4L80e

[kwmech]

So for the past 3 months I've been swapping from a 700 to a 4L80 in my 91Suburban. Got a 2wd core from the wrecking yard, turned out to be a Goodwrench rebuild, pretty clean in appearance but unknown mileage. Had to take it apart anyways to swap out the output shaft to 4wd. Went through it completely, dual fed the direct, installed a TCI 2.75 gear set, Fairbanks shift kit. Installed it, no reverse. At this point my work load and bench was full of customers stuff so I removed and took it to the local trans shop to figure out what I did wrong. Said what I did looked ok, but they made a couple of small changes. Got it back thursday eve and installed it yesterday. Put oil in this morning, .... wait for it.





no reverse again.







Any ideas? where's clinebarger when you need him

[YoungPup1977]

Do you have all forward gears. Meaning all up shifts 1-2 2-3 3-4 and TCC work like they should ? If they do.....
Let’s look at what is applied in reverse. Do you have an apply chart for the 4L80E ?

[YoungPup1977]

Check the reverse servo first.... the easy stuff first. This was a core so you don’t know the history of this trans correct ?

[kwmech]

Don't know the history, but it was completely apart and rebuilt with everything being checked...2 times so far. Not sure about the upshifting yet, because don't want to drive it if I can't back up. Still needs to be programmed. Sitting there it should bump into reverse while I'm at least adding fluid.

[YoungPup1977]

Ensure the trans is full of ATF first. Since you have done it twice I am sure by now you know how many quarts the 4L80E will hold. If everything has been checked twice not sure if I can add anything here. The direct clutch is applied in 3rd and reverse that’s why I asked about upshifts...2-3 shift for third gear would shed some light since it’s common with reverse.
Good Luck !
One more thing. What are you using to control the 4L80 ? The engagement is good in forward but not reverse while sitting still. Correct ?

[kwmech]

Have a Quick 4 unit. Correct, good engagement in Drive while sitting still, nothing in reverse

[b454rat]

Doubt its the same situation, but I had the tranny replaced in a 99 Tahoe I had couple years ago. Had a reman sticker on it, but couldn't confirm it. It rev'd really high before ingaging, forward or reverse. Buddy installed it, kept moving it around back an forth, and after a bit it was fine. Kinda like V/B was sticking. Doubt its the same for your case, but just throwing out some useless info lol...

[kwmech]

I'll give it a shot. Been rolling around in my head all day and had the same thought wondering if something in the valve body is sticking

[YoungPup1977]

If the PR / Boost valve is stuck normally it would impact engagement into forward gears as well....since we are talking about no reverse, it would be nice to know how 3rd gear works or not (slipping into 3rd or no 3rd)

Any changes to the feed thru the center support for 3rd (direct drum) area during your rebuild ? Explain exactly how you did this.

Did you inspect the VB thoroughly, like checking the reverse checkball sleeve. this can cause a no reverse condition in a 4L80E by being worn out and the checkball is not seating/sealing correctly. SONNAX makes a fix for this, its a easy fix.

How was your separator plate where the checkballs seat in the plate, any excessive wear ? Checkball #7 and #11 were OK ?

How did the direct drum air check thru the center support during your rebuild ?

I always use the 200R4 center support seal in the center support on the 4L80E which enhances the sealing of the case to center support area of the 4L80E. not many builders do this but it sure works for me....


****sonnax part number for the reverse checkball Sleeve - part # 34200-38 1995 and later 4L80E transmissions *****

[kwmech]

I am going to have to double check the valve body. It's gotta be there

[kwmech]

Currently putting the 'burb on on stands in the rear to see if it shifts into 3rd. Haven't done that yet. Haven't driven it. Not going to drive it without a reverse gear. My property is all uphill.




Update: Put the rear on stands to run it and see it shift. Shifts 2-3-4. Step on brake to stop tires, goes into reverse. Huh? Shut it off, to do other things. Start it up....no reverse. Shift through the gears have reverse. Let it idle in park for a couple...no reverse. Unplug the trans no shifting and no reverse...not electrical, in the trans somewhere.

