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Looking to replace the rear upper control arms. Are there different OE sizes (lengths) of upper rear control arms on the 70-72 A-body? Year One shows different upper rear control arms depending upon whether it's a 10-bolt or 12-bolt rear axle. Different lengths of course would affect the pinion angle. Thanks.
Looking to replace the rear upper control arms. Are there different OE sizes (lengths) of upper rear control arms on the 70-72 A-body? Year One shows different upper rear control arms depending upon whether it's a 10-bolt or 12-bolt rear axle. Different lengths of course would affect the pinion angle. Thanks.
68-72 factory uppers are the same length. If you are looking at aftermarket ones get the ones with the offset hole towards the bottom on the rearend side. You will be able to use them for either rearend.
The factory parts book shows upper arm P/N 9798214 for all 68-72 A-body cars with any of the axles used (Type O, Type C, or 10-bolt) except for the "442 suspension" which uses 9798211. I can only assume the different P/N is due to different stiffness of rubber bushings for the FE2 suspension.
I'd call Year One and ask them what the difference is (knowing in advance they prob won't be able to answer). Aftermarket adjustable ones are pretty widely available
the "chevy" 12 bolt rear housing has a bulge on one side that interfears with the lower "flange" on the upper control arm on one side... so they trimmed the flange and a small reinforcement plate was welded on that the bolt goes through.
I believe that fix is only needed if running a CHEVY 12 bolt... not the BOP 12 bolt. or Chevy or bop 10 bolt. I am not 100% positive though.
the "chevy" 12 bolt rear housing has a bulge on one side that interfears with the lower "flange" on the upper control arm on one side... so they trimmed the flange and a small reinforcement plate was welded on that the bolt goes through.
I believe that fix is only needed if running a CHEVY 12 bolt... not the BOP 12 bolt. or Chevy or bop 10 bolt. I am not 100% positive though.
Again, the factory parts book shows the same upper control arm P/N for Type O, Type C (ie, CHEVY 12 bolt), and corporate 10-bolt for all 1968-72 cars.
68-72 factory uppers are the same length. If you are looking at aftermarket ones get the ones with the offset hole towards the bottom on the rearend side. You will be able to use them for either rearend.
The offset hole on the aftermarket arm may be to make it universally fit any rear housing, if there is a clearance issue described below. Wouldn't the offset hole slightly change the angle of the pinion though, like changing the arm length?
Thank you all for your replies. Some sellers of aftermarket rear upper arms (other than YearOne) mention their arm is for a 10-bolt. But I'm inclined to think that the factory parts book is the most reliable.
The offset hole on the aftermarket arm may be to make it universally fit any rear housing, if there is a clearance issue described below. Wouldn't the offset hole slightly change the angle of the pinion though, like changing the arm length?
There are only two holes. The only thing that can change pinion angle is the center-to-center distance between the holes.
Right, so if one hole is offset, the center-to-center distance may change, depending upon where the hole is located, albeit slightly.
Depends on whether it was offset at 90 degrees to the original centerline or on a radius from the other hole. The latter would be the same center-to-center distance.
Frankly, depending on the amount of offset, the length difference is negligible. Trig is your friend. a^2+b^2=c^2. Assume the center-to-center distance is a foot. If you offset the hole by 1/4", that's a whole 0.002" difference in center-to-center length. For a 1/2" offset, the length difference is 0.010". Even if you offset the hole by an inch, it's still only a 0.040" length difference.
Depends on whether it was offset at 90 degrees to the original centerline or on a radius from the other hole. The latter would be the same center-to-center distance.
Frankly, depending on the amount of offset, the length difference is negligible. Trig is your friend. a^2+b^2=c^2. Assume the center-to-center distance is a foot. If you offset the hole by 1/4", that's a whole 0.002" difference in center-to-center length. For a 1/2" offset, the length difference is 0.010". Even if you offset the hole by an inch, it's still only a 0.040" length difference.
Thank you Pythagoras, for the refresher on trigonometry. My slide rule confirms the accuracy of your calculations.
I'll use the 9798214 P/N you supplied and cross-check after-market arms against it. Thanks Joe!
early cars had a longer upper control arm 13" hole to hole
the 2 part numbers may be because there are 2 different upper arms
the 12 bolt chevelle
and the rest of us ...........
differences shown in pictures ... 71 chevelle 12 bolt posi 331 reinforced
control arm ... and they are trimmed
and a std pair for my 69 Judge 10 bolt nodular posi 355
Scott
I don't know anything about Pontiacs or Chevys. I only know what's in the Oldsmobile Parts Book. There are only two P/Ns for the 68-72 Cutlass line, one for "442 suspension" (ie, FE2) and one for all others.
The parts book does not differentiate between Chevy and Type O axles.
The parts book does not differentiate between US and Canada cars.
