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Repair input shaft on 4.329 ADAPTER ASM., Speedometer Driven Gear

my kids took the truck

my kids took the truck

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The input shaft on speedo adapter is stripped. The speedometer gauge started jumping around and then quit altogether. I had the transmission and transfer case rebuilt and the problem showed up right then, by luck I didn't blame the shop for this as it was just a coincidence this failed at the same time. I asked the service shop to rebuild the box while they were pulling the transmission again to ship it back to the transmission shop to fix a leak. They said they fixed it with a washer shim. So when I got the Blazer back, I took a look at what they were talking about. Maybe they thought I couldn't afford anything more than a washer, that is the nicest I can be towards them on this point. Their 'washer fix' caught the last 1/8 to 1/16 inch of the good remnants of the key--it failed the first time I got over 60 mph.

After searching, I found there isn't anything online about opening these up and changing that shaft.

These fall under different part numbers depending on over/under ratio

The input key
4.330 KEY, Speedometer Adapter Drive - 73-78 PN 867209
use w/ adapter PNs 326569, 330192, 332537, 368022, 368025, 368026, 465434, 465435

I found new old stock and bought it--I will post what it looks like opening this up [NOTE, TURNS OUT LATER IT IS ONLY FOR AC DELCO BOXES]

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I split the case, pulled out the center idler gear, and found that the key won't budge. I gave it a few good hits and nothing. The old key must be a tight press in there if it is a two-piece part there in the center--I don't see on either side any provision on the gear or the other coupler for the index key on the shaft key. The key (PN 867209) is otherwise a perfect fit.

Any suggestions?


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I just checked a couple of the ones on my shelf, and that drive key pulls out easily away from the nut side. No disassembly required for the box.
 
there is a pin holding this together: there is one on the input and one on the output side--I saw it on this instruction manual posted to eBay

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An update: I sent the box to Texas to let them use their expertise before I broke something. They can't find parts but are looking.
  • First, a good thing because in this model the drive shaft did not press off the gear as indicated.
  • Second, the AC Delco-brand shaft I bought is for an AC Delco adapter box and that does not work since what I have is a Borg-Warner box
  • Third, they suggested a new $200 ish box they sell -- I asked to look for the $20 replacement part before we talk about new (for that price, I was leaning to just having the shaft repair welded and filed back to dimension)
 
If it's the male part that's stripped, how about grinding/filing it back to a smaller square shape, then fold a couple of shims out of thin sheet stock to make up the difference?

Can the output of the speedometer gear be crimped into a smaller square shape? Would this make it incompatible with the speedometer cable? (I'm trying to understand if both sides are damaged or just the adapter input.)

Is another adapter box available on eBay?

Also, have you looked up if speedometer drive/driven gears exist that you could just eliminate the adapter?
 
Blue85 said:
If it's the male part that's stripped, how about grinding/filing it back to a smaller square shape, then fold a couple of shims out of thin sheet stock to make up the difference?

Can the output of the speedometer gear be crimped into a smaller square shape? Would this make it incompatible with the speedometer cable? (I'm trying to understand if both sides are damaged or just the adapter input.)

Is another adapter box available on eBay?

Also, have you looked up if speedometer drive/driven gears exist that you could just eliminate the adapter?
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Yes to all of that: all on the table. The sheet metal sleeve is a cool idea--another option is to surface weld and machine back to size.

Three factors: (1) labor cost for fabrication; (2) my access to a shop; (3) replacement parts including the entire device.

Addressing those factors: I've shipped the adapter to Texas where shop rates are lower. Here in the San Francisco Bay Area, it's $150 an hour for people that know shit and goes up from there into the range of skilled work. They have a replacement new adapter, this is just fun and games now to see if the OEM can be fixed just to do that. If needed, they can send it out for surface weld and machine to size and it will be pennies on the dollar to California rates.

The shop in Texas thinks they found a NOS replacement shaft. Just waiting to hear.

I'm an engineer living in an apartment. Usually I'd be managing a heavy equipment shop and could get one of the Union mechanics to take this as lunch-break side work. I'm not in the field so that isn't an option.
 
I don't think it needs to be precision machined. You could probably weld on 2 sides and get it close enough with a grinder. There may be volunteer here to try it, but they would likely need both sides to get the fit right.
 
SOLVED

The end of the story -- Steve ([email protected]) at https://texasindustrialelectric.com/ got the adapter rebuilt and the price was under $100. It took three months but they seem to have a new inventory now of shafts so could be quicker going forward.

For reference -- I included the part that was returned and that looks like the diagram posted above.

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