Have not been inside yet

[YoungPup1977]

Originally Posted by kwmech

Currently putting the 'burb on on stands in the rear to see if it shifts into 3rd. Haven't done that yet. Haven't driven it. Not going to drive it without a reverse gear. My property is all uphill.




Update: Put the rear on stands to run it and see it shift. Shifts 2-3-4. Step on brake to stop tires, goes into reverse. Huh? Shut it off, to do other things. Start it up....no reverse. Shift through the gears have reverse. Let it idle in park for a couple...no reverse. Unplug the trans no shifting and no reverse...not electrical, in the trans somewhere.

Have not been inside yet

Do you have engine braking in manual low gear ? If you have engine braking in manual low I would think the servo/rear band is working so it would lean towards a internal leak.... Did you build this trans yourself ?

[kwmech]

Originally Posted by YoungPup1977

Do you have engine braking in manual low gear ? If you have engine braking in manual low I would think the servo/rear band is working so it would lean towards a internal leak.... Did you build this trans yourself ?

I did build it myself, thought I could handle it since I've been doing autos for close to 40 yrs. This was first 4L80. Not a whole lot different from a 400 in the bottom end where reverse is. Trans shop said they pressure checked everything before they reassembled. My next step I guess is to run a pressure check if I have time tomorrow.

If I start in low and manually shift it shifts into 2 then 3 then 4. Let the engine idle for a second then will go into reverse. Let it idle in park for a minute or more..no reverse. Hard to check engine braking with the tires off the ground

[YoungPup1977]

Originally Posted by kwmech

I did build it myself, thought I could handle it since I've been doing autos for close to 40 yrs. This was first 4L80. Not a whole lot different from a 400 in the bottom end where reverse is. Trans shop said they pressure checked everything before they reassembled. My next step I guess is to run a pressure check if I have time tomorrow.

If I start in low and manually shift it shifts into 2 then 3 then 4. Let the engine idle for a second then will go into reverse. Let it idle in park for a minute or more..no reverse. Hard to check engine braking with the tires off the ground

To better understand the issue you are having, it maybe to the point you need to put the wheels on the ground and drive the vehicle. This way it will allow you to feel the up shifts a lot better (maybe 3rd isn't as good as it should be) and to see if you have engine braking in manual low... its not like you are going to burn up the trans in 3 seconds...
How are you going to diagnose this thing and have a good feeling before you start ripping into the trans and looking for answers.

Even if everything has been checked twice, you still have no reverse.... start by understanding exactly what the trans is doing prior to dropping the pan. test drive correctly to understand your issue.
* good upshift into 3rd indicates the direct drum is working
* engine braking in low indicates the low/reverse band maybe working
________________________

during your building process, did you check the low/reverse servo pin length ? Is the reverse band new ?
Did you fully take the VB a part to thoroughly check for any checkball issues, any valves sticking, etc... do you know where checkball #7 is located ?
I have to ask again, do you have an apply chart ? this would help you understand exactly what elements are applied in each gear to assist in trouble shooting.


Thanks for listening.

Good Luck !!

[kwmech]

Pressure check gives me 62# at idle. RPM increase gives it 115ish. Power brake it 150 ish. Reverse when working 115. No load let it shift 100.

Seems like I have an internal leak. Pressure boost valve? If I drive this it'll burn up

[YoungPup1977]

Originally Posted by kwmech

Pressure check gives me 62# at idle. RPM increase gives it 115ish. Power brake it 150 ish. Reverse when working 115. No load let it shift 100.

Seems like I have an internal leak. Pressure boost valve? If I drive this it'll burn up

Not sure what you are saying here... What are the values you expecting first of all ? Park reverse etc etc.....

I think you are onto something, Good Luck.

[kwmech]

according to what I've read, reverse..when engaged... should show pressure at close to 300

[YoungPup1977]

Originally Posted by kwmech

according to what I've read, reverse..when engaged... should show pressure at close to 300

,

yep, what about forward gears ? Every thing good on all forward gears ?

[kwmech]

Forward I'm getting different readings 115-150 very inconsistent

[YoungPup1977]

Not sure if you have engine braking in manual low, not sure of the shift into 3rd.... your pressure test is incomplete. Can’t help the unwilling.....

Your fix is in this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=668062

Good Luck to you !!!