4l80e TRANSMISSION - 1996 Tiffin Allegro

[RM Art]

Hi!

This is about...

4l80e Transmission - 454 Engine - 1996 Tiffin Allegro - 37K orig miles - great condition overall conditions, all new fluids

4l80e transmission serves us perfectly well under all other conditions... except for the following circumstance:

Trying to backup a verv, very steep grade [starting from standstill due to need to jockey into position to be able to back up]... our 25' RV will not complete the length of that steep grade. Almost at top of the grade [grade is 100' long] RV comes to standstill. Even with accelerator floored reverse movement stops. One of the few times I tried to backup the RV up this grade the drive wheels did begin to peal-out when progress ceased. Other times the reverse movement simply stops; no wheel spin. Basically the trany stalls with engine floored and still running. The steep grade is black top driveway that I take all sorts of cars, trucks and suv's up and down.

Upon movement stall; I immediately stop trying to continue backing up in that circumstance so as to not over stress the drive line or maybe hurt the trany's internals.

Question: For what reason would a 4l80e transmission "stall out" such as that? When the stall occurs the 454 engine with gas pedal floored drops way down in rpm and sounds considerably stressed. I only tried backing up this grade a few before stopping my attempt to do so.

The reason I'd like to back up the grade is for placing the RV in best position on our property. And, the reason I don't try going up frontwards is because I would need to back down... due to curves, trees as well as other reverse steering impediments that could create disaster.

Question:

I thought the 4l80e transmission would simply continue backing up the RV until top of grade is reached. Does reverse movement stopping while engine is still running mean there is a problem beginning to occur inside the transmission? Or, is it as it should be if when starting from standstill to back up a very steep grade the 4l80e transmission will simply "stall out" in its reverse gear?

1st photo shows RV parked behind trees at 90 degree angle to the driveway's steep grade, at bottom of grade... in a specific parking area I cut out and concrete paved.

2nd photo shows straight-on of steep grade that has 1 lane street at bottom and flatish paved area on top.

As you can see there are several stationary impediments along side the grade that makes maneuvering a "tight squeeze".

Although the photos don't clearly show the steepness... It's steep enough so that walking up or down is a task for anyone - young or old!

[RickNC]

There is a significant difference between 1st gear ratio and reverse. I forget exactly but it is something like 2.5:1 for first versus 2.0:1 for reverse. Assuming nothing is wrong with your transmission the only cure s I can think of is likely a higher stall speed torque converter or a higher rear axle ratio.

It must be a real PITA lugging everything down that steep driveway to load up the motorhome., Here is a possible solution

[GypsyR]

Any chance you've tried it "dead cold"? Dead cold means you let it sit all night long and then first thing in the morning go straight into reverse and try it as quickly as possible.

Just as an experiment. If you make it then it means more than likely your transmission has the original "short lip" piston seals that are known to bypass fluid when hot and the neutraling out in reverse is just the first symptom. if so, then your transmission needs those replaced. Down side is that means a "rebuild" as the seals are deep enough in there it doesn't make much sense not to at least freshen up everything while in there. Bright side is that those same direct clutches are also needed for third and fourth and you wouldn't want to lose those two gear sin the middle of a trip.

On the other hand, if it behaves the exact same way, I'm barking up the wrong tree.

Possibly trying a very steep hill in low (manual first) gear might lend a clue if it's a reverse band issue. Maybe. There are other elements also in play in manual first so it's not sure fire.

[RM Art]

Originally Posted by RickNC

There is a significant difference between 1st gear ratio and reverse. I forget exactly but it is something like 2.5:1 for first versus 2.0:1 for reverse. Assuming nothing is wrong with your transmission the only cure s I can think of is likely a higher stall speed torque converter or a higher rear axle ratio.

It must be a real PITA lugging everything down that steep driveway to load up the motorhome., Here is a possible solution

Attachment 290202

Thanks, Rick! No need to traverse the steep incline for loading the RV.

Oddly enough... due to the very hilly area we live:

Whether the RV made it up the incline onto the large flat spot or it stays down lower than the incline, where it's now parked - We would still be driving from an upper road down to the RV with all supplies in our SUV. So... one parking location or another stocking up is fairly simple with not too much effort.

[RM Art]

Originally Posted by GypsyR

Any chance you've tried it "dead cold"? Dead cold means you let it sit all night long and then first thing in the morning go straight into reverse and try it as quickly as possible.

Just as an experiment. If you make it then it means more than likely your transmission has the original "short lip" piston seals that are known to bypass fluid when hot and the neutraling out in reverse is just the first symptom. if so, then your transmission needs those replaced. Down side is that means a "rebuild" as the seals are deep enough in there it doesn't make much sense not to at least freshen up everything while in there. Bright side is that those same direct clutches are also needed for third and fourth and you wouldn't want to lose those two gear sin the middle of a trip.

On the other hand, if it behaves the exact same way, I'm barking up the wrong tree.

Possibly trying a very steep hill in low (manual first) gear might lend a clue if it's a reverse band issue. Maybe. There are other elements also in play in manual first so it's not sure fire.

I may try that some day. However... in its generally parked direction, just aside the one lane road, trany fluid would no longer be completely cool by the time I drove around a fairly large area in order to get turned in correct position for backing up the incline. There is a way I could keep the fluid cool by parking it in an odd position down below overnight.

I see what you say and will speak with my trany expert. I'd not quizzed him on this: "... the original "short lip" piston seals that are known to bypass fluid when hot and neutralizing out in reverse."

Also, seeing as I only tried reversing up the grade three immediate repeat tries from a dead stop at its exact bottom, and that during one of the three tries when RV ceased to move upward the drive tires broke loose and began screeching... Chances are the trany short lip piston seals are not too wasted - Yet!

I'm going to see if I can get the flat spot up top ready for the RV to turn around - once it's up there. If so... The angle that the one lane road is for entering the steep grade makes me confident that instead of beginning from dead stop in reverse I could successfully ascend the grade in forward at some speed [4 to 6 mph??] while trany is in manual low.

[EyezOpen]

.....

[D Gardiner]

I'm guessing the weight of the RV on your slope is the primary issue. If you had transmission clutch slipping issues, you would have felt them by now on other roads.

The main thing I worry about that you could overheat the transmission fluid by stalling out the transmission converter on the hill.

The second item I'd worry about is damaging one of the spider gears in the differential, when the wheel begins to spin.

4L80E ratios: 1st. 2.48, 2nd 1.48, 3rd 1.00, 4th 0.75, Rev 2.07. The torque percentage loss from 2.48 to 2.07 is only 16 percent, but that can be enough to not crest the hill in reverse.

The 454 outputs 380 ft. pounds of torque at 1400 rpm, so you should have enough grunt from the engine.

[GypsyR]

If you went up to a point where the coach stopped moving and the tires started spinning that's not a transmission problem, it's simply losing traction because the drive is just too steep for the vehicle.

[RM Art]

Originally Posted by GypsyR

If you went up to a point where the coach stopped moving and the tires started spinning that's not a transmission problem, it's simply losing traction because the drive is just too steep for the vehicle.

Yes. I too believe that is the problem.

When I get it set up so I can drive uptop in forward gear; then turn around uptop so I can drive down in forward... everything is solved. That super heavy grade, with so many constrictions on its sides, is simply too steep for backing either up or down. Driving up or down in forward gear I believe will be relatively easy.

The area up top may need a tree removed to enable turning the RV around. I do not want to back down... in other instances of heavy rigs going down backwards there have been some disturbing occurrences.