1986 sbc th350 ran dry on ATF :o

[Davidj]

a few years ago i bought this beauty for my step father who always loved square bodies, but he isn't mechanically inclined. of course i knew i'd be the one keeping it on the road. had a few small issues in the beginning learning about carbs, distributors, timing etc. but finally got her running BEAUTIFULLY! for about a year... today i get a call "your dad's stuck in someone's driveway. the truck won't move." well... great.. i show up to the scene to find it kicks into reverse great. could drive her home in reverse if i didn't know better. checked the ATF and it was low. like low low. and burnt. dark dark red. ran to the store and grabbed two qts of atf and she drank it down easily. (checking every half qt. to be sure i'm not overfilling.) so, two qts of atf and a tow strap later, i have it home and plan on getting more atf tomorrow. my questions though, are:

1: why would it still have reverse (although it kinda slams into gear) but not D, 1, or 2? (no rev drop, no jerk forward. feels like neutral)
2: where the heck could it all have gone? (never seen a drop of fluid under it that i didn't cause by poor aim XD)
and
3: i guess the real question is, should i top it off and as long as drive comes back, just keep her choochin? or maybe with a little advice, there's some preventative maintenance that should take place?

if there's a little tinkering that can be done to prevent further issues or possibly modify this (in my opinion, kinda gutless) th350, ill be happy to do it to keep this old girl happy, and keep my dad proud to own her. An afterthought: i did check the linkage on the side of the trans. the U shaped piece seems to be tight and rotates at the same rate as the bolt that holds it in when selecting gears. any advice is appreciated. thanks!!

 

[NickTransmissions]

1: why would it still have reverse (although it kinda slams into gear) but not D, 1, or 2? (no rev drop, no jerk forward. feels like neutral)
2: where the heck could it all have gone? (never seen a drop of fluid under it that i didn't cause by poor aim XD)
and
3: i guess the real question is, should i top it off and as long as drive comes back, just keep her choochin? or maybe with a little advice, there's some preventative maintenance that should take place?

1. Fwd clutch and/or rear roller clutch assembly has failed; reverse uses the low reverse clutch and direct clutch to work

2. Perhaps was underfilled to begin with; try topping it off to see if anything happens in Drive/2/Low

3. See #2. If it doesnt work, yank it out for overhaul. Likely needs it given your description of the fluid's appearance, etc

 

[Ricko1966]

No leaks missing transmission fluid pull the line off at the vacuum modulator,if there's fluid in that line the mystery is solved.

 

[Tonimus]

As Ricko says, if it's really not leaking anywhere, out the modulator is the only other place to go. A new modulator and vacuum line solves that. As far as the trans going into reverse, not uncommon when super low on fluid. Linkage issues can also keep it from engaging forward gears properly.

Could have also toasted the forward clutches due to low fluid levels.

 

[Rustisbest]

Check the radiator for a pink milkshake too. The cooler can leak internally.

 

[Tonimus]

Check the radiator for a pink milkshake too. The cooler can leak internally.

So used to running external coolers I forgot! Definitely this too.

 

[Davidj]

Update: I topped it off while in neutral and idling. Waited for it to warm up. Put it into reverse, rpm’s dropped. Solid engangement. Reversed a bit to test. Works great. Put it back in neutral. Rpms returned to idling speed. Put it in drive and only the slightest drop of rpm’s. Barely noticeable but definitely a slight drop. No engagement feeling. No movement when raising rpm’s a bit to test. Kept it in drive ~20 seconds to see if it was just engaging slowly and no difference. 1 and 2 feel the same. Put it through all gears a few times and every time, reverse engaged. D, 1 and 2 did not. Watched a few videos today about the vacuum modulator today. I’ll be checking that this afternoon when I get out of work along with the radiator. There is a smaller one strapped to the front of my coolant radiator. Is this the external cooler mentioned above? Thanks again for advices!!

 

[Tonimus]

Update: I topped it off while in neutral and idling. Waited for it to warm up. Put it into reverse, rpm’s dropped. Solid engangement. Reversed a bit to test. Works great. Put it back in neutral. Rpms returned to idling speed. Put it in drive and only the slightest drop of rpm’s. Barely noticeable but definitely a slight drop. No engagement feeling. No movement when raising rpm’s a bit to test. Kept it in drive ~20 seconds to see if it was just engaging slowly and no difference. 1 and 2 feel the same. Put it through all gears a few times and every time, reverse engaged. D, 1 and 2 did not. Watched a few videos today about the vacuum modulator today. I’ll be checking that this afternoon when I get out of work along with the radiator. There is a smaller one strapped to the front of my coolant radiator. Is this the external cooler mentioned above? Thanks again for advices!!

It could be. More likely it's your AC condenser. Check the passenger side of the radiator. There should be two hard lines going into the tank there. If there's nothing hooked up there, then you'd have an external cooler somewhere. Probably.

 

[Davidj]

Got ya. It does seem like an aftermarket thing. On the passenger side in the back by the firewall in the black box was where I thought the ac condenser was but I’m not incredibly familiar with ac systems. I’ll see where the lines are heading when I get home. On my way now. Appreciate the quick responses!!

 

[YakkoWarner]

Update: I topped it off while in neutral and idling. Waited for it to warm up. Put it into reverse, rpm’s dropped. Solid engangement. Reversed a bit to test. Works great. Put it back in neutral. Rpms returned to idling speed. Put it in drive and only the slightest drop of rpm’s. Barely noticeable but definitely a slight drop. No engagement feeling. No movement when raising rpm’s a bit to test. Kept it in drive ~20 seconds to see if it was just engaging slowly and no difference. 1 and 2 feel the same. Put it through all gears a few times and every time, reverse engaged. D, 1 and 2 did not. Watched a few videos today about the vacuum modulator today. I’ll be checking that this afternoon when I get out of work along with the radiator. There is a smaller one strapped to the front of my coolant radiator. Is this the external cooler mentioned above? Thanks again for advices!!

Depending on your truck, a small secondary radiator-looking thing in front of the main coolant radiator may also be an external oil cooler. Follow the lines from it - if they route back to the oil filter area thats most likely an oil cooler - if they go all the way back to the transmission (or tie into the trans cooler lines that attach to the main radiator) than its more than likely an external transmission cooler.