3.90 Ring and Pinion search 1960 C10

[Submariner616]

Looking for some help finding new 3.90 ratio ring and pinion set for my 1960 C10. All I can find is a 3.38. That's all the local differential shop can locate. I checked the Yukon site and all they have is 3.38. I believe it is a 9.375 inch 12 bolt gear 10 bolt cover. Thanks!!

[Warrens69GMC]

not new-

http://www.ebay.com/itm/GM-55T-3-90-...hY99d3&vxp=mtr

[Clyde65]

HO-33 not a 12 bolt.

3.90's are like hens teeth dude!

From Captb Fab wisdom...
Captainfab
60-66 Nut



Join Date: Mar 2007
Location: Coeur d'Alene, Idaho
Posts: 19,700
Re: Rear End Questions
The HO33/35 designation refers to the 1/2 ton differentials used from the second design '55 thru the '62 model year. In '63 the 12 bolt ( 8-7/8" ring gear) was introduced, and in use in the C10's thru the '82 model year.....'79-'80 in the K10's. The bearings and seals will be the same from '63-'82 in a C10. The brakes will be the same from '63 thru about '75-'76, with the self adjusters starting in '66.

[Submariner616]

Everyone says I should go with 3.38 for lower RPMs at highway speeds, but the truck is all stock as built and I'm am trying to keep it that way because it is such a good original barn find. Plus, it already is rather lacking in acceleration and 3.38s would make it worse!

[GASoline71]

if it has a 10 bolt cover it is not a 12 bolt. Unless someone swapped in a BOP 12 bolt with a 10 bolt cover (kinda rare). But I'm guessing as Clyde pointed out, your rear end is probably an Eaton HO.

Gary

[Warrens69GMC]

55T

https://www.yukongear.com/diffdetail...ame%3DGM%2B55T

[Submariner616]

The pictures of a used one on eBay that Warrens69GMC sent below shows 12 bolt holes on the gear. The cover has 10 studs with 10 nuts holding on the cover. When one says 12 bolt or 10 bolt rear, are they referring to the number of bolts holding on the cover or holding on the gear?

[Submariner616]

That's the one, Warrens69GMC. Exactly like that, but a little dirtier! Too bad Yukon only offers a 3.38 for it. Am I being to0 picky trying to keep the 3.90?

[Warrens69GMC]

see link above-answers your question about your differential

[Submariner616]

Yep, got it. 10 bolt cover, 12 bolt gear. I wonder why no one makes the 3.90 replacement for 12 years of trucks that used it. It's a pretty good balance for acceleration, right between the typical (as I knew them) 4.11 and 3.73.

[61K10]

There was one or two on e-bay but $$$. whats wrong with your org one?

[Submariner616]

I'm envious of your 4X4. You asked what's wrong wrong with the ring and pinion gears I have. I am experiencing a vibration in the drive train that does not change with engine speed, just truck speed. The Powerglide was just rebuilt,new U-joints, and new driveshafts and that didn't get rid of it (that's not why I rebuilt it). I took it to a very reputable differential specialist to get an estimate on refurbishing the entire rear axle ($750), and after test drive,he thought the ring and pinion gears MAY need replacing, but if he found they were fine once he got in there, he wouldn't replace them, just all the bearings and seals. He said if he had to replace them, all he could find were 3.38 and not 3.9, so I was looking around to see what I could find.

[mongocanfly]

Unless you've got a nut and bolt original one of a kind with a stack of paperwork truck, I'd probably just swap to a newer rearend before I'd shell out 750 to refurb plus the cost of gears..
Even if you go with 3.38 a simple tire od change to a inch or two shorter will put your rpm and mph back close to the same as with the 3.90 and current tire..how tall are your rear tires now?

[mongocanfly]

Read on this.http://www.onallcylinders.com/2015/0...l-drive-ratio/

[Warrens69GMC]

If you are using the truck in the same configuration now, and will continue to use it, finding a gearset that you could put away (the ebay auction) might not be a bad idea to get them. You may not find another set.

[Submariner616]

It is very original (not every nut and bolt) and completely stock. Wheels are original three piece 15 inch rims with 7.00 X 15 tires, tube, bias ply, about 28 inches diameter.

I have resisted every urge so far to update it (power disc brakes, power steering, A/C, tilt wheel, 4 speed automatic, new bigger small block, etc). It is a long bed stepside, big rear window, original 283 small block, Powerglide 2 speed automatic).

Good idea about picking up a spare set.

[Submariner616]

My 1960 C10 project

[Warrens69GMC]

nice!!

[MikeB]

Did you get the driveshaft balanced? That's something that will vary with road speed. Been there, done that!

T-shooting driveline noises from Ransy's Ring & Pinion:

Part 1: https://www.ringpinion.com/Technical...e_(part_1).inc

Part 2: https://www.ringpinion.com/Technical...e_(part_2).inc

Also from Randy's:

What is this whirring noise?

Whirring noise only while decelerating at any or all speeds is most likely caused by bad pinion bearings or loose pinion bearing preload, and almost never by bad ring and pinion gears.

A howl or whine during acceleration over a small or large speed range is usually caused by worn ring and pinion gears or improper gear set up.

Rumbling or whirring at speeds over about 20 mph can be caused by worn carrier bearings. The noise may change while turning.

Regular clunking every few feet may indicate broken ring or pinion gears.

Banging or clunking only on corners can be caused by broken spider gears, lack of sufficient positraction lubrication, or worn positraction clutches.

Rumble while turning may indicate bad wheel bearings.

***A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.

Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints or worn transfer case or transmission parts.

[Submariner616]

Great links to what problems make what sounds. Thank you.

The sound is hard to describe in words, but you can feel it as much as hear it. Kind of a cyclical harmonic, low in tone. The truck had it when I got it. A little over 80,000 original miles, barn find, that had been parked well over 5 years. The yoke from the rear drive shaft was stuck/frozen/seized in the front driveshaft.

As I began my restoration, my goal was to make it drive-able at first. I had the transmission rebuilt, new drive shafts made, and new u-joints and carrier bearing installed. The differential had little to no oil in it, so I filled it. I rebuilt the brakes and installed new drums. I replaced the front wheel bearings.

She runs along fine on the freeway now at 65 MPH, smooth as can be, except for that sound. Differential specialist was able to reproduce it on test drive. I thought if I had the entire rear axle refurbished as part of my restoration with new axle bearings, axle seals, differential bearings and seals, and inspected the differential parts for wear or damage I would cover it. Including new ring and pinion gears, $750 parts and labor.

[Clyde65]

Wow! That's a great price! Rebuild kit is $230ish alone!
I had my 71/72 12bolt rebuilt with new gears, axles and all bearings etc for around $1650.

[GASoline71]

Originally Posted by Submariner616

The pictures of a used one on eBay that Warrens69GMC sent below shows 12 bolt holes on the gear. The cover has 10 studs with 10 nuts holding on the cover. When one says 12 bolt or 10 bolt rear, are they referring to the number of bolts holding on the cover or holding on the gear?

"Bolts" refers to the bolts that hold the ring gear to the carrier. Also they only refer to GM 10, 12 and 14 bolt axles. The Eaton and the Dana are not "10" bolts. The Eaton is an HO and then Dana is usually a Dana 60. They just happen to have 10 bolts or studs with nuts holding on the cover. Just a little useless info.

Gary

[Submariner616]

Best explanation I've seen! Thanks!