Canuck Posted August 26, 2023 Share Posted August 26, 2023 I have noticed that the left side upper rear control arm has a plate welded on it. I found a replacement control arm for the right side but it does not have that plate. Were there two different styles of upper control arms? Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted August 26, 2023 Share Posted August 26, 2023 That is the F-41 rear suspension upper control arm. Only one upper control arm will have that plate. Should be the passenger side upper I believe. 3 Quote Link to comment Share on other sites More sharing options...
Canuck Posted August 26, 2023 Author Share Posted August 26, 2023 2 hours ago, MC1of80 said: That is the F-41 rear suspension upper control arm. Only one upper control arm will have that plate. Should be the passenger side upper I believe. Mine has the plate on the driver's side but not on the passenger side. 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted August 26, 2023 Share Posted August 26, 2023 Mine has the reinforced arm on the left side. Found this info too: https://www.chevelles.com/threads/informational-post-10-bolt-vs-12-bolt-rear-upper-control-arms.733202/ (hit the 'See More' link, to see the rest of the pics) https://www.chevelles.com/threads/informational-post-convert-10-to-12-bolt-rear-upper-control-arm.733498/ EDIT: It appears to be more of a 10/12 bolt rear end thing, than a F41 thing? 4 Quote Link to comment Share on other sites More sharing options...
Canuck Posted August 26, 2023 Author Share Posted August 26, 2023 Great info! It turns out the right one of the 12 bolt and both the L and R for the 10 bolt are the same. It is just the left one for the 12 bolt that is unique to allow clearance. Quote Link to comment Share on other sites More sharing options...
jft69z Posted August 26, 2023 Share Posted August 26, 2023 2 hours ago, Canuck said: It turns out the right one of the 12 bolt and both the L and R for the 10 bolt are the same. It is just the left one for the 12 bolt that is unique to allow clearance. I tried looking in the Factory Assembly Manuals for all 3 years too, but couldn't find anything at all. I was hoping they'd narrow it down a little with a different part number, but no luck, in any of the sections/options. Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted August 26, 2023 Share Posted August 26, 2023 Just fyi, the 10 bolt arms bolt right up to the 12 bolt with no clearance issues. Idk why the difference between the one 12 bolt arm and the 10 bolt. Quote Link to comment Share on other sites More sharing options...
jft69z Posted August 26, 2023 Share Posted August 26, 2023 39 minutes ago, MC1of80 said: Idk why the difference between the one 12 bolt arm and the 10 bolt. They mention something in the article I think, maybe the 12 bolt case is a little larger, so they trim a little off the arm. Then they add the plate to stiffen it back up. Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted August 26, 2023 Share Posted August 26, 2023 26 minutes ago, jft69z said: They mention something in the article I think, maybe the 12 bolt case is a little larger, so they trim a little off the arm. Then they add the plate to stiffen it back up. I understand what you say they are saying. Lolol. I just know the 10 bolt arms work also on a 12 bolt. 1 Quote Link to comment Share on other sites More sharing options...
jft69z Posted August 26, 2023 Share Posted August 26, 2023 1 hour ago, MC1of80 said: I understand what you say they are saying. Lolol. I just know the 10 bolt arms work also on a 12 bolt. I agree, they're the same, except for the reinforced one it appears. The assembly manual only has one part number shown. Unfortunately, I couldn't find a part number for the other one. If I was still working, I'd look thru the parts manuals I have on hand. That's not likely to happen today... EDIT: So, it started to bug me, lol. Interesting stuff. The assembly manual shows the upper arms listed as "9790978". However, that number doesn't show up on a google search, or the GM Parts manual I have. What does show up for most applications, without 'SPEC PERF SUSP' is part number '9790979'. That also shows up in google searches for upper control arm for most of the usual parts sources. Next, it lists a separate left & right upper arm for the SPEC HIGH PERF , '9789332' & '97889333'. Didn't see that one coming at all (Tom either, in a subsequent phone call). These part numbers show up later, in a 1990 GM parts list that says 'Discontinued'. I included the lowers too just for informational purposes. EDIT-2: (Just got off the phone with Dennis, he's going to look thru his stuff to see if there's any visual difference between a standard upper arm, and a F41 right arm. We already know the left arm has the reinforcement, what is different on a right F41, that they had a specific, separate part number for that?). Another oddity, just for more confusion, nowhere in the assembly manual, or parts manuals, does it discern between a 10 or a 12 bolt rear end....regardless of F41 or not. Hmmmm, see what you started Aaron? 😁 UPPER CONTROL ARMS: LOWER CONTROL ARMS: 2 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted August 26, 2023 Share Posted August 26, 2023 I've always known it as part of the F-41 suspension package that usually was installed in super sports that came with 12 bolts. I wonder if any of the non SS cars (mostly Chevelle's) that had the F-41 suspension ordered had the 12 bolt style upper arm. 🤔 Quote Link to comment Share on other sites More sharing options...
