HD rear end cover 1970 LS-5

[Markus 38206]

On many publication it can be read that the original cover is used to crack in the area of the spring-mounting surface. Is this really critical? I have just bought a rebuilt rear end (3.55) for my 1970 454 LS-5. It comes with the original cover which I would prefere. Should I swap the HD cover from my old rear end? Is it a must for the 3.55-Big Block? Any experience out there?
Thanks.

[Joe L.]

Re: HD rear end cover 1970 LS-5

Markus-----

The primary reason that the 63-79 differential covers crack is improper spring installation procedures. I've never heard of one breaking in service. If I ever did hear of such a thing happening, I would strongly suspect that the cover was cracked during an improper spring installation procedure and, subsequently, failed.

The main reason for using a "HD" rear cover is as a replacement when you crack your cover while performing an improper spring installation procedure. This may be necessary since the GM cover of the original design for 63-77 models is long-since GM-discontinued. The "HD" rear covers are of several designs. Some, in order to provide extra strength (apparently, to help keep folks from breaking them while performing an improper spring installation procedure since you don't need the extra strength for any other reason) compromise the installation of the spare tire carrier by providing insufficient clearance for the carrier.

If your cover is ok there's no real reason to replace it with a "HD" cover. Just make sure that you install the spring properly. Make sure the spring is de-arched before tightening down the retainer bolts AND make sure that the spring center bolt head is not too long to completely fit in the cavity provided in the cover.

[Markus 38206]

Re: HD rear end cover 1970 LS-5

Thanks Joe. How works the correct installation procedure exactely? How should I reach the de-arched status before tightening the bolts?

Further question: I have heard about "rear crossmember locationg kit". This is an aluminum plate which is installed over the crossmember cusions. What's the exacte function of this? Is this something to make a "hard" connection between differential and frame? Makes this sense?

[Joe L.]

Re: HD rear end cover 1970 LS-5

Markus-----

Just follow the procedure in your factory service manual; that's all you need to do.

Forget the "crossmember locating kit". You don't need or want it for any street application.

[Ed Jennings]

BTW, diff ratio was

originaly 3.08:1 vs 3.55. At least that was the ratio on my 71 LS5, and I suspect the 70 was the same. Bubba may have already been in your rear. But then again, who knows for sure.

[Markus 38206]

Re: BTW, diff ratio was

Ed, I can guarantee that there was 3.08 in by factory. First it is an AC-equiped car and second I have the original 3.08! The 3.55 is an exchange , just for fun. At the end I don't think, because you had a 3.08 in your 71, you can tell that I had a 3.08 in my specific car too, can you?

[Ed Jennings]

Re: BTW, diff ratio was

No, I can just tell you that the 3.08 was the STANDARD rear gear with the LS5, and that MOST were delivered that way.

[John H.]

Re: HD rear end cover 1970 LS-5

Joe -

Unless they changed the rear spring installation procedure in the CSM after 1969 (that's the most recent one I have), following the CSM procedure is almost guaranteed to result in broken rear cover ears, as it says to torque the four retaining plate bolts fully before connecting the spring end links. Did they change the CSM procedure after 1969?

[Joe L.]

Re: HD rear end cover 1970 LS-5

John-----

The 1970 Chevrolet Service Manual (including 1969 Corvette) instructs that the spring clamp plate bolts are not to be torqued down until the weight of the car is on the suspension (i.e. spring de-arched and "flat").

[John H.]

Re: HD rear end cover 1970 LS-5

Joe -

Thanks - I guess it took them a while to figure out the failure mode and its root cause and get it into the CSM.