Help with 70 Z28

[SS427]

I am very confused. Several years ago I restored Mark Mitchell's Classic Copper 70 Z28 which had factory installed manual steering. On that manual steering box is the pitman arm casting number 3964881 (as seen in this photo). The 5679142 box, arm and all steering components were original to the car.

Enter 2020 and a new Z28 restoration on a Cortez Silver RS/Z28 which came to me with power steering but per the buildsheet it should have manual. Great, so I have a correct 54679142 box and took the 3964881 that was mounted on the power steering box off to use on the manual box but was confused because I know that the pitman shaft is a larger diameter on the power steering cars than on the manual. Sure enough, the 3964881 pitman arm that I have will not fit on the manual box shaft but has the exact same part (casting) number. What gives?

I was on Nasty Z28 on an old thread and some claimed the 3964877 is the correct arm while others say that is not correct on the Z28 and it should use the 3964881 arm for the manual box. I fail to believe the GM would machine the pitman shaft opening for either a power steering car or a manual steering car without changing the part number but that is what I have and this arm will NOT fit (sloppy) on the manual pitman arm. Some of the guys on Nasty also said the 4881 arm is 7" long. Mine measures 8 5/8" overall and 6 7/8 center to center.

Can someone clear the air and does anyone else have a 3964881 arm on a manual steering box or one made for a manual box they would part with?
Thank you in advance for any help you can provide.
Rick

[BCreekDave]

Watching this.
I think what we will find out is that the forging number is the same as that was the length, but the part number was different which determined the broached hole size.
The Z28 used the same manual steering box as the 6 cylinder Camaros. They quickend the ratio by using the longer 8 inch arm. The power steering cars used the used a specific steering box and the 8 inch pitman arm with a larger broached hole. The steering linkage is the same for manual and PS Z28's. Same with the idler arm. The non-Z28 PS cars used a shorter 7 inch arm with a different steering link that offset to the front to comp for the shorter pitman arm.

I think the "M" stamped on the arm in your photo indicated the manual steering '881 arm

[bbbentley]

Bingo-“...I think what we will find out is that the forging number is the same as that was the length, but the part number was different which determined the broached hole size.”

[SS427]

The really odd part is when I do a search on the 3964881 it ONLY comes back as a PS arm and is never listed for a manual and yet as can be seen in my photo, there is one mounted on a manual box.

Dave, I don't think the "M" stands for manual as doing a little research I am hearing of several different letters stamped there. On the 3964881 arm that I have that came in on the latest car there is no letter stamping at all.

[Lynn]

I think they are right on the money. That forging number is not the part number.

Just like 186 sbc heads; all 186 heads have the same casting number, but they may be different part numbers depending on whether they came with 1.94 intake valves or 2.02 intake valves. They start as the same casting but are machined differently.

I had a couple of pitman arms with the same forging numbers; but two different size holes for mounting to the pitman shaft.

[BCreekDave]

Rick,
I think when you do a search on that 881 number it will only come back with the PS part as they made far more of those than the manual, Z28 only '881 arm. They may be a bit hard to find. Not sure how many years used them. Probably at least 70 and 71.

[ronzz572]

Rick I sent some requests out to people I know with original manual steering cars. I will try to have some answers tomorrow if possible.

[ronzz572]

I think they are right on the money. That forging number is not the part number.

Just like 186 sbc heads; all 186 heads have the same casting number, but they may be different part numbers depending on whether they came with 1.94 intake valves or 2.02 intake valves. They start as the same casting but are machined differently.

I had a couple of pitman arms with the same forging numbers; but two different size holes for mounting to the pitman shaft.

I'm going to agree with Lynn here. There should be 4 different Pittman arms that share the same casting numbers. 2 Longer arm for Z28 specific 1 manual steering 1 power steering. And 1 shorter manual 1 shorter power steering for standard non z28 cars. All should have the 881 casting. Identifying them will require measuring them. I see no other way to identify them presently.

[Steve Shauger]

Pitman arm use has been discussed on first generation Camaros, and second follows the same discipline:


For instance the 227 casting # is for the fast ration (5.8 ") and is used for both power steering and manual. however the splined holes are different diameters. The manual steering box has a smaller shaft and PS has a larger shaft.


Here are good links explaining Pitman arm lengths and uses:


https://www.yenko.net/forum/showthread.php?t=144940&highlight=pitman




https://www.yenko.net/forum/showthread.php?t=145523&highlight=pitman

[BCreekDave]

FWIW, some photos.

Photo of the shaft diameter difference between a PS and manual box. The calipers were set off of the PS shaft. The minor diameter (diameter closest to the nut) looks to be pretty close on both pitman arms. The difference is in the taper of the shaft. The PS shaft has a much greater taper so the the other side of the spline hole is much larger on the PS '881 arm compared to the MS '881 arm. The calipers are showing this difference.
160365

Photo of the pitman arm markings from a 1970 Z28. Power steering arm on top and manual steering arm on bottom. The manual steering arm is stamped with a letter "M" at the spline area. Arms are identical length with only difference the spine diameter size.

160366

[bergy]

forgings - not castings. always look for the thick parting line flashing on forgings.

[SS427]

Thank you for that information. The steering gear is fully rebuilt and restored. Now all I need to do is find the pitman arm.

[Ricks72Z28]

Rick,

I found this in my collection, and just not sure on how to validate since I do not have a manual gearbox. Correct 8 inch arm and part number.

Rick

[Ricks72Z28]

Rick, disregard I found out the part is for a PS car.....

Rick

[SS427]

Thanks to a very nice gentleman in Maryland (Steve) he is sending me the correct arm at no charge. The people on this site never cease to amaze me!!!

