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Topic: 1995 GM Tranny - 4L80E? - One time leak?

Posted By: MacManOne on 09/10/07 10:45pm

Hello to all GM transmission experts. Here's the story as brief as possible.

* 95 Chevy chassis, 19,000 LB motorhome, tranny has never before leaked enough to require adding fluid.

* Today climbing a long grade in 2nd gear we saw smoke quickly appear out the back and pulled over.

* Transmission fluid was leaking onto my crossover pipe, and seemed to be coming from the top of the tranny -- or at least not from the pan gasket, and not from the rear seal. All the hose connections are dry.

* Engine was hot, but far from overheating.

We let it sit for about 20 minutes, started back up and no problem since.

Any ideas what happened?


Mac & Chris
2001 National Islander, 330 Cummins Diesel
2008 Honda CRV toad
Full-Time 9/2004 to 4/2013

Posted By: Gale Hawkins on 09/10/07 11:16pm

There is an overflow line that I can see with the engine dog house top removed on my 1992 P30 MH chassis. Could it have be over full by some and when it got heated in the hard pull the expansion caused an overflow?

I would ask a professional shop their thoughts. If it is now working fine it must have been a transit thing but "something" caused it to happen.

Posted By: alfredmay on 09/11/07 09:43am

This is a known problem with this transmission [4L80E] "puking" fluid when hot. It used to spill fluid out the dip stick onto the engine until GM put a locking/leak proof dip stick on it. The locking dip stick has a lever that is moved up or down to open and close it. This transmission has a vent that is located on the top of it with a short hose attached to the vent. When the trans heats up fluid is released thru this vent. Some people have lengthened the hose and placed a radiator type fluid capture bottle at the end of the hose. That way the fluid can be retrieved. Other folks have run the trans 1 quart low. I have been thru this. There is not much you can do except for what I have stated. There is nothing wrong with your transmission.

Note: Due to invalid formatting, all formatting has been ignored.

Alfred May
2005 Excursion V10 4.30 4x4
2002 Cedar Creek 30RBS TT by Forest River
Reese Dual Cam
Tekonsha Prodigy

Posted By: BruceMc on 09/11/07 11:12am

That's good to know... My K2500 has the 4L80E transmission. When I changed the fluid & filter before our last trip of ~1400 miles, I noted in the factory manuals ( that it took 5 quarts for a fluid/filter change. Problem was, it actually takes about 4 1/2 quarts - 1 pint too much. I had lots of hard shifts and some long shifts where I didn't before, but the unfortunate part of the story is that I had not towed this particular fiver (or that much weight) over a long distance before. I had no history to work from. Perhaps it would have been the same before I changed the fluid.

I later removed a pint and have towed once since then. I get a hard upshift from 1st to second on rare occasion, typically after towing over steeper hills. The tranny seems much better mannered than before. I understand having too much fluid is as bad as too little. Oddly tho, I've had the fluid/filter changed twice before, once by the dealer and once by a quickie change outfit and they both overfilled it.

Not long after we purchased the truck, we rec'd the new locking dipstick in the mail - it was a recall campaign delivered to your doorstep.


'16 Forest River Sunseeker 2250SLEC Chevrolet 6.0L
'00 Four Winds 26Q Class C (Ford E350 V10)
'96 Kit Sportsmaster 212f Fifth Wheel/'93 GMC Sierra K2500
'91 SunLite poptop truck camper
and the first: a Wildernest flip-top canopy.

Posted By: MacManOne on 09/11/07 09:04pm

I think you guys are right. It performed fine today, not a drop of leak. I took a few photos of the tranny (easier to reach my hand up there than my head) and I think I see the vent tube. Looks like it used to have a rubber hose on it to direct fluid to the ground.



Posted By: Gale Hawkins on 09/12/07 12:12am

I read today at an oil change place GM in 2007 replaced the 4L80 with the 6L90 which has two over drives and a low gear of like 4.03 or somthing 4+. Maybe they had addressed this issue but after the 4L60 in my Blazer I have been so far impressed with my GM Good Wrench Remanufactured 4L80 that has 16K miles on it in a 1992 chassis with 90K miles which is about to get new exhaust manifold bolts. If it had not been for back firing at max shift points due to a failing distributor Pick Up Coil I most likely would not have gone under the MH on a creeper at night with a flashlight. The $13 new pick up coil fixed the backfiring but was a pain because you have to remove it and pull off the gear and pull the shaft to replace the pick up coil. Tonight at Advanced I learned I could have gotten a rebuilt one with lifetime coverage for only $90 which is about equal the parts cost alone.

Posted By: Woods on 09/12/07 12:25am

The 4L60E trans have the same problem...

TV: 01 Dodge 2500 quadcab 4X4: Cummins,auto(Goerend TC/VB & deep pan),TC lockup switch,gauges,edge comp,rv injec,holley fuel pump,permacool fuel/water filter,big banjo fuel bolts,180 stat,high flow exhaust w/K&N filter.

RV: 26ft 2003 Aerolite.

