low trans fluid th700-r4 91 k1500

C

columnshift

Joined
Oct 6, 2014
Messages
264
Location
Minnesota
So i have a 1991 chevy k1500 4x4 with 350chev and 4 speed which would be the th700-r4, 60k miles. (yes 60k, not 160, yes original, yes really)

I admit not checking as often as i should being... the vehicle hasnt seen much use despite age. And was mostly letting my girlfriend drive it and just changing oil. Then last week it was stuck in 1st (when in drive or overdrive) but if she shifted into 2nd gear it would take 2nd. So i check the most obvious and yeah its a bit low on trans fluid noticibly below the cold mark.

I'm going to just add up some fluid but it seemed like a good time to ask other questions.

Whats the best fluid to add - i'm not changing the fluid at this time (and i'm sure thats a PITA dropping the pan and everything) just adding, should i use the newest formulation and its compatible with the old (whats it up to dexron 6 or something? i'm so out of "buying trans fluid" mode i can barely remember) or do i just use some of my new old stock ATF fluid still on the shelf from 15 years ago if it's compatible and that's just as good. (does it matter if an open or closed container) Not looking to be 'cheap' i just figure it doesnt matter hugely if i'm only adding a half quart or some small amount... right? :-/

Second, as soon as it's not the middle of winter and i'm not putting all my bills to credit card, would it be adviseable to change the fluid on a 32 year old th700-r4 with only 60k original miles to help it last longer? Does old fluid still in the trans 'go bad'? (its never been changed, had original fluid i'm sure cuz I put 42k miles on it/I got this truck with 18k a few years ago)

I've heard warnings about powerflushing/backflushing transmissions - that the car stealerships like to sell everyone on. Hearing totally mixed results - from "thats the dumbest effing thing ever" to "yeah do it if you start early in the transmissions life" which i'd think 60k hopefully still is.

I'd like to drive this truck for a long time - it's so nice, so this is far more about what to do next summer when I can consider a fluid change and other postponed maintenance thats too hard to DIY in the cold.
 
IMO, you would be fine using either Dex VI or a reputable brand of Dex/Merc. If it were mine, I’d do a pan drop and filter change at your convenience.
 
Any Dexron VI will be fine. Maxlife is also a good choice.

Since GM was too stupid to include a drain plug in the transmission, get an aftermarket pan that has one. This will make future ATF changes much easier :)
 
Top if off with your NOS Dexron/ Mercon fluid. I don't have a good feeling-- transmissions tend to move until they're 2 quarts low then they don't. Losing a gear, or most of the gears, could be a deeper problem.
 
Well left unsaid is the fluid had to go somewhere... so i'm assuming there's a slow pan leak i'm not quite catching, possibly one more apparent while driving than while standing still cuz I don't remember seeing puddles of trans fluid tho I think there was signs of drips the last time I was under there. So i'm guessing a gasket change at least when I have a chance to drop the pan.

Is there any reason to be afraid of dexron VI? (hope its not like the old universal 'dexcool' something or other that became a nightmare, i still have some of that from back in the day too and assume that just belongs in the garbage :)

I'll take a picture of where the trans fill mark is, I dont know how far down is too far, or where it should be unwilling to shift up a gear. I didn't want to go test drive it now that I know it's a bit low too. I don't know much about auto transmissions other than the rule of "pink and no stink is probably good". I know pretty much ANY job for an auto trans is $$$ and i'm just trying to baby things until i'm out of my house and am in a better decision to make objective decisions and repair postponed everything in my life right now. : P I'll tap up the fluid, recheck the level after it settles, drive it and see if that fixed the no-shift and report back.
 
My topic changed so i'm reposting now that I added fluid to the cold level (needed 1 quart to read in the range) and it didn't change anything.

I properly test drove the pickup (since I wasnt going to do it before adding fluid).. it goes 1st to 2nd beautifully, then when it tries to shift into 3rd/drive the rpm flares up and the vehicle loses speed. :-/ I can lock it in 2nd gear so it doesnt shift to drive limiting me to speed but it wont flare up at least.

Vehicle is 1991 chevy K1500 4x4, 350 chevy and would be th700-r4 transmission. 61,000 original miles. I don't know why one would die so early... vehicle hasnt been doing towing or anything. Though on the highway the topper resistance has always made it struggle a bit to hold overdrive being within a few mph of wanting to downshift if I tried to drive any faster. I would have thought the trans would downshift to avoid overloading itself but maybe it didnt. If those conditions due to wind resistance are 'hard' miles i've driven it about 40k miles (I took ownership at 18k) between minneapolis and fargo like that.

