When replacing the bushings and bolts this past winter on a 66 with the 1970 12 bolt , noticed the drivers side upper control arm was making wear marks on the housing near the ear where it attaches. Also the control arm had PONT stamped in it. I also replace the 70 12 bolt with a 66 12 bolt.

Now someone told me that thats the wrong control arm. The correct control arm has a little cutout and a special washer welded on to reinforce the cutout area. This cutout allows for clearance so there will be no wear problem.

How necessary is it to replace the arm with the correct arm and must I do it right away or can I wait a few months, like until this winter?

Thanks, JIm

There must have been a lot a 12 bolts put into cars that came with the 10 bolts. So someone must have encounted this problem?

There must have been a lot a 12 bolts put into cars that came with the 10 bolts. So someone must have encounted this problem?

I don't think they used different upper control arms for 10-bolts versus 12-bolts... I have never notice any differences or clearance problems. I do recall seeing this "washer", but its welded to the arm, right? Not a separate piece...

I have swapped 12-bolts into several 10-bolt cars, and always used the arms from the car... These were ALL 1966 Chevelles, and mostly 1966 rearends (I did swap a 1969 12-bolt into my El Camino once, but it was a factory BB/12-bolt Elco...

I recall hearing something about 1964 arms/rearends being slightly different (only 10 bolts offered then), so maybe the arms are from a 1964 Pontiac?

I recently acquired a set of upper control arms that are for a 66 12 bolt I think. On the inside side of the driver side control arm there is a notch cut out on the bottom side of the end that connects to the ear/ bushing on the rear axel. There is a special reinforcement washer welded to that area. I think the notch is there to allow clearence as the lower end would make contact with the axel housing. The control arm that was in the car made a notch in the old 72 rear axel housing that I took out of the car. When I put the replacement 66 rear axel in the control arm was really tight to the housing and I am thinking that it will also make a ware mark on the housing and I should replace it with the correct upper arm with the notch; but just woundered how necessary or how soon I should do this.

When I replaced my 10 bolt rear on my 64 to a 70 12 boltrear. I had to grind the driverside control arm to get clerance. Iīve read somewhere on the net that they used different arms 10 vs 12 bolt but donīt remember if it was all years or just some. Mine also was factory adjustable, exentric washer.

Marcus

Just received a set of upper arms and one has the special washer, will install; but how critical to do it right away? Can I damage the housing?