lost motion

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Loftfield
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lost motion

Post by Loftfield » Fri Jul 26, 2019 7:03 am

Two days ago a friend who parlayed his Vietnam crew chief experience into a lifelong job repairing helicopters found that he no longer had any slow speed. Removing the floorboards revealed that the slow speed pedal turned on the shaft a bit, but then caught and would engage the band when fully depressed, very depressing! With hogshead removed we found that the pin that holds the cam to the slow speed pedal shaft was shearing, was actually bent, causing the lost motion in the pedal on first depressing the pedal but allowing engagement later. This pin had been obtained from a well-known parts supplier and installed three and a half years ago. Now seeking any advice on replacing the pin? Use the same one from a supplier? Get a harder pin somewhere? What are folks doing with this issue? Many thanks for the help.

Tom Loftfield
Brevard, north Carolina


Rich Bingham
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Re: lost motion

Post by Rich Bingham » Fri Jul 26, 2019 10:00 am

Any more we have to be our own final quality check on reproduction parts. A harder pin would certainly help, but a sloppy fit of the pedal on the shaft will always be troublesome. If you have "the touch", compare the hardness of a replacement pin with an original one. Tap with a prick punch or nick with the edge of a file. Not a Brinell test, but it can tell you if a pin is too soft for the duty.
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Original Smith
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Re: lost motion

Post by Original Smith » Fri Jul 26, 2019 10:12 am

I don't believe the issue is the pin. I'm sure Ford probably just used soft steel pins. It appears to me the pedal shafts were not made to the correct dimensions. Why anyone would put a loose fitting pedal shaft into a pedal is beyond me. I would have corrected the problem when it occurred, not months or years later. Some people call it common sense.

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RajoRacer
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Re: lost motion

Post by RajoRacer » Fri Jul 26, 2019 11:16 am

That particular cam pin to shaft installation can be quite difficult at best as it is difficult to secure the hogshead, then swing a large hammer onto a drift to peen the pin - if the pin wasn't peened absolutely tight, tight & tighter, it could easily fail due to movement.


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Re: lost motion

Post by Adam » Fri Jul 26, 2019 11:22 am

I agree with Original Smith that the pin is not the problem. Its how the pin was installed. The pins are plain old, soft, “hot rolled steel”.

The trick is that the pin has to COMPLETELY FILL THE HOLE and be properly riveted over on both ends. If it isn’t, then all the force of the pedal motion is only bearing on a couple high spots which rapidly wear until something doesn’t work anymore, or breaks.

The holes in the pedal, and the holes in the shaft have to be precisely in line, a precise diameter, and the pin has to be a good slip fit in the holes (maybe +.000” to -.003”). “Press-riveting” it cold in a hydraulic press gives way better results than riveting with a hammer.

If you don’t have the knack for riveting, an “easy” way to get pedals tight every time is to sweat-braze the pedals to the shafts. (Before assembling the pedals to the cover)

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RajoRacer
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Re: lost motion

Post by RajoRacer » Fri Jul 26, 2019 1:36 pm

You guys realize he's referring to the internal low pedal cam inside the hogshead - that's a tough one to get at.


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Loftfield
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Re: lost motion

Post by Loftfield » Fri Jul 26, 2019 5:13 pm

Thanks to you all for the concepts. I wasn't there when the pin was fitted, but the guy was a helicopter repairman, and as he phrases it, you can't fix it on a cloud. My experience with him has been that he is an ace mechanic. However, I take the points raised and will share them with him for this fix. When the units were disassembled all were absolutely tight, no play between shaft and cam, old pin required serious pounding to get it out, so....... maybe not peened adequately, I don't know. Oh the mysteries of the Model T!

Tom Loftfield
Brevard, NC


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Re: lost motion

Post by Scott_Conger » Fri Jul 26, 2019 6:31 pm

Pin shear on a device loaded like a low-pedal cam is pretty unusual if both the cam and the shaft are neat fits and there is NO chamfer on either side of the shaft. I personally would look to see that the cam and ramp (pedal support) are a match and in good shape. Both pair of ramps should work in tandem. Since you're in there, be sure to scrutenize both very carefully.

I will bet that once disassembled, there will be some damage seen on the entry/exit of the hole in the shaft and/or cam. If this is so, then the shaft or cam MUST be built up or replaced. It does not take much unsupported length to start deformation and stress risers on pins in shear. I will bet the shaft was damaged during the last pin removal and clean-up around the hole removed material.
Scott Conger

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Re: lost motion

Post by modeltbarn » Fri Jul 26, 2019 10:27 pm

Proper size and installation of the rivet are very important on any rivet, but the other thing on the low speed pedal is the internal notch and cam. If they are worn excessively they can make it much harder to press the pedal, resulting in more force against the rivet.

Pull the hogshead, change the pedal shaft, notch and internal cam. The rivets will be the proper size for the new holes; if anything the holes may be a little tight. I've had to drill out the rivet hole in the internal notch a few times. Once you have everything new it should work much better.


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Re: lost motion

Post by Kohnke Rebabbitting » Fri Jul 26, 2019 11:06 pm

When I was 14, I put in my first peddle shafts. The brake peddle came loose, two times. That is two hogs head removals. I didn't like that.

We had a can full, about a quart FORD can of peddle pins NOS, that were cold roll metal. Also we had a big box full of NOS peddle, and high speed shafts.

Drilling the pin holes over size, should never be done, an it weakens the shaft. as the space between the out side of the hole, and the out side of the shaft is thinner.

Long story short, we cured the problem, with a stick welder, and for many years now, with a wire welder.

The peddles, are all tacked, or full welds, on the ends of the peddle shafts. The top and bottom of the slow speed notch, where it will not interfere with the band. Also, between the two pinned clutch release forks, on the high speed shaft. I have never had a set come loose since then.

If you want to replace them again, it takes about a minute to grind the weld off, and no Model T parts were damaged, in this process.

Herm.

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