Possible tranny problems

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antoniora

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Good morning everyone. I have a 1977 Chevy C20 Scottsdale 5.7 350 engine. My father and I received this truck for my grandfather. We decided to get it ready for use as a farm truck. Due to a very bad oil leak I did valve cover gaskets and oil pan gasket. We did a tune up with new plugs and wires and a distributor. We went ahead and did the transmission pan gasket because it wa a beginning to leak. After we performed all those maintenance, it was time to test drive. I started it up and the engine sounds good. I put it in reverse and I notice I was pushing the gas pedal a little harder before it would actual move. Same for putting in drive and it would take a moment before it would move. The other day I was driving it and around 30 mph I notice and heard that it didn't shift so I decide to push the gas further and it shut off. I turn the truck back on and drove around 30 mph and it shut off again. I felt like it would not shift. It did one time shift but the truck shook hard. I feel like there is a transmission problem. I've been a mechanic for about 5 years and haven't dealt much with diagnosing trans problems. I have always been told don't drain the trans fluid after a certain number of miles. The truck only has 97k.

Can anyone assist me on this.

Also does anyone have a diagram of the vacuum lines.
 

crazy4offroad

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If it has been sitting a while it could just be a gummed up valve body in the transmission but it kinda sounds like a broken sprag. If it makes a lot of noise, like screetching and a sound like something jangling around in there, it could be the sprag.
 

MadOgre

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Good morning everyone. I have a 1977 Chevy C20 Scottsdale 5.7 350 engine. My father and I received this truck for my grandfather. We decided to get it ready for use as a farm truck. Due to a very bad oil leak I did valve cover gaskets and oil pan gasket. We did a tune up with new plugs and wires and a distributor. We went ahead and did the transmission pan gasket because it wa a beginning to leak. After we performed all those maintenance, it was time to test drive. I started it up and the engine sounds good. I put it in reverse and I notice I was pushing the gas pedal a little harder before it would actual move. Same for putting in drive and it would take a moment before it would move. The other day I was driving it and around 30 mph I notice and heard that it didn't shift so I decide to push the gas further and it shut off. I turn the truck back on and drove around 30 mph and it shut off again. I felt like it would not shift. It did one time shift but the truck shook hard. I feel like there is a transmission problem. I've been a mechanic for about 5 years and haven't dealt much with diagnosing trans problems. I have always been told don't drain the trans fluid after a certain number of miles. The truck only has 97k.

Can anyone assist me on this.

Also does anyone have a diagram of the vacuum lines.

Ive heard that ******** all my life and it is just that ********! Think about it. When ever the transmission is running, there is tranny fluid being sucked up from the pan and pumped through out all the various passages. So why would it change or hurt anything, to drop the pan change the filter and add new fluid?

For that matter how could it do any damage to do a flush and pump out the old while replacing with fresh fluid?

If for some strange reason a person would want to and somehow was able to do a reverse flush that might be a different story but even that doesn't stand up to scrutiny either.

That myth involves the idea that you are gonna pump all the contaminants from the pan into the passages. Well who in the hell puts the dirty pan back on with all the sludge still in it ???

I cant stop laughing when I hear these ****** lube employees spouting that stuff off LMAO. Just goes to show you how much they know or that they actually don't know a damn thing about what they do for a living! YIKES!!!


I have done tranny flushes on high miled transmissions many times. You know what it does. They drive incredibly better. Like Day and Night better!

Its a good idea to run some additives in well used transmissions.

I use Valvoline Max Life. It works real good! Every tranny I have put that stuff in works noticeably better afterwards.

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It costs me $32 for 5 liters but the stuff has every type of additive you can get and it works for both of our new vehicles as well as the old stuff. It is based on conventional base oils but then has all the additives including synthetic additives. So its like the best of both worlds.

I run this stuff in my power steering/Hydro boost system on my ol squares too. Works fantastic.

I use it regularly in my 90' 4L60/700r4 and that tranny runs like a champ, every time it shifts its beautiful!
 
