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-   -   Transmission? Poor acceleration. (http://67-72chevytrucks.com/vboard/showthread.php?t=732617)

telly 03-12-2017 10:52 PM

Transmission? Poor acceleration.
 
Ok, I guess I'm ready to hear what I don't want to hear. Here's the story:

Had someone helping me to change the oil in my 72 C20. Turns out they drained the transmission and then added 4 quarts of oil to the engine. I drove it about 10 miles then started to feel a lack of acceleration. Got it back home and figured out what happened, so I refilled the transmission and changed the oil. Problem is I'm still having acceleration problems. What's the chance the transmission isn't damaged and not in need of repair? If not a transmission problem, what do you guys think?

Edit: I used Dex/Merc transmission fluid to refill.

clinebarger 03-12-2017 11:15 PM

Re: Transmission? Poor acceleration.
 
Draining the transmission pan then driving the truck around will smoke a transmission in a hurry!!!!

Guessing this is a TH350 as it's one of the few GM units to have a factory drain plug you can actually remove without a fight.

telly 03-12-2017 11:43 PM

Re: Transmission? Poor acceleration.
 
Yes. The tranny pan has the drain in its front/center.

Is there any hope for the tranny? It still moves the truck, and can accelerate, but it's not nearly as strong as it was.:barf:

cadillac_al 03-13-2017 10:07 AM

Re: Transmission? Poor acceleration.
 
Your trans is toast. I burned up a couple th350's when they were only a qt low. I lost a trans line once and th350 was toast in 1/2 mile. I have never had a th350 with a drain plug. That would be handy sometimes but not this time. Th400's are much more forgiving on being low on fluid but not the th350's. Sad story.

telly 03-13-2017 10:16 AM

Re: Transmission? Poor acceleration.
 
I'll crawl under it today to see if I can identify the transmission. I don't know that it is a th350 or not. I bought the truck from someone who bought it from someone who married an engine and transmission to a neglected shell. I was given no information about the engine or transmission, and I'm not much of a gearhead. I am able to work on my vehicles, but I'm definitely not real knowledgable.

Right now the truck accelerates decently from a stop (although not like it did), but the lack of acceleration is really noticeable in higher gears.

68gmsee 03-13-2017 11:37 AM

Re: Transmission? Poor acceleration.
 
More than likely friction clutches burnt causing them to slip.

I've seen used TH350's -at least in this area -for $150-$300. I'd probably consider a rebuilt one before a used one these days but in the past I have installed used ones from running vehicles and had good luck.

kwmech 03-13-2017 07:49 PM

Re: Transmission? Poor acceleration.
 
If they drained a full 4 or 5 quarts out of the transmission, I'm surprised that the truck was even able to move at all, let alone drive it down the road for any distance. I've had them just a couple quarts low and they would take a good 10-15 seconds just to jump into gear.

telly 03-13-2017 10:26 PM

Re: Transmission? Poor acceleration.
 
Well, it is a TH350. Sucks, but I guess I have to give in and believe the truth. :censored:

kwmech 03-14-2017 01:22 AM

Re: Transmission? Poor acceleration.
 
Pull the drain plug again and see what the oil looks like. Could pull the pan also and have a look see

telly 03-14-2017 01:40 AM

Re: Transmission? Poor acceleration.
 
Oil looks good. I drained a bit tonight because it was a tad too high.

What am I looking for when I take off the pan?

cg285 03-14-2017 08:18 AM

Re: Transmission? Poor acceleration.
 
that transmission will quit moving somewhere around 3 qts low. how were you able to drive it 10 miles with it 4 qts low?

telly 03-14-2017 09:14 AM

Re: Transmission? Poor acceleration.
 
No idea. But it took a full jug of fluid to refill.

68gmsee 03-14-2017 06:17 PM

Re: Transmission? Poor acceleration.
 
Nothing wrong with the TH350 for regular driving and light hauling. Tons of cars and trucks had them in late 60's thru early 80's. Unless you want to upgrade to a newer one or intend to run it hard, rebuilding yours may not be a bad idea.

storm9c1 03-15-2017 06:52 PM

Re: Transmission? Poor acceleration.
 
How are you checking the trans fluid level on the dipstick? Engine running or not?

telly 03-15-2017 08:34 PM

Re: Transmission? Poor acceleration.
 
Yes, checking the fluid level with the engine running and at normal operating temperature.

storm9c1 03-16-2017 07:23 PM

Re: Transmission? Poor acceleration.
 
Quote:

Originally Posted by telly (Post 7887121)
Yes, checking the fluid level with the engine running and at normal operating temperature.

