I have done searches, used calculators, read articles but just keep getting more and more confused. I'll get half way through an article and realize it's about a 700R4 or something else. I have a 1986 IROC with 305 carbed, T-5 five speed tranny, 3.23 rear gears and 235/60/15 tires (about 26" dia.) and what I need to know is the correct (or near enough) drive gear and driven gear for the speedometer cable. I tried the Hanlon site and got that my drive/driven ratio should be 0.401 and the chart showed I need an 8 tooth drive and 20 tooth driven @.400 ratio OR 7 tooth drive and 17 tooth driven @ .412 ratio. I have a 7 tooth (purple) drive gear and a 19 tooth (white) driven gear which will be @.368 ratio that I will have to use. how much different will this make the speedo? I get confused with ratios. Any advice might help.

 

Anybody????

 

Use your 7 drive.

Get an 18 driven.

It will be accurate.

ABSOLUTELY ZERO online gear "calculators" produce accurate speedo gear combinations. Not Hanlon, not the one anyone is going to post in response to this post of mine. None of them. Not even the one RB83L69 might come in and post about "search for this...." They're all at least one tooth off. Don't worry about them. What I posted is a certified GM combination.

 

Trust JMD's advice about T-5 speedo gears
I went through the same thing(with the calculaters),In the end,I left it up to JMD,bought the parts from him
And I've never been happier,speedo no longer jumps around,and it actually reads correctly!
Thanks again
Steve

 

What would an 18 driven gear cost? and where could I get one?