Midyear differential carrier front support bracket ID

[Jeff S.]

Can someone describe the differences? If I recall correctly, the '63 has no reinforcement washers at the forward holes. How does one identify carrier support brackets for the other model years? Thanks in advance.

Jeff

[Joe L.]

Re: Midyear differential carrier front support bracket ID

Can someone describe the differences? If I recall correctly, the '63 has no reinforcement washers at the forward holes. How does one identify carrier support brackets for the other model years? Thanks in advance.

Jeff

Jeff------


There were 4 brackets used over the 1963-79 period.

The first, used for 1963-only, was GM #3820186. This bracket had no welded-on washers for reinforcement of the bolt holes used for attachment to the differential carrier. I think this bracket might have 2 holes on the top surface.

The second, used for 1964 and, possibly, early 1965 was GM #3843683. I've forgotten the details on this bracket. However, I don't think it had any welded-on reinforcements, either. I think this bracket might not have the 2 holes on the top surface.

The third, used for 1965 through 1968, was GM #3868799. This bracket had reinforcing washers welded on to the sides of the forward-most (towards front of car) holes on either side.

The last was GM #3921657. It was used for 1968 with THM-400 and all 1969-79. This bracket has a thick steel plate welded-on to each side with bolt holes for attachment to the carrier.

[Jeff S.]

Re: Midyear differential carrier front support bracket ID

Thanks, Joe. Would the 1st, 2nd & 3rd all be 'usable', fit and function wise, on any model year C2?

[Bob R.]

Re: Midyear differential carrier front support bracket ID

Any of them could be used on any year however to be visually correct the 63 could only be for 63 and so on. You could alter the 64 - 65 to look and function correctly on a 63 by drilling a couple of holes and the 63 could be used on 64 - 65 by filling in a couple of holes. The 63 emergency brake cable attaches to that part which requires a hole for the fastener.

[Joe L.]

Re: Midyear differential carrier front support bracket ID

Thanks, Joe. Would the 1st, 2nd & 3rd all be 'usable', fit and function wise, on any model year C2?

Jeff------


Yes, just as Bob describes.

However, my preference is for the 69-79 bracket. GM did not change the earlier brackets because they worked just as well as the final iteration. The fact is that the holes in the 63-64 and 65-68 style brackets elongate. This results in a "clunking" noise when starting out from a stop. There was even a service bulletin issued about this problem instructing Chevrolet dealers to weld on thick washers to reinforce the holes. Even this was not a "permanent fix". The "permanent fix" was the 1969-79 bracket. That's the one I recommend for all C2 and C3 (to 1979). Of course, it's not NCRS-correct for 1963-68 but it's functionally superior.

[Richard M.]

Re: Midyear differential carrier front support bracket ID

Also, if you decide to upgrade to the 1969-1979 bracket on the earlier years(like I did on this 1966 chassis), be prepared and acquire the correct longer bolts which mount it to the differential. Those reinforcements are much thicker than the welded washers on the earlier parts.

[Joe L.]

Re: Midyear differential carrier front support bracket ID

Also, if you decide to upgrade to the 1969-1979 bracket on the earlier years(like I did on this 1966 chassis), be prepared and acquire the correct longer bolts which mount it to the differential. Those reinforcements are much thicker than the welded washers on the earlier parts.

Rich-------



Yes, longer bolts must be used on 63-68 when using the GM #3921657. For 1963-E65, the forward bolt hole in the carrier is not a through hole and is threaded on each side for short bolts used on each side. Nevertheless, the short forward bolts need to be a bit longer.

The rear through bolt for 1963-E65 as well as both bolts for L65-79 need to be longer, too. The original longer GM bolt was GM #3921658 which was later replaced by GM #458987. The latter is now discontinued, too. These bolts were special bolts with a pilot tip and a hole for a cotter pin used in conjunction with a slotted nut. The length of the bolts is 4.81".

[Bob R.]

Re: Midyear differential carrier front support bracket ID

The front bolts on a 63 - 64 rear diff do not go through they thread right into the rear differential

[Richard M.]

Re: Midyear differential carrier front support bracket ID

The front bolts on a 63 - 64 rear diff do not go through they thread right into the rear differential

Right, a horrible design IMO, so you don't need the longer pass through front bolt for those as they 2 stock fronts are long enough, but still need the longer one for the rear. You need to drop the diff down for that one on the 63/64. I had to do that on my '63 coupe IIRC.

I also remember when I was upgrading to the later bracket I broke one of those front bolts on that '63 and had a heck of a time drilling it out while preserving the threads in the differential. IIRC I released the front snubber bracket bolt and pulled the diff down using ratchet straps to get clearance. I got that broken bolt out, but it was stressful.