4L80 only wants to backwards in the morning

Need some input here people. Have been trying to help out Kevin with his Land Cruiser conversion.

Got to see it complete today for the first time. Exceptional workmanship and attention to detail. Other than feeling like you're riding a pogo stick (big tires and really big springs) everything works the way its supposed to, except when the tranny fluid gets above 205 degrees. Reverse decides to leave town.

Thought it might be line pressure, but other than backup mode, the trans shifts normally with clean crisp shifts. He is controlling it with a Beauman Controller (US Shift) and it allows a laptop to monitor the tranny during operation. Even allows you to modify the program on the fly. The controller is doing everything its supposed to at the right time so don't suspect the controller and as there is no electronics involved with reverse, other than line pressure, suspect all is well from a bits and bytes point of view.

The tranny was overhauled by LenTech here locally (well known guy in the Ford game with a bunch of patents for the AOD) and they have been more than helpful with the conversion. Will be contacting them on Tuesday (holiday here on Monday) to get their input and we will be contacting Beauman just in case they have run across this issue before.

Only thing I can think of, is the trans sat on Kevin's floor for close to a year before he installed it. Perhaps something dried out in the interim or the reverse band actuator is binding after it warms up. Cold it works perfectly and the issue only rears it's ugly head after the tranny fluid gets above 205 degrees.

Something is definitely engaging in the tranny when you put it in reverse but the rest of the drive train doesn't seem to get the message. Played with the shifter a bit in the reverse position a bit, suspecting linkage, but to no avail.

Could really use your help as it is a total shame that after 8 years of work and enough money to help out a third world nation, that Keven is stumped at this stage. The irony of the whole thing is that he made a concerted effort to keep everything as mechanical as possible and the thing that has us stumped is the only part in the equation that requires input from a puter.

Really appreciate any input you could give. Something isn't adding up here.

Bill

Sounds like a seal or valve issue.

Likely a seal on the reverse clutch that's leaking, and when the oil gets hot and thin there is not enough pressure to keep the clutches applied.

Sadly this is not going to be an outside fix.

The puter is not part of this issue.

Try this check

Once the reverse stops working, try driving forward and at about 20 mph select 1 st gear

If 1st will not engage manually then its an issue with the low/rev band.
It could be the servo has a seal issue, or that the apply pin is too short.

Check it out and let us know

Missy

Thanks Bill for helping me out with this.

Robyn,

I tried the 20mph test you mentioned and I get great engine braking in 1st (almost went face first into the steering wheel first time I tried it :) )

I've removed the reverse servo and everything looks good (no broken seals)

I'm down to it being the apply pin. I've read somewhere that these pins have rings on them indicating the length. 1 ring being the shortest, 2 being a little longer, 3 being a little longer then 2 and no rings being the longest. I currently have a 2 ring pin in my setup. Do you think getting a longer pin would help?

Any good place I can get these?

Also wonder if getting a Transgo HD2 kit would help prevent any of theses issues (from what I understand it keeps line pressures in check)

Thank you for all the help

It's been a while since I have been into a 400 or 4L80

There is a gauge to measure the length of the NEEDED PIN.

Too long and you burn it up.

The fact that you have manual low would negate the need to change the pin.

The oil flow to the servo is different for manual low as opposed to reverse.

Manual low uses the rear band and the forward clutch, and reverse band.

Reverse uses the direct clutch and reverse band.

There could be a subtle leak in the direct clutch circuit, or an electrical fault.
(The fact that it's a hot only issue makes me ???? the electrical thing)

Here is a great diagnostics on the no reverse in the 4l80e
https://www.google.com/url?sa=t&rct=...7-LoL6TF1eLC9w


Follow this run down and see what shakes.

The fact that it works cold makes me suspect a hydraulic issue, such as a shaft to drum seal on the direct clutch, or possibly the center support area.

Center supports are held into the case with several lugs in the aluminum case and a large tapered snap ring holds the entire assembly in place.

There is also a hollow bolt that goes through the channel casting (case) and tightens the assembly up into the case and feeds the oil to it.

A bolt left out or loose can do it.

Check the pressures and see WTF

Remember

Direct (3rd gear) takes far less holding power than reverse.

Reverse drives 2 planetary gear sets to make things go backwards and takes way more pressure to hold things.

I suspect that the 3rd gear clutch is not receiving proper pressure to hold.

This said, the feed through the VB is different for forward.

Could be an improper check ball as well.

The fact that this gearbox has been apart recently and messed with could indicate and issue with a check ball, a seal in the direct clutch circuit or ???

The transgo dash 2 is great, but you need to find the issue first, not bandaid it with the kit

Missy

Just wanted to give an update on my transmission issues.

Ended up having to pull the trans out of the truck and bring it back to the shop. After closer inspection 2 issues where found.

1- reverse servo cover was not 100% flat. After air testing, air was seen bubbling around the cover (even with the gasket). The cover was flat sanded until the bubbling stopped.

2- center bolt was achieving proper torque without the bolt being properly seated. After cleaning up the thread, the bolt was able to seat properly and then proper torque was applied.

Transmission was retested last night at the same temperatures as before and the issue is now gone. :D

The transgo HD2 kit was also added to the transmission.

Now to go work on the other little issues I'm seeing with the truck.

Thank you for all the help.

Great to hear all came out well.

The center bolt and servo covers are two trouble spots that often cause issues.

The air test is always a good part of the test protocols as the box goes together.

One thing that has bitten many a tranny tech is excessive wear in the large lugs in the case that hold the center support into the case.
If the center support can wiggle at all, the center bolt will loosen up in time and result in a failure of the direct clutch, and also no reverse.

Ahh yesss, the joys of the auto boxes

Enjoy

Robyn