Missing something at spring perch?

[russ]

The hole on the spring perch is much bigger than the stud on the brake armature housing. Is there supposed to be a bushing here?
I've several perches and armature housings and they all fit this way.
Perhaps i've forgotten a part?
http://s298.photobucket.com/albums/mm28 ... nt=207.jpg

[Matt Kroll]

There is no bushing Russ. Just a washer and a nut (see my spring perch below). The hole is oversize to allow for tolerance stack-up, and to allow the parts to be assembled. If the hole were made to size, you would never be able to "rotate" the brake armature stud through the hole.

[Bob C]

Russ, The spring shackles are backwards.

[Drew Mashburn]

Matt:

That's the prettiest spring shackle I've ever seen!

-- Drew

[russ]

Yeah, i've gotta get those shackles turned around. Nothing on the front end is tightened or cotter pinned yet, till i've got it all in place and am satisfied there will be no further need for dis-assembly...like shackles being in backwards. Thanks for the heads up. I read about the king pins locking pin having the nut on the front side so it could be removed without interferance at the sheetmetal, so i figured the same with the shackles...oops.

Matt, thanks for the explanation and pic. I don't doubt you for a second, but i'm not sure what you mean by the following line..."tolerance stack-up"?
Also, does one disregard accurate positioning of the stud before tightening? Seems like a really crappy design with so much slop in there.

The hole is oversize to allow for tolerance stack-up, and to allow the parts to be assembled.

[russ]

Drew, i had George do the king pin bushings. It was a pleasure to watch him work. Thanks for the referral.

[Drew Mashburn]

Russ:

Thanks for using George. He's a great guy and knows how to work on the oldies. I hope you enjoyed looking around his shop. It's a trip!

-- Drew

[Matt Kroll]

... i'm not sure what you mean by the following line..."tolerance stack-up"?
Also, does one disregard accurate positioning of the stud before tightening? Seems like a really crappy design with so much slop in there.

The hole is oversize to allow for tolerance stack-up, and to allow the parts to be assembled.

Stack-up is merely the sum of the manufacturing variation. The distance of the armature stud to the lip on the opposite end that fits into the king pin cup, the depth of the counterbore in the king pin cup, the position and angle of the king pin bore in the axle, the position and angle of the spring perch hole in the axle, the position of the hole in the spring perch, the position of the spring perch hole relative to the stud that goes through the axle, and finally, any irregularities in the taper on the spring perch stud and mating taper in the axle all were machined to within a certain tolerance, maybe +/-.010" and in some cases +/-.005", with angular tolerances of +/-.5 or+/-.25 degrees. When added all together, especially in the case were the measured values were either all near the plus or all near the minus side, you could have a relatively huge variation in the position of the stud relative to its mating spring perch hole.

[Matt Kroll]

Matt:

That's the prettiest spring shackle I've ever seen!

-- Drew

I appreciate your comments Drew, and thanks for not telling me that "it don't 'sposed to be like that!"

[Drew Mashburn]

Matt:

Hey, it's your truck. Do it to it like you want. I'm was serious. Very pretty!

-- Drew

[Jared275]

Russ,
What is meant by "the tolerance stack-up" is the interaction of manufacturing tolerances for the parts. For example say that you have a bolt with a major diameter of .250", the person manufacturing the bolt cannot hit .250" every time so a tolerance is given say +/- 0.01". There is also a tolerance on the hole that is passes through, say the hole is .275 with a tolerance of +/- 0.01. With this bolt and hole size and tolerance there could be a min clearance of .005" (.265-.260), nominal clearance of .025, and a max clearance of .045 (.285-.240). As you can see the clearance on the high end is substantially larger than the bolt. In the case of the shackle hole; the diametral interface of the bolt and hole is not critical to the function of the shackle therefore the nominal size and tolerance of the hole is relaxed (increased clearance). That is why the hole is much larger that the stud. If you have further questions don't hesitate to ask.
Regards,
Jared

[spectria]

Russ,
What is meant by "the tolerance stack-up" is the interaction of manufacturing tolerances for the parts. For example say that you have a bolt with a major diameter of .250", the person manufacturing the bolt cannot hit .250" every time so a tolerance is given say +/- 0.01". There is also a tolerance on the hole that is passes through, say the hole is .275 with a tolerance of +/- 0.01. With this bolt and hole size and tolerance there could be a min clearance of .005" (.265-.260), nominal clearance of .025, and a max clearance of .045 (.285-.240). As you can see the clearance on the high end is substantially larger than the bolt. In the case of the shackle hole; the diametral interface of the bolt and hole is not critical to the function of the shackle therefore the nominal size and tolerance of the hole is relaxed (increased clearance). That is why the hole is much larger that the stud. If you have further questions don't hesitate to ask.
Regards,
Jared

WOW Jared!

I am not worthy...

[Matt Kroll]

Matt:

Hey, it's your truck. Do it to it like you want. I'm was serious. Very pretty!

-- Drew

Thanks. Maybe I did get a bit carried away, as some of the prettiest stuff is hidden:



My "Parts is Parts" gallery: http://www.smokypond.com/gallery/pictur ... tsisparts/

[russ]

Excellent! You knew what i was drivin' at. I'll be using the freeplay twixt the stud and hole to adjust for best fit of actuating arm cup and operating pin. The slop makes sense in this case.
Barely made it in under the wire on learnin' somethin' new every day...11:47 PM here.

[russ]

Hey Matt, this isn't the first time i've noticed how much you enjoyed building your truck. It's your idea of a thing of beauty, and coincidentally...mine too. Not likely mine will ever look similar to yours, but it'll be a great driver all the same.
Did you do your own plating? I recall seeing years ago, photos of an elaborate setup of multiple plating stations. Was that yours? Regardless, great truck you have there.