• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

95 4L80 Low Line Pressure and No Line Rise under throttle

I didn't think about it till now, but when you did the rebuild, did you flush both the internal radiator cooler and the standalone cooler separately getting all the built up crap out? back when I had my radiator pulled and repaired (plastic tank was cracked) I used some brake cleaner and the air blow gun to flush out the internal trans cooler. boy did a LOT of nasty black junk come out!! I flushed it till it was clean and dry before I reinstalled the radiator. one other thought too is can the coolers be partially clogged or one of the steel lines slightly kinked that run up from the trans to the coolers?
 
yeah i did flush the cooler when i had the trans out. I think there is only one cooler right? at least i thought so for this truck.

i guess the lines could be plugged but the temps on this trans seem to stay down, i dont ever notice it get hot or a burnt smell to the fluid or anything, so i dont think my failure was temp related. However i will be putting a temp gauge in here shortly.
 
I know on the turbo charged 6.5's they have two coolers in front of the condenser, drivers side is for the engine oil and passenger side is for the trans. lots of the 454 gassers had an aux cooling fan mounted there on the passenger side. I can't speak for the older pre 94 trucks if they only had the cooler in the radiator or not. I was thinking that if they didn't get flushed before, maybe they were the cause of the debris in those screens!
 
Ok I am back and in need of help. Got to about 150 miles with the reman VB and ive been driving with the gauge the whole time. So far all pressures have been good but went for a short drive today and a few miles in pressure started to not respond to throttle again. I would give it gas and pressure would stick to about 60 psi, and i could feel the trans begin to slip when starting from a stop. Few miles home so i tried to limp it back but it got worse. I unplugged the trans to command max line and it still sat around 60 most the time. Sometimes pressure would jump up to 120 or 150 but it was random, under throttle, and most the time would drop back down to 60. Then it started to oscillate between 30 psi and 100 jumping back and forth, and sometimes even falling to 0. Really not sure what is going on now, but i feel like the only thing i haven't changed on this trans now is the case itself.
 
brhynard said:
Ok I am back and in need of help. Got to about 150 miles with the reman VB and ive been driving with the gauge the whole time. So far all pressures have been good but went for a short drive today and a few miles in pressure started to not respond to throttle again. I would give it gas and pressure would stick to about 60 psi, and i could feel the trans begin to slip when starting from a stop. Few miles home so i tried to limp it back but it got worse. I unplugged the trans to command max line and it still sat around 60 most the time. Sometimes pressure would jump up to 120 or 150 but it was random, under throttle, and most the time would drop back down to 60. Then it started to oscillate between 30 psi and 100 jumping back and forth, and sometimes even falling to 0. Really not sure what is going on now, but i feel like the only thing i haven't changed on this trans now is the case itself.
Click to expand...
Sounds to me like you have filled your replacement VB with debris like your 1st one.
 
Yeah I think you're right. Do you think this stuff is just getting through the filter somehow? Seems like if it passes thru the main filter it would be smaller than the screens protecting the PCS but I don't know. I guess it's a trans pull now.
 
You were right. Pulled the pan and lots of black crap in the oil again, probably worse than last time. The PCS solenoid was clogged up with junk again as were the screens. I pulled the trans out though and looking at the clutches I can't really figure out where all this is coming from. Most of the clutches look great except some indications of heat on the steels of the intermediate clutch. Not really sure what to look for here to determine what exactly went wrong. Any ideas?

The oil I dumped out of the TC looked the same as everywhere else, no loose friction material or anything coming out of there that I saw
 

Attachments

  • 16449623673721918481393224841978.jpg
    16449623673721918481393224841978.jpg
    110.4 KB · Views: 10
  • 16449623857724976099356038570234.jpg
    16449623857724976099356038570234.jpg
    104.3 KB · Views: 10
  • 1644962408180749515630561272813.jpg
    1644962408180749515630561272813.jpg
    123.3 KB · Views: 11
  • 16449624268373412885175810834840.jpg
    16449624268373412885175810834840.jpg
    116.8 KB · Views: 10
brhynard said:
You were right. Pulled the pan and lots of black crap in the oil again, probably worse than last time. The PCS solenoid was clogged up with junk again as were the screens. I pulled the trans out though and looking at the clutches I can't really figure out where all this is coming from. Most of the clutches look great except some indications of heat on the steels of the intermediate clutch. Not really sure what to look for here to determine what exactly went wrong. Any ideas?

The oil I dumped out of the TC looked the same as everywhere else, no loose friction material or anything coming out of there that I saw
Click to expand...
Dismantle the pistons too. Be sure that their cavities are not loaded with debris.
 