OK, just making sure. Sorry, doesn't sound like good news then. I'm still baffled at how you drove it at all with that much fluid lost. Should have slipped like crazy or as mentioned, never even went into gear. That's been my experience.

telly 03-16-2017 08:59 PM

Re: Transmission? Poor acceleration.
 
The truck still moves, just not much acceleration. I'll be driving the Camaro for the next month or so. Oh well, it could be worse.

garyd1961 03-16-2017 09:27 PM

Re: Transmission? Poor acceleration.
 
Quote:

Originally Posted by telly (Post 7888662)
The truck still moves, just not much acceleration. I'll be driving the Camaro for the next month or so. Oh well, it could be worse.

What do you mean by no acceleration? Do you mean the motor doesn't rev up or do you mean that the motor does rev up but the truck doesn't go?

telly 03-16-2017 10:01 PM

Re: Transmission? Poor acceleration.
 
Quote:

Originally Posted by garyd1961 (Post 7888687)
What do you mean by no acceleration? Do you mean the motor doesn't rev up or do you mean that the motor does rev up but the truck doesn't go?

It will run down the street. It will get up to speed (even freeway speed), but it does not have much "power". It doesn't come out of the box like it did, and it definitely doesn't accelerate well enough for me to want to pass someone on a two-lane highway.

That being said, it's been sitting except for me taking it "around the block" a few times to assess the situation.

garyd1961 03-17-2017 10:05 PM

Re: Transmission? Poor acceleration.
 
One more time. Does the motor rev up when you give it the gas? If not you may have a motor problem and not a trans problem.

telly 03-17-2017 10:19 PM

Re: Transmission? Poor acceleration.
 
I'll go fire it up and see how high the rpms go.

I don't have a tach, so I don't know the rpms for certain. It doesn't seem to be hitting real high rpms though. If true, any ideas? What might have happened while there was waaaaaay too much oil in the block?

telly 03-17-2017 10:43 PM

Re: Transmission? Poor acceleration.
 
I see where having way too much can cause the rear main seal to blow, but I don't have any leaking oil on the driveway.

Ironangel 03-18-2017 05:15 AM

Re: Transmission? Poor acceleration.
 
When is the last time the motor got a new set of plugs? If the trucks been sitting for any length of time before the mishap, maybe bad fuel and or a clogged fuel filter? Also, over filling the crankcase can lead to fouled plugs. Might take a look at the wires and caps on the distributor making sure they're all fully pressed on to the terminals. It's easy to inadvertently pull a wire loose when pulling the transmission fluid dip stick. I'd definitely install a new set of plugs before I gave up on the transmission. The fact that the 350 turbo is still pulling the truck is testament to how tough they actually are. If you did fry the clutches there should be some tell tale indicators such as a burnt smell in the fluid as well as suspended clutch material in the fluid causing it to be a bit darker than the bright red translucent fluid that was added. If the poor acceleration proves to be some fouled plugs, I'd buy the tranny a pint of this, http://www.lubegard.com/~/C-303/LUBE...uid+Protectant and myself a six pack of these, http://www.binnys.com/beer/Bud_Light...num_40500.html ;)

telly 03-18-2017 03:28 PM

Re: Transmission? Poor acceleration.
 
This truck has been my daily driver...I only commute about 5 miles round-trip. I changed the plugs a week ago, changed the air filter, and reset the timing. I don't smell anything burnt when the truck runs, but it does have some white/gray smoke coming out of the exhaust pipes. I'm definitely down with the second link you provided, but I already have put Bar's Leak into the transmission fluid to help with any slipping.

When the weather dries out a bit I'm going to crawl under the truck and drain the tranny again, then drop the pan to see what's what. That way at least I'll know if there is metal shavings or not.

How would I go about "drying out" the block (removing the excess oil that may have been pushed into unwanted areas)? Where all do I look for issues?

storm9c1 03-18-2017 05:46 PM

Re: Transmission? Poor acceleration.
 
I agree with others, if trans was slipping, you hear the engine rev up but the truck won't accelerate. From your description, engine isn't even revving. So... let's reset.

What have you changed since the incident? Oil, spark plugs, timing. OK. Anything else?

Excess oil in the engine probably didn't hurt anything as long as you drained it and refilled it to the proper level since then. If the cylinders were washed out, you may need to burn it out of the cylinders, which should have happened with a few drives already. Did you pop off your PCV hoses and make sure they aren't full of oil? Otherwise there really isn't anything else that would worry me.

The spark plug change and timing change does concern me. What gap did you use on the new plugs? Do you have HEI? Did you make sure you didn't accidentally swap any plug wires? Recheck the firing order.

How did you check timing? Did you make sure vacuum advance was unhooked and plugged? What timing values did you end up on?


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