In an 89 IROC - Do you need to change the speedo gears?

no

Okay.. then why when I've gotten 2 different 240kph speedos from Daz do they both read 10 kph high?

I put on in my 85 that had a 140 speedo and it read fine with a GPS and with someone letting me know that was behind me. Maybe the cable is just worn, streched or kinked somewhere and throwing it off

Hmm okay.. Tested both with a GPS and they're consistently reading 10 kph too fast. I'll check the cable

maybe it was fast with the old speedo too.if it is its the speedo gear

that could be another issue i forgot to mention.

maybe your tires are to big

Speedo on my 90 and my 92 were both out stock

Sorry Hawk I don't really understand what you mean there. Can you re-phrase?

@Daz

Possible, but unlikely. Seemed like the 180 worked just fine til the needle got busted off ..

@Mr. B

Same size as they've always been .. still tryin to figure it out

simply put, the 240 speedo in my 1990 was out from the day I got it, same with both my 92's, speedo would say i was doing 100 but gps would say around 90, with my T56 swap I am running a Dakota Digital so the speedo was now been corrected to match my 4:10's, but in stock form it was out

Just put in a new "correct" speedo gear.

Speedo in my TA is out as well....or the police radar was out.

Lucky I have an honest face.

Yeah I've had the exact same problem with both speedos I've tried. Would love to go digital but not entirely in the budget right now.

Perhaps I'll take Project's suggestion and just try another speedo gear. Couldn't hurt at this point

Or just know that its 10 out and call it a day, GM sux with there Speedo accuracy, my friggen Escalade Ext is out too and its bone stock including the origanal factory tires still, it has dual speedo's, the usualy guage and a digital dash read out, they are 4kmh different, so if the dial speedo is reading 100k the diggital read out on the dash is 96kmh, annoys me to no end, GPS has the dash read out as correct, havnt run the GPS in the ESV as of yet

Just so u know, the mechanical gears are not 100% accurate, they use the same plastic gear for a 3:27 rear as a 3:23 rear and same for a 3:45 rear as a 3:42 rear, sure not much out but obviously one of them wont be bang on

just put smaller tires then