Important! Speed sensor or faulty instrument cluster?

[joatrash]

*updated* Speed sensor or faulty instrument cluster?

Hello all!

My name is Joe and I hail from Sweden. Been lurking here for a bit, getting to know the place. I'm currently shopping for my first Vette... looking at '88s cause that seems like a good year (and I love the 80's feel).

I'm looking at a ride tomorrow that is in pristine shape except for a couple of problems and I thought I'd get some advice from y'all before I see it and start haggling over the price.

1. She's got the sporadic non-working seat/door lock problem, which I assume is due to a worn wire under the seats. (Got that pretty much covered.)

2. (and this is the harder one) She has a faulty speedometer.

The speedo lights up, but doesn't begin working until she's been driven a couple of miles. Then it starts working. Sometimes while driving the speedo will drop to "0". If it's working and you shut the engine off, chances are it'll NOT be working when you start her up again. It seems to me that this could be a heat-related issue (i.e. either the tranny gets hot or the digital cluster does and a bad solder or joint will then expand and make contact.)

Searching the forum seems to suggest the dash panel or the speed sensor is at fault. But which is it most likely to be?


Also... the car is an '88, with a TH700 (not sure which axel ratio). While searching for a (potential) replacement speed sensor, I have found that there seems to be TWO different models... but every place I look only seems to have ONE available. Have the original two been consolidated into one "general" replacement?

Any last minute help or advice on the problems (or parts) would be great. With any luck... I'll be driving a Vette home tomorrow!

Thanks!

/Joe F
Sweden

 

[gmjunkie]

Hello all!

My name is Joe and I hail from Sweden. Been lurking here for a bit, getting to know the place. I'm currently shopping for my first Vette... looking at '88s cause that seems like a good year (and I love the 80's feel).

I'm looking at a ride tomorrow that is in pristine shape except for a couple of problems and I thought I'd get some advice from y'all before I see it and start haggling over the price.

1. She's got the sporadic non-working seat/door lock problem, which I assume is due to a worn wire under the seats. (Got that pretty much covered.)

2. (and this is the harder one) She has a faulty speedometer.

The speedo lights up, but doesn't begin working until she's been driven a couple of miles. Then it starts working. Sometimes while driving the speedo will drop to "0". If it's working and you shut the engine off, chances are it'll NOT be working when you start her up again. It seems to me that this could be a heat-related issue (i.e. either the tranny gets hot or the digital cluster does and a bad solder or joint will then expand and make contact.)

Searching the forum seems to suggest the dash panel or the speed sensor is at fault. But which is it most likely to be?


Also... the car is an '88, with a TH700 (not sure which axel ratio). While searching for a (potential) replacement speed sensor, I have found that there seems to be TWO different models... but every place I look only seems to have ONE available. Have the original two been consolidated into one "general" replacement?

Any last minute help or advice on the problems (or parts) would be great. With any luck... I'll be driving a Vette home tomorrow!

Thanks!

/Joe F
Sweden

I think you will find the problem where the cluster plugs into the harness in the dash!!(Purdy Common) Remove the cluster, Inspect and Clean connections allot of times is all it takes!!

 

[Paul Higg]

Hey Junk, one question not related to this post. Is that you in that picture? In the red Vette? If so, what is all that smoke? Were you smoking the tires? What year is that Vette?

Just curious.

BTW - Thanks for your help on the ASR, I am going to troubleshoot it this week and remove the tires to clean the sensors, carefully.

 

[gmjunkie]

Hey Junk, one question not related to this post.1.Is that you in that picture? In the red Vette? 2.If so, what is all that smoke? Were you smoking the tires? 3.What year is that Vette?

Just curious.

1.Yeah,I'm a movie Star!! (Adam Sandlers movie"Mr Deeds")

2.Yeah, and Loco Weed!!!otflotfl

3.2003 Z06 Vert,I riped the top off myself!!!!

Would you like me to Autograph and send you a Photo?????

 

[Paul Higg]

A face behind the name! I was rolling on the floor this morning Junk when I read your replies. You sure you weren't a comedian too?

Good photo. 'Cept, how'd you balance that rotor on your head? Wasn't it heavy? Or is that a halo for helping everyone?

<grin>

 

[joatrash]

OK, let's get back on topic.

I am now the owner of a red 1988 Vette! As I said, the speedo is basically dead (lights up, but shows "0" for the most part... sometimes shows signs of life but doesn't give the correct speed). Also, the digital TRIP METER is dead... doesn't count upwards.

I took out the cluster, but all the solder joints looked OK. There was a teeny, tiny bit of oxidation on the pins that really shouldn't affect contact. I sprayed them (and the connector sockets) with electrical contact cleaner. Just to be sure, I re-soldered the connection pins associated with speed with some fresh material as best I could... even if they looked fine to me. (Not that I'm any sort of electronics expert...)

