My car has a 700R4 in it and the speedometer drive was all buggered up. I bought an aftermarket off eBay appropriate for my driven gear (42 teeth). When the new drive housing is installed correctly and the hold down fork is engaged in the grooves, the gear doesn't turn. I have to rotate the housing nearly 180* for the gears to mesh. What's going on here???
It can be rotated to get it to engage. It has 4-positions, so it can accommodate a bigger range of gears. If you want a dedicated one that you don't have to clock: https://www.summitracing.com/parts/ado-25512339
Do Mopar parts really apply to a 700? I seem to recall that the GM adapter has it's gear tooth range shown on it, and it only fits one way. Anyways...it would really help to see what parts you have, including the gear on the output shaft (color/tooth count), and how the thing looks when it's installed.
It is the image that matters. There are clocking 700R4 housings. I had this one in my Chevelle. Take a good look at it at see how closely it resembles the other picture that I posted. It started out destined for an AMC product.
As Gimpy's second photo shows, the housing has to be clocked for the driven gear you are running. I've gone to this site for speedometer gear info a bunch of times Speedometer Drive Gear, (transmissioncenter.net)
My brother says that the clockable ones came from transfer cases, and that is what he used in mine. He says: NP208 fits TH400. NP231/242 fits TH350/700R4. When Chrysler acquired Jeep (then AMC), that became a Mopar product.
I've always used the ones with the proper gear number cast into it. No problems if you do it that way.
that's the way i remember it also. I bought a "package" of plastic gears that all had different tooth counts for an R4 that i had and the gear only went in one way.
still no pics of what the OP has....we can guess all we want, but it won't help much. All the GM stuff I've ever had was from old transmissions, so I was unaware that you could use Mopar stuff in the 700. I've only used Mopar stuff in Mopars.
Ok guys, here's what I've got. You can see the grooves where the fork is supposed to index into. I have it rotated nearly 180*. The numbers cast in the housing correspond to the driven gear. I have a red drive gear and green driven gear fwiw.
The green 42 tooth driven gear must have the correct housing. It only goes on one way with the fork. The housing is unique for the 40 to 45 tooth driven gear selection. Get a new gear and housing because your old gear may have a crack at the base of the gear. Ask me why I know.
The housing has 42 cast right in it, along with a bunch of other numbers in the 40's. Yeah it works, but the speedo is inaccurate. I wanted to get this sorted out before I try swapping gears
Ok, we didn't know that your speedometer was inaccurate. Here is how you do it. With "known accurate" speed (get an app "speedometer"), go out for a drive and hold at a steady speed, record the indicated speed of your speedometer. Example: real speed via GPS = 65 mph, indicated = 59 mph. That means that your green gear is spinning about 9% too SLOW (6/65=0.092) . On the other hand, the driven gear needs to speed up by a factor of 10.7% (6/59=0.107). So the gear needs to spin 10.7% faster, which means fewer teeth. Since we don't know what gear will give you the desired tooth count, we fudge a little bit and use the equation for the reduction of the 42 tooth gear to get where we want to be, so you then do the math again. So we then use 6/65 = 0.092, or 9.2%. That tells us we are about 10% fewer teeth.... The 42 tooth gear should be replaced with a gear that has (42 x .10=4.2) fewer teeth. That ain't gonna happen, so you have to round off the 4.2 to 4, so that would indicate a 38 tooth driven gear. That would be a BLUE gear, but you can't use the BLUE gear with the housing made for a GREEN gear. You shouldn't have to disturb your RED drive gear. Since the gears are fairly inexpensive, you might get a RED, BLUE and BROWN gears. one of them with work just fine. This is just an example, your numbers will be different. Of course you could use one of the "online calculators" that inputs tire size, rear end ratio, etc. to come up with the same answer, but use the actual distance from the center of the tire/wheel to the ground, not the published diameter of the given tire size. And be sure to get the correct housing for whatever gear you select. Two 2.078" diameter housings, each made from either aluminum or plastic, are available for driven gears with 34 or more teeth. One fits gears from 34 - 39 teeth and the second one fits gears from 40 - 45 teeth. More here: https://www.tciauto.com/speedometer-gear-calculator#700R4 Keep us posted.....
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