I really wish i had a way of looking at the clutch inside the converter to see if the black crap is coming from that. Because looking at these clutches, i cant really say with confidence that its coming from them. But unfortunately, if i cut apart the converter i will lose my core charge and i have to imagine thats pretty hefty on this.

I do wish i knew if the converter was causing my problem though. This crap has to be coming from somewhere!!
 
Well when the trans went into the vehicle it had a reman pump and a reman converter, with a full kit (clutches, bushings, seals, bearings, paper gaskets, etc). The converter i picked up at a trans shop and swapped them my old one. So when the full trans went in the vehicle it definitely got a different converter however i cant vouch for the quality of it.
 
Just out of curiosity, not that this would be the cause of this last demise on your tranny, but what fluid are you using? I know GM recommends dextron 6 but as we have all learned that is a no no! the fluid is thinner and can't handle heat like the old dex 3.

just a thought if you haven't already installed on, is a trans temp sensor so once you get it back up and driving you can monitor temps
 
Pressure gauge with electronic sending unit. Dont run a live hose/tube/line into the cab.
Several warnings in this forum about live fuel gauges, transmission fluid may not be as flammable but, it might still scald and create a terrible mess within the cabin.
 
brhynard said:
I would give it gas and pressure would stick to about 60 psi, and i could feel the trans begin to slip when starting from a stop. Few miles home so i tried to limp it back but it got worse.
Click to expand...

IF you decide it's slipping: S T O P and call a hook! Get AAA, add towing to your auto insurance, maybe it's even on your cell phone bill. USE IT! Time waiting for the hook is time saved in the shop putting out a bigger more expensive fire.

Maybe you can save the transmission by not slipping it to ruin. All you are doing PUSHING a slipping transmission is quickly burning out the clutches. No, burn up can be quicker than the last mile or two home.

LIMP HOME MODE can only do so much to save the damn thing. Low pressure is going to slip and burn clutches even in LIMP HOME MODE. I suspect the ECM may have/had trouble codes for slipping?

The entire system is full of debris. Count the oil coolers, literally follow the lines. Throw away the air to oil cooler as there is no way you can 100% flush it out. I would even suggest replacing any rubber cooler line sections.

I would condemn the radiator trans oil cooler. Have it replaced by a radiator shop or get a new radiator. (Sadly a brand new radiator I got was leaking. Had Trans oil floating in the radiator. I don't go there anymore as they warranty repaired it and claimed No Problem. I dropped the pan and found water drops.)

If you used a contaminated container to fill, yeah, the TCC clutch could be the debris source. But you are not sure: condemn the radiator trans oil cooler anyway. Just. To. Be. Sure.

A garbage rebuild TC is no end of trouble. So is one full of coolant, debris, crap. With the picture of the coolant in the trans oil warranty on a converter just isn't what you are after. You may have more than one problem or just coolant in oil. If they handed you a used converter ... did you add oil to it or otherwise inspect it for old oil prior to install?

Swapping parts in a debris filled transmission isn't working as you noted. :facepalm:

Other than the sprag or bearing that failed (Shop couldn't tell what went first) and went through the OD planetary with a "BOOM!" My 4L80E failures have been from a Torque Converter Clutch that won't hold the Diesel TQ anymore. IMO the TC clutch is a weak point on the 4L80E and aftermarket like Yank Converters with a triple disc is a solution I used. I literally just changed a slipping TC and no trans rebuild that wouldn't hold at 35 MPH (custom tune to do so) but the Yank did.

Yes a 6.5TD can light the rear wheels up through 2nd gear with a Yank high stall converter and other adjustments and/or bolt ons like a big turbo. Lighting them up LOADED in reverse with a trailer is exciting to say the least.

I would look at a GM Reman transmission exchange complete with torque converter. All the above is an educated guess that may be missing some small dammed detail like a crack or other serious internal oil leak.
 
The blueing on the steels is from low line pressure. The clutch material is most likely from your converter. It sounds to me like you rebuilt your trans without finding out why your trans failed in the 1st place. Transmissions do fail, but the majority of them fail because something else takes them out. You always, ALWAYS find the root cause of the initial failure BEFORE putting one back together. This is the single biggest cause of repeat failures is repairing the failure without finding the cause of it, and then the repaired unit fails in the same fashion again and again. You're going to have to set down with a manual and vacuum check every circuit of your valve body, pressure check each clutch circuit and look for pressure leaks, and go over it with a fine tooth comb. With the quantity of clutch material that you have in yours you will most likely end up having to replace your radiator and external trans cooler as it is next to impossible to fully flush them. Then after putting it back in hook up a pressure gauge, take a bidirectional scan tool, and verify that you have the correct pressure for each amp step.

And Dex vi is fine in a fresh rebuild as the new seals will be compatible, it is seals from before 05 that were the problem.
 
You must log in or register to reply here.
Back
Top