Jump to content

Possible rear end swaps for 521


Recommended Posts

Well my 521 rear end decided to blowup, lovely grinding coming from it now. It must somewhat be in pieces since it wants to physically lock the rear wheels. I think this is a good time to swap to something with a more reasonable gear ratio into my truck. I've heard the whole 620 rear end will just drop right in? What years are best and is the difference between the automatic transmission rear ends and the manual transmissions? Any helpful and educational advice would be appreciated :-)



Link to comment
  • Replies 7
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

What year 521? It matters.


521 rears (the whole axle) are pretty much unique width wise- 620 ones are wider. So it's best to swap 3rd members. Problem is, 620s have the same rear ratio for most years as most years of 521s.


521s that came with J13 engines have 4.88 ('68-69). L16 521s had 4.375 ('70-72).


Most 620s had 4.375s as well- all except '72-73 HD (4.88), '73-74 Automatics (4.625) and '79 Manual Transmission (4.11). So EVERYTHING from '75-78 was a 4.375, as were '74 M/T and '79 A/T (and some 1/2T '73s).


3.889 ratios were found in 2WD, manual transmission '81-86 720s.

Link to comment

If you look in the passenger fender of the 720's it will tell you the axle and ratio. It has a section on it that says axle or something. Look for an HL prefix. The other axle was a c-200 I believe. Easy to distinguish between the two. The gear ratio will follow the HL. Hope this helps.

Link to comment

I think they went with the h-233b with the v-6. I pulled and h-190 3rd member out of a 1990's HB. I dont know the exact year but i'm sure they used them well into the 1990's?

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.