99K2500Sub

Hello . I have an 1999 Suburban K2500 4l80e trans . It started off not wanting to shift out of 1st unless u let off the gas and was going over 20mph. Very annoying .Now it has no reverse it catches slioghtly sometimes .

I took it to a trans shop they looked it over and said that the shift solnoid for 2nd was bad and that it also controls reverse ,and that the trans needed rebuilding . Can they tell that in a couple hrs?

That was about 2yrs ago . I am mechanically knowlagable and have worked on cars all my life , just not transmissions .Can anyone advise me what to do?I'd really like to get on the road and after finding this site and doing some research changing the solnoids shouldn't be too bad . Oh also they said the solnoids were 500usd ea. I just looked them up , they are like 30?

Anyways can some one pls help me?

slow67

iTrader: (2)

Reverse will work no matter what the solenoids are doing. You have an internal trans issue.

99K2500Sub

That What I was thinking and was suspicous of what they told me . I'm hoping to come across someone who can point me in the right direction thats experianced at diagnosing this transmission .

slow67

iTrader: (2)

First I would do a pressure test in each gear and post the results. Then possibly a detailed description of what happens while driving in each manual gear (if its normal and if it has engine braking).

99K2500Sub

I will have to look into presure tests. It does engine brake in 1st but is very hessitant to shift from that point . It will not shift until 25 mph and you have to left off the gas or it will not shift . So to drive it I put it in D run it up to 25 and ease off the throttle till it shifts then go on my merry way. I dont drive it anymore since the reverse started acting up . U can put it in R and hold down the gas steady and it will eventually "surge " and move a little . I,m understanding that when the 4l80E is in reverse the following happens:

1.1-2 solenoid ON
2.Direct clutch is applied
3.Low and reverse band is applied.

Given that 2nd and reverse are the problem , and they both use the 1-2 solenoid to operate , Doesn't it seem that the 1-2 solenoid is bad ?

I know there is alot more to it than it appears but does reverse fail if 1-2 solenoid fails? If not what role does the 1-2 solenoid play?

I'm thinking it's going to pay off by changing out that solenoid it's cheap and all I need to purchase is the solenoid , pan gasket ,fluid and a new trans filter while I'm in there .

What do you guys think? Worth it? If I take to any shop they want to get the rebuild out of me and charge 500 per solenoid . It kinda makes me sick to think that my truck has been sitting based on a 30 dollar part that shops want to turn into a 3,000 dollar job .

slow67

iTrader: (2)

Reverse doesnt rely on the 1-2 solenoid at ALL. If you unplug a working transmission it will still have reverse. Solenoid is NOT your problem.

99K2500Sub

Is there any thing that go wrong in the valve body that would cause reverse to fail , I've read some things that tell me yes but am not sure . I'm not equipped to pull the transmission trying to be sure it's not somthing simple under the pan that i can fix .Like I said every shop around here wants their money for rebuild and are not willing to work with you and fix the problem instead of just replacing everything approach. I'm unemployed and have limited funds but abundant resources and enough experiance to do this if possible.

slow67

iTrader: (2)

Is there a difference between taking off in OD vs D?
The delayed shifting could be because of a low pressure situation, or even the PCM detecting an issue and delaying the shift.

Do all the other gears work?

99K2500Sub

No difference between taking off in d or od . all other gears seem to work .

slow67

iTrader: (2)

The next step (since you can't pull the trans) is to put a pressure gauge on it. Find a 0-300 PSI gauge and put it on the test port.

Its possible the low band is worn (not enough to engage reverse, but enough for engine braking in 1st). It also could be hydraulics, hard to tell without a pressure gauge.

99K2500Sub

Thanks I,ll look into getting my hands on a presure gauge and research what readings I'm looking for .

99K2500Sub

Bump for others advice ? Simply put with no preasure gauge to do checks based on all the above in this thread . Is there ANYTHING that can fail in the valve body to cause reverse to fail it catches slightly sometimes . I know I can change the 1-2 solnoid it's been checked and is malfunctioning . I would like to change it but not if I'm still going to have no reverse . Remember I'm limited to the valve body so if it can't be fixed from there I cant do it . I really wish I knew a private Trans guy here in Denver that would work with me .

slow67

iTrader: (2)

1-2 Solenoid won't effect reverse, there are passages across the 1-2 shift valve to let reverse work in both applied and released positions (of the 1-2 shift valve).

Jake's Performance

iTrader: (2)

You're getting advice from a very knowledgeable guy. He understands 4L80E hydraulics better than probably most professional big name builders.

Other than a shifter adjustment issue causing the manual valve to be mispositioned, your problem isn't in the valve body.

You could try lengthening the low servo pin but it's probably a temporary repair.

FLT

iTrader: (1)

Your getting very good advice here, it's time to find a trans tech you can trust in the Denver area. I would stop with your band-aid approach and get the job done right! you'll be money ahead trust me. Your going to find us professional trans builders on this site will give you the correct advice.

Chuck/FLT

Jays_SSZ28

iTrader: (2)

The 1998 4L80E in my silverado had 060,000 miles on it when I pulled it out of a junkyard truck.
When I installed it I found it had no reverse.
It also was pushing 550+ psi in reverse.

I pulled the trans out and apart, there was nothing major wrong with it but I replaced the band anyway, and added a pressure limiting boost valve.
After that it worked fine for a few months, then the reverse servo piston broke, because apparently it was slamming the case instead of applying the band (when I first got it).

I picked up a used servo assembly with a longer pin. It worked for approx 2 years after that, then it started slipping in reverse again. I put a longer apply pin in it again and it's been working for 4 years now.

The least you could do is take the valve body off and apply air pressure to the reverse feed hole. You should hear a dull thud, not a sharp bang. If you hear a sharp bang it's either the pin too short or the band worn. You could weld and grind the pin tip to make it longer. To check the length take the o-ring off the accumulator piston (inside the reverse servo piston) and put it between the cover and piston, with the return spring left out try to push the cover up to the case. The band is close enough if it gets tight right before the cover hits the case. Reinstall the o-ring.

Also break the filter open and look for garbage in there. If theres a lot you might want to consider a rebuild. If you found and fixed problems with reverse and the filter was somewhat clean, replace the boost valve. Or check for high pressure when you get it back together.

99K2500Sub

No doubt Slo67 knows his stuff . But why no mention of the deal Jaysssz28 came up with?
There is alway some part of the puzzle that can fail . Not to mention when you google 4l80e no reverse it's a very common problem with a range of causes and fixes .

I guess I,ll just junk the damn thing .

Jake's Performance

iTrader: (2)

I mentioned the servo pin above but if it was working and now doesn't, it's not because the pin got shorter. It's because the band is worn. It is designed as nonadjustable because there isn't enough material to allow adjustment. And that material went somewhere.Hence the" temporary repair".

stlled

I have a '99, chevy 2500 pu 4x4, 5.7 with a 4l80e. I am having a take off issue / and a shift issue, When I take off from a stop the truck will hesitate almost like your trying to take off with the e-brake engaged,you can hear the engine trying to go and gaining rpm but it does not want to move , only lasts for a second or 2 then will go to a normal acceleration with a shutter. if you hit the gas just right you can barley feel it, at highway speeds it does not seem to know what gear it wants to be in, it will go into 3rd from everdrive when the pettel is barley pressed then may go back to OD and the lock up seems to engage and disengage at will . Any Ideas im not really wanting to have the trans rebuilt if its a sensor
Please help
thanks