Tech: GM/Chevrolet 700R4 speedometer issue

[Adam]

I'm hoping that someone here is familiar with the GM TH700R4/4L60 auto transmission. I have one retro-fitted in my '62 Impala and I've been trying to find out why the speedometer isn't working. I pulled the cable from the trans to see if it was a broken cable, but the needle flickers fine when I twist it.

Insead, I found this:





This shot is of the end that goes deep into the trans (the other end has a notched/squared off inlet that the speedometer cable slides into. It appears to have sheared off inside the trans - there's an inspection cover which I'm assuming cradles the gears that drive this shaft.

Now, I have no idea what series of 700R4 this car has, or what the transmission was originally fitted to. I bought it reconditioned from a shop in Portland, OR but considering I'm now 12k miles away, I'm not expecting much help from them - I'm hoping I can just fix it myself. I'm going to get back under the car and try to get as much info as I can from the casing, to try to identify the unit. Is there anything specific I should be looking for and can anyone tell me what this part would be called so I can try to order a new one.

Many thanks!

[Radioactive]

It looks like it broke off the gear, If I remember when I did one there was different gear for different rear end ratios. I think I might have put some kind of adapter to get my speedo accurate.

Here is a picture of the other end.

http://www.transmissioncenter.net/64_38cutawayspeedogear.jpg

How to:
http://www.73-87.com/7387garage/drivetrain/spdgears.htm

It looks like all you have to do is remove the sleeve. Install new driven gear.

[fastfredracing]

You will most likely need to know the color of the plastic gear on the output shaft, or how many teeth it has ( more like spiral lines) . You may just get away with replacing the broken piece that is in your hand, but more likely than not, there is wear to the gear on the output shaft. Inspect it carefully , you will be looking for it to be scalloped out in the middle. If it is , it should probably be replaced. You can source these gears right through your local GM dealer, but I always seem to have a hard time getting the right ones on the first try.
I would pull the tail housing off the trans, fish out the rest of the broken gear, and then you will be able to count the teeth on the gears you will need. This will be a good time to do the output shaft( driveshaft) seal, and there is also a sealing ring between the output housing , and the trans case, usually re-useable, but better off to replace.

[Adam]

Awesome, thanks guys - very informative. Without any GM/Chevrolet dealers here, it'll be a little trickey to source - but I sincerely appreciate the help.

[Tobra]

Is Holden out of business?

[Adam]

No, they're still in business, but they wouldn't know much about this sort of stuff. They only ever used the 4L60E version of this transmission on local GM cars, which I'm told has an electronic speedometer. The two Holden dealers I called wanted me to give them a VIN, which is pointless in this case. I need a transmission specialist, preferably one that services American GM stuff... but I think I'll need to pull the back end off the transmission.

[Tobra]

Can they get GM parts like this if you provide the part number? Seems like somebody here could suss out what you need if you were to post a photo of the bit you need. Failing that, I should not be a bit surprised if you could get someone around here to pop down to the Chevy dealer and get you one.

[johnsjmc]

look on ebay and search 700r4 speedo gear . at leat a dozen pop up