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Old 03-11-2020, 08:20 PM
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Default Help with 70 Z28

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
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Old 03-11-2020, 08:38 PM
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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
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Old 03-11-2020, 09:00 PM
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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.”
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Old 03-11-2020, 09:18 PM
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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.
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Old 03-12-2020, 01:22 AM
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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.
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Old 03-12-2020, 01:27 AM
BCreekDave BCreekDave is offline
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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.
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Old 03-12-2020, 02:03 AM
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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.
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Old 03-12-2020, 12:27 PM
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Quote:
Originally Posted by Lynn View Post
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.
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Old 03-12-2020, 01:44 PM
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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/showthre...ghlight=pitman




https://www.yenko.net/forum/showthre...ghlight=pitman
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Old 03-12-2020, 02:21 PM
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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.
Name:  Manual 70 z28 steering box.jpg
Views: 1167
Size:  89.7 KB

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.

Name:  pitnam arm marking-1970 Z28 PS and manual.jpg
Views: 1071
Size:  125.2 KB
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