jft69z Posted August 26, 2023 Share Posted August 26, 2023 6 minutes ago, MC1of80 said: I've always known it as part of the F-41 suspension package that usually was installed in super sports that came with 12 bolts. I wonder if any of the non SS cars (mostly Chevelle's) that had the F-41 suspension ordered had the 12 bolt style upper arm. 🤔 It looks like if it had F41 (or Monte with 454 or 72 Custom), those parts are on the car. 1 Quote Link to comment Share on other sites More sharing options...
Dtret Posted August 27, 2023 Share Posted August 27, 2023 I have the gm 70-75 parts manual and illustration manual that the gm dealers used and it’s not there either. I felt the need to keep searching since I failed Joe ( and essentially the group) on having the regular upper arms. As I was looking through the suspension parts I got , I realized I didn’t buy the rears because they weren’t f41. Which as it turns out are what we all need to see. Maybe I’ll hit the road tomorrow and go buy them from him. Lol. Quote Link to comment Share on other sites More sharing options...
Canuck Posted September 6, 2023 Author Share Posted September 6, 2023 On 8/26/2023 at 3:03 PM, jft69z said: Hmmmm, see what you started Aaron? 😁 😁🤣😛 1 Quote Link to comment Share on other sites More sharing options...
Canuck Posted September 6, 2023 Author Share Posted September 6, 2023 My 70 small block car with a 12 bolt rear but no sport suspension has it so it is a 12 bolt thing rather than a F41 suspension thing. 1 Quote Link to comment Share on other sites More sharing options...
MC1of80 Posted September 6, 2023 Share Posted September 6, 2023 10 minutes ago, Canuck said: My 70 small block car with a 12 bolt rear but no sport suspension has it so it is a 12 bolt thing rather than a F41 suspension thing. Interesting indeed! Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted September 6, 2023 Share Posted September 6, 2023 I didn't know they put a 12 bolt in a small block car. Shows what I know 😅 Quote Link to comment Share on other sites More sharing options...
Canuck Posted September 6, 2023 Author Share Posted September 6, 2023 3 minutes ago, cny first gen 71 said: I didn't know they put a 12 bolt in a small block car. Shows what I know 😅 The only Montes that had a 10 bolt were the ones with the 350 2-barrel engine. All others had the 12 bolt. 3 Quote Link to comment Share on other sites More sharing options...
jft69z Posted September 6, 2023 Share Posted September 6, 2023 55 minutes ago, Canuck said: My 70 small block car with a 12 bolt rear but no sport suspension has it so it is a 12 bolt thing rather than a F41 suspension thing. Do you have any cars there with the F41 Aaron? If so, can you see if the right side upper arms differ at all between the F41 and non-F41? Reason being, for whatever reason, they list a different part number for the left & right F41 arms, even compared to the non-sport version. 1 Quote Link to comment Share on other sites More sharing options...
Canuck Posted September 6, 2023 Author Share Posted September 6, 2023 The right upper control arm for my 71 SS (12 bolt with F41) is the same as my 70 (12 bolt without F41). I also have a 10 bolt Monte without F41 in my garage but I'm pretty sure we know that control arm will not have the extra welded plate on the right upper control arm. 2 Quote Link to comment Share on other sites More sharing options...
Scott S. Posted September 6, 2023 Share Posted September 6, 2023 When I switched from the 8.2" 10 bolt to the 12 bolt I had clearance issues on the driver's side. Found this that explains it. Quote Link to comment Share on other sites More sharing options...
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