View Full Version : chevy turbo 350 problems.. any one else ever have this prob?

03-29-2004, 08:23 AM
last night the wife and I went to pickup my 40 from storage.. During the winters when I am thrashing on other cars I store the car in my buddys garage thats about an hour away from home

The car started right up and I backed out of his garage with no problems. as I was leaving my buddys place it was running great.. I wasnt in any hurry to get home and it had been quite awhile since I had driven the car so I was babying it..

I drove about 1/2 mile to a gas station to put air in the tires. then drove about 4 more miles before I had to stop at a traffic light..

then it happened.. as the light went green i put my foot down and nothin forward motion at all. luckily I was able to push the car into another gas station and called a coworker to help me pull it to his house..

anyhow.. when I checked the tansmission dip stick I wasnt completely full of fluid, but it wasnt in the FILL ME NOW area either..

has anyone ever had a similar problem?? if so what was the cause?
I searched old posts with no luck.. i cant believe i could have burnt it up..

fwiw I had the trans rebuilt by a local shop less than 9 months ago.. (granted I did put 15000 miles on the car since then 10,000 of them pulling a camp trailer) but gee wiz..

at least this didnt happen in the middle of washington state or 1/2 way home from florida last fall..

anyhow anybody got some tips to share? thanks in advance


03-29-2004, 08:31 AM
Maybe the fluid pick up clogged up? Smell the fluid on the dipstick, that will tell ya if it's burnt or not. Also if the fluid is black and not a nice red color will also tell ya. later plmczy

Missing Link
03-29-2004, 08:55 AM
uh oh. That's not good. Take a look at the modulator, or possibly just replace it. (Not the T37 Space Modulator, the vacuum modulator on the side of the trans.) It's been a while since I dealt with a th350 but that is a starting point. One more thing to consider is that if the car sat all winter without being run, ATF has a tendency to become like varnish. It could possibly just need a fluid and filter change. Keep me posted, dude.

Fat Hack
03-29-2004, 09:09 AM
Had that happen a couple of times.

Once was way up north in Canada...600 miles from home! Grandpa said "Just give 'er lots gas and hold the brake once in a while!". It worked...the trans barely moved, then slipped some, then BANG...back to working!

He said that dirt can block a passage, and that you can usually "blow it out" by upping the pressure a bit! Sounds caveman stupid, but it's worked for me on two or three occasions!

Also, after extended storage, your converter drains back into the may have air trapped in the system that just needs to 'burp' itself out.

GM auto trannys can handle ANYTHING...I've run them out of fluid, overheated them, abused the shit of of them, and only had ONE fail...and that was a TH250 Metric in a Monte Carlo that survived three years of bracket racing, so it didn't owe me a dime!

03-29-2004, 05:11 PM
Happened to my wife when she borrowed my pickup to go pickup some carpet. Mine got just low enough to injest a little air...mixed with the nasty old fluid and it came puking up the dipstick tube as a really un-appetizing brownish foam! The little truck came coasting to the side of the road and she started burning up her cell phone. 3 quarts later, it was back to normal again.

03-29-2004, 05:37 PM
I would check the fluid and filter first, the modulator. Doesn't sound like it's anything really weird. Though I did have a dynaflow that would puke a quart every three weeks or so then was fine for a while, kinda like a cat with a hairball.

03-29-2004, 05:44 PM
I had the same problem until I ran an external trans fluid cooler..never had another problm since.

03-29-2004, 08:23 PM
sawzall this is a very good question. I also have had some weird shit going on with my Chevy Turbo 350. Mine does fine as long as I'm moving but if I sit very long in one place it starts burping fluid out of the dipstick and rear seal. I have been driving the car for years and this just started in October of last year. I do have a external cooler but have been thinking I might need one with a fan on it. Where do you guys usual mount your cooler? Mine is on the front of my radiator.

03-29-2004, 08:57 PM
For you all that had or have problems, how old are your trannys? We have a th350 out of a 77 nova and havent had a problem, but maybe this can be a warning for the future

03-29-2004, 10:04 PM
you have wear particles /sediment settled in the bottom of pan blocking the intake of the pickup-change the filter- wash the pan out and drive another two years!

Sam F.
03-29-2004, 10:15 PM
i havent had that problem..but i have had a problem were the one in my 56 likes to THOW UP all over the floor every once in a while,,mostly when i pull it out,..then pull it back in the garage, its fine if i drive it,,but its weird and messy

03-29-2004, 10:15 PM
Zman how to I check the modulator??

Lesabre I do run an external cooler.. Its in front of the radiator and it’s the largest you can buy.. no fan though.

Buford T

this is a mid 80’s gm trans that I had rebuilt this time last year. Just before we took the car out west.. FWIW I had a turbo 350 out of a 77 nova that was around forever.. I just sold it on ebay last week and the guy picked it up at 10 am Sunday morning.. I went to fetch the car at noon. Perfect timing as always…

Choprods.. I am praying your right. I’d be thrilled to swap in a filter tomorrow and drive it again Friday..

