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 Anyone hear of this before?

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lakeffect
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PostSubject: Anyone hear of this before?   Sat Sep 30, 2017 11:15 pm

Ealrier this year a local rebuilder screwed rebuilding something they screwed up last year. The trans (4l60) had to betaken to a second shop who got it running correctly with one exception. The speedometer sender was not sending a pulse from the time the original shop rebuilt it the second time.

Changing the sender  and the buffer did nothing to help get a pulse. Why? Because the Plastic gears driving the sender were not engaging to rotate and produce a pulse that the ECM and dash can receive.

Several auto sites with 4L60  sections seem to contend that there are/were two different tailshaft housings

One is meant for speedo driver gears with tooth counts in the 30's. The other is meant for drive gears with tooth counts in the 40's.

The difference is reported to be that the 40+ tooth count  housing has a slightly offset shaft hole to accommodate the larger gear diameter compared to the 30"s count housing.
So when someone replaces a 30'"s count gear into a 40"s count housing by mistake, the drive gear is offset enough to not engage the gear on the pulse sender.   Hence no pulse.

The question becomes why someone can't count how many teeth a gear has when they take it out and put the same damn part back in.

Dave
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Fred Kiehl

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PostSubject: Re: Anyone hear of this before?   Sun Oct 01, 2017 11:57 am

You are correct. There are two different VSS housings. One for 39 tooth gears and less, and the other for 40 plus tooth gears. You can tell them apart by the offset of the shaft center. I have posted this numerous times on this forum, and the ISSF.

It is too bad that the people you had work on your trans don't have any idea about the VSS. They rebuild transmissions. My question is; why the moron would not put the original part back in. It should be in the parts pail/bucket that came out of the transmission. I would make the original shop pay for any costs you incurred. The gears are color coded, and also marked on the perimeter of the gear. A lot of the gears are difficult to find.

The 40+ tooth gear will not fit in the trans with the 39- tooth VSS. So, I assume the idiot put a 39- tooth gear on your 40+ tooth VSS. One interesting observation is that it does not matter what tooth drive gear you use, it will not affect the VSS you use.

I am glad you got the situation fixed.

The speedometer display changes inversely to the number of teeth on the driven gear. The change is about 3-4 mph per tooth. With an 18 tooth drive gear (most common), a 3.23 ratio axle with a 28 inch tire should have a 42 (green) to 43 (purple) tooth gear. Smaller tires require a larger gear. You can get 15-19 tooth drive gears, and 34-45 tooth driven gears. Make sure you note that the gear does not have a shaft on it if you order one.

Once you have it close to the speed, or wherever you start, you can get a square wave modifier to fine tune the speedometer for about $80. This is the easy way if you change tire size. There is also a calculator on http://www.transmissioncenter.net/. I did make an extension cable to hook the modifier between the socket and buffer.

This information does not pertain to the 4L60E, only the 4L60/700R4.


Last edited by Fred Kiehl on Sun Oct 01, 2017 12:15 pm; edited 1 time in total
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lakeffect
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PostSubject: Re: Anyone hear of this before?   Sun Oct 01, 2017 12:12 pm

Well, getting fixed at least. Forty three count gear on order from Summit.  Since both my EBL board in the Corvette ECM and the dash are prpgrammable for pulses per mile, it only mattered as to what Summit had in stock, and ready to ship. There is a "measured mile" nearby to get that squared away.

Second shop billed the first for repairs. Doubt they'll accept more charges, but we are on that aspect of it as well
   Thanks Fred.
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