Do new brakes rods really stretch??

I agree with Maxwell, though the amount of stretch over the lifetime of a car most likely can not be seen by the naked eye..........

as an example, as I get older, I am shrinking......... ;)
 
Post #13 mentioned a big fella pushing 660 lbs on the pedal. 660 lbs pressure would require a right leg that could dead lift 660 lbs. all by itself. Not gonna happen with me. :)

I don’t think a brake rod will stretch, but it will change it’s length as the ambient temperature changes. In the early days of the country when the surveyors mapped out the townships and sections they used a 66 link steel chain 100’ long for measuring.

WHOOPS, got it backwards there. It is 100 links and 66' long. Sorry.

They had to adjust their reading of the length as the temp changed. A 20ºF change in temp would work out to about a 8” change in the measurement with the chain in one mile.

I think driving on a day where the temp is changing would affect the brake rod length much more than any stretching would. So for me it is not a problem. I don’t have to go to the gym now to build up my right leg. Mother Nature has me beat already.

Post #21 “stores all his cranks vertical as he claims they will deform if stored horizontal”
This can happen if the crank is stored horizontally without support under all the main bearing journals. If it is only supported on the ends, then the middle can sag.
 
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I was poster #13 and agree that it is VERY unlikely to happen.

Also, If I dig hard enough I might be able to find the receipt that I got from having to get a $3,500 NASCAR billet crank straightened along with a severe ***-chewing from solely letting it sit on a steel workbench too long. It was only out a small amount, but needed re-grinding, and the cost was as much regardless of the amount of distortion.
 
If you took a kinked rod, straightened it in a large vice, Also straightened the forged eye, then trued it with a BFH you could lengthen the rod. I have seen a few junk yard rods that look amazingly good after the rework. As for factual lengthening I got nothing to add. Streching by mechanical force seems counterintuitive to me.
I think the extending of the threads would correct any length problems of an OEM Rod even if they are not rolled. Stick to the original rods.
 
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Temperature changing the length of the rod will make no difference, as the length of the frame between the parts attached to the brake rod will also change with temperature.

Both are steel with the same thermal expansion coefficient (0.00000645in/in/deg F).

With a 100F temperature change a 50" brake rod will change 0.032". The portion of the frame between the rod ends will change an equal amount, nullifying any effect.
 
RockHillWill said:
I was poster #13 and agree that it is VERY unlikely to happen.

Also, If I dig hard enough I might be able to find the receipt that I got from having to get a $3,500 NASCAR billet crank straightened along with a severe ***-chewing from solely letting it sit on a steel workbench too long. It was only out a small amount, but needed re-grinding, and the cost was as much regardless of the amount of distortion.
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I Agree, I experienced this with a freshly ground 6 cyl diesel crank. It was stored horizontal on a shelf for a month. When installed it would bind up when the mains were torqued down. I measured the runout at about .005. I left it lay in the block supported by the mainbearings for a few days while deciding what to do. I went back and torqued it down again and it turned freely.
Forged steel cranks probably are less prone to warp/sag than cast iron but why take a chance. Bill
 
Karl said:
Interesting how these urban myths start. The mechanic who does most of the local veteran and veteran motor rebuild work and who I respect greatly stores all his cranks vertical as he claims they will deform if stored horizontal. It just can't be true but I can't convince him otherwise . I asked him if they would warp under their own weight why doesn't a camshaft bend form the force the open valve springs exert on it when the car is stopped - No answer yet on that one -Karl
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Karl, The camshaft is supported by its bearings when it is holding a valve open.
The cranks don't have a problem either when they're supported by their bearings.
A long shaft supported only at both ends will sag under its own weight.
Steel is more likely to recover/spring back where cast iron will take a set.
You should listen to that old mechanic, he knows what's going on.
Bill
 
I was hoping that the Ford Barn member who posted the concept of the brake rods stretching would respond to this thread. He just may have some incredible information on this subject.
 
Even at my age, I look for older folks to ask questions of. If you look in some old 'mechanics' books from the teens and twenties like the 'Dykes' manuals, you will see all forms of 4-wheel brakes, 4-wheel steering, etc., etc. All we are doing now a days is 'polishing' what those old guys have already figured out.

Besides, comedian Richard Prior used to say that the reason you don't see many old fools, is that you don't get old being a fool!
 
RockHillWill said:
I was poster #13 and agree that it is VERY unlikely to happen.

Also, If I dig hard enough I might be able to find the receipt that I got from having to get a $3,500 NASCAR billet crank straightened along with a severe ***-chewing from solely letting it sit on a steel workbench too long. It was only out a small amount, but needed re-grinding, and the cost was as much regardless of the amount of distortion.
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Really. The crank was distorted but did solely sitting on a bench cause it. I Know that was the explanation and lecture you got but I remain a sceptic. There is cold creep is observable in peanut butter but I doubt you will ever see it in metal. Karl
 
bbrocksr said:
Karl, The camshaft is supported by its bearings when it is holding a valve open.
The cranks don't have a problem either when they're supported by their bearings.
A long shaft supported only at both ends will sag under its own weight.
Steel is more likely to recover/spring back where cast iron will take a set.
You should listen to that old mechanic, he knows what's going on.
Bill
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Ok You got me thinking . However if they set with sitting wouldn't all our rear axle housings be sagging badly after all these years of sitting
 
Carl, are you familiar with the wear patterns on the rear hubs?

As far as engine issues are concerned: rotating issues at 3,000 RPM are some what more of a concern at 10,000 RPM.
 
Karl said:
Ok You got me thinking . However if they set with sitting wouldn't all our rear axle housings be sagging badly after all these years of sitting
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Karl, The rear axle housings were designed to be supported only at the ends.
The fact that they were only supported at the ends required that they be designed strong enough to achieve this.
Cranks and Cams were designed to have intermediate support and without this support they will tend to sag.
Both when used as designed work quite well.
Bill
 
If brake rods sag from gravity and are repeatedly subjected to pulling strains i guess it is possible they could stretch. Would be interesting to test. Or extremely boring to test.
 
I imagine a hopped up 'banger' getting a A up to about 95MPH (I'm sure some can do better so lets skip that). If one were to make a habit of running it that fast and stopping heavily on a paved surface, and with all due upgrades to the drums, shoes, etc, yet still on 'push n pray' brakes, they might see a stretch that would take a dedicated measuring practice to find. The actual force should be easy enough to calculate AT THE BACKING PLATE with all the rods, pedal and levers in play. All are multipliers designed to give a pantload of force at the shoe. I'll go out on a limb here and say the largest percentage of A drivers here will NEVER stretch their brake rods. I don't see many stock Model As traveling interstates at 60-70MPH, in fact I never see that and hope the 2 or 3 that can don't have to dodge an animal or texting driver :eek:
 
Mark Maron

Can you please elaborate on your claim: "HOWEVER, we are finding that the REPOP Rods are "STRETCHING" this is one the reasons people are fining they have to adjust them more than usual". for the rest of us?

Thanks.

Pluck
 
Of course they stretch, just not much. My guess is you compensate for the stretch by tightening the adjuster 1/16 of a turn per lifetime.........
 
whirnot said:
Of course they stretch, just not much. My guess is you compensate for the stretch by tightening the adjuster 1/16 of a turn per lifetime.........
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Ummmmm, would you explain how you tighten the adjuster 1/16 of a turn?? Looking at the illustration below, wouldn't turning the "adjusting clevis" 1/16th of a turn make the clevis pin not align?? :confused:

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