Tach/Speedo/Transmission Problem - Chevrolet Forum - Chevy Enthusiasts Forums

Tach/Speedo/Transmission Problem


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  #1  
Old  November 30th, 2007, 3:24 PM
Tach/Speedo/Transmission Problem

Hi everyone,

This is my first post on this site. I have a 95 Suburban 5.7 Ltr. Automatic transmission, about 125K miles. Yesterday I came home from a week long 700 mile trip. I parked for about 10 minutes, then got in to drive home. The first thing I noticed was that the little orange indicator that tells you what gear you're in was gone. As I started to drive I noticed that both the Speedo and the Tach were not functioning at all. All other dash lights and gauges were working. Then I noticed that the transmission was not shifting. It sounded fine, but would obviously start out in a higher gear and stay there, no downshift or upshift. The vehicle had been working flawlessly to that point. Today I checked all the fluids and fuses, no problems there. This afternoon, as I came up to a stop sign, everything clicked back on and all is now working as normal. I assumed that some kind of sensor or speed controller had gone out, but my mechanic says that the speedo and tach do not run from the same place, and he is scratching his head. It didn't help that the truck healed on the way over to his shop.

Any ideas?

Thanks in advance.

  #2  
Old  December 3rd, 2007, 1:07 PM
RE: Tach/Speedo/Transmission Problem

craziest thing, my truck dida similarthing. i have the 350 with the 4l60e. I was hauling my buddies 63, did just fine over the hills and another hour or so till i stopped at the gas station. i noticed my tcase leaking, but hadn't noticed any problems, so i decided to deal with it when i reached the destination. As soon as i was back on the road, the speedo and tach went effin haywire... si i pulled over and changed the fluid in the tcase on the side of the road, checked the trans fluid, everything seemed fine, no more leaking, nadda, but when i got on the road again, then gauges just quit, then OD slipped and crapped, then 3rd followed shortly after that. That was a month and half ago, it hasn't healed itself, in fact 2nd has gone since then, although it will get second for a few minutes when i first start off, then it goes again. This leads me to think that it might be the electronic controls... but no money to do anything about it. it's quite depressing. I don't know what to say about your's, but maybe you can help me out?

  #3  
Old  December 3rd, 2007, 1:30 PM
RE: Tach/Speedo/Transmission Problem

So far, no one has had any idea about this. I was hoping for more input on this site, but it's a strange problem. We don't have any leaks or other problems, it seems electronic. It was used again yesterday, and everything is still working. Time will tell I guess.

  #4  
Old  December 3rd, 2007, 1:43 PM
RE: Tach/Speedo/Transmission Problem

if its like a ford take the speed sensor out of rearend check and clean on ford ther is one bolt that holds it in rearend housing hope i was of some help

  #5  
Old  December 3rd, 2007, 1:46 PM
RE: Tach/Speedo/Transmission Problem

also instrument cluster could be going bad

  #6  
Old  December 3rd, 2007, 2:56 PM
RE: Tach/Speedo/Transmission Problem

I suspect either the alternator is on its way out, the battery has an intermittent internal short or a ground wire has a bad connection from the frame / chassis to the engine - in that order of likelihood. Tachs and speedos on those are driven by little motors in the gauge cluster. They are picky about voltage levels. They tend to bounce around or fail in low voltage conditions. The transmission needs full electrical power to function. Alternators tend to go intermittently, and then fail totally. Electrical components on their way out tend to rear their ugly head when hot. It makes sense that after the long drive and then the heat soak while off, coupled with the strain of starting the engine, that the problem showed itself. These vehicles are known for eating up alternators. On the other hand, you don't want to just throw parts it and over spend to fix it. Here's what I would so (and have done in similar situations - with success) I would check / improve the ground connection to the engine (neg. lead on battery to the engine) and get a new battery if the one in there is close to its age deadline. If it repeats the symptoms, and no check engine codes are occuring, have the alternator checked or just replace it with a rebuilt one from a parts store.

  #7  
Old  December 4th, 2007, 7:24 PM
RE: Tach/Speedo/Transmission Problem


ORIGINAL: Rivernut

I suspect either the alternator is on its way out, the battery has an intermittent internal short or a ground wire has a bad connection from the frame / chassis to the engine - in that order of likelihood. Tachs and speedos on those are driven by little motors in the gauge cluster. They are picky about voltage levels. They tend to bounce around or fail in low voltage conditions. The transmission needs full electrical power to function. Alternators tend to go intermittently, and then fail totally. Electrical components on their way out tend to rear their ugly head when hot. It makes sense that after the long drive and then the heat soak while off, coupled with the strain of starting the engine, that the problem showed itself. These vehicles are known for eating up alternators. On the other hand, you don't want to just throw parts it and over spend to fix it. Here's what I would so (and have done in similar situations - with success) I would check / improve the ground connection to the engine (neg. lead on battery to the engine) and get a new battery if the one in there is close to its age deadline. If it repeats the symptoms, and no check engine codes are occuring, have the alternator checked or just replace it with a rebuilt one from a parts store.
Thanks Rivernut, that makes the most sense of anything I have heard yet. I checked today and found that the battery is pretty old. We bought this thing used a year ago, and it's primarily used to haul a church youth group around. I am going to replace the battery and clean up all the ground first, then check the alternator if the problem returns.

Thanks to everyone who has posted on this.

  #8  
Old  December 5th, 2007, 2:19 PM
RE: Tach/Speedo/Transmission Problem

Update: when I went to replace the battery, i found that the negative Battery cable was only finger tight(!) I'm amazed I didn't have a problem sooner. So, new battery, clean tight connections, alternator seems to be working, now we'll see if the problem comes back.

  #9  
Old  December 6th, 2007, 12:42 PM
RE: Tach/Speedo/Transmission Problem

Isn't it nice when it's something simple? You can damage an alternator if it is run without the wires hooked up. Good thing you got it before that happened.
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