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quaddriver

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a trans flush I would never do - that does recirp crap into it. dont be lazy - drop the pan.

that being said, there is some truth to a failure occurring after a change...the seals swell differently and what was almost a leak, becomes a leak. It only takes one impossibly small seal leak in a pack to make it fail, and it cascades quickly.
 

quaddriver

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ps, is the tranny a 350 or a 400? if 400...did a vacuum line rot?
 

antoniora

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I'll have to check. This is my first time working a vehicle so old lol. I grew up in a dealership environment and didn't see many vehicles pre 2000. I did drop the pan and change the filter and gasket. It does t sound right. Like it doesn't want to shift.
 

antoniora

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a trans flush I would never do - that does recirp crap into it. dont be lazy - drop the pan.

that being said, there is some truth to a failure occurring after a change...the seals swell differently and what was almost a leak, becomes a leak. It only takes one impossibly small seal leak in a pack to make it fail, and it cascades quickly.

----I did drop the pan. I don't understand. The day before I performed all the work I drive it and it shift fine. After I did the gasket and putting new trans fluid in it runs and sounds like crap. It won't go over 30 mph and you can here the trans whining that it's in high revs but won't shift.
 

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a trans flush I would never do - that does recirp crap into it. dont be lazy - drop the pan.

that being said, there is some truth to a failure occurring after a change...the seals swell differently and what was almost a leak, becomes a leak. It only takes one impossibly small seal leak in a pack to make it fail, and it cascades quickly.

You obviously don't understand how to do a tranny flush then LOL.

To do a flush you still have to drop the pan! OMG why would you do a flush just to leave the old filter and sludge in there ? WTF dude!!!

You drop the pan, clean it, install a new filter and then fill with ATF. Then you can hook your lines up to the cooler lines to finish flushing out the rest of the old fluid.

Anything else is just a waste of time!

And like I said you have to use some quality fluid with all the additives! If you run that Valvoline Max Life it will actually stop old leaks!

Your just trying to perpetuate that old wives tale which really gives me a good laugh LOL
 

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----I did drop the pan. I don't understand. The day before I performed all the work I drive it and it shift fine. After I did the gasket and putting new trans fluid in it runs and sounds like crap. It won't go over 30 mph and you can here the trans whining that it's in high revs but won't shift.

Did you correctly install the pick up tube from the filter? Did you buy the correct filter? What else did you do to the truck? Do you have the correct fluid in it?

Don't buy this ****, for even one second, that putting new fluid in, wrecked your tranny! That is complete ********!
 

quaddriver

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Your just trying to perpetuate that old wives tale which really gives me a good laugh LOL

absolutely not.

do not flush a trans. Period. End of story. There is no fluid path or possibility that this will work well. drop pan. drain converter (if not tapped, tap it) refill.

Back to the OP: I didnt mean that you flushed it, I was responding elsewhere. Why I asked what I did, is that there is a vacuum modulator on it. If the line running to it is bad - rotten, fell off whatever, it will not shift properly - very very late.
 

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What ever ED! LOL Don't flush a tranny OMG LMAO I really cant stop laughing LMAO That is like the dumbest thing I've heard in a long long time!
 

Georgeb

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"To flush or not to flush. That is the question."
But seriously, aside from the banter if it worked before the service and doesn't work now it seems to be something got disturbed. Since it doesn't run properly and doesn't want to shift the suggestion that there is an issue with the vacuum modulator seems to be the first place to look. After that dropping the pan again to make sure all is as it should be is next.

Did you shift it to dive then reverse, back to drive, back to reverse, into park and then recheck the fluid level after the service? I didn't notice you mention doing so. If not, even though it seems obvious recheck the fluid level while idling in park just for piece of mind.
 

DoubleDingo

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I was thinking the level was low too. I have a clear gallon jug I marked with 1 quart, 2 quart, 3 quart, 3-1/4, 3-1/2, 3-3/4, 4 quart just for drain and fill of automatic transmissions. That way the fluid added back is exactly how much was drained. And before draining, I make sure the level is checked after the tranny is good and hot so it's an accurate reading. Doing that ensures it's refilled with clean fluid to the correct level. Then if anything goes awry I know it's not related to low fluid level.
 

smoothandlow84

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Im gonna say...its low on trans fluid. Idle it until at normal operationg temp, check trans dipstick fluid level with it in park. Something was definately disturbed when the pan was dropped. Pull the pan and check for foreign matter of parts of any sort. Worst case...take it into a trans shop and let the pros go through it.
 

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