tgilligan

Hey Guys,
I need to pick up a speedo gear housing as mine is leaking. Saw them on OPGI’s website and became confused as how do I know if I need the 35T-39T or the 40T-45T? I’m assuming this the number of teeth but without being able to get under the car and remove it at the moment, is there a way I can identify which would be proper for my application. It’s a stock TH350 automatic with no changes to the gears or rear end. Is there one that I could safely default to?

matt69olds

The large speedo housings are stamped on the outside what gears fit. Get a old toothbrush and some brake clean and start scrubbing, you should be able to read it.

geardoc66

Do you really need to replace the housing? The housing contains a small lip seal for the driven gear shaft and an oring where the housing goes into the transmission. Both can be replaced easily. If anything wears out, it is usually the shaft on the driven gear where it rides on the seal.

joe_padavano

^^^THIS. Unless the housing is damaged (which is EXTREMELY unlikely), just replace the inner and outer seals.

Fred Kiehl

If you need seals or gears, you can get them at most speedometer service shops.

If you know your tire size, and gear ratio, you can probably calculate your VSS gear ratio. Most transmissions have an 18 tooth drive gear. Here is a calculator: https://transmissioncenter.net/produ...41-product_cat.

If you can see the end of the driven gear, the color will determine the number of teeth. There is a chart on the same site.

If the VSS is electronic, it has different gears than the cable driven units, with no shaft.

The hub of the 40+ gear VSS will be centered. The 39- VSS hub will be offset a little.

joe_padavano

The speedo gear housing seal kits are available everywhere. About $14 on line.

47 Convertible

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Just went through finding a puddle of transmission oil on shop floor and found fluid leaking from speedometer housing. My transmission shop had recently put in a new gear and a new large gear housing to try to get my speedometer reading somewhere close to accurate after changing rear end ratio and tire size. The new gear was a plastic item as the shop says good metal speedometer gears in high tooth count are no longer available for 700 transmissions except used from ebay and similar sources and those are increasingly rare.

Less than 150 miles after install the new plastic gear was dished in the middle from wear apparently allowing the shaft to flex and ruin seals and thus, the oil on shop floor.

To the point that has been made by other posters, speedometer gear wear will wear out seals. In my case very quickly. Don't bother replacing the gear if all you can get is the $12 plastic item

They replaced the after market gear with a used lower tooth count original gear and new seals. End of oil leak but now speedometer shows constantly faster readings than actual speed by about 8 to 10%. I'd rather live with the known error than have to purchase cheap plastic import gears by the dozen.
Jerry

joe_padavano

There are literally millions of GM cars on the road with all-plastic speedo gears that don't leak. You might want to find out what the real problem is with your trans or speedo cable.

geardoc66

You may also want to ask the shop that performed the work whether they lubricated the seal and gear shaft before installing them. Assembling and running the components dry out of the box may damage them as this area relies on splash for lubrication and it may take some time for the transmission fluid to get there.

olds 307 and 403

Do the rear seal AND bushing while the housing is out as well.