My speedo is reading 15mph lower than the actual speed I'm doing. I just got the car and soon realised that it wasn't right so clocked it with a friend. I've been told that someone may have had the needle of and put it back on again at a different point and that could be what the problem is.

Anyone have any ideas as this is annoying.

Thanks,

RMK




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1987 IROC-Z Auto (LB9)
Black/grey with kick *** looks

Mods
None yet as I just got it Tell me what to do to it and I'll do it though.

 

that's probably it if it's always 15 off. take it off, put it on and give it a try, it may take a few times to get it just right

 

Maybe you have some pretty serious gears in there!!

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'82 Firebird, dead stock, 9 bolt disc rear, over 200,000 miles and still going strong, more to come...

 

What my rear end gears? If they were different would that then put the speedo out?

RMK

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1987 IROC-Z Auto (LB9)
Black/grey with kick *** looks

Mods
None yet as I just got it Tell me what to do to it and I'll do it though.

 

I'm not sure, I would think the different gears would make a difference, but have heard that all the spedo's on thirdgens were calibrated the same. Anyone know for sure?

 

Changing tire sizes even changes the speedo's calibration. Not by too much though. I had a 3.23 rear end with 295/50R15 and at 31 mph (radar) my speedo said 30. Big deal, right? Well I changed to 3.27 rear and it's dead on. In my Elcamino I changed tires to a 205/55R15 from 215/70R14. Now it's about 5 mph off at 30. It says 35. I don't know if this could be your problem. 15 mph is a big difference.

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'82 Firebird, dead stock, 9 bolt disc rear, over 200,000 miles and still going strong, more to come...

 

The guy who had it before me had 225/50/16 tires on the front and the 245/50/16 on the rear. However I'm a little dubious as to whether that would make that much of a difference.

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1987 IROC-Z Auto (LB9)
Black/grey with kick *** looks

Mods
None yet as I just got it Tell me what to do to it and I'll do it though.

 

Yeah, I don't think that your problem is ratio. Try the needle changing thing. That might work.


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'82 Firebird, dead stock, 9 bolt disc rear, over 200,000 miles and still going strong, more to come...

 

don't mess with needle... the gears in the rear end have probably been changed... you need to find the correct gears for the speedo calibration located in the trans tail shaft...

zroc