The parts book only differentiates between standard and upgraded suspension. According to the parts book, all 68-72 cars without FE2 got the same upper arms, whether Type O, Chevy axle, or corporate ten bolt. All cars WITH FE2 got the same arms, meaning that Canadian built 442s with the Chevy axle got the same arms as US built cars with the Type O. These part numbers I posted above are for upper arm assemblies, meaning the metal arm plus the rubber bushings. As I said, the only differences I could see related to the suspension would be either the stiffness of the bushings or the use of a reinforced arm.
12 bolt Chevy has the largest ring gear out of all the casting the outer dimension does not leave enough room for the 10 bolt and 12 bolt olds driver side upper control arm to travel with out rubbing just below the control arm bushing to the center of the casting.... SO 12 bolt Chevy control arms have a bit shaved off the control arm just below the bolt hole where it would rub on the cast center section... and the reason you will see the control arm with a tack welded support plate because of having to do this.
SO really you can use any upper control arm and do the mod yourself for the clearance to use on the 12 bolt Chevy and weld a washer in if you want more support also.
1964-1967 are longer as stated from hole eyelet to hole eyelet.
1968-1972 are shorter as stated.
This was because GM moved the chassis cross member back a 1" or so to give a hair more room for the back seat...LOL. YES a Hair...
This was also done in the Impala line too control arms for the uppers were longer in the earlier years and later shorten for more room to increase back seat area by a hair....
Hope that clears up everything ion the REAR differential control arm deal .
I know it is a OLD post... but it looked like some one referenced it and it looked like it could use a bit more info.
If we go back to an old enough parts book, such as the Nov 71 edition, we see that there were regular and stiff bushings, the latter was 388266. Later in the 70s GM supplied the soft bushings under that part number but originally it was stiff. Also, there was a special left upper control arm, 9792783, for the C axle, with the trim and reinforcement because the ear was closer to the main part of the pumpkin with the larger ring gear of the C differential.
Returning as the OP ... Are there any tips, tricks or issues to be aware of when removing and replacing the rear upper control arms ('70 Cutlass conv'ble.)? Attached are removal / install instructions that appear correct. (I am installing OE bushings.)
I want to replace the bushings for the other end of the upper control arms on the pumpkin as well. Can I use a removal tool to squeeze them out?
Thanks in advance.
Last edited by Toms cutlass; March 18th, 2020 at 05:15 PM.
When I did mine a few moths ago I had the whole rear end out of the car, so I used the drill and hammer method. Vintagechief use this tool for his rear end bushings with the rear end in the car and said it worked perfectly. https://www.jegs.com/i/Ridetech/029/85000011/10002/-1
I just finished replacing my upper & lower rear control arms w/ UMI Performance control arms on my '71 CS convertible. I very briefly read the document you posted - very briefly.
It's easier to remove/install the rubber bushings & metal sleeves of the upper control arms at the attachment ears at the top of the differential, but this requires dropping the entire rear axle i.e. removing removing the brake lines. I did not drop my axle & instead I was able to remove & install the new bushings & metal sleeves w/o completely lowering (removing) the rear axle. It's a tight space for sure, but it can be done w/ the correct tools. To save myself the trouble of finding the exact size metal sleeves to extract (remove) & compress (install) the bushings & sleeves, I picked up a special extractor/installation set which worked easily & flawlessly - saved me significant time. I'll look for the part number and shoot it over to you after I post this.
The one item I suggest is to ensure you coat every bolt, nut, washer and all bushings & sleeves for all control arms with a very liberal coating of water-proof grease during assembly.
Picture (below) during my rear end rebuild. It isn't necessary (I don't suppose) to support the propeller (drive) shaft. I thought it a good safeguard for support while raising and lowering the rear axle while I was working on the rear end.
There are more images towards the bottom of the link demonstrating the basic working areas: https://classicoldsmobile.com/forums...ension-141577/
Raise the car as high as possible and place jack stands under the frame forward of the rear wheels. Remove the tires, disconnect the driveshaft from the rear, put a floor jack under the pumpkin for support, disconnect the shocks at the bottoms, disconnect the rubber brake line hose from the main line, lower the rear, pull the springs out, and tilt the rear back a bit so you have good access to the rubber control arm bushings. Use the tool posted above that Norm used to remove and install the bushings. R & R the upper arms and reassemble following the above steps in reverse.
Thank you very much for the detailed instructions!
The fuel tank is already removed providing extra room. Disconnecting the brake line is something I'm likely to do anyway, since I'm also planning to replace the rear axle brake lines, the rear axle hose, as well as the front-to-rear brake line. (May as well category.)
Eric, Please explain what you mean "tilt the rear back a bit" ...
I'll use several rounds of penetrating oil on the bolts/nuts too and wait a few days for penetration. Should I use only manual wrenches or is an impact wrench ok to use? How about heating the bolts/nuts?
