What is backlash?

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dmatchett
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What is backlash?

Post by dmatchett » Thu Mar 03, 2016 5:33 pm

Backlash is basically defined as the play between the two meshing gear. Or, in other words it is the difference between the actual tooth thickness and real tooth thickness, usually when the gear is reversed there is a lag between the pinion and gear, this is generally due to backlash.There are certain advantages of backlash:
Proper amount of back lash is given for smooth running of the gears.

No backlash means the gears need to be manufactured with very high degree of accuracy, proper backlash provides better lubrication,
it prevents the overheating of gears. Also tightly meshed gears are subjected to jamming and eventually seizure of system.

There are few disadvantages of excessive backlash too, excessive backlash results in impact loads during reversing.

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tschafers
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Re: What is backlash?

Post by tschafers » Thu Mar 03, 2016 5:51 pm

Backlash allows for expansion due to heat which is why race cars and heavy duty truck run more backlash than production vehicles. Also Milled gears run more backlash typically 0.008"-0.015" because of greater expansion while hobbed gears run 0.005"-0.008"due to less expansion. This is why you need to determine the style of gear you have to get backlash correct. To do this look at the face of a gear and milled gear face is larger on the heel end than the toe, hodded gears are equal face heel to toe.

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Re: What is backlash?

Post by dmatchett » Fri Mar 04, 2016 11:00 am

Very true....I was not aware of the difference in backlash settings for the milled and hobbed gears...very good info...thanks

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Re: What is backlash?

Post by tschafers » Fri Mar 04, 2016 11:22 am

You find more and more hobbed gears as it is a dry cut method and is more environmentally friendly. The process started in Europe and has made is way to the states. All Jeeps are this way now as they use DANA rear ends that use this method. The first one I did I could not believe the backlash spec was so tight so I had to find out why. Also when checking gear contact tooth pattern, hobbed gears give you an opposite pattern for pinion depth than milled gears. You better know what you have or your adjustments will be 180 degree off.

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dhritsko
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Re: What is backlash?

Post by dhritsko » Fri Mar 04, 2016 11:47 am

Thank You guys for the education I'm getting .
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Re: What is backlash?

Post by zzyzxpat » Fri Mar 04, 2016 11:55 am

Pat Schulte
AAMCO Transmisssions
Temecula, Ca.

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dhritsko
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Re: What is backlash?

Post by dhritsko » Fri Mar 04, 2016 11:57 am

well looks like I will be doing some reading this weekend . Homework ! Hope there isn't a test right away :-)
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Re: What is backlash?

Post by tschafers » Fri Mar 04, 2016 12:50 pm

The DANA website has great information and tooth contact pattern charts for both types of gears, here they are in a document.
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Re: What is backlash?

Post by dmatchett » Fri Mar 04, 2016 1:11 pm

Just to add some extra data, Gleason is the company that makes the equipment for making ring & pinions, the
old manufacturing process was a 5 cut procedure (face milling) tooth diameter tapers from one end to the other
and as advance technology surface any new manufacturer buying new equipment are using the 2 cut procedure
(called face hobbed) with the tooth uniformed or same width from end to end and is seen more in the market
today, I'm quite happy to see the previous posting shown the different backlash requirements for the gears and
I will list it again as this is very good data.

"face hobbing" 2 cut teeth are uniformed use 0.005"-0.008" backlash

"face milling" 5 cut teeth taper from one end to the other use 0.008" -0.0015" backlash

This will vary on racing conditions especially the Ford 9"

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