1975 Other Chevrolet Models Speedometer shakey then is off.

WIK

MEMBER
1975 CHEVROLET
V8
2WD
AUTOMATIC
42,000 MILES

I have a 1975 Chevy Monza 2+2 with a 5.7L V8.

The speedometer shakes when it reads up to 25mph, then it steadies itself and is off. When it says 30, it's 25; reads 35 going 30; 40 is 33; 45 is 38; 50 is 40; and 60 is 50. I'm assuming that 70 is 60, 80 is 70 etc (10mph difference after reading 50/going 40).

The speedo didn't work for about 9 years, and I just got the entire car fixed professionally over the past 2 weeks; got it back yesterday (Feb. 7 2008). The speedo is a huge improvement since then, but I was wondering if it would either settle into place after useage or if I have to drop the transmission (tip from a few grease-monkey buddies). It shifts when it's supposed to, it's just the speedo.

The mechanics used a gps to track it, and since it is an older model, the parts were very hard to find. Any help is greatly appreciated.

Thanks.

Friday, February 8th, 2008 AT 9:58 AM

1 Reply

INDYUKE

MECHANIC
416 POSTS

The speedo gearing is set up for each vehicle's scenario. Tire and wheel size, tranny type, etc. Putting on different size aftermarket wheels will change the speed of the car at a given rpm level. So the speedo won't be accurate.

Get the system checked, you could have a kinked speedo cable or a loose connection that would cause it to jump like it does. If your indications are still off, you might need to change the speedo gear ratios. They're little plastic things, normally come in a set and don't cost very much, especially if you get them off the internet.

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Friday, February 8th, 2008 AT 3:24 PM