Ok, It's probably been gone over before, but I'll ask again anyway. Why are there two lower arm frame mount holes on the 65-70?
I've heard some theory that it's was for wagons to help the rear sit higher? But then had it discounted with other talk that a wagon came on the bottom hole. Better traction on the lower? Is there an advantage to using one over the other? Air ride?
Also, is there anything out there in an assembly manual regarding this? Just curious all of a sudden about it.
seventy2plus2 said
Nov 30, 2021
My 70's only have 1 hole, same as the 69 frame under my Parisienne.
cdnpont said
Nov 30, 2021
OK, 65-68? Thanks.
65Camino said
Nov 30, 2021
Try it in them. See what difference it makes. Let us know afterwards.
cdnpont said
Nov 30, 2021
I'd think you might get a little extra ride height in the upper hole. Figure the holes are about 1" apart, and the spring sits about 3/4 of the way down the arm. So maybe a 1/4" increase?
North said
Nov 30, 2021
Could it be related to two different possible sized differentials available in those years? I can't imagine they would do that to change ride height when all that was needed was a different spring application.
gparis7 said
Nov 30, 2021
In the course of restoring my 68 Impala SS427 I read that the extra holes are to accommodate adjustment of the lower control arms. I think I read it in the factory shop (chassis service) manual, as I used it to verify the correct holes for my application when I re-installed the LCAs. I don't recall why this adjustment capability exists; I'm not even sure the manual said why.
Prefectca said
Nov 30, 2021
Are there also holes in the frame? It looks like to me that the brackets are drilled to fit either side.
Mark... Maybe a "one arm fits all". Do the arms fit Chevy (Yes), multi fit for buick Olds?? Just throwing in my .2 Cents. Might even be a "needed" pilot hole to fabricate the arm? BUT, after 40 years of Corvette experience, that "extra" hole is for a reason. It would be "too much" $$ to punch another hole for no reason.
Remember, the 60's, there was a lot trying to save $$ using parts to fit more than one make/model....
You need an assembly line guy to jump in here...
Prefectca said
Nov 30, 2021
I just found this online from the 1967 Impala manual.
If you were to change it to the other hole, would it not also alter the driveline and U joint angles?
65Camino said
Dec 2, 2021
Guess, it depends on the spring combo.
cdnpont said
Dec 2, 2021
Alrighty then, we'll call it (somewhat) solved. Thanks to all for their input!
F41 and Wagons use the bottom hole.
All others use the top position.
But wait! We still need an answer as to why. And what years have the double position? 68 yes, 65/66 and 69/70...no confirmed. I think my 67 has it too. Might it be a 67/68 thing?
This 2 position mount was used in 67/68
Yes Don, makes sense the HD or F41 springs might be taller than the regular passenger car. Moving the LCA mounting down maybe preserved that same ride hight as all other passenger cars?
As far as moving the mount back and fourth to the different holes changing the pinion angle? No Idea, but it certainly looks like it would. Bottom hole moves the pinion plane down relative to the top hole position. So when down, in order to equalize it, adding shims to the top mounts would bring it back up?
Anyone know if F41 or wagons had the shims behind the UCA frame mounts that all others did not?
-- Edited by cdnpont on Thursday 2nd of December 2021 03:07:31 PM
I was disappointed to see my car only had the one mounting hole. This winter I hope to do a complete differential swap and install the F41 bar as well. I wanted to make it authentic by moving the bolt to the other mounting hoke!
cdnpont said
Dec 2, 2021
I feel your pain.
4SPEED427 said
Dec 2, 2021
One thing I noticed when I took this picture. Notice the distance from the bottom of the control arm to the centre of the bolt in the 2 pictures? They are not the same height. One of those bushings must be shot.
Ok, It's probably been gone over before, but I'll ask again anyway. Why are there two lower arm frame mount holes on the 65-70?
I've heard some theory that it's was for wagons to help the rear sit higher? But then had it discounted with other talk that a wagon came on the bottom hole. Better traction on the lower? Is there an advantage to using one over the other? Air ride?
Also, is there anything out there in an assembly manual regarding this? Just curious all of a sudden about it.
OK, 65-68? Thanks.
I'd think you might get a little extra ride height in the upper hole. Figure the holes are about 1" apart, and the spring sits about 3/4 of the way down the arm. So maybe a 1/4" increase?
In the course of restoring my 68 Impala SS427 I read that the extra holes are to accommodate adjustment of the lower control arms. I think I read it in the factory shop (chassis service) manual, as I used it to verify the correct holes for my application when I re-installed the LCAs. I don't recall why this adjustment capability exists; I'm not even sure the manual said why.
Paul
Mark... Maybe a "one arm fits all". Do the arms fit Chevy (Yes), multi fit for buick Olds?? Just throwing in my .2 Cents. Might even be a "needed" pilot hole to fabricate the arm? BUT, after 40 years of Corvette experience, that "extra" hole is for a reason. It would be "too much" $$ to punch another hole for no reason.
Remember, the 60's, there was a lot trying to save $$ using parts to fit more than one make/model....
You need an assembly line guy to jump in here...
Thanks Paul! Exactly what I was looking for.
First revised into this drawing in 67, but is this just the detail that was added, or the actual engineering of the dual hole?
Paul
Would the wagon take a different rear spring ?
Might be the combination of the two.
-- Edited by 65Camino on Tuesday 30th of November 2021 09:13:17 PM
I guess that's where I saw it - in the assembly manual. I got a lot of specialized info from that one.
Check out page 4-10 of the chassis book
think they talk about station wagon or f-41 option
dont have my book with me right now.
If you were to change it to the other hole, would it not also alter the driveline and U joint angles?
Alrighty then, we'll call it (somewhat) solved. Thanks to all for their input!
But wait! We still need an answer as to why. And what years have the double position? 68 yes, 65/66 and 69/70...no confirmed. I think my 67 has it too. Might it be a 67/68 thing?
Yes Don, makes sense the HD or F41 springs might be taller than the regular passenger car. Moving the LCA mounting down maybe preserved that same ride hight as all other passenger cars?
As far as moving the mount back and fourth to the different holes changing the pinion angle? No Idea, but it certainly looks like it would. Bottom hole moves the pinion plane down relative to the top hole position. So when down, in order to equalize it, adding shims to the top mounts would bring it back up?
Anyone know if F41 or wagons had the shims behind the UCA frame mounts that all others did not?
-- Edited by cdnpont on Thursday 2nd of December 2021 03:07:31 PM
So Mark does your 65 have both holes?
My 66 has F40 and no options for mounting.
Nope, same as your 66 Carl.
I was disappointed to see my car only had the one mounting hole. This winter I hope to do a complete differential swap and install the F41 bar as well. I wanted to make it authentic by moving the bolt to the other mounting hoke!
I feel your pain.