I'm assuming i'm probably screwed and just going to be finding myself trying to buy a new transmission. >_<
 
So you put on 40k w/o issue until now? have done any fluid changes? am wondering what the bottom of the pan looks like, what it might have for junk.

Does sound like the band for 3/4 might be dying. Low miles, but high years.

Any tranny cooler? does it hold lockup well?
 
Stumbled across the prior thread (I don't blame the OP for starting a new one, I think I would have too). Link.

I admit not checking as often as i should being... the vehicle hasnt seen much use despite age. And was mostly letting my girlfriend drive it and just changing oil. Then last week it was stuck in 1st (when in drive or overdrive) but if she shifted into 2nd gear it would take 2nd. So i check the most obvious and yeah its a bit low on trans fluid noticibly below the cold mark.
Click to expand...

Second, as soon as it's not the middle of winter and i'm not putting all my bills to credit card, would it be adviseable to change the fluid on a 32 year old th700-r4 with only 60k original miles to help it last longer? Does old fluid still in the trans 'go bad'? (its never been changed, had original fluid i'm sure cuz I put 42k miles on it/I got this truck with 18k a few years ago)
Click to expand...

Solves my question.

Did a quick look. Search link. Sounds like, check TV cable (unlikely) and governor (more likely), for the "didn't want to leave first" problem.

The 3rd gear issue though, this year might have a kickdown lever? not sure, I took a couple of looks at links but it's not mine to search. ;) Search link. IMO, if it's slipping in 3rd it's got issues, issues that well justify dropping the pan and doing a fluid exchange (I call it a flush, others take umbrage). Put differently... the more you drive it "as is" the more likely it's taking yet more damage.

Might want to loop in @clinebarger for the rest as I'm no mechanic.
 
3-4 Clutch is smoked, Look closely at the TV Cable & Adjustment because if something is wrong with the TV system causing low/late pressure rise.....It will smoke the 3-4 Clutch again.

In fact.....it would be a good idea to install a pressure gauge now & check for Pressure Rise as soon as the accelerator pedal is pressed.

If in fact this unit has 60,000 miles.....DO NOT get rid of it.....Trust me, There are few low mileage 700R4 cores!! Have it rebuilt.
 
columnshift said:
So i have a 1991 chevy k1500 4x4 with 350chev and 4 speed which would be the th700-r4, 60k miles. (yes 60k, not 160, yes original, yes really)

I admit not checking as often as i should being... the vehicle hasnt seen much use despite age. And was mostly letting my girlfriend drive it and just changing oil. Then last week it was stuck in 1st (when in drive or overdrive) but if she shifted into 2nd gear it would take 2nd. So i check the most obvious and yeah its a bit low on trans fluid noticibly below the cold mark.

I'm going to just add up some fluid but it seemed like a good time to ask other questions.

Whats the best fluid to add - i'm not changing the fluid at this time (and i'm sure thats a PITA dropping the pan and everything) just adding, should i use the newest formulation and its compatible with the old (whats it up to dexron 6 or something? i'm so out of "buying trans fluid" mode i can barely remember) or do i just use some of my new old stock ATF fluid still on the shelf from 15 years ago if it's compatible and that's just as good. (does it matter if an open or closed container) Not looking to be 'cheap' i just figure it doesnt matter hugely if i'm only adding a half quart or some small amount... right? :-/

Second, as soon as it's not the middle of winter and i'm not putting all my bills to credit card, would it be adviseable to change the fluid on a 32 year old th700-r4 with only 60k original miles to help it last longer? Does old fluid still in the trans 'go bad'? (its never been changed, had original fluid i'm sure cuz I put 42k miles on it/I got this truck with 18k a few years ago)

I've heard warnings about powerflushing/backflushing transmissions - that the car stealerships like to sell everyone on. Hearing totally mixed results - from "thats the dumbest effing thing ever" to "yeah do it if you start early in the transmissions life" which i'd think 60k hopefully still is.

I'd like to drive this truck for a long time - it's so nice, so this is far more about what to do next summer when I can consider a fluid change and other postponed maintenance thats too hard to DIY in the cold.
Click to expand...
I got the 4l60e in my 2001 Blazer. Got 107k miles on it. Original transmission. Just recently did a full flush and a filter change on it with Maxlife Multivehicle ATF, and she shifts like butter 👍
 
supton said:
Did a quick look. Search link. Sounds like, check TV cable (unlikely) and governor (more likely), for the "didn't want to leave first" problem.

