U Joint Conversion Size? Which one to get?

[Boots97]

Hi Everyone,

I currently have a 1997 Chevrolet K1500 ECSB Z71 with the Vortec 5700. My rear axle rusted out (again) and I plan on having my shop swap it out for a heavy half (14 bolt 6 lug) rear axle. From what I've read, I need 2500 U bolts and U bolt plates (I would've replaced those anyways bc I live in MN) and a conversion U joint. I've read a bunch of threads on this and I'm not sure whether or not I need a Moog 447, Moog 448, or Moog 348. IIRC @boy&hisdogs did this conversion on his 98 and he needed the 448. I'm ASSUMING that I'll need that as well, but I'm not sure.

 

[boy&hisdogs]

Hi Everyone,

I currently have a 1997 Chevrolet K1500 ECSB Z71 with the Vortec 5700. My rear axle rusted out (again) and I plan on having my shop swap it out for a heavy half (14 bolt 6 lug) rear axle. From what I've read, I need 2500 U bolts and U bolt plates (I would've replaced those anyways bc I live in MN) and a conversion U joint. I've read a bunch of threads on this and I'm not sure whether or not I need a Moog 447, Moog 448, or Moog 348. IIRC @boy&hisdogs did this conversion on his 98 and he needed the 448. I'm ASSUMING that I'll need that as well, but I'm not sure.

I bought a few and tried them until one worked. Unfortunately I don't remember which one it ended up being but it almost doesn't matter since GM was so inconsistent with their U joints across the GMT400 years and sub models. You just have to suck it up and spend the money sometimes to keep from chasing your tail. Buy from somewhere with a generous return policy and you should be fine.

I bought a U joint flip kit and just took measurements from the actual axle, I didn't buy one specifically labeled for a 1500 or 2500.

 

[RichLo]

^ Yea, your best bet is to get accurate measurements of your driveshaft and rear end then go in to a parts shop and ask for all of the above u-joints and measure them before you buy one. Or if they are a good parts shop they will be able to find the right one with just the measurements.

When I swapped a 14b FF into my 1/2 ton I used a 447 FYI. Not apples to apples but thats a very common one.

 

[Nad_Yvalhosert]

Moog 447 is the correct part #.
My 6 lug 14 bolt came from a 2500 light duty. It was first installed in my '88 1500, now in my '00 Yukon Denali.
Best upgrade I've done!

The leaf springs are the same width, 1500 to 2500, so the plates are the same. Always replace the u-bolts anyway. Here in New Yuck, they can't be removed without a fire wrench anyway.

 

[Boots97]

I bought a few and tried them until one worked. Unfortunately I don't remember which one it ended up being but it almost doesn't matter since GM was so inconsistent with their U joints across the GMT400 years and sub models. You just have to suck it up and spend the money sometimes to keep from chasing your tail. Buy from somewhere with a generous return policy and you should be fine.

I bought a U joint flip kit and just took measurements from the actual axle, I didn't buy one specifically labeled for a 1500 or 2500.

Yeah that's what I decided to do last night. I bought the Moog 448, Moog 447, and Moog 348 bc even on RockAuto that sells GM branded yokes and driveshafts it was giving me mixed results.

 

[Boots97]

^ Yea, your best bet is to get accurate measurements of your driveshaft and rear end then go in to a parts shop and ask for all of the above u-joints and measure them before you buy one. Or if they are a good parts shop they will be able to find the right one with just the measurements.

When I swapped a 14b FF into my 1/2 ton I used a 447 FYI. Not apples to apples but thats a very common one.

That's what I wish I could do. Unfortunately, my truck is at the shop so I'm unable to do that.

 

[Boots97]

Moog 447 is the correct part #.
My 6 lug 14 bolt came from a 2500 light duty. It was first installed in my '88 1500, now in my '00 Yukon Denali.
Best upgrade I've done!

The leaf springs are the same width, 1500 to 2500, so the plates are the same. Always replace the u-bolts anyway. Here in New Yuck, they can't be removed without a fire wrench anyway.

Yeah I'm pretty sure it's either a 447 or 448. Those seem to be the most common conversion U Joints. I thought the plates and U bolts had to be replaced bc the 14 bolt housing was wider than the 10 bolt. Either way, I would've replaced them anyways much like you did. MN is no kinder to U bolts than NY.

 

[Schurkey]

When I swapped a 14b FF into my 1/2 ton I used a 447

Moog 447 is the correct part #.

I used a Precision 447.

The leaf springs are the same width, 1500 to 2500, so the plates are the same.

I thought the plates and U bolts had to be replaced bc the 14 bolt housing was wider than the 10 bolt.

Yup. The 9.5" axle housing is bigger-diameter than the 8.5" housing, so the plates under the axle that the U-bolts torque against are bigger. The U-bolts might be the same, since they go across the spring, not around the top of the axle housing. However, the U-bolts get replaced regardless. Beware of torque specs on the U-bolts, the originals were coarse thread, the replacements are often fine-thread, and maybe larger-diameter steel rod.

You must be registered for see images attach

Once upon a time, I had photos comparing the two sizes of plates. Must have lost them on a failed computer's hard drive.

 

[Boots97]

I used a Precision 447.




Yup. The 9.5" axle housing is bigger-diameter than the 8.5" housing, so the plates under the axle that the U-bolts torque against are bigger. The U-bolts might be the same, since they go across the spring, not around the top of the axle housing. However, the U-bolts get replaced regardless. Beware of torque specs on the U-bolts, the originals were coarse thread, the replacements are often fine-thread, and maybe larger-diameter steel rod.

You must be registered for see images attach

Once upon a time, I had photos comparing the two sizes of plates. Must have lost them on a failed computer's hard drive.

Thank god I bought plates for the 2500/3500. I also bought U bolts for a 2500/3500 just in case. I'm getting a shop to do all this and I'm also buying nylon lock nuts too.

 

[Caman96]

I don’t think you need Nylock nuts. Can’t remember, but it’s a serious torque on them.