620 / 720 diff carrier interchange

[BarryA]

Need more "freeway-friendly" gearing in the 620 KC - before going to the effort to pull a diff center section out of an auto trans 720, is the info that a search turned up correct that 620 and 720 diff carriers interchange, and that 2 wheel drive automatic trans 720’s normally came with 3.90:1 differential gearing?

[Z-train]

Actually it's a 3.89.There will be a fender tag calling out the ratio on the bottom of the tag.If you find two of them,stuff one in an envelope and mail it to me-thanks. :blink:

[BarryA]

Actually it's a 3.89.There will be a fender tag calling out the ratio on the bottom of the tag.If you find two of them,stuff one in an envelope and mail it to me-thanks. :blink:

 

Forgot about the tag - assume it should be on one of the bolts holding the diff carrier into the axle housing? Automatics turn up in the yards around here periodically - if I run across another 3.89 tag I'll be happy to pull it and send it along......

[Z-train]

No-it's on the drivers side inner fender(fenderwell).I was just kidding,but if you do find one....... ;)

[datzenmike]

pass side inner fender below the hood hings. Near bottom TRANS/AXLE:... FS5W71B.... HF38. 38 means 3.889. 41 is 4.11, 43 is 4.375 and so on ... good hunting. Avoid the 4X4s because the drive shaft flange changed in around '82? Go with 2wd.

 

[BarryA]

No-it's on the drivers side inner fender(fenderwell).I was just kidding,but if you do find one....... ;)

 

This one was on the passenger's side, near the hood hinge - I popped the tag off, but I don't need it. Be happy to drop it in an envelope and send it your way if you want it - just PM me an address.........