstick and tube from the previous trans. i'm not sure how to verify whether the stick is correct. i would ASSume it's ok, because the aftermarket Mr. gasket pan is stock depth?

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.
 
Those are very good pressure readings so we will assume you have no internal pressure leaks. Have you pulled the pan yet?
 
i haven't dropped the pan yet, but plan to.

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.

2) i didn't want to do a stall test----GM and ATI recommend against it, but someone on another site suggest i do one:

The converter stalls at about 1500 in Drive and Reverse.

But a funny thing happened----after doing the stall test in drive, the slipping went away for a while.
 
A mystery wrapped in an enigma. Those pressure numbers still look very normal, lack of slippage after the stall test is a head scratcher.
 
I'm in the minority here I'm certain. Personally, I've chased enough ghosts in my life that I'd quit worrying about it. I'd go and beat the dog shit out of it and it's either going to expose the actual problem, blow up and you'll have the excuse to rebuild the whole thing, or nothing will happen and you'll have to make the decision to live with how it drives or do something about it such as replace it or rebuild it.
 
had a remaned 4l80-e years ago always burp fluid up the case vent hose . it was so bad i built a catch can and would dump it in to the dipstick tube every week . then 1 day i had to take a trip with a trailer threw a BIG city and summer time heat . i watched my temp gauge go way high and slam back down real fast and from that point on she never burped again and also never skipped a beat . years later i had a shop tear it apart to swap the 2wd tail shaft for a 4x4 shaft and they did not find any problems inside .

so run it if it blows it blows . or contact the shop that remaned it and let them deal with it .
 
Well, no major junk in the trunk at least?

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i'm totally befuddled by this. i think the trans has to come out irregardless because i think the converter is wrong for my application. It's "just" driveshaft, crossmember, kickdown cable, cooler lines, vacuum modulator, shift linkage, converter bolts, engine to trans bolts.....
 
x2 that looks like a LOT of clutch all over the pan . . . .looks like a brownish milk shake in the pan from what i can see .

that thing has problems . show us a pic of the inlet suction on the filter . and a shot of the fluid color .
 
One guy I knew who ran a transmission shop had a saying :
"If the pan's fill of glitter---it'll soon be a quitter"..

But there is exceptions to every rule..by all rights the TH400 in my GTO should have fried after I rocked it from drive to reverse ,stuck in a snowy field ,for a good 20 minutes till I smelled burning clutches and it whined like a siren, till I took off the pan ,dumped out a pile of sooty looking clutch dust,put on a new filter and filled it back up--then it quieted right down,and still did good burnouts and second gear chirps for the 2 years I had it after that..
 
I've seen much worse!...my GTO's TH400 had it almost full of what looked like burnt coffee grounds..!..I never expected it to live after the beating I gave it but it did..

Some automatics we pulled at the junkyard that sat several years and got bought ,ended up not working so well,despite them being fine when we first got the vehicle in as junk...one customer bought 3 TH350's for his '71 Buick Special,each one had a different problem-one slipped in all gears,the second one we gave him had no reverse,the third one drove perfectly,had reverse,but the park pawl was broken,so the car would roll away in park..(he fixed that by using parts from one of the others "in the car" without having to pull the trans back out a 4th time)...

We did an autopsy on the other two transmissions that used to be OK,and found the fluid was like a strawberry frappe and the bottom of the pan on both had rusted and a layer of rust,like a sheet,had peeled up off the bottom of the pan,and got sucked against the filter--the valve body was surface rusted too--another customer who wanted a transmission was given one as a core to rebuild for free,we were just going to scrap it--a few weeks later he drove the car in he put it in without doing a rebuild,all he did was replace the filter,pan,and used brake cleaner to wash out the valve body and it worked good again!..
:screwy:...wish I could be so lucky..
 
1) i would like to re-iterate, and it should be somewhat apparent, that i don't know jack-shit about transes; Since the pan is painted black on the outside, i ASSumed that the inside bottom is also black. After reading the initially painful, but honest and appreciated comments, i scraped my finger along the bottom and the metal sludge is CAKED on there----the bottom of the pan is actually silver, not black.

i am hosed, and the trans is hosed. But, at least we likely know the trans is screwed.

More pics:
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