swapping from 3.23 to 3.42 10 bolt in a 1991 Camaro with an A4. Is it worth the hassle of changing out the speedo gears in the trans considering the ratio isnt a big jump?

How much will the speedo be off? Im thinking about 3-4mph or 6%.

If I do need to change speedo gears then does anyone know what colors I will need in an A4 trans with 3.42s? Ive looked online but its all talk about 3.73s or the older cars without the electronic VSS

 

It could have been a little bit low before. It could have been a little bit high.

Verify against several sources. Lots of mile markers against odometer. GPS on your phone. Radar stations showing your speed.

Just because it was OEM before doesn't mean it was +/- 0.1% or less.

Just because the odometer is spot on doesn't mean the speedometer is.

GM used 15 / 41 or 15 / 42 with 3.42 rear gears and third gen stock-sized tires.

 

Yup, use GPS to help see how far off it is.

 

Not going to be 3 - 4 mph.

That would mean, sitting still, there would be a 3 - 4 mph error; at 30 mph, there would be a 3 - 4 mph error; at 150 mph, there would be a 3 - 4 mph error; etc.

In the real world, speedo gear errors don't work like that.

In the universe I live in, assuming speedo gears were perfect (they're not... they're ratios of whole numbers, therefore only come in certain discrete steps, NEVER "exact") there would be about a 6% error, AT THE VERY LEAST, at ALL speeds. I.e. 0 mph sitting still, around 2 mph around 30, around 9 mph around 150. Could be more.

Depends on your definition of "worth" and "hassle".

Personally, I'd do it. To ME, lots of worth, and very little hassle. One of the eeeeeeeezyest and cheeeeeeeeepest attentions to detail that exists in the grand scheme of "car" things, right on up there with electrical systems although not quite as eeeeeeeeeeeeeezy. Others may well disagree for reasons of their own. Me, I'm a perfectionist; although if you ask my employees, they'll tell you that perfection is the ABSOLUTE MINIMUM standard, without which they won't continue to have a job, but we look for every possible opportunity to exceed that. Other people are much ... less.