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Discussion Starter #1
i have a 79 with the 9'' and when i shift from drive to reverse the rear end has so much play it spins a bit then clunks when it stops, im putting a 6.5 in lift when i get back from iraq and i plan to run 38 when i can afford them, i was going to re gear it and i was wondering if that would fix the play, and for that truck with a c6 and a mild build 4oo what gears should i go with, i want to be able to go 55 but not much more, i was thinking 4.88
 

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oscar espinoza
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Well the rear end moving either ur perches are don't or the u bolts are loss....I had my perches messed up fo about a year...it's not purty
 

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internal rotation play, better known as backlash cannot be measured with the turning of the driveline. you have too many moving parts which all have some backlash and all add.
 

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I think he means his drive shaft turns like there is slop in the R&P.

If you have a Detroit Locker its perfectly normal, if not, then you want to pull the diff and get it checked out.
 

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Discussion Starter #5
yeah its acting like there is slop in the r&p, its running the factory rear end right now, but i wont be driving it any till i put the lift and new gears in it, that will give me a good chance to check it out, im hoping that the new ring and pinion will stop it from being so loose
 

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I think he means his drive shaft turns like there is slop in the R&P.
I understand that, the problem lies in the fact you cannot check backlash (or slop as you call it) using the drive line with the differential installed and the axle on the ground with tires on it.

backlash is some wheres around .008-.012 of a inch, your drive line is probably turning 1/8-1/4 of a rotation in the diff making you think you have excessive backlash.

you have a tiny amount of motion in all the parts.

axle shaft splines to side gears
side gears to pinion gears
ring to pinion.

all of those add up.


but by all means check it out, and if your regearing because of the lift then don't worry about it.
 

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4.88's sounds good to me.

The difference between that & 5.13's is minimal.
 

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My bronco had same problem, it was splines on rear axel shafts not the R/P. But the truck was very high in miles.
 
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