My speed on the 700R speedometer is of by about 15 MPH. I just took the gear out and the only numbers on it are written with some sort of marker. I am looking for advice on how to get the correct gear to match up. My speedometer shows 72 when I am going 55. The numbers look like 114. Thanks Joe
look for a number that is cast into the plastic, not written with a pen. With that much error, you're probably going to have to change the drive gear also. The charts in the link in the post above will help you figure it out. But before you get too far, test the odometer reading, see how far off it is from what it should be. I always get the gears set up so the odo reads correctly, then I adjust the spring in the speedometer to get it to read correctly, also.
Can you look inside at the drive gear, and note what color it is? They are color-coded by tooth count. The drive (on the output shaft) and driven gears establish the speedometer drive ratio. You may need to change both of these gears to arrive at where you want to be.
At least with Saginaws and Muncie standard transmissons the color of the driven gear is the indicator of ratio so...
If you post the color of your drive gear, we should be able to tell you what you need to correct this. I believe that is a 34T driven gear, which is the smallest. A driven gear with a higher tooth-count would operate the speedometer more slowly. You have all of the available ones to choose from. Unlike earlier transmissions, the speedometer gear holder is not fixed position. It can be installed in , I believe 4-positions, to accommodate the range of gears.
Might need to go to an adapter unit for that ratio, too....so maybe just leave the transmission alone, and figure out exactly how far off the odometer is, and get one made up for it. Although 15 and 45 will get you close, if the rear tires are tall enough.
You can also calculate your tooth count if you will drive at a steady speed let's say 60 miles per hour as indicated by a GPS speedometer on your phone and then compare it to the reading of your speedometer and then figure out the percentage off that it is and use that ratio to find the new tooth count. It may take more than one one try to get it spot on but those driven gears are pretty cheap. Replacing the drive gear is a pain but not that difficult. You have to pull the tail shaft housing. The drive gear just slips on the shaft and a clip between the gear and the shaft holds it in position. You can probably find some YouTube's on the subject. EDIT/UPDATE: that gear looks like a 44 tooth gray gear. That's next to the slowest made for 700r4. This seems rather weird since you're running 30.9 percent high! I'm not so sure you can get from point A to point b without the external adapter as mentioned above. Even if you're driving gear is brown with 20 teeth switching to the 15 tooth gray drive gear that only gives you a 25% reduction in driven gear speed.
I am still on my first cup of coffee, but I believe that what is required here is a 23.6% higher tooth count driven gear. 34T x 1.236 = 42.024. 42T green gear.
I'm pretty sure that's a 44 tooth driven gear if you count the gears and I believe it's gray, and he needs a higher tooth count, and I believe the 45 tooth is as high as they go.
I'm on the small screen, so it is hard to count on the teeth. If it is 44, it will need a ratio adapter. They were often found on T5's, and can me found for sale on eBay.
Check the link in my previous post. If you got the box that reduces 26.7%, you could then trim-up the remainder by changing the plastic gear.
Well, $88 will get you to 52.78 MPH at 55 on the speedometer. From there, you would just need to swap the driven gear to get to 55, unless that's close enough. It would be off by just 2.22 MPH at 55.
Thanks guys, Ya I knew it was off some but it is close enough for this old truck I watch the tachometer mostly. I started out with 10 and 36 it’s for a 456 but only 26” tires it was off quite a bit with 31.5 tires. Something else they make two driven gear housings one for 36 37 38 39. And one for 41 42 43 44 so I had to buy another housing for the 44. There usually stamped on them as picture shows. My transmission was originally a electric speedometer but kit did the trick.
After looking at the numbers and the fact that I am not capable of taking the tailpiece off (working on a garage floor) maybe a GPS speedometer is the answer? If not the speedometer I can just use a generic GPS and keep the original speedometer which I really like the look.
Can't run the 10 tooth drive gear with that driven gear. The pitch is wrong. That is a drive gear for a Chevy 350 Bullitt housing and a small diameter driven gear. Bill
I had that 10 and 36 and that housing installed in my 700r4 for several hundred miles. But the spedo was to fast if I remember right about 12 mph somewhere there about.
Hello, During our time driving around with 4:56 gears in our 58 Chevy Impala, the speedometer was a little crazy and off the correct speed by a lot. If those highway speed mileage signs are fairly accurate, then the 58 Impala had problems in showing what was the correct mileage and speed. So, why? When we put in the 4:56 gears, it was calibrated to the 3:55 stock gearing. We bought a 4:11 gears for that unit and had it installed. The dealer folks that did the install did not tell us about the speedometer difficulties. We thought the speed was fairly accurate and we were happy. We never had a ticket for speeding as timed by hand held radar units. The only ticket I got was when I was going 25 (showing on the speedometer) and was clocked at 30 in a business zone approaching another school a ½ mile ahead. The 25 zone sign was not showing for a ½ mile, but the ticketing officer said we were going too fast. So, guess what rear end gears we had installed for the Saturday drags at Lion’s Dragstrip? yup… the 4:56 Positraction gears. We got fooled again! Or did not pay attention while driving home from our own hard days work at school. Jnaki Before you tear your transmission apart, take a look at why you are running a 4:56 gearing. That may be your culprit even with the gearing you show in your photos. You even say “I also have 4:56 gears so it is a major mismatch.” So, you know it may affect your speedometer. Check the reason you run 4:56 gears and if you can put the stock rear gears back in, it may simplify the speedometer calculations. Our answer to the similar problem was to stay with the 4:11 gearing. It was close enough on those road sign checks, gave us plenty of go power off of the starting line, and we were cautious when in low speed areas as posted. But, we had the complete 4:56 Positraction rear end sitting in the backyard garage for an instant changeover for the drag competition at Lion’s Dragstrip or the Bixby Knolls Cherry Avenue Drags.
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