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1958 AD-12 Shredded bushing

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1 Old Master

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1958 7.5hp AD-12: The bushing surface on the bottom of the "driveshaft housing & seal assembly", (#14 in the diagram: http://www.marineengine.com/parts/j...&manufacturer=Johnson&section=Gear+Case+Group
) was shredded. Installed a new housing, polished the mating surface on the gearcase pinion shaft, and the driveshaft immediately binds up when tightening the housing down, (insufficient clearance between the bushing and the pinion shaft). Any ideas? Thanks!
 
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This is classic.-----------The spring in that shock absorber is broken.------The unit gets longer and jams up.-------First take the lower unit apart.---------Many folks have ways of solving the problem.
 
It could just be expanded and not broken. You will have to inspect it. If just expanded, pound or press it back together.
 

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Thanks for the quick reply!

When I remove the pin in the shock absorber, is this thing going to go BOING and fly across the shop?

If the spring is broken, are there new ones available? If not, can this be repaired?

The OD of the shock absorber is .991" and the OD of the bushing in the driveshaft housing is .750" and it is flush with the surface of the bronze bearing/bushing. Is this a problem?

EDIT:
Am I correct in assuming that the spring is what preloads the shock and the thrust washer?
 
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The 1/4" gap between the thrust washer and the driveshaft indicates it is stuck in "slip mode", correct? There should be zero gap?
 

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I`m wondering if it has something to do with the forward gear bushing can you feel the gears slamming into each other when you turn the driveshaft?
 
The entire motor is disassembled, with the exception of the powerhead. The gear case is nearly pristine.
EDIT: The propshaft & gears are still on the bench!
 
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You are making it too complicated. With the shock absorber in place, sitting on the flat washer, there should be "some" clearance between it and the bearing housing. More than a few thousandths. The actual amount isn't important, as long as there is that few thousandths. Let's say that if you leave the gasket out, the bearing housing should go down flat against the surface of the gearcase. Then with the gasket in, the bearing housing will be lifted up enough to provide the required clearance.

Ok, now let's look at the anatomy of it. Refer to the picture I posted earlier. The shock absorber consists of two sections, with a very strong spring inside. Normally, the whole thing rotates as a single unit. But if the prop hits a stump or rock, the spring winds up and releases its grip. In that mode, the upper section of the absorber rotates on the lower section--i.e. "released". When the obstruction is gone, the spring returns to its normal gripping function. Note that in the released mode, there is nothing preventing the two sections from expanding away from each other except for contacting the bearing housing. But that is not a hard contact and is not harmful. That is what I meant when I suggested that it might just be expanded. If that is the case, just press it back together and get on with life.

On the other hand, the spring may be broken. Pretty common. When it breaks the ends ride up on each other, forcing serious expansion of the unit. That causes hard contact with the bearing housing, and resulting heat damage. If the spring is broken, you are supposed to replace the entire shock absorber assembly. Some people have welded them. Hat's off to them if it works.

So how do you tell if it is broken? One way is to see if you can rotate the sections on each other. If you can, it's busted. Another way is to clean out the center hole very well, then get it out in the sunlight and peer down into the hole. If you can see the broken ends, well there ya go. My advice is replace it.

Hope this shock absorber class helps. I might not take the time to write it all again.
 
Thank you so much for the excellent Shock Absorber 101 class! I greatly appreciate you sharing your knowledge, experience and time, as I'm sure other members do as well.

I have the shock separated, and now I'm fighting to get the spring out... I WILL win this battle... somehow.

I have fully restored a 53 Elgin 5hp, 73 Johnson 6hp, 87 Johnson 9.9hp, and now this 58 Johnson 7.5hp. Other than this shock deal, everything went very smoothly. Had to fabricate a few special tools, and some parts along the way, but that's to be expected.

Chuck
 
When those springs in the shock used to break and expand, I used to put them in a press, push them back to the correct dimension and weld them in place. The shock function was gone but the customer didn't get hit for the big price they wanted for it.
 
1 Old Master said:
Thank you so much for the excellent Shock Absorber 101 class! I greatly appreciate you sharing your knowledge, experience and time, as I'm sure other members do as well.

I have the shock separated, and now I'm fighting to get the spring out... I WILL win this battle... somehow.

I have fully restored a 53 Elgin 5hp, 73 Johnson 6hp, 87 Johnson 9.9hp, and now this 58 Johnson 7.5hp. Other than this shock deal, everything went very smoothly. Had to fabricate a few special tools, and some parts along the way, but that's to be expected.

Chuck
Click to expand...

Maybe you should consider making some solid "non"shock absorbers to sell. Seems like there should be a market for them. My suspicion is that the springs are breaking from being under stress for so many years. They weren't that troublesome back in "the day".
 
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