I think the bushing tool is available for rent at the local parts store.
Last edited by Toms cutlass; March 19th, 2020 at 01:03 PM.
Thank you very much for the detailed instructions!
The fuel tank is already removed providing extra room. Disconnecting the brake line is something I'm likely to do anyway, since I'm also planning to replace the rear axle brake lines, the rear axle hose, as well as the front-to-rear brake line. (May as well category.)
Eric, Please explain what you mean "tilt the rear back a bit" ...
I'll use several rounds of penetrating oil on the bolts/nuts too and wait a few days for penetration. Should I use only manual wrenches or is an impact wrench ok to use? How about heating the bolts/nuts?
I think the bushing tool is available for rent at the local parts store.
Since the only connections you have left at this point in my instructions are the lower control arms, I mean roll the top of the rear back to get better access to the upper control arm bushings in the housing.
Since the only connections you have left at this point in my instructions are the lower control arms, I mean roll the top of the rear back to get better access to the upper control arm bushings in the housing.
I knew Eric was referring to the rear, but it might not have been apparent what he meant was the axle (calling it the rear in this case).
Since in the original post he said roll the rear back, I thought you might have thought - hmmm....roll the rear of the car back? LOL
I think the bushing tool is available for rent at the local parts store.
I have a couple bushing tools with various metal sleeves. If you rent one at the local parts store, there's a good chance it won't work - here's why.
The point where the control arms attach to the top of the pumpkin have a large rounded edge which doesn't allow a general set of bushing removal sleeves to gain entry. If you had your own set, you could/might be able to cut out that edge to get a metal bushing sleeve into position. I had thought about it, but I wasn't in the mood to begin sawing away some of my bushing sleeves to (1) make them narrower and (2) cut out the piece to fit the rounded edge. Your call. If the set you rent won't fit you can always take it back. Eric got it to work, but he probably has more metal bushing sleeves than I do.
I have a couple bushing tools with various metal sleeves. If you rent one at the local parts store, there's a good chance it won't work - here's why.
The point where the control arms attach to the top of the pumpkin have a large rounded edge which doesn't allow a general set of bushing removal sleeves to gain entry. If you had your own set, you could/might be able to cut out that edge to get a metal bushing sleeve into position. I had thought about it, but I wasn't in the mood to begin sawing away some of my bushing sleeves to (1) make them narrower and (2) cut out the piece to fit the rounded edge. Your call. If the set you rent won't fit you can always take it back. Eric got it to work, but he probably has more metal bushing sleeves than I do.
I didn't use a special tool. I drilled around the rubber in the bushing and removed the innerds, then crushed and hammered out the outer sleeves. Then hammered the new bushings in.
Rather than mess around, maybe it's just easier to drill out the rubber bushing part and punch out the metal outer sleeves the way Eric did ... after I "roll the rear."
Did you have a question? Did you purchase the tool? Are you still considering the purchase? Posting for the benefit of others? Or, you already have the bushings removed?
I posted to supplement this thread, and the great knowledge you and others have shared, for the benefit of others. Doing several R&Rs in this job, including rear brake line, axle lines and hose, shocks, lower control arms, fuel tank/sender, straps, etc. collecting all parts first. Car is up and tank out. Evaluating whether to acquire bushing removal tool. Dropping axle would provide more room to access the upper bolts of the upper arms, as well as the main brake line to rear hose connection. Thanks again Norm.
Last edited by Toms cutlass; March 24th, 2020 at 01:54 PM.
I posted to supplement this thread for the benefit of others. Doing several R&Rs in this job, including rear brake line, axle lines and hose, shocks, lower control arms, fuel tank/sender, straps, etc. collecting all parts first. Car is up and tank out. Evaluating whether to acquire bushing removal tool. Dropping axle would provide more room to access the upper bolts of the upper arms, as well as the main brake line to rear hose connection. Thanks again Norm.
At this point with all the other mods your doing, I suggest you bite the bullet and just drop the rear out of the car. Your just 2 lower control arm bolts and either remove the brake assy and parking brake cables, or disconnect the rear cables up front and slide it out in the open. I assure you its much easier with it off the car to do the bushings and brake lines with the rear sitting on the bench or stands. Then you can clean and paint it all pretty-like.
This is what I did with mine https://classicoldsmobile.com/forums...nstall-140057/
That's tempting me Eric, and I've considered that. (Like so often is the case in restorations, this started out as a simple fuel/sender, etc, R&R, and now this.) My concern with pulling the whole axle out is getting it back in, aligned so that I can bolt it back up. If I drop the axle and "roll the rear" as you eloquently described it, leaving the lower arms connected, I'm confident I can align it aligned to bolt the upper arms back in. (I also don't have the luxury of an extensive amount of room to work.)
February 27th, 2018, 11:59 AM
