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Proud owner of Arizona '93 K3500 6.5 turbo diesel 4x4 crew cab that still has factory plastic on carpet.

C

capt.marvel49

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Need help with local shop's disastrous attempts to replace 4L80E tranny.. After three months and three failed replacement tranny's (all of which either shifted hard or failed to stay in fourth gear, or some combination thereof) they don't seem to know what to do. Help!
 
If you are in Arizona look up Allstate Transmission in Phoenix. Jeff bought the place from his dad and they took care of a few 4L80E's behind my 6.5TD's.

allstatetransmission.net

The Best Transmission Repair Shop in the Phoenix Area

We diagnose and repair your transmission with the best customer service in the Phoenix area. Competitive prices and honest service make us the best.
allstatetransmission.net

As to shifting hard or not staying in 4th. The Service Engine Soon light is a present for a bulb check only. Check codes as transmission codes will store without turning the light on.

Brake switches are famous for, well, braking. They also control the TCC unlock.

The TPS on the injection pump being faulty or out of adjustment could be one cause of harsh shifting.
Probe the TPS wires with a GOOD DVM ignition on. You want 0.5V or slightly more on two of them at idle (key on engine off) with the cold start solenoid disconnected. Make sure you have set the idle and high idle RPM before messing with the TPS.

So can a cracked RPM sensor where you would expect a distributor to go on a gasoline engine. Further the 1993's I had from Arizona, in Arizona, would have the insulation fall off the transmission input RPM and output RPM sensor wires. Look at the wires coming off the sensor and where they join into the main harness for this. 2 wires and they short out with no insulation.

A good scanner can show you input RPM etc to help troubleshoot this.

Four RPM sources for your confusion: Alternator for tach only if equipped, engine RPM, and two RPM sensors on the trans. The Engine RPM can fail and tach works fine...
 
Welcome to the forum @capt.marvel49 I'm no tranny expert or anything close but I do recall our trans expert resident @THEFERMANATOR saying about some of the differences in the valve bodies on them and changes that were done over the years. yours being an early 4L80E (pre94) used a different valveing than the newer ones. it's possible the replacements they used might have been like most all other auto parts reman parts where they like to do a one part fits all thing which never works right again once replaced with the old core gone. A good trans shop will know this and the "parts changer" shops just install whatever arrives from the parts delivery!
 
Thanks a lot for the responses. I had reviewed a number of THEFERMANATOR's threads before joining and they were most insightful. I have an inquiry into the shop regarding the replacement tranny's (three so far) year of manufacture and will report back as soon as I receive that info. After suggesting that the shop simply have my original tranny rebuilt they revealed that they had relinquished it (without my consent) as a core. They don't seem to realize that 91-93 tranny's are unique, so I expect that I will need an expert's input in that regard.
 
The shop might not know the year they were made, but something they can look up in their supplier's application guide would be if the tranny that they show to fit your truck is also the same listed for a 95 truck with the same specs. if their supplier shows the same tranny, then there is your issue. they most likely will show a different trans for anything 96+ due to the OBD1 and OBD2 systems. I'm sure the shop WW mentioned can find the issue and get you fixed up, but would also void any warranty you have with the current shop.

you can take it to the shop WW mentioned explaining the situation your in and have them go over the truck checking to make sure everything with the engine side of things are up to spec ruling out things like the TPS sensor, voltage, and wire connections that could cause issue. then once it's deemed a problem with the trans, go back to the shop who did replacement trans for warranty. BUT mention nothing to that shop the fact you have taken it to another shop. there was a fellow member here who had a similar experience and had taken to another shop who did some repairs on the truck not the trans, he told the trans shop what he did and they immediately refused to warranty anything.

ether way you go, if the shop who installed the trans is still working with you and willing to warranty the trans, continue to work with them getting it right. The auto parts "one size fits all" senario I mentioned might not be what's happening here and there is something going on alike WW said. Might even be a loose or left disconnected ground wire somewhere they are able to find and fix for you at no charge
 
Welcome to the forum 49.
Could You please get a several pics of this truck ? To hear of one in such pristine condition is rare, if at all.
Maybe we could smell that new/old stock truck smell that it came with from the factory. 🤷‍♂️🫣😹😹😹
 
Thanks again for the input. I ordered my '93 truck new from the factory and instructed the dealer to leave the factory plastic on the carpet, where it remains. It has always been garaged, has it's original paint in excellent condition (except for the driver's door, which was replaced when a doe ran into it at the crest of Wolf Creek Pass), and its grey cloth interior shows virtually no wear. It is a dark blue/green color and has a long bed with a factory liner. It has 175K pampered miles and has been extraordinarily reliable until this tranny fiasco.
If my recollection from reading THEFERMANATOR's posts is correct, attempting to put a '94 or later 4L80E tranny into a '93 truck is the equivalent of trying to force a square peg into a round hole, and will result in hard shifts, potential damage to the tranny (and truck), and other problems, all of which seem to have taken place with the shop's three attempts to replace my now missing original tranny (which, incidentally, I had requested that the shop have rebuilt before discovering that it had been sent off as a "core"). The shop is in the process of making its third warranty claim and appears to be in denial about the need to use a compatible (91-93) tranny, and will continue t repeat their mistakes, and it appears that I will have to put my truck in storage while they try to figure out what to do. I now need specific advice/instructions to gently guide the shop in the correct direction. I was hoping that THEFERMANATOR would chime in on this.
Regarding photos of my truck, I have several on my phone, but have not yet figured how to post them here.
One last thing - In July I was in the process of delivering the truck to my nephew in Wisconsin then the tranny downshifted to third gear and would not upshift to fourth. After checking the fluid, which was clean, I was able to trick it into upshifting into fourth by turning the ignition off and on and made it back to Flagstaff from Albuquerque and told the shop that I suspected an electronic versus a mechanical issue. They insisted that it was a mechanical problem and after over $7K and three transmissions I am now told that it will take at least six weeks to locate another transmission. Go figure.
 