I also noticed a sticker on the cluster that was dated 1990, so it must've received some care then. Another thing... there were some strange air bubbles on the surface of certain processor chips and other components, which was kinda odd.. some kind of protecting coating?

Anyway... the problem is still there. I'm starting to wonder if it isn't the speed sensor after all. The only time the speedo shows signs of life seems to be at certain RPMs.. possibly while the tranny is in overdrive. (The analogue odometer DOES work, however... and I think the cruise control works too, but I'm not certain.)

Oh... and I might have access to a spare speed sensor from a 1990, with the same axel ratio, and... would that fit my 88? I may also be able to get hold of a digital cluster from either an ´87 or a ´90 to test with.


...thoughts?

 

[Paul Higg]

Joe, it might just be a speed sensor. Did you pull any codes from the ODB plug? It will definitely tell you if it is a speed sensor. Do you know how to pull codes with the ODB plug and jumping pins and reading what the codes say on the speedo? Do you have an FSM? If not I can help (a little as I have a 94.) Someone here with an 88 with an FSM will tell you how to pull codes, what they mean, and how to fix it. I would post and ask how to do this because our years are different.

Paul

 

[joatrash]

Paul, thanks for jogging my clogged mind. It didn't enter my head to check for error codes. (In my defense, I've been driving a 73 Firebird for the last few years...)

It's been a while... but I used to know how to pull the codes with a paper clip on my old '87 Trans Am... I'm guessing the procedure is similar or identical. I'll get on it!

 

[Paul Higg]

You're welcome. A paper clip will work fine. On my 94 I jump ins 4 and 12. That's fourth from the left on the top and fourth from the left on the bottom.

Lemme know what codes you get and maybe the FSM may be close, if not someone with your year will have the DTC's.

Good luck.

Paul

 

[joatrash]

Darn it! The one time I was HOPING for an error. Just checked the ECM... clean as a whistle... no error codes.

I was rally hoping is was the sensor, 'cause that's a pretty quick fix in my current situation.

Hmm... the speedo WAS working just before I shut her off (driving around a parking garage). Will the error code clear automatically if the problem ceases to exist?

 

[gmjunkie]

Darn it! The one time I was HOPING for an error. Just checked the ECM... clean as a whistle... no error codes.

I was rally hoping is was the sensor, 'cause that's a pretty quick fix in my current situation.

Hmm... the speedo WAS working just before I shut her off (driving around a parking garage). Will the error code clear automatically if the problem ceases to exist?

I'm purdy sure you'll need a Scanner to get to any speed sensor codes!!Theres some areas in the ECM that you can't get at with a paper clip!

 

[joatrash]

Ahh... Well, my "goto guy" for transmission woes has a diagnostic tool (and sensors available) so I'll run the car by him tomorrow morning and see what happens.

 

[joatrash]

Went by the mechanic today and borrowed his scanner. for some reason, the darn thing refused to connect to the car... got to the "connect the cable to the diagnostic outlet" stage and then nothing. Weird.

However, my mechanic asked me if the Cruise Control is working, which it IS. He said that if the CC works, then the Speed Sensor is working too.

So it looks like my cluster might be the culprit after all. I think I'll grab a refurbished one off ebay and see it that solves my problem.

Thanks guys,

 

[Paul Higg]

Keep us posted. Others may learn from your experience.

Paul

 

[keremarsan]

Hello from Istanbul / Turkey

1) Speedometer is faulty
2) There is Drive attached to outgoing part of the transmission shaft
and driven gear with specific teeth number attached to speeddometer , the driven is green , the driver gear is red ( attention to number of teeth on geras )
The driven gear is attached to speedometer ( at the end of the transmission THM700 R4 also named 4L60 )
The driver gear is mounted on the outgoing shaft of the transmission , same level of speedometer.

If the problem is speedometer, I think easy take it off and change )
If the problem is green gear ( on the speedometer ) you can easly change it when taken it out

If the problem is red gear , you must to complety take away the exhaust , driveshaft and take away the extremity part of the transmission ( this part can be separated from main transmission body )

The drive gear ( red , on the trans shft ) can borken ( I had this problem also ) before completly desintegrated, some time speedo works , sometimes it does not .

Some info for THM 700-R4 below but I am not sure :

Part number , Drive gear
number of teeth colour
A 8628793 17 Red

Part number number of teeth colour
X 25522491 42 Green


Hope it helps

bye

 

[keremarsan]

I want to say :

the reason is I think option 1 or option 2 ( I think it can not be understood on my first post )

 

[joatrash]

Hey guys!

I got my new instrument cluster installed yesterday and now everything works fine! (and here I was getting used to judging speed by the revs...) Think I might go over the old one and try to restore it myself... can always use a spare, haha.

Thanks for all the help!


/Joe