Oh did I mention that the car is scheduled to appear at an “event” this Friday.. If the trans is in fact “toast” I’ll be going kamikaze on it later this week..

Thanks for all the help thus far. You guys are great…

03-29-2004, 10:19 PM
also[my luck] -you could have debris from any rubber hose connections in trans lines if they are not all steel.........hope that isnt the cause.......

03-29-2004, 10:38 PM
Maybe you all can help me too, in this vein of TH350 problems...

I have an '85 Chevy Scottsdale parts chaser pickup. The TH350 has seen better days apparently...She runs fine when going forward, but reverse is M.I.A. unless everything is "warmed up". The trans seems to be saying (after I put it in reverse) "OH, YOU WANT TO GO BACKWARDS, HMMM, Lemmie Think!...and THEN after more than a few seconds it goes into reverse...but slips if I give it gas. Fluid is up to snuff, nice red color, doesn't smell burnt. It's even worse when cold... When it's butt cold out, I have to wait at least 30+ seconds while revving the motor before it shifts into reverse. If it's some sort of early warning sign/adjustment, I'd like to hear it; if the trans is shot, let me know... The truck is for sale for the right price, BTW. It will be on E-Gay soon if not. Too many "projects".

Fat Hack
03-29-2004, 10:42 PM of my old Nova did that when it got low on fluid. If it was warm, reverse engaged pretty quick. If waited till it felt like going in!

You sure about the fluid level?

Throw an extra quart in and see what'll puke out whatever it doesn't want!

03-29-2004, 11:58 PM
put a half pint of DOT brake fluid in it...whatDhell-its broke anyhow........might help

03-30-2004, 12:21 AM
Jeff, I am also thinking you need to change the filter. Guys, would a modulator problem not let it engage at all? That doesn't seem right. The modulator allows the tranny to shift when the pressure is built up, but to not move at all... that's something different. When I changed the modulator on the '46, I had to drop the tranny down and then you can have it out in 5 minutes. If the gears on the modulator cam are worn, you have to replace it, but sometimes it's hard to tell.

Fat Hack
03-30-2004, 08:34 AM
Yeah, a modulator problem usually affects shifting. When I first got my old Pontiac on the road, I freaked out because it wouldn't shift out of low gear on the very first test run around the block.

Looking it over back in the driveway, I found that I had reached down and stuck the vacuum hose for the modulator onto the adjustment screw rather than onto the nipple it was supposed to go onto. A quick an easy fix!

(That car had an aftermarket adjustable modulator)

You can check a modulator with a hand-held vacuum pump. It should hold vacuum. If it doesn't...or if it sucks out tranny fluid, it needs to be replaced!!

03-30-2004, 08:57 AM
well I got the car home last night.. I'll try to get the pan off tonight and see whats goin on in there..

thanks again to everyone for all the tips.. I've obviously never had a problem like this..

chad.. I am hopin like heck that I can get the damn trans pan off while the trans is in the car.. remember the 40 is alot smaller than the 46



03-30-2004, 09:33 AM
That would be rough, to drop the tranny for the filter! I'd change the modulator anyway then! They're cheap.

Ok, I think I've messed my terms up. Above when I mentioned the cam and gears, on the drivers side of the tranny, what is that called again? Modulator is on the pass side and runs off vacuum. I don't think Napa would give him "one of those gear thingies on the side". Doh.

03-30-2004, 10:41 AM
Ask Dave aka "shifts". He is the god of automatic trannies.

03-30-2004, 10:49 AM
It's the GOVERNOR. Man it sucks getting old...

03-30-2004, 11:16 AM
Saw,there are severar thing that can do that .If the car moves after sitting it could be a clodded filter,still not good because the debire clodding it is coming from some where .A broken pump gear could do it also usually from cracked flywheel.PS any of you PA boys want a 1950 GMC pickup .You can call me about trans or truck at 973 627 6110 truck is free to some who could it.Spring cleaning at shop.

03-30-2004, 11:21 AM
I made the mistake of changing a trans filter in a TH350 once. It was fine before hand, I figured changing it as preventive maintance would be good. Afterwards, it never shifted the same... I'd go up this certain hill, and stop at the top of it. Well, it would slip really bad for a couple of seconds, and then hit really hard. I'm pretty sure I knocked some dirt loose somewhere, and it was getting caught in the valve body.

03-30-2004, 11:37 AM
Neither the modulator or governor would cause a no movement problem. You say you have no forward movement, but does it move in rev? Did you notice if it had any howling type noise when it stopped moving? A clogged filter usually makes a sound like a low power stearing pump.Did it move again after sitting for a while? Give me some more info & I can help you out. DAVE

03-30-2004, 02:54 PM
dave.. your name and number are here on my desk.. I was going to call but figured I would try the other stuff first..

as for reverse.. no no movement there either.. I havent tried to move the car since the problem occured.. I didnt hear anything unusual from the trans prior to the problem occuring..

again I got the car home till monday night at 10pm and may not get to look at it till wednesday night..

friday may already be out of the question...


