I'm rewriting this post because for some reason the site would not post even though I was logged in and it lost the post (with all of the detail info in it). I've scanned through all 10 pages in the forum after a search for the word 'speedometer', but didn't exactly find my answer. This is the short version of my question. What is correct for a '70 1GS455/GSX (with A/C) and TH400, 3.42 gears (assuming G60-15 with a 26.4 tire height)? a 36-39 housing, with a 15 and 39 drive/driven gear set -OR- a 40-45 housing, with a 15 and 40 drive/driven gear set -OR- a 40-45 housing with 17 and 44 drive/driven gear set -OR- a 40-45 housing with 17 and 45 drive/driven gear set Thanks in advance.
For my car with 3.42's and G60 tires I used the 15 and 39 tooth combos. It is accurate. I will look in the assembly manual to see what the factory combo is.
The assembly manual calls for 17 and 44. I ran it through the gear calculator and both combos are good. Think I went for the 15 drive gear because I couldn't find a 17. Hope this helps.
Thanks John. Yes, it seems the 17 drive gear is harder to find. This will save me some $$$ since I can reuse my 36-39 housing. Thanks!
Currently, I have 275/50R15s on the car which I understand are no longer made by BFG. These compute to requiring a 40.06 driven gear with a 15 driven. If I go with 235/60R15s, it would be a 39.6 driven gear with a 15 driven. -- In both cases, after rounding, I'd need a 15/40 which would require a new 40-45 housing (extra $). If I reuse my 36-39 housing, get a 15 and a 39, I've read that for every tooth on the driven gear, its about 3% or 2-2.5MPH difference. -- I can live with that.
26" MT STREETS, 3:42 Rear gears, 15 Drive. 39 Driven. Got the 15 tooth TCI Drive gear at Summit Racing.... If and when I step up to 3:73s, I'll need to change to a 42 Driven...Jim
