Community Forums

leobadger · 04-01-2020, 07:44 PM

Driving down highway shifting from drive to overdrive heard a bang and lost that gear was able to gethome in 3 gear at 3200 rpm instead of 1900 rpm
Any ideal of what happen because transmission works great except no over drive

Thank you

Jean

Bob_C · 04-01-2020, 09:14 PM

Google 4L80E trans....

leobadger · 04-02-2020, 06:39 AM

Thank you

CJ7365 · 04-02-2020, 10:47 AM

Quote:

Originally Posted by bob caldwell

Google 4L80E trans....

WOW, you could answer every question on every thread on every forum with your advice.

Geeeeez, if you can't help just bypass the thread.

Bob_C · 04-02-2020, 10:54 AM

Quote:

Originally Posted by CJ7365

WOW, you could answer every question on every thread on every forum with your advice.

Geeeeez, if you can't help just bypass the thread.

Pictures give a person a better look at what makes up the OD part of the trans....and keep your remarks to yourself.....if you can't contribute....I've rebuilt more of those then you'll ever see....

leobadger · 04-03-2020, 03:54 PM

Thank you but his answer was helpfull i did nt know the type of transmission i had so from research could be electrical body valve orfull tranny will see ehen out

Quote:

Originally Posted by bob caldwell

Pictures give a person a better look at what makes up the OD part of the trans....and keep your remarks to yourself.....if you can't contribute....I've rebuilt more of those then you'll ever see....

Mark_K5LXP · 04-03-2020, 06:35 PM

The "bang" part is concerning.

When you say "no overdrive" does it try to shift from third and over-rev like a missed shift, or does it just stay in third and not want to shift to OD no matter what RPM, speed or engine load?

If you've got OBDII you might be able to pull drivetrain codes and get a better idea what it's upset about.

The 4L80/85's have a known issue with the valve body that's covered in a GM service bulletin. Another failure point is the electrical connector on the side can leak transmission fluid causing problems with electrical signals. Not saying any of this is your problem specifically but they're known issues with 4L80/85's.

If you're "lucky" it's a valve body or solenoid problem that can be fixed without dropping the tranny. I don't have a good handle on specific details but shift patterns on some trannies are influenced by engine sensors, so that's another variable to check. Pulling OBD codes would be my first step. Something to know about OBD is some drivetrain codes self-reset, so the best time to get codes is as soon as you can after the problem happens.

Mark B.
Albuquerque, NM

leobadger · 04-04-2020, 08:53 AM

Thank you i was there a month ago drive was going perfect until i down shift in kentucky for a hill then shift back in 4 go on for 10 sec then heard a bang tranny work fine for 1 2 3 gear until i got home 1500 miles

Try it a few times after that there is no 4 gear at all

So will get Rv to tranny shop will keep you update

Jean

Quote:

Originally Posted by Mark_K5LXP

The "bang" part is concerning.

When you say "no overdrive" does it try to shift from third and over-rev like a missed shift, or does it just stay in third and not want to shift to OD no matter what RPM, speed or engine load?

If you've got OBDII you might be able to pull drivetrain codes and get a better idea what it's upset about.

The 4L80/85's have a known issue with the valve body that's covered in a GM service bulletin. Another failure point is the electrical connector on the side can leak transmission fluid causing problems with electrical signals. Not saying any of this is your problem specifically but they're known issues with 4L80/85's.

If you're "lucky" it's a valve body or solenoid problem that can be fixed without dropping the tranny. I don't have a good handle on specific details but shift patterns on some trannies are influenced by engine sensors, so that's another variable to check. Pulling OBD codes would be my first step. Something to know about OBD is some drivetrain codes self-reset, so the best time to get codes is as soon as you can after the problem happens.

Mark B.
Albuquerque, NM

tomwalt · 04-06-2020, 10:56 AM

Thank you for this post leobadger. I have an 4L80 xmission too and drive mostly in hilly country. Previously I would shift out of OD for going up hills, but was told to just leave it in OD and let the xmission system figure out the correct gear to be in. Now I still downshift for going down hills to save on braking, but leave it in OD otherwise. What do you xmission experts think?

Bob_C · 04-06-2020, 11:27 AM

Really depends on the 'hill'.......with my Dodge, if it's a long uphill pull, I shift out of O/D, then trans shifts into 3rd and still has converter locked up.....less rpm......and steep enough downgrade, I'll also turn O/D off and let compression help ........

leobadger · 04-07-2020, 05:03 AM

Quote:

Originally Posted by tomwalt

Thank you for this post leobadger. I have an 4L80 xmission too and drive mostly in hilly country. Previously I would shift out of OD for going up hills, but was told to just leave it in OD and let the xmission system figure out the correct gear to be in. Now I still downshift for going down hills to save on braking, but leave it in OD otherwise. What do you xmission experts think?

Did not see him yet all close here until 4 msy with that virus sowill wait when things go back to normal

Mark_K5LXP · 04-07-2020, 08:00 AM

Yep, I do "anticipated" shifts into third and back to 4th depending on what I see ahead. For some reason if I let the tranny decide it goes from lugging in 4th and downshifts to 2nd, screams at high rpm for a second there then up to third. So I save that back and forth by just doing it myself, which is usually pretty easy to predict by speed and gas pedal. In general the 8.1 torque, trans and rear end ratios are pretty well matched and does fine on the flat/interstate so downshifting isn't frequent. Up in the mountains here 4th is wishful thinking with those grades, altitude and speeds, so 2nd/3rd is the usual mode.

I've driven manuals all my life and would love to have that simplicity and utility in my RV. I get why auto trannies have become the standard but they sure can be a pain when there are issues.

Mark B.
Albuquerque, NM

tomwalt · 04-07-2020, 08:36 AM

Thank you for the replies.

SteveJ. · 04-07-2020, 09:02 AM

Quote:

Originally Posted by tomwalt

Thank you for this post leobadger. I have an 4L80 xmission too and drive mostly in hilly country. Previously I would shift out of OD for going up hills, but was told to just leave it in OD and let the xmission system figure out the correct gear to be in. Now I still downshift for going down hills to save on braking, but leave it in OD otherwise. What do you xmission experts think?

I have the same tranny in a Roadtrek with a 5.7 engine. With the trailer behind it I'm at 11,000 lbs. This particular trans has a propensity to build heat quite quickly when pulling a load up a grade if the torque converter is not locked in. If I have a grade in front of me I drop the trans into 3rd, get a torque converter lock and build speed.

I do have an app in my phone that monitors trans temperature. Not knowing how hot the trans is getting can be detrimental to it's longevity.

Also, if not done yet, switching to DexronVI is a good thing to do.

My set up only has single core radiator, I'm sure yours would have the dual core. That has to help. I also have the factory trans cooler up front, about 12x12, with a small pusher fan in front of it.

These seem to be good trannys until they are abused(over heated). Mine has over 200k on it.