Below the reply box there is an attach files rectangle.
From Your phone, Tap that rectangle, choose photo library.
I always tap one pic at a time to make sure they upload to the this site okay. After it gets uploaded then tap the insert button within the pic; choose full image, pic will go to wherever the curser had been left in the reply box.
After typing in a reply, I always tap the return button on my type page in my phone. That drops the cursor a notch, then go to the pic and tap insert/full image and then the return button again, then back to upload an image, tap, after it is uploaded, tap the insert and image will again appear where the cursor was left. Repeat as often as necessary.
I think each post will hold up to five images, then have to go to the next post box after tapping the post reply button on that post.
 
capt.marvel49 said:
after over $7K and three transmissions I am now told that it will take at least six weeks to locate another transmission.
Click to expand...

Where are you, pickup, located?

Call a GM dealer parts department and get price and availability of a transmission, including core cost, via your VIN.

You spent $7K and either get results or fight for a refund including taking them to court. Breach of warranty and loss of use: present them with cost to rent a 2500 pickup if yours doesn't get fixed.
 
Both in Flagstaff, AZ. Trying to avoid the legal route, for the time being.

Will call a Chevy dealer and check on availability of a tranny, but not sure they appreciate the subtle differences. between the years.
 
capt.marvel49 said:
Both in Flagstaff, AZ.
Click to expand...

Have you had any luck checking the TPS and brake switch as mentioned above? A combo of the TPS being out of adjustment and/or bad brake switch could be hard shifting. At the minimum pull codes.

If this hasn't been fixed I would suggest you get them to the shop I recommended in Phoenix. I would ask them about any deals they can do for towing, maybe you know a buddy with the equipment to get them there, etc.

You don't want to attempt driving them there.

Then present the shop with the estimate for repair including towing down there.

If you don't want to go to court to get your money back, well, write it off, leave a bad review, But at least use the damn good shop to get them going.
 
Thanks for the advice. So far we are on transmission number four after the local shop, in desperation, had the local Chevy dealer check their third installation only to be told that the transmission was defective.
It appears that the transmission shop in California (TRC) keeps sending the local shop post ‘93 transmissions without advising them of doing so. At least two have promptly failed.
As my truck’s original transmission was sent to TRC as a core months ago and cannot, apparently be found, I suspect that TRC is treading water hoping that the local shop would convince me that hard shifting and repeated transmission failures are normal.
As the assistant manager who has been assisting me is a friend, and as he has tried, repeatedly, to get TRC to provide an appropriate transmission without success, I am reluctant to immediately seek legal recourse as the local shop continues to try to make things right. I have been feeding my friend the Fermanater’s advice and he seems to be listening, but no amount of that will cure incompatible transmissions. So, I wait, for now.
John
 
if the shop is working with you and their supplier is the one sending the defective or incompatible units. it might be worth something for the shop to get an ok from their supplier to send the current trans off to an actual rebuilder to have it inspected to see what the issue actually is. if it's simply an incompatibility issue with post 93 vs pre, the rebuilder can possibly correct the issue by replacing the valve body or other things making it "the right one for your truck" all the while the shops supplier paying for that to be done. it might come out if this that the supplier would learn not all 4L80E's are the same! and then that knowledge would make them a better supplier on top of making a better rap for the shop using them too. a sort of win-win-win situation for you, the shop, and the supplier.
 
If my reading of the Fermanator’s posts are correct, modifying a post ‘93 tranny to make it work would require, among other things, installation of a 40 tooth reluctor wheel as well as modifications to address the lack of an output speed sensor, a different wire harness, a change of valve bodies, addressing the different signal requirements from the transfer case to enable shifting into 4WD low, and installing a TCM that will not instruct the force motor to make a cleaning cycle every ten seconds and which otherwise sends the correct signals to the later transmission. I may have missed or misstated some of the necessary modifications and, I’d so, I apologize. In any event the above changes (and any others I may have missed) seem to be why the Fermanator strongly recommends rebuilding the original ’93 tranny.
John
 
if I'm not mistaken, your truck is a 93 so the factory TCM will have the instructions in it for force motor clean cycle. others might know, I wouldn't be able to tell, but can the physical appearance of the trans be identified on the case whether it's for a 93 or if for a newer year? like having the port for the second speed sensor and what not.

I know were just guessing on the fact the trans sent to the shop is compatible for your truck or not. it might be the right one and have some sort of internal issue the supplier keeps repeating on their rebuilds and not realizing it. can also be something in the truck causing things. something a shop that specializes in transmissions would most likely find and report back to the shop that is replacing them. it was just the thought of the shop that did the replacement could work with by them bringing in a "third" party to pinpoint what's happening.
Lord knows I've been in situation where new parts were installed and still it doesn't work right or even worse than before it was even worked on. sends me scratching my head and grasping at straws. Every shop at sometime or another will get at least one vehicle they can't figure out even after throwing the book at it where they need help!
 
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