96 GMC K1500 4WD

A slipping automatic transmission is the first sign of serious internal troubles heading your way. More often then not this condition will lead to a complete transmission overhaul. Here is an email question about this common condition as well as a good example of the likely symptoms.

A visitor writes, Thank you for your website. You have pushed me to further educate myself about the mechanical side of cars. Here is some information about my trucks problem before I take it to a transmission shop or general car repair place.

I have a 96 GMC K1500 4WD. I am having slipping automatic transmission problems.  If I drive like grandma and ease up to Highway speeds I can feel all gears engage and pull, 1, 2, 3, and 4. If I take off fast From a stop or if I’m driving 6Omph and stomp it for passing gear I can see the Rpm gauge surge to 3500-4000 and hear the engine running great but no power at The wheels.

I have to let off the gas for the transmission to begin to pull again as it falls back to the higher gear. My auto scan tool from Actron says I have no codes set in the computer. I have purchased the all data online auto repair manuals for my trucks.  I have gone through the related info to become familiar as possible with this problem. After a physical inspection, my fluid level is correct and no burnt odor. I have no leaks, the wiring harnesses and connectors look fine.

Because I do not have a code, can I assume that my, vss, tcs and other related sensors have no failures or intermittent shorts? My truck has over 120,000 mi on it. From my research I’m thinking the problem is inside the slipping automatic transmission itself (clutches slipping etc.?)

I would greatly appreciate any advice you could give me based on your 25yrs of experience in this area. I am a service tech in the industrial laundry machinery business. I have a mechanical/electrical background but not in the auto field. As they say, I know just about enough to get into trouble.

If you think the slipping transmission needs to be replaced, would you suggest any upgrades I should ask for during the rebuild? By the way, I’ll be letting the shop do the removal and reinstallation as well so any warnings in this area would be great.  Thank you for any help you can give.

Answer to slipping automatic transmissions

96 GMC 4x4

With the high miles on your 96 GMC K1500 4WD and the age of the unit it sure does seem that internal problems would be the most likely cause of your problems. Worn lip seals allowing fluid pressure to bypass the clutch apply pistons often create a slipping condition.

This can be confirmed with a line pressure check with a mechanical gauge connected to the test port. A stall speed test is where you power brake the vehicle (apply the gas and brake at the same time) and will verify the pressure bypassing condition.

In most cases the only way to solve this is with a complete transmission overhaul were you replace all internal seals and wear items like clutch disks and bands. Also sometimes when the trans has been slipping for a while new friction plates are required to be replaced do to scoring on the face of the hard metal discs. The only way to determine the amount of internal damage is with a tear down and inspection.

As far as removing the transmission, you mentioned your Chevy truck is a 4×4. A good thing to check when you get the truck back is the transfer case seal. The shop will have to separate the transfer case from the back of the transmission on your model. They make a gasket for this sealing area. Often shops will just use rtv silicone. This is not as long lasting as a fiber gasket and tends to leak sooner or later.

Find more auto repair information and all the latest post to the auto repair information blog.

Repair diagram

Thanks for the response about online auto repair manuals. I understand what you mean about All-Data and Mitchells in reference to their auto repair information quality. I had looked at the two, and tried the “demo” on All-Data which actually let me view (as you know) actual info like I would get in a subscription to a particular vehicle.

The one downside I [thought] was when I looked up DTC’s and test procedures for them it always referred to the Manufacturer or Dealer type scan tool. Even though it listed, in one place, a choice of tools (manufacturer/dealer, other, etc) to view this info for, it said that info was not available for any except the Manufacturer style [dedicated] diagnostic tool?

I got to this by clicking on the online auto repair manuals “Honda demo” since my daughter has a Honda (older than the demo, but I was looking to see what all it included). I then clicked on Powertrain Management and then Computers and Control Systems all these along the left column.

Then I clicked on Reading and Clearing Diagnostic Trouble Codes under “Testing and Inspection” in the right column. This brought me to a page which had links to With Manufacturers Scan Tool, With Generic Scan Tool, Without Scan Tool and “Clearing Diagnostic Trouble Codes”.

If I click on Using Generic Scan Tool, I get the page saying the Manufacturer doesn’t provide auto repair information for this. While it may be painfully obvious to most, I wasn’t sure the info would all work with a tool like the Actron CP9180 or the AutoXray AX6000 or such.

You raised another topic related to online auto repair manuals. You said you think the Actron CP9180 will generally do the job most folks need for DIY auto repairs.

I had been looking at such tools as the Auto Xray AX7000 and Auto ingenuity laptop scanners for their ability to do “manufacturer specific” and “other than powertrain” code diagnostics. Are these not generally a good return on money (bang for the buck) for the DIY car repair guy? I really appreciate your time and thoughts.

