J-56 Brake Caliper Support Brackets

[Michael S.]

I have a pair (right/left) of J-56 front disc brake caliper support brackets
GM #3948880 and #3948879. These are cast iron brackets.

I remember that there was a mid-year disc brake version and a 68 up disc brake version of the same support bracket with the same GM part number. How do I tell the difference to determine if I have a pair of mid-year J-56 disc brake support brackets or 68 up J-56 front disc brake support brackets???

[Michael H.]

Re: J-56 Brake Caliper Support Brackets

Mike,

I believe the set you have would be correct for 69. There were other numbers for 65-67 and also another set for 68. I don't remember the earlier numbers but if no one else posts these before I get back, (Daytona 500) I can look up the # changes.

[mike cobine]

Re: J-56 Brake Caliper Support Brackets

Mike,

If I remember correctly, the '67 and earlier were one group and interchanged.

The '68 would interchange with the midyear but were slightly different I think in how they fit on the steering arms due to changes in the geometry. Roll centers for '68 dropped slightly and so several suspension pieces changed, some a lot, others ever so slightly.

The '69 up had to go around the larger spindle of the '69 up cars. I won't swear to it, but I believe the spread on the two spindle mounting holes are further apart on '69 up.

[William O.]

Re: J-56 Brake Caliper Support Brackets

The 1967 J-56 front disc brake caliper support brackets that I have are casting numbers are:3862783 3862784.

[William O.]

Re: J-56 Brake Caliper Support Brackets

Picture of J-56 front disc brake caliper support brackets :

[Michael S.]

Re: J-56 Brake Caliper Support Brackets

Thanks for the responses. My brackets have the part numbers recessed into the casting rather than raised as shown in the above picture. The numbers are not stamped but recessed as they appear to be part of the mold from which the part was cast.

My brackets appear identical to the brackets in the above photo. I guess I should measure the hole spacing as noted above.

[Dick W.]

Re: J-56 Brake Caliper Support Brackets

Mike, a few years back there were some reproduced brackets floating around. I did not see any to tell you the differences. Maybe someone else can. Vendor made several other casting that appeared pretty close.

[Joe L.]

Re: J-56 Brake Caliper Support Brackets

Mike------

The difference in the 3 sets of supports used over the 66-75 period relates, primarily, to the SIZE of the 2 holes which fasten to the steering arm bolts. The hole SPACING for all of the supports is 3-5/32" center-to-center.

The hole size for the 3882783-4 supports is 15/32". The hole size for the 1968-only 3925397-8 supports and the 69-75 3948879-80 supports is 33/64".

Curiously, the right side 1968-only support was replaced for SERVICE in 1969 by the 69+ right side support, GM #3948880. However, the 68-only left side support was never replaced for SERVICE by the later part. It was discontinued without supercession in May, 1975.

The reason for the difference in hole size for the 65-67 supports and the 68-75 supports is, of course, the fact that the steering arm-to-spindle bolts, which fasten the support to the assembly, were different for these year ranges. 65-67 used 7/16"-20 bolts; 68-82 used 1/2"-20 bolts.

The forwardmost hole in the supports, which fastens the support to the caliper mounting bolt, is the same for all of the supports----15/32".

[William O.]

Re: J-56 Brake Caliper Support Bracket on ebay

FY
Brake Caliper Support Bracket on eBay sold for $1038.53

Item number: 8038396959I:

Regards,

Bill

[Michael S.]

Re: J-56 Brake Caliper Support Bracket on ebay

Holy Sleet Batman!!!!!