Posted By: MacManOne on 09/12/07 08:43pm

Gale Hawkins wrote:

...I have been so far impressed with my GM Good Wrench Remanufactured 4L80 that has 16K miles on it in a 1992 chassis...

I think very highly of the tranny myself Gale. Mine is original equipment, and has 97,000 miles in a 19,000 pound motor home. We go out west every year. A big part of the time we're either going up a mountain at wide open throttle in 2nd or 3rd, or coming down a mountain with the tranny braking our descent. The engine was rebuilt 20K ago, but the tranny keeps on going.


Posted By: Gale Hawkins on 09/12/07 09:56pm

Mac I understand 4L80’s are just about bullet proof if serviced and not overheated. The previous owner stated the reason he lost the transmission after 76K miles was because he did not have tach or transmission temperature gauge and one day in KS it failed to shift out of second and he ran it a long ways doing 65 MPH. Afterwards he added a tack, external cooler (at keeps it at 140 degrees if moving down the road getting air flow) and the gauge. My hearing is not good so I have removed the CD changer and speakers. I refuse to operate a truck without the sound feedback on how it is performing. In the old days one could tell the moisture content of the soybeans based on the sound the combine was making. [emoticon]

I do have a few questions about mountain driving. If you are going up a mountain it sounds like you just put in on the floor and let the transmission determine the gear you are in and your RPM’s? Now that I have my 454 tuned up in part I am beginning to appreciate their power but did not know if one should hold back a little on the throttle or put the petal to metal when climbing? I know on take off if I hold it on the floor mine will shift at 35 and then go into 3rd at 60 MPH.

Having never driven a fully loaded truck in the mountains they give me more concern then going up because I got passed by a semi once that had his brakes so hot you could smell them and they were not holding the load but the road became straight enough so he could just let it run out. It makes me watch my rear view mirror going down a mountain now.

What are some your worse experiences? Do you just start out in first if in doubt or do you get on the brakes to drop your speed enough to force it down one gear. Have you seen times when in first you had to brake as well to keep from red lining your engine? How close redlining can one run a 454 (what is redline for a 454) down a mountain without causing any type of damage. When using your brakes do you get on and off of them or ride with a little pressure at all times? If one’s engine dies (runs out of gas, coil failure, etc) while going down a mountain will you loose your entire engine breaking ability? What about the power assisted brakes?

We are planning a trip to the Grand Canyon late next spring and go north from there. I live on a hill and about 200 foot section is about 20 degrees and if I pull out of my drive and am up to about 10 MPH just coasting when I hit the steep part I will get up to about 22 MPH but hold there for the short distance. We just do not have much of anything steep here in Western KY relative to a mountain.

Thanks for your and others thoughts and experiences with transmission braking in the mountains. Having my wife and 10 year old twins in the MH increases my cargo safety concerns more so than if it was just me. I do not have a toad set up yet and am seriously thinking of doing my first mountain trip without one since we will be making major stops only and not side trips to antique malls 20 miles off the interstate or staying much more than one night at one site. My GB Pursuit at 32 foot and with a functional rear view mirror is not that hard to drive or turn around in tight places and sitting 2 foot above the engine gives good visibility.

Posted By: MacManOne on 09/13/07 08:43pm

Hi Gale,

I can tell you what I do (which may or may not be the best thing). Our old southwind has 4 disk brakes and 2 drums (tag axle) all with high quality semi-metalic pads. We're towing a honda civic, and use a Brake Buddy. The combined weight is under 22,000.

Going Downhill: If I know the grade and the speed of the curves I'll start out at the speed I'm confident of maintaining on average. When I don't know the grade, I'll start out with a lot of caution and be ready to adjust.

For example - a typical 6% or 7% grade, 40 MPH curves, I'll put her in 2nd and brake to 35 before each curve. Also I won't let it go over 45 MPH any time on the way down. So I have a 10 MPH swing. I brake fairly hard at 45, make the brake buddy come on and help, and then get off of the brakes at 35.

When I say XX mph curves, I mean that we follow the yellow recommended speed signs religiously.

Going up hill - If it's a short hill, a mile or two, I'll manually downshift to where I can maintain a good speed wide open without winding it too tight. That's about 65 in 3rd, 45-50 in 2nd for me.

If it's a really long hill, I'll slow down. So let's say it's 12 miles long and I could go as fast as I wanted in 3rd. I'll take it down to 60 MPH and hold it there. If the highest gear I can make is 2nd, I'll take it down to 40 MPH. 1st is 20. This way I'm only at partial throttle and the engine isn't working very hard at all.

I've intended to put in a tach for a couple of years. I have a 3" Autogauge sitting in a cabinet and haven't put it on. Must do that soon. But I'm sure that I haven't over reved the engine. We did a full balance job on it during the rebuild, and I've never wound it out more than I would a stock motor.

Hope that helps.


Posted By: Gale Hawkins on 09/15/07 11:15pm

Mac it really does help to know what has worked for another for a long time. I have heard tell that some states do a better job than others in making clear the total length of a hill.

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