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6.5L Turbo Diesel 1992-00 6.5TD - Discussion forum for the 6.5L engine.

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  #1  
Old 04-07-2006, 06:57 AM
danbenili danbenili is offline
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Red face Transmission (4L80E) First and Second Gear Only

Hello,

This is my first Diesel and my first Chevy Truck.

My transmission only has First and Second Gear Only (no reverse, third or OD). I bought it this way, please don't ask why - I get enough grief from my wife.

I've done a lot of searching on the web and have found conflicting info on the root cause and what the fix would be.

I don't now very much about transmissions but my gut tells me that it is more likely an electronic or hydraulic problem rather than a catostrophic mechanical failure. But maybe this is just wishful thinking and am in denial about the possibility of replacing a sun gear, sun ring, sun shell, sprag or some other part requiring a rebuild (or close to it).

I bought the ATSG (Automatic Transmission Service Group) manual "THM 4L80-E" for this transmission ($25 download PDF).

In the troubleshooting charts they call out this specific condition "FIRST AND SECOND GEAR ONLY"

INSPECT COMPONENT FOR CAUSE
Solenoid B (311)
Stuck Off
Loose Connector
No Voltage to solenoid
Solenoid o-ring failure
no PCM signal to solenoid
2-3 Shift Valve Stuck

Quad Driver Module Failed

Possible Codes:
68 Overdrive Ratio
81 QDM & Solenoid B Fault
85 Undefined Ratio
87 Solenoid B Stuck Off


I was getting a code 87 and quickly (maybe hastily) went and replaced the 2-3 Shift Solenoid. This did not fix it.

While I was in there I should have checked the voltages to check for loose connecter, no voltage to solenoid and/or no PCM signal to solenoid.

I also should have checked the 2-3 Shift Valve

Does anybody know if I should see voltages if the truck is not running, but the ignition is in the "on" position and I put it in reverse or 3rd?

Any experiences that you can share would be appreciated. I'll post back with my results.

Thanks!

Paul

P.S. I bought a B&M Automatic Transimssion Drain Plug Kit #80250 to make future transmission fluid changes less of a hassle - in my opinion balancing a tray of hot tranny oil over your chest or face should be avoided

P.S.S. I may have posted this in the wrong forum.... should it go in the "2500HD/3500 HD Trucks & Drivetrain" forum?
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Last edited by danbenili; 04-07-2006 at 07:33 AM.
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  #2  
Old 04-07-2006, 07:55 AM
BobND BobND is offline
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I've OH'ed lots of slushboxes, but never a 4L80E.

A guy that rents property from me has a 1994 with the exact symptoms your's has.

We have not torn into it, yet, but from what I have been reading, the "no reverse" is a "red flag" for a "hard parts" failure, rather than an electrical or solenoid failure.

Reverse is supposedly all mechanically selected by the manual valve, and (except for pressure control), shouldn't suffer from a 'puter, wiring, or solenoid problem. It is likely the problem is in the DIRECT clutch, or associated sprag.

I'd be curious as to what you find out, if you get into yours in the near future, as it will be a while before the one we're dealing with gets checked out.
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Old 04-07-2006, 08:35 AM
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I had the same problem. No shift out of first till a very high rpm, then a slam-shift to second, and nothing else. My speedo went nuts as well.

It turned out to be a faulty output shaft speed sensor. there are two shaft speed sensors, one for input, one for output, and the computer uses them to determine clutch slippage. if one dies, the computer sees it, and forces a 'limp-home' mode. I dont think it lights the SES when it happens.

The sensors are like $40 at autozone, and its a 5 minute deal to change them.

Tim
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Old 04-07-2006, 08:42 AM
danbenili danbenili is offline
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Hi Tim,

My symptoms are a little different - no slamming etc. It drives normally but without reverse and won't shift into 3rd. It does sound like the sensors could be the culprit.

Did you have reverse?

Paul
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Old 04-07-2006, 08:43 AM
16gaSxS 16gaSxS is offline
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I'm with Bob, I had a 2 gear and reverse ok problem it drove me nuts it was something electrical , poor connection or short the exact problem was never found after much work it just went away. If you have a electriconic problem you go 2 nd gear only as a default. You can work through your codes. There are a number of componets that are can be changed if you drop the pan. If you change them all out it will cost serveral hundred dollars. (been there done it). If you have a honest and good transmission sho they maybe able to help. A local sho the owner check mine and drove it twice and he told me it was the electronics. Good luck keep us posted maybe someone that know these trannies can help you more.
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  #6  
Old 04-07-2006, 12:22 PM
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Cowracer Cowracer is offline
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Quote:
Originally Posted by danbenili
Hi Tim,

My symptoms are a little different - no slamming etc. It drives normally but without reverse and won't shift into 3rd. It does sound like the sensors could be the culprit.

Did you have reverse?

Paul
Yeah, I did, now that you mention it...

Still and all, its probably a good thing to take them out and at least check them. I checked resisiance through both of them and found them vastly different. I cant remember what the resistance of the good unit was.

tim
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  #7  
Old 04-07-2006, 01:42 PM
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JohnC JohnC is offline
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I'm voting with BobND. Reverse is purely mechanical, so no reverse is a mechanical problem.

First check for codes, but I'm betting you're in for some hard parts.

(sorry...)
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  #8  
Old 04-08-2006, 06:43 AM
redbird2 redbird2 is offline
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Unhappy no reverse

I would agree when we have one come in with no reverse we start by pulling the pan you will most likely find big pieces in the pan (NOT GOOD)

reverse mean hard parts failure it take comb of clutchs working togeather to make reverse.

I think its time for trip to trans shop or time to order a rebuild and install yourself, if it is a hard parts failure make sure you clean the lines out, I normally replace the coolers as there cheaper than the transmission to replace

good luck keep us posted
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  #9  
Old 04-09-2006, 11:04 AM
danbenili danbenili is offline
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Default Update-Valve Body Out

Thanks for all the replies and suggestions. I now feel like I'm on a mission.

I pulled the valve body out today. Transmission is still in truck.

Tranny oil could use a change but still has a red appearance with no burnt smell. No metal chunks or slivers in pan, just small accumulation of "silt" on bottom of pan - gone with one wipe of the rag.

Everything looks clean, no junk in the passageways. Looking up through to other areas of the transmissions - the gears that I can see all look good - nothing missing - sharp distinct edges.

Looking at the "Powerflow Chart and Shift Solenoid Pattern". Looking at what reverse, 3rd and 4th(OD) have in common, is the "Direct Clutch"...

I'd like to rule out the "First and Second Gear Only" Condition outlined in the ATSG manual as it points to rule out electronic malfunction prior to pulling everything apart (aside from the 2-3 Shift valve - which I checked and didn't appear to be stuck - pulled the roll pin, slid it out-bounced it against spring).

I think the transmission electronics expect rpms on the input shaft before you can test, I tried with the system on, but engine offf and couldn't get voltages to change on solenoid's A and B.

Anybody have tips on testing the electronic inputs to the solenoids? I tested the solenoids by putting juice to them and they "click".

Thanks,

Paul
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  #10  
Old 04-09-2006, 11:34 AM
BobND BobND is offline
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Be carefull randomly putting current to the tranny solenoids!

I'm not sure about the 4L80E, but MANY transmission solenoids have a diode built-in for voltage spike suppression, and if you power up the solenoid with reverse polarity, you'll blow the diode open, or short it out.
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