1984 gmc c1500 classic

[Davski3271]

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I have a 1984 gmc Sierra c1500 with a 1972 5.7l engine and th350 auto transmission. I was having issues in 2nd gear so I decided to replace the trans filter and on the bottom of the pan was grey greasy sludge I was wondering what it might be from? I haven't tried driving since changing just in case there was damage. This is the first time I've changed the filter since owning it so I'm not sure on the history. Any answers would be appreciated thanks.

 

[1973c10]

Welcome to the site

 

[AuroraGirl]

Is that all sticking to a magnet or is it just floating in the ATF?

i would say its high mileage, high wear, and varnish

If that is the Original trans fluid, its possibly animal byproducts and separating addittives etc...
If its an old fluid, but after 1975 before 1990s or early 90s, its not so much animal byproducts likely, but it could be just be a cumulation of clutch mud, debris the filter couldnt take, varnish, any additives someone may have added, etc...

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this is dexron 2 on the left when its not old and worn(looks dark) and on the right(worn and burnt, trans is toast)

your fluid being deep red is interesting.

I dont want to recommend anything that could hurt it, but without knowing its history, and the red is still red.

I would strain some of your old fluid, like a couple quarts, let some sit to see if it has separation of anything happen, if it doesnt, Use that and a very conservative change of DEXIII spec fluid from walmart or something.... new filter... drive.

I would also do a shift kit, but before driving.

I would change that fluid after some amount of miles. Also check your trans cooler for plugging and flow, clean it if it needs some attention(its in the rad)


The reason for the conservative change is new ATF has cleaners, your system might have untold **** just waiting to dislodge and plug a cooler line.
But you may have a not-old unit that could go for a adjustment or a shift kit... hard to say

 

[Babs]

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[Davski3271]

I just changed it over to dexIII changed out the filter. Im not too sure on the history. I bought it about 5 years ago. I picked up some lumber for a project and it stalled twice and was having some issues with getting up to speed. I adjusted the carb and its been running great. I didn't drive it though until a few days ago and that's when I was noticed an issue when going above 20 it shifted into second the engine was a little shakey and while driving it was making a sweet burning smell I turned around and parked it. I dropped the transmission pan to replace the filter and that's when I noticed the whole bottom of the pan covered in the grey slimey material. Sadly I didn't test it to see if it was magnetic I wiped it all out with some rags and put it all back together. I checked the rags and it has a small amount metal flakes but not alarming. After draining the transfuild I checked the connections on the radiator the lower line dripped out some fluid and the upper connection had no fluid in it. I put some shop air through the radiator with the lines off to see if it was blocked and it just shot out some transfluid that was in the radiator nothing seemed clogged. I will look into putting a shift kit in it. Thankyou for the information!

 

[AuroraGirl]

I just changed it over to dexIII changed out the filter. Im not too sure on the history. I bought it about 5 years ago. I picked up some lumber for a project and it stalled twice and was having some issues with getting up to speed. I adjusted the carb and its been running great. I didn't drive it though until a few days ago and that's when I was noticed an issue when going above 20 it shifted into second the engine was a little shakey and while driving it was making a sweet burning smell I turned around and parked it. I dropped the transmission pan to replace the filter and that's when I noticed the whole bottom of the pan covered in the grey slimey material. Sadly I didn't test it to see if it was magnetic I wiped it all out with some rags and put it all back together. I checked the rags and it has a small amount metal flakes but not alarming. After draining the transfuild I checked the connections on the radiator the lower line dripped out some fluid and the upper connection had no fluid in it. I put some shop air through the radiator with the lines off to see if it was blocked and it just shot out some transfluid that was in the radiator nothing seemed clogged. I will look into putting a shift kit in it. Thankyou for the information!

Unfortunately its sounding like you may be looking at some 2nd gear wear(not outrageous given the age) if your shift kit doesnt proove to really fix or long term help things, I would avoid driving it and either have it rebuilt(cheap) or find another trans/

however, you have an unknown modulator and kickdown status's as well
you should replace the modulator (the thing on the back of the transmission, has a metal vac line run to it with rubber on the ends, one goes into it, the other goes into the intake manifold usually. Replace the rubber, too.

