Rear diff

[David Brady]

I pulled the cover on saturday and changed the lube, it was making some noises I didn't like. It looked okay except the ring gear carrier moved sideways more than a 1/8". No sign of metal except a little silver in the lube. I have the 3.08 gears in the 1/2 ton 2 wheel drive. One shop says I can go to 2.73 gears. I rarely tow anything with this but does anyone have input on the bearing life? I am at 185K to date. My book says that those bearings should be shimmed to preload and shows a special tool for checking that.

[JohnC]

Originally posted by JDave:
It looked okay except the ring gear carrier moved sideways more than a 1/8".If you're saying what I think you're saying, i.e. that you could move the ring gear side to side 1/8", then you've got big problems. You are correct, the carrier runs in preloaded bearings and should have zero sideplay. Also, backlash is measured in single thousanths of an inch. 1/8" play raises he!! with that setting.

I'd get to the bottom of it immediately. The ring and pinion will be junk if allowed to run as is for even a short period. AFAIK, there are no special tools necessary to set bearing preload. There should be an adjuster that screws into the right bearing cap that sets the preload. It should be locked in place by a lock tab held by a bolt.

[ 11-09-2004, 08:42 AM: Message edited by: JohnC ]

[lineman]

JDave,you have too much play in the rear end.I have been busy around here changing out rearends.Just got through doing my son's 1/2 ton Z-71. He had 180k on it.I went totally through the thing for about $450.00.I put in new ringgear and pinions for about $110.00 ( GM over runs ),and all new Timkin bearings and axle seals,along with a new Auburn locking unit.Last nite we finished my neighbor's Z-71. He had 140k on his,but his factory locker fell apart.And just the day before my 14 bolt in my 3/4 ton gave out at 204K,so I'm fixing to dive off in it. I will go all the way through it too.I'm going to put a new Eaton locker in it. Not too hard to do, just time consuming.I have a backlash measuring device to check the backlash, but I agree that there should be no side to side movement.Rebuild it useing the higher gear ratio for better mileage,but redo all of it since you are in there anyway.I would also install a locker or limited slip in it for the added traction.It's worth the money.....Lineman

[catmandoo]

my 92 is also running 3:08's and i have 425,000 on it,can the speedo be recalibrated for the 2:73,i thought 3:08 was as high as they go??

[More Power]

I would recommend gearing that puts the engine's rpm torque peak right at the speeds you drive.

3.42's give you approximately 1900 rpm at 70 mph with an OD trans and stock diameter tires. Going too tall can actually decrease fuel economy, cause more frequent dowshifts and put more stress on an automatic's torque converter (due to a low rpm diesel torque impulse thing - hard on a lockup TC).

For a sneak peek at a new rear diff article, you can visit the following link. smile.gif

http://www.thedieselpage.com/reviews/randys.htm

MP

[ 11-10-2004, 10:23 AM: Message edited by: More Power ]

[David Brady]

My tires are short and wide and I do a lot of freeway driving at 70 - 75. I did want to see if the VSSB would fit with the 2.73 gears. I hope I don't replace the gears, but if I do I will look at this ratio. I would like to be at the 18-1900 RPM when cruising instead of 2200. My truck is a different configuration from most diesel rigs. I am setting up to replace the bearings next week and will baby it until then.

[JohnC]

Originally posted by JDave:
... I have the 3.08 gears in the 1/2 ton 2 wheel drive....
I would like to be at the 18-1900 RPM when cruising instead of 2200. My truck is a different configuration from most diesel rigs. OK, I'll bite. How different could it be? I thought ALL 6.5s came with either the NV4500 or the 4L80E trans'. Either one should get you roughly 2000 RPM cruise at 65 mph with 3.73 gears. If you're seeing 2200 with 3.08 gears, you must have something really strange. Are you running 10" wheels or what? Or do you cruise at 95?

(OK, I worked the math backwards and you must be running something like 24" tires. I think you owe us a picture!)

I'd baby that rear by parking it. If the bearings are that worn you could be a heartbeat away from an axle grenade. Then the ratio would be the least of your problems!

[ 11-10-2004, 06:37 AM: Message edited by: JohnC ]

[David Brady]

Most trucks I've seen are used for towing or 4 wheel drive for off road, which can mean bigger tires. I bought my truck used because it had the diesel and it was 1/2 ton so I thought it would ride smoother than some other trucks. The previous owner had lowered the truck 4-5" and put 15" X 8" mag wheels. I have trouble getting tires as tall as stock to fit, especially up front. I have the 4L80E but my current set of 30x9.5 tires in the back is the tallest and skinniest set of tires I've got for it. It works good for commuting and rides fine so I just want to maximize the fuel economy. I go up and down freeway everyday and at 70 I'm in the slow lanes, #3 or 4. The torque conv locks up at 58-60 MPH, 1600 RPM or so, from what I've read that's normal. It's not the lowest truck I've seen but it's the lowest diesel I know of. When I'm running with traffic I can see that I'm in the 2100+ RPMs. I have replaced the alternator yrs ago but I thought it was identical.

[lineman]

More Power, thanks for the sneek peak! It was perfect timing for me and my 14-bolt.Glad to know that I selected the right locker - limted slip.This is why I love this place! Keep up the good work !......Lineman

[Barry Nave]

JDave
Alt pulley maybe why your showing the high RPM's. Pulley to small. I had done that myself yrs ago on my 95. Now I make sure to reuse my pulley when I need to change Alt.

[sidedump]

Has the inst. cluster back ground been changed? The needles could be on wrong.