Hello... I'm trying to figure out what is the proper transmission speedometer gear for me.. I changed the rear end to highway gears ( 3.42 changed to 2.56 ) and I want to make sure I have the correct gear to register speed and miles correctly ...( I could take a picture and show the Brown Gear I have but I can't figure out how to post a picture.... ) Says 36,37,38,39 on the outside of the housing... 71 Turbo 400 BB transmission ... Help ...lol
If you'll tell me what the diameter of the back tires on your car are, I'll try to help you. And, is the BB tranny an original '71 stage 1 with the original speedo gears? Can you tell the color of the drive gear inside the tail housing? You may have to change that too but, I'll know more after you tell me the back tire diameter you are running.
There are two gears inside the housing. The drive gear is inside the tail housing and the driven gear is behind the housing that bolts the outside of the tranny. the numbers on the housing are the driven gears that will fit inside that housing. Depending what gears you need for your 2.56 rear end, you may have to change the housing in addition to the gears.
I'm using 15 inch Buick mags... Gear inside of the housing is yellow... To the best of my knowledge,it's the original Transmission.
What size tire will you be running on the rear? When you say "inside the housing" do you mean inside the tail shaft housing or the gear that comes out when you remove the housing on the tranny? I need to know the color of the drive gear on the tail shaft inside the tranny.
If the transmission is a 1971 BB or OW, it has a 16 tooth DRIVE gear. From the 1971 Buick Chassis Manual, The correct DRIVEN gear for the 3.42 rear would have been a 41 tooth (yellow) gear, or a 42 tooth (green) gear depending on the original size tires. The Brown gear is a 39 tooth gear. Not sure why that would have been in there. In any case, to figure out what DRIVEN gear you need with a 2.56 rear gear, you can use this online calculator, http://www.tciauto.com/tc/speedometer-gear-calculator If we assume you have a stock rear size tire, we can use the stock tire height of 26.6" Problem is, if you input 16 tooth DRIVE gear, 26.6" tire height, and 2.56 gears, it recommends a 31 tooth gear. That gear does not exist. That means you either have to change the DRIVE gear, or get one of those reducers that go inline with the speedo cable at the transmission. If you swap the DRIVE gear to an 18 tooth, you can use a 35 tooth (pink) DRIVEN gear. This all assumes a stock 1971 BB or OW THM400 and G60-15 tire height.
DRIVE gear is yellow? That would be an 18 tooth gear. Use a 35 tooth DRIVEN gear. My info says GM part number 9780628, https://www.ebay.com/p/NOS-GM-97806...e-Chevy-35t/658544464?iid=202137288249&chn=ps
But the outer housing on it has numbers 36,37,38,39 ..... I don't think 35 is correct.... The one I have is a 39 I believe...
There are only 2 different housings, one takes 35-39, and the other is 40-45. That housing will accept the 35 tooth even if it isn't on the housing.
It is red or pink, GM part number 9780628. I linked you to a really cheap one on Ebay with free shipping. https://www.ebay.com/p/NOS-GM-97806...e-Chevy-35t/658544464?iid=202137288249&chn=ps All this assumes you have an 18 tooth DRIVE gear. The TCI site says yellow is 18 tooth.
I would try to count the teeth on that yellow gear. Make sure before you get the 35 tooth pink or red gear.
Yes... I met you years ago... I'm the guy who had the convertible in Gray primer... she used to look like this when you saw it a the KMart in Syosset about 15 years ago