By the way, I found that the demo on the Mitchell site, while it showed some good examples of graphics, [I found] less than useful to determine whether I liked the format of their site or not. Sorry if I am rambling I know you are not necessarily an advocate for one online auto repair manuals over the other, I just get off on rants.

Thanks again for the response
George

Online auto repair manuals

Hi George: You make good and true points about online service manuals. They are directly ported from the manufacturer. In extremely complicated diagnosis this can leave the diy auto repair guy out in the cold.

The results you experienced with the Honda vehicle could be different for subscriptions to other make vehicles. The information supplied to all-data depends on the ability of that manufacturer to co operate. And some company’s furnish more information then others.

But there is no better choice for auto repair information that I know of. In fact the online professional automobile manual is far seperior in the way it represents repair diagrams and troubleshooting tree charts. Take a look at this auto repair manuals video for a common repair to see what I mean.

I also find that in some cases I can put on my thinking cap and break out my multimeter to get past a step that they say requires a manufacturer scan tool. Or worst case scenario skip a step in the troubleshooting diagram and see where it leads me.

Diy auto repair scanners

As far as the Actron 9180 it is only about 140$ and does include a snap shot mode and an o2 sensor test. So I consider it a good value. But a laptop scanner has many advantages over it. The main one is the amount of data the laptop car scanner can display at one time.

I do not have a laptop but we do at work. We use the elm scan 5 blue tooth. It is very slick but also can get stuck on some manufacturer specific codes. I find these codes are rare and generic codes are much more common. But the auto repair world is like a box of chocolates ” you never know what your gonna get”

Yes I have told the mitchell people they need to get up to speed and offer a demo like all-data. The e-auto repair system is very similar to alldata it just harder to dig out the information your looking for. But is also ported from the car makers manuals.

Nice talking with you and good luck with your auto repairs.

Mark

Auto Mechanic

This was an auto repair information blog when I started it two years ago. Things stayed on topic, but changed a little when gas prices started to climb in early 2008. This is also when I purchased the water 4 gas systems and decided to share the details of my project with visitors. In today’s post I wanted to return to the original reason I started this blog. And that was to supply auto repair information for people that like to fix their own cars.

After fielding many questions over the last couple years on my car repair help page I have noticed one very common piece of advice that I continue to dispense. It also happens to be the first step in almost all of my automotive diagnosis procedures that I personally use. And this is the visual inspection. It is very common that I will uncover the cause of the car problem by simply performing a thorough visual inspection.

Auto repair visual inspections

I’m going to provide some examples of what to look for, and some of the most common things that I have found. It would seem that a visual inspection during these winter months are more important then in the summer. But regardless, I perform this procedure as a quick first step in automotive diagnosis no matter what the weather is like.

My first example actually happened yesterday and got me thinking about how I should share this with website visitors. I was working on a 2006 Chevrolet 3500 series van. The driver’s complaint was the check engine light was on.

I scanned the vehicle and found a map sensor code. The first thing I did was perform a visual inspection of the map sensor, the connector and its wiring harness. The first thing I noticed was little black chips of plastic that were laying on the intake manifold. These were obviously pieces from the conduit that protects the map sensor wiring harness.

I followed the harness back and found a spot where a rodent had chewed through not only the protective conduit, but also completely through the ground wire for the map sensor. There was no need for any scientific check engine light diagnosis because it turned out just to be a quick repair of a single wire.

Auto repair diagnosis

Another example of diy car repair diagnosis. My nephew called me from up north and said that he had an ABS light on. I live in Florida now, so I was not able to work on his vehicle. But I did notice in the news that they had recently gone through an ice and snowstorm. So I walked him through some simple steps to do a visual inspection on his own car.

I explained to him where the wheel speed sensors and wiring harnesses were located. When he poked his head around the wheel, he noticed a 15-pound ice burg was stuck and pulling on the wiring harness to his left front wheel speed sensor. Since my nephew is not very mechanically inclined, he was forced to take it in for repair.

But he was armed with the information to provide the service center that saved him Diagnostic time, and also the down time of his vehicle. The weight from the ice and snow that collected on the wiring harness broke the wires where they attach to the sensor head.

Auto repair safety

My nephew would have liked to continue to drive around with the ABS light on as opposed to spending the money on car repairs. In fact, I had to talk to his mother to force the repair to be completed. Antilock brake systems are a fantastic safety feature. During winter weather with ice and snow a properly operating ABS system may save your life or at least prevent damage to your vehicle or other drivers.

In closing I would recommend that when ever you have a warning light on your dash fix it. Either using do it yourself auto repair techniques or a car repair shop. And take a few minutes to perform a thorough visual inspection that is related to your problem. External damage by rodents and road debris can be highly visible and solve your car problems.