Twelve bolt growl on decel

[biggerman]

Ok guys, I just finished the rebuild of my 12 bolt passenger car rear end in my El Camino. I installed new 3.08 gears from USA Gear, new carrier bearings, new pinion bearings, new crush sleeve, seal and nut. The gear mesh pattern was right in the middle. I set the backlash at 7 thousandths (6-10 is spec from book) and the pinion preload was 21 inch lbs.

The rear is quiet on acceleration but makes a slight ruga, ruga noise when you let off the gas during deceleration. It is within spec if you go by the numbers.

I was a bit confused about pinion preload for this rear end, as the book from USA gear said 14-19 in lbs. and the Chevrolet spec says 20-25 inch lbs. I attempted to stay within the 14-19 but couldn't. I tightened the nut until there was no play in the pinion, and checked it. It was 9 in. lbs. I turned it maybe a 1/16th of a turn and checked it again and it was 21 in lbs.

Just a few other details to note.

· I have a series two carrier and had to use the spacer plate under the ring gear.

· This is the second time around for this rebuild. After the first try, I went out for a break in drive and the rear clunked a couple of times and then the growl of the pinion bearings.

I went home and pulled the cover and found metal stuck to the gear! It turned out one of the spider gear thrust washers fell out during reassembly and had been chewed by the diff. I completely disassembled it again, cleaned it thoroughly, purchased and installed new bearings, races, seal, crush sleeve, nut etc. and reinstalled it all to the specs.

I’m just wondering if the noise is something I’m going to have to live with. The gears had some scuffs where the washer went through, but there were no chips or broken teeth. The washer material is softer than the gear set, so it didn’t do much damage.

I can’ afford to replace the whole mess again. The rear is not running hot, as I drove it yesterday for about thirty miles and the diff was warm but not hot.

This was my first run at a diff rebuild, so It was a learning experience. Do you guys think it will quiet down as the gears wear in?

All my research says the ruga, ruga on deceleration is a loose pinion nut, but I don’t want to over tighten it and burn up the pinion bearings.

Thoughts and opinions are welcome.

[bryant]

the pinion bearing preload differences depend on what is lubricating them when setting the preload. the lower numbers are with gear oil. the higher numbers are with bearing grease.

how much preload is on the carrier bearings?

does the carrier slide in and out? if you dont have enough preload on the carrier bearings they will allow the carrier to shift and cause the gears to move off pattern.

did you debur the pinion bearing race lands in the housing? when knocking out the old races, a riser is usually created on the bearing land and needs to be removed before the new races are installed or the new races can sit cockeyed in the the housing.

ring gear spacers are a bad idea. they severely reduce the the amount of the machined center that the ring gear needs to center on. i have seen several sheer off the ring gear bolts. i also ive seen a lot of spacers that are not a consistent thickness. this will change the back lash at different points. this can be checked by checking the back lash with the ring gear turned to at least 4 different points.