The 3rd gear issue though, this year might have a kickdown lever? not sure, I took a couple of looks at links but it's not mine to search. ;) Search link. IMO, if it's slipping in 3rd it's got issues, issues that well justify dropping the pan and doing a fluid exchange (I call it a flush, others take umbrage). Put differently... the more you drive it "as is" the more likely it's taking yet more damage.

Might want to loop in @clinebarger for the rest as I'm no mechanic.
Click to expand...

Responding now because i've been too heartbroken to deal with anything so I just parked it the last month and drove my other car. (which is ALSO now not working and now i'm REALLY heartbroken and in trouble as a moneyless college student :( )

Searching the link showed things stuck in 1st gear, but it will get from 1st to 2nd just fine. Which is why I was wondering if it was a clutch. I was assuming even opening a transmission is going to cost $$$ for something possibly broken and needing replacement anyways.

It's too cold for me to do any work and i'm too crippled up in my body to do things myself and i'm lacking confidence in my ability to not screw things up... but if the trans is dead the trans is dead. I'm pretty sure there are places that could do a trans flush (this isn't a diy) not just a fluid replacement, because if something is stuck i'm sure just changing fluid isn't going to free anything up... I was finally forced to drive the vehicle again today (using only 1st and 2nd) limping to college and back because my other car is down and now i'm trying to figure out if there are any better possible solutions...

Is it basically if a trans power reverse flush type thing doens't bring it back to life i'm probably buying a replacement transmission I assume? Automatics are usually pretty simple they either work or dont in the hydraulic era.

--
To supton - yeah 40k with no issue, no fluid changes, and i'm not able to check that in winter (and the damage is already done if so). What I found so strange is it was like throwing a switch - it didnt "start to slip", it just woke up the next day and there was no 3rd gear to go into INSTANTLY. It's held lockup well when driven but the engine likes to shift at highway speed due to air resistance mostly out of OD lockup and minor hills - trying to hold 77mph with one of those large-rear toppers would often cycle the lockup converter, which I didn't like, but it wouldn't USUALLY need to shift down to drive.

There's no lockup to hold now because in 2nd only I don't want to drive it much over 30mph.


The other posters verified part of my curiosity though, is there some other part which could have contributed to it dying early, but since it's already died i'm not sure how to check myself. I've now had multiple mechanic visits with multiple vehicles tell me everything is fine with cars which have died or had serious problems afterwards and i'm balanced between not trusting their opinions now when I thought they were reputable, and having too many barriers to doing the work myself. (too cold, too crippled, struggling with TBI making it hard to understand how to do things I used to do, etc)
 
Last edited:
I have yet to find any definitive answer of why the 3-4 clutches fail; if they're going to fail, they just do. I kn ow of more than a few early 3rd Gen F-Bodies that lost 3rd gear ~60k miles. Back then, I always figured anything after ~60k miles was just borrowed time.

The 4L60E in the Safari lost it's 3rd gear at 131,267 miles. I rebuilt it in 2014 and it's been operating normally ever since. Other than cooked frictions, steels and lots of black residue everywhere, nothing points to a root cause of failure. Before it lost 3rd gear, the 2-3 shift did feel kind of weird in that it felt like the clutches were coming on and off.

I had to drive it back to town on the back roads in manual 2nd. Light traffic that day after Xmas....
 
So it's not unheard of it's a known failure mode...

Is having a low mileage original rebuilt by a local shop going to cost any less, or be any better than ordering some mail order trans rebuilder th700? Is rebuilding a stock transmission going to be better for longevity than buying something with the same? I remember hearing later years have some improvements and i'd heard earlier years had some problems (I wasnt sure if that included 1991 but I dont remember it all) and I didn't know if a rebuild would fix that, including maybe too conservative valve body tuning that holds it too hard in OD or lockup wearing things out by causing gear hunting... or not.)
 
atikovi said:
A 91 with 61K? Not impossible but do you have proof it's correct? That transmission shouldn't go bad with those miles unless it was beat on hard or was under water.
Click to expand...
Really? A 700R4 in a 6000+LB 4x4 truck can't go bad in 60K miles? Those things couldn't live behind Camaro 305s back then.
 
I found the bookstore here to be of great value when I did the 4L60E.

ATSG Bookstore

ATSG transmission rebuild manuals, downloads, discs, tools, parts, and more direct from the source!
atsgbookstore.com atsgbookstore.com

As far as what modifications and parts work best together, I purchased the rebuild kit for it from here:

probuiltautomatics.com

Pro-Built

Welcome to Pro Built Automatics
probuiltautomatics.com probuiltautomatics.com
 
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