Then the kickdown linkage should be checked for proper adjustment.

Modulators are cheap

 

[Davski3271]

I replaced the modulator and checked on the kickdown cable it looks like when the last owner did the engine/ trans swap they ran a new kickdown cable and it is too long and not the right one. Anyway I left it disconnected took it for a test run with the new fluid/filter and modulator. Then I took it for a mile test drive everything seems to be shifting good all the way up and down. I still plan on getting what I need for the cable to be reattached, getting a shift kit.

 

[Corvette Ed]

Welcome aboard from East Tennessee. Sounds like Lady Luck may be on your side.

 

[Davski3271]

Well I reconnected the kick down cable. On my second adjustment I tried going in reverse and I noticed a whistling sound and It really didn't want to move very easily. So I checked out the rear diff and some nasty oil milk shake. Could there be a problem with diff breather on it? can they cause water to get in? Just wondering if I should replace the breather? Thank you everyone

 

[RecklessWOT]

Well I reconnected the kick down cable. On my second adjustment I tried going in reverse and I noticed a whistling sound and It really didn't want to move very easily. So I checked out the rear diff and some nasty oil milk shake. It looks like there is a diff breather on it can they cause water to get in? Just wondering if I should replace the breather? Thank you everyone

I'll bet the guy you bought it from used to tow a boat trailer with it. Backing the rear end down a boat launch into water is a quick way to get water in the rear end. Generally a breather won't let water in while driving, if anything they usually get clogged and that causes leaks/ weeping seals. Definitely good you changed the oil, breathers are cheap it wouldn't hurt to toss a new one on there. How did things look inside the rear? hopefully you caught that one just in time too...

But I really doubt that had anything to do with it slipping in reverse.

 

[Davski3271]

I'm just letting it sit to drain a little more while I go out to get new oil. I have to clean all of the brown oil out but all of the gears looked in tack no visible damage but I have not rotated the rear to check everything out yet. I was just a little worried about the whistle so I decided to check out the diff good thing I did too. The truck sat most of the summer I have a brake job to do on it because its pulling to the right maybe something is stuck.
I've owned it for 5 years with minimal maintenance decided it was time for some belts and while I had everything off I replaced the alt, thermostat and water pump. The coolant neck and power steering line were starting to leak so those got replaced as well. After I did all of that I was like time to drive and it was nope. The trans and diff I should have done after I got the truck since you never know what the last person did to it I wasn't thinking but its all hindsight now.

 

[AuroraGirl]

Well I reconnected the kick down cable. On my second adjustment I tried going in reverse and I noticed a whistling sound and It really didn't want to move very easily. So I checked out the rear diff and some nasty oil milk shake. Could there be a problem with diff breather on it? can they cause water to get in? Just wondering if I should replace the breather? Thank you everyone

First time with Melted Beaver?
Mine smelt that way at least
Water, dirt seem to have found their way in but it isnt out of the reasonable for it to be water + wear and not heavy on the dirt but time and normal use otherwise.

My hose was broken up top and it was likely dirt and water collecting for years while ontop of it a dirty dusty bed.

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if your use will involve water activities like a boat, high dust, mud ,etc GM issues a TSB about relocating the vent for the axles to make for better water and life spans. you should put a vent on yes and you would prob be wise with a new hose. The noise unfortunately may be a RIP noise if its worn enough

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this is from a ford but see its more grey or shale colored, I would expect an older 84 probably under normal use would look worse than this but maybe not so much brown. but the real question for wear will be the teeth on the thing and you see mine, not close, but any excessive wear or pitting or grooves or oddly shaped teeth would indicate some wear. but you do have wheel bearings at the ends you cant inspect without pulling which you may want to and if you dont see anything there you should spin the driveshaft and check for play there. that would to me, i think, make sense to be the pinion bearing but im not so confident on that Im still learning axles lol.