I guess one good deed deserves another. About 2 minutes after Steve called me with his offer, we were checking out at a convenience store when a clerk in their office went into multiple seizures. I did not know it but Annie saw it and called my attention to it. I was able to administer first aid and call dispatch with her vitals and got her to relax until EMS arrived. My way of paying it forward? Maybe.

[BCreekDave]

Steve's a good guy and it sounds like you are hero to someone! Maybe you missed your calling? Great way of paying it forward for sure!

[ScottG]

Rick, helping to save someone's life is worth more than a pitman arm. Thanks !

[NorCam]

Was following this thread on the pitman arms and just read your last post Rick. Very good of you, and amazing that Annie picked up on that. Give her a big hug as you are both great people. Glad you have a pitman arm coming from Steve as well.

[SS427]

Annie has been around me and the fire department long enough to recognize things. Thank goodness for that.

[L16pilot]

Way to go Rick and Annie! I started taking First Aid and CPR classes a few years ago just in case I was ever faced with that situation. I hope I am never faced with that situation, but just in case, I feel I am at least a little prepared.

I'll get the pitman arm pulled from the box and shipped to you tomorrow...like I said, you're one of the good guys and your actions just proved it.

[SS427]

My pitman arm showed up today. Thank you very much Steve. You saved my ass and did it out of your own pocket. Much appreciated!

[BCreekDave]

My pitman arm showed up today. Thank you very much Steve. You saved my ass and did it out of your own pocket. Much appreciated!

Curious...does it have n "M"

[Mulsanne Blue]

My pitman arm showed up today. Thank you very much Steve. You saved my ass and did it out of your own pocket. Much appreciated!

Rick, Great thread. This has been a topic unresolved over at NastyZ for some time. Could you provide the hole-to-hole center dimension and tapered splined hole diameter? I'm also converting back to manual on my '70 z. Have the box and was going to try using a 881 casting off a p/s, but not now. So the hunt is on. Thanks, Scott

[SS427]

Curious...does it have n "M"

Yep

[SS427]

Could you provide the hole-to-hole center dimension and tapered splined hole diameter?

Using a tape measure for the center to center it looks to be 6 15/16". Using a caliper the splined end measures 1.033 on the small opening and 1.077 on the big opening.

[L16pilot]

My pitman arm showed up today. Thank you very much Steve. You saved my ass and did it out of your own pocket. Much appreciated!

Glad to help Rick :)

[ronzz572]

My final conclusion is that all 1970 specific camaros used the 881 forged pitman arms. I haven't explored 71 and newer. Also are stamped P for power steering and M for manual on the steering box end. The faster ratio streering is created in the steering box for faster ratio steering, Not the longer pitman arm as thought. So there should only be 2 choices for a pitman arms. Manual M or P power steering. Please if anyone has anything different to share. I would like to hear

[BCreekDave]

Maybe there is a bit more to this, I'm not sure.
I base this on the 1970 Camaro Supplement to the Chassis service and Overhaul Manual, page 13 in the Specifications section. Section 9 the Standard and Power steering specifications.

The "Gear Ratio" specs for the 6 cylinder and the Z-28 (and maybe the stand-alone F-41 option?) are both listed at 24:1. When you look at the overall it changes from 28.3:1 for the 6 cylinder to 22.3:1 for Z-28. To me, the only way this change could happen would be beyond the steering box and to the linkage. This would happen then with a longer arm on the Z-28. The longer arm would move the linkage farther for a given rotation of the box input shaft.

Other V-8's list a different box ratio of 28:1 and a still different 33.1:1 overall ratio. If you do the math, the 6 cylinder and the other V-8's have the same offset from the box ratio to the overall ratio at 0.84:1, meaning that the pitman arms are probably the same.

So, I think there are two different pitman arm lengths and 2 different box ratios for manual steering Camaros in 1970.

[Mulsanne Blue]

Using a tape measure for the center to center it looks to be 6 15/16". Using a caliper the splined end measures 1.033 on the small opening and 1.077 on the big opening.

Great. Looks like you solved the mystery of the '70 z pitman arm. Thanks for posting the dim's.

[Mulsanne Blue]

My final conclusion is that all 1970 specific camaros used the 881 forged pitman arms. I haven't explored 71 and newer. Also are stamped P for power steering and M for manual on the steering box end. The faster ratio streering is created in the steering box for faster ratio steering, Not the longer pitman arm as thought. So there should only be 2 choices for a pitman arms. Manual M or P power steering. Please if anyone has anything different to share. I would like to hear

Found this on eBay. The "P" is clearly stamped on the box end.

https://www.ebay.com/itm/Nos-GM-1970-1981-Chevrolet-Camaro-Power-Steering-Pitman-arm/112970784824?fits=Model%3ACamaro&hash=item1a4d956038:g:XrcAAOSw5rFa6FMK

[Mulsanne Blue]

Maybe there is a bit more to this, I'm not sure.
I base this on the 1970 Camaro Supplement to the Chassis service and Overhaul Manual, page 13 in the Specifications section. Section 9 the Standard and Power steering specifications.

The "Gear Ratio" specs for the 6 cylinder and the Z-28 (and maybe the stand-alone F-41 option?) are both listed at 24:1. When you look at the overall it changes from 28.3:1 for the 6 cylinder to 22.3:1 for Z-28. To me, the only way this change could happen would be beyond the steering box and to the linkage. This would happen then with a longer arm on the Z-28. The longer arm would move the linkage farther for a given rotation of the box input shaft.

Other V-8's list a different box ratio of 28:1 and a still different 33.1:1 overall ratio. If you do the math, the 6 cylinder and the other V-8's have the same offset from the box ratio to the overall ratio at 0.84:1, meaning that the pitman arms are probably the same.

So, I think there are two different pitman arm lengths and 2 different box ratios for manual steering Camaros in 1970.

Great work. Math wins again.