NP241 Speedo gear housing install question - answered

[AJs72K5]

I picked a mechanical speedo gear and mount for the 241 I just installed on the K5. What the heck is the secret to installing this thing with the 241 already on the truck. I tried freezing it for a little while and greased it up. Nada. Any help is appreciated. Thanks!

 

[4X4HIGH]

I'm assuming your 241 was an original mechanical speedo? If not there are other parts that need to be swapped, like the whole output shaft and tail housing.

 

[AJs72K5]

I'm assuming your 241 was an original mechanical speedo? If not there are other parts that need to be swapped, like the whole output shaft and tail housing.

Yes, the 241 is an original mechanical speedo. I've already done an SYE conversion on it. The speedo mount is just really snug. It's tight enough that I can't just push it in with my hands

 

[AJs72K5]

If it makes any difference, the speedo mount came off of the tailshaft of a transmission of a mid 80's 2wd burb. I can post up pics if that helps.

 

[AJs72K5]

OK...so the answer is I pulled the speedo gear housing from the wrong truck. I was under the impression that GM was pretty much universal on these things. I was wrong

The speedo gear housing I pulled was from a 700r4 tranny. The same one should fit a TH350 and a TH250 as well. It measures 2.1" in diameter and looks like this:

The one I needed fits a TH400, NP208, and a NP241. It measures 1.935" in diameter and looks like this:

They look almost identical except for the length of the shaft just below the threads for the speedometer cable. Needless to say, I'll be headed back to PickNPull this weekend.

 

[dyeager535]

They also used different "sleeves" as GM calls them, based on the drive/driven gear combo...the offset of the sleeve in the bore is different.

 

[AJs72K5]

That is correct. It's based on the tooth count of the driven gear for the speedo.

 

[dyeager535]

Don't see it referenced much on the trucks, so perhaps the trucks simply used adapters instead of the offset sleeves. But I know this from my dealings with GM cars of the vintage. Worth mentioning anyways...surprised no one has ever torn the speedo gears up because of it.