69-72 BB Alternator bracket difference questions

[Enoch]

Top bracket when did they go from the no hole to the round hole then oval hole in the middle, or did they overlap?
Lower Bracket when was the change from stepped to flat?
Thanks. http://www.yenko.net/ubbthreads/pics/usergals/2015/06/full-905-26975-img_3111.jpg
http://www.yenko.net/ubbthreads/pics/usergals/2015/06/full-905-26979-img_3112.jpg
http://www.yenko.net/ubbthreads/pics/usergals/2015/06/full-905-26980-img_3113.jpg

[bbbentley]

The flat bottom and no hole top are 1969, I believe only 69. May hear different.

[SS427]

I have documented some very early 1970 Chevelles with the no hole upper bracket but that is rare.

[Enoch]

Thanks guys I was at least on the right track! So Rick do you think the 70-up bracket with the round hole (as opposed to the larger oval hole) was a transition piece? Thanks again.

[Mr.Nickey Nova]

I have the flat bottom bracket and round hole upper on my 70 L34 Nova built third week of January if that helps.

[hiperf69]

I believe ,
Top Brkts are
'69 no hole
'70 round hole
'71-2 oval hole maybe even '73
'74 oval hole but Brkt. is more cut away on the back side
Lower Brkts.
I think changed in '74
Also have had people ask about ' 70 upper Brkts. As to where they are threaded for the Ground strap.
I understand that different plants used different hole locations
and have had them like that.
Maybe there is paper memo's or running change's
or maybe some of those were just built on Monday's!!
Joe

[Mr70]

I agree with most of what has been said.
My October '69 Leeds assembled 1970 Chevelle originally came w/the top Alt.bkt. shown on the far right,and with the the negative battery cable grounded to the block,not to the bkt.with a star washer under it digging in.
And the designated hole for it was never tapped.
Nearly every top bkt.I see,has that hole tapped and you can see where the star washer bit into it,leaving a noticeable impression.

I think I have a 1970 production service bulletin stating the battery should now be grounded to that top Alt. bkt.,not the block like in '69,but there seems to be a few early '70 assembles that didn't pay attention,or get the memo in time.

[RPOL88]

Do all factory bottom brackets have markings on them or were some without?

[SS427]

Here is a survivor 1970 SS454 Monte Carlo I looked at in New Ulm, MN manufactured on 10B/69. Notice no third hole for the ground cable and no ground cable as it was grounded at the block.

[SS427]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Enoch</div><div class="ubbcode-body">Thanks guys I was at least on the right track! So Rick do you think the 70-up bracket with the round hole (as opposed to the larger oval hole) was a transition piece? Thanks again. </div></div>

Like many items I think a lot of plants used up their inventory in many cases even though the new design was different. This Monte also had plastic rivets holding the solenoid to the wire gutter which was the first time I had seen this on a 1970 A-body.

[Donnie]

I think they were grounded to the head until some time in Jan. 70 then it moved to the bracket.

[Unreal]

I thought the flat lower bracket was 69 only, and had the pressed in spacer. I thought the offset one was after 69.