I've been looking for a diff, and have been seeing HD rears advertised. I'm familiar with the HD rears but what is actually different about them?Is it just the yokes or is there something internal that is different too? Is there anything needed to change to put one in a car without an HD diff already?

 

Are you talking about GM spec HD rearends or rebuilt HD rearends?

 

In general IMO HD is just the yokes but years ago when I pulled things apart on an L88 the bearings were all of higher quality , rear end and trailing arms. Leads me to believe L88s-LT1s might have used hand picked parts to come up with a better unit. Just a guess.

 

The heavy duty rears still use the same case so nothing changes in the dimensions or how it bolts up.

There is only about 5 items that can be improved on the rear. I will list them in order of importance.

1. the yokes. I'm a firm believer in custom Hardened about $300 each. Mine are nearly 20 years old and they look brand new. Where the stock ones last a year or two.

2. The posi units. I used to break the posi unit housing every year or two. the Eaton cone type is an upgrade over stock. But the full on tom's differentials $800 units last for years even with over 600 hp.

3. The gears. You don't really hear about people breaking or waring them out. I used Richmond 4.11 for 20 years and they still looked new and I just installed US gears.

4. Heavy duty rear end cover. They are about $120. Some people crack the cover. I think that it is self induced from improper setup or weak inch pound rear springs, wheel hop.......

5. I also have the HD billet internal main caps. I don't believe that they are necessary for the average Joe. Kind of like billet steel main caps with ARP studs in your engine block.

I personally only upgraded things as they broke. So IMO it's stupid to overkill in one area and leave weak links all around it. So I also have better U-joints, shafts, outer spindles.........

 

How can you tell the bearings were a higher quality?

 

The owner of the L88 was a machinist and a machine repairman and knew bearings and was a bit of a bearing snob. He was looking things over after they had been cleaned and he brought to my attention the codes that are etched in alongside the bearing numbers. He ask if this was the normal bearing quality on vettes , I had no idea what the letters were for, so I dug out some old bearings to compare to. He was impressed and said they were obviously a better bearing. If I remember right the letter code was OO or if they were numbers 00 . He called them "double oughts".

 

Thanks for the feedback. I have just seen some people advertise their rears for sale as factory "HD" units, came from a big block car so is the "HD rear", etc. I thought it was people fluffing their desciptions but I've seen it enough I started to think there must have actually been an HD rear available from the factory. I know the diffs themselves are all the same, so lead me to think the differences must be in the yokes, half shafts, etc. I've found a rebuilt 3.55 rear that's advertised as an "HD" for $550, doesn't come with the yokes though. It was rebuilt by "a guy", and is not from a name brand rebuilder or corvette parts retailer so that has me a little worried but that price seems really good even with the added risk.

 

Without the yokes it's just like any other diff. Nothing special in them.


JIM

 

Thanks, that's what I was thinking but wanted confirmation.