03-30-2004, 11:31 PM
just cracked the seal and started drainin the trans.. fluid looks really really clean so far.. no visable leaks from the trans anywhere...

03-31-2004, 10:09 AM
Hey Jeff, I am very confident that I DID NOT break your convertible. I hope you get it going soon...


03-31-2004, 06:27 PM
just got the pan down and the filter out heres a pic of whats goin on...


03-31-2004, 06:30 PM
thats metal in the previous photo.. and some dirt mixed in for good measure.. heres a shot of the pan.. with the requsite magnets and the layer of metal covering them...

03-31-2004, 10:42 PM
SO is this fatal? can I try to swap in a new filter and fluid and give it a shot or would that be a waste of my time and money?

thanks in advance


04-01-2004, 01:00 AM
Even if you put a new filter and new fluid in it and it did work it won't last long. Pull it out and have it fixed or replace it with and good one so you don't have to worry about it.

04-01-2004, 10:06 AM
Saw ,I am leaning to the concluson the the trans is bad ,but you have about a 10% chance that the debire was lurking in the the trans cooler (radiator).Change oil clean filter and dont stray far from home.

04-01-2004, 10:53 AM
Jeff, you drive the shit out of that car. I think I would bite the bullet and swap it out.

04-01-2004, 11:07 AM
I agree with Flatdog & 46mopar, the trans looks like its had it. Are you capable of doing a rebuild yourself? If so , I have rebuild videos & books for loan to HAMB members.
I can also fix you up w/ any parts you will need. Give me a call. DAVE

04-01-2004, 11:37 AM
Jeff, you drive the shit out of that car. I think I would bite the bullet and swap it out.

[/ QUOTE ]

yeah.. its comin out.. shifts I'm callin you..

04-01-2004, 11:38 AM

the trans cooler was new last april as well!

04-01-2004, 01:15 PM
No hope then.

04-01-2004, 01:31 PM
With all that metal in it make sure you clean out the lines and the trans cooler well or replace both to be safe.

04-01-2004, 05:43 PM
Damn that sucks. better to have it at the beggining of the driving season then in the middle. You car is just trying to tell you it is mad for you putting it away for the winter. next year keep it in the living room and start it once a week.

10-21-2007, 02:06 PM
Hello all
I am having a problem with my parts\car hauler TH350 4x4 and I found this old thread
The problem is no forward action but reverse seems to work ok:confused:
I first noticed minor slipping going up a hill the next day I couldn't even make it up the hill luckily it was close to home and I was able to turn around (on the hill) and make it home
I checked the fluid -a little low but not burned -so I topped it off -nothing -I revved it up pretty good -barely moved -couldn't get out of the yard
My question is where do I start? -can I check for clogs in the valve body etc. or am I tearing down\swapping? -it seems like line pressure is not engaging in drive -could reverse still work? I can rebuild the thing but don't quite understand enough to troubleshoot this one
Also could over revving while manual shifting blow something out?
Could have loosened something up
I only ask because I may have gotten a little excited after a tuning session;)
I'm just wondering if anyone can help me before the autopsy

10-21-2007, 02:11 PM
always check the modulator and the vacuum hose going to it. see if it has a split in it..

10-21-2007, 03:01 PM
the vacuum modulator has nothing to do with engagement into gear! IF the vacuum line was off , clogged ....... it affects the up shifting only.

IF reverse works good / great.... this indicates :

1. you have good pressure to operate the trans

2. the input shaft is connected to the forward drum and power is transfered from the torque converter to the trans. The forward drum drives the direct clutch in reverse with the direct clutch pack applied in "R"


Have you shifted to manual "1" with the shifter? IF the roller clutch is NOT holding , the vehicle will move forward properly in manual 1st gear.

IF the vehicle still does not move forward;

Your problem is in the forward clutch pack. The forward clutch is just that.... it applies in ALL forward gears. No forward clutch equals NO forward motion.

You might try removing the pan and look. Pop the pan back on , fresh fluid and see what happens... waste of time in this case, IMHO.

Pull the trans out and apart

10-21-2007, 04:18 PM
I have not been able to shift to the lowest gear since I bought the thing only drive and L2 -the shifter seems to bottom out
Of course the previous owner said the trans was rebuilt
Could a clog in the valve body stop it from engaging forward?
I will try to get it in L1 by fixing the shift linkage or doing it from underneath
Thank you
UPDATE: ok I got it in L1 -no change -won't even pull a little now!
Could it be the clutches without burning up?
Seemed to go all at once -What would prevent it from engaging forward? I guess the next step is to drop the pan and take a peak

10-21-2007, 07:39 PM
What should I be looking for?
I'd hate to take it out and tear it down only to find a blocked circuit in the valve body or some thing non terminal that could have been fixed
Doesn't look like I'm going to start on it today
Can anyone show me which port engages the forward clutches or any tests I can do to know for sure or suggest a website with "how to" pictures? I've never had one just quit like this without burning up or running dry