I keep breaking the driven gear on my 700R4 speedometer. I have an early (89 ish) 700R4 that has a 28 spline input and as far as I know it came out of a 2WD truck. My tire is Ø30.16" O.D. and rear gear is 4.11. I come up with a 15 tooth gray drive gear and the first time I used a 40 teeth black gear that lasted about 1,500 miles, the second time I used a 41 tooth yellow gear (speedo read about 5 miles slow first time) and this gear lasted about 5 miles, replaced with another 41 tooth gear and another new drive gear just to be sure and that lasted about 35 miles. The driven gear is breaking off at the end of the shaft inside the tailhousing. The speedometer cable appears to be free and turns easily. I have the correct housing for the 40-45 teeth gears. I watched a few videos online about putting on the drive gear and they mention some tailshafts have 2 holes in them for the clip and to use the front hole but my tailshaft only has one hole in it. The transmission was missing the driven gear housing when I got it but it had a plastic gear on the tailshaft so I ***ume it was originally a mechanical speedometer. I even put ****m on the gears last time and turned it over several times by hand to see what the wear pattern on the teeth looked like and it appears to have good engagement and not too deep. I am out of ideas, anybody got an suggestions?
Look on Bow Tie Overdrive web site. Look at their chart. Fill in the blanks and it will show you which color drive gear and driven gear you need. That will answer part of your question.
Does the gear housing have numbers on it? I don't recall if the TH350/700 one does...but the 400 they made two different ones, for different diameter gears, and if you have the wrong one, it puts the gear too close or too far away. and you checked the speedo cable lubrication, I hope (this page shows the two different housings) http://www.laspeedometergear.com/700R4 Drive Speedometer Gears.htm
Get in touch with Rusty...e1956v He knows this stuff inside and out. HRP http://www.speedoservice.com/
I have confirmed the 15 tooth and 40 or 41 tooth gear combination is correct for a Ø30.16" tire and 4.10 gear. The gear housing does have numbers on it (40, 41, 42,43). The center of the housing is offset ≈0.070" to accomodate the different gear size. I can only ***ume the 0.070" offset is correct, it was an AC Delco part. The speedo cable was new, I didn't add any lube to it. I can pull out the cable and put some lube (White Lithium Grease??) into the housing then put the cable back and see if that changes it. You think an unlubed cable would be enough to break the driven gear?
New cables used to come with a packet of grease. I would use a lightweight grease, but not the white grease, because it dries out
Not sure if it is the same problem but I, am working with the same thing on a 32 for a friend with a VDO speed sensor and found if you tightened the sensor it bottomed out the drive gear and forced it too deep in the tail shaft housing and bound up the gear . I put a AN washer between the cable and housing. I found this out by removing the tail shaft and installed it and it bound up tight. It also damaged the gear on the output shaft so it had to be replaced. He had just replaced the speed sensor and after breaking 2 gears I went to the last thing replaced.
So I took the speedo cable out and lubed it with a graphite lube and some lightweight grease, put in a new driven gear and this lasted about 20 miles this time. Anybody else got any suggestions?
Stewart Warner speedometer http://www.speedwaymotors.com/Stewa...e-Speedometer-Mechanical-3-3-8-Inch,1107.html Another person has suggested that sometimes the drive gear can "walk" off the clip on the tailshaft and that could be breaking the driven gear. Everytime I have put a new driven gear in the drive gear has still been on the clip so I don't see that happening.
Disconnect the cable at the speedo head, drive for 40-50 miles... If there is an intermittent 'binding' in the speedo head, it may not occur until the bushing warms up...
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