Help I.D the noise before my K5 selfdestructs

[tRustyK5]

My old 81 Jimmy came stock with 2.76's. They're not that common, but they were out there. Lucky you...

For me, on 33's with those gears the only time I really used 4th gear was freeway. Worse yet, I towed with those gears and tires.

Sounds like your diff needs a rebuild.

Grabbed the pinion yoke , gave it a shake and it has lots of play and my U joint caps have play in the pinion straps

play in the straps sounds like a wrong U-joint was installed. There are several variations depending on year and stuff. The common ones are the 1310's, and S44 joints. Then if the diff has been swapped from another vintage you get the fun of conversion joints.

A 'wrong' joint could definitely have finished off the pinion bearings...

as for the solution it depends on what you want to do. If you're staying stockish and on 31's and can find a good set of 1/2 ton diff's with say 3.42's or 3.73's...it's a pretty easy swap and will make the truck a lot more responsive. If you plan on 'building' the truck anyways it'd probably be better to find a set of 3/4 ton diff's right away and start dealing with the rest of the stuff needed to run those (3/4 ton is all 8 lug stuff)

Rene

 

[496truck]

X2 Now's a good time to decide where your truck is going in the future.

In the interim, if you need it up and running, get a set of pinion bearings (with new races) and a new crush sleeve and a new pinion seal. Remove the carrier, remove the pinion and the old seal. A long punch and a hammer will drive out the old bearing races and use a brass punch to install the new ones. The inner pinion bearing will have to be pressed off the pinion gear (do not remove the shims) and the new one pressed on. Put the pinion stuff back together with the new crush sleeve and new pinion seal, no carrier yet. You will need a beam type, inch pound torque wrench, maybe a dial type will work just not a click type. You will need an impact gun to install the pinion nut and keep checking the turning force it takes to turn the pinion, you are looking for 12-15 inch pounds of turning force to turn the pinion assembly in the diff. I believe that's the spec for new bearings, someone will correct me if I'm wrong.

I use a 1/4" drive beam type inch pound torque wrench with a 1/4-3/8 adapter and a 3/8-1/2 adapter to go into the big socket. A 1/2 drive impact gun will work to install the pinion nut and a really big set of channel locks to hold the pinion from turning while blasting it on. This is a bit of a process, blast a little, check the turning force, blast a little, check the turning force, etc...

 

[magik235]

At least you found the problem. That is always good for the mind if not for the wallet.

 

[cdoggwsu]

I've been tracking this exact same problem since I bought the '88 a couple years ago! The symptoms are identical...absolutely no noise when on the pedal but coasting or clutch in it grinds away. At first I thought it was wheel weights grinding on the TREs but no luck there and everything else in front looked good. Since it directly responds to the gas pedal/load on the drivetrain and it's speed related it's got to be somewhere between the tranny output and rear tires. Also no difference driving in 2x or 4x so TC didn't seem to be the culprit either.

I checked all the fluids and diffs for signs of grinding. No shavings or unusual looking wear anywhere. New joints in the rear driveline didn't help and the rear pinion felt tight, no excessive play in any direction - the angle isn't spectacular due to the lift, but it's certainly not the worst I've ever seen.

I've been meaning to pull the rear driveline and take it for a spin to see if that eliminates anything but just haven't gotten around to it. Hopefully it is the rear diff since I already have axles to replace the 10 bolts.

On the upside, it hasn't gotten any worse since I got the truck so it can't be that bad, right?

 

[lowlifeym]

Well , got in there again tonight a little and found that the pinion nut was really loose . I could turn it by hand !
Tightened it up with a ratchet to see if there was still play and probably have it up to 80 ft lbs , and the play in the yolk is gone . I think I'm going to try tightening everything back up and fill it and see what that gives me . I wasn't able to find a 2.76 around here , one wrecker found one 1/2 way across the country for me and it would be $750 .
My question now is if I had backed off the pinion nut , I would have marked it as per GM recommendations and tightened it to an extra 3 in lbs of rotational force , but since the nut was loosened for me , how do I tell how much to re-tighten ?
I've read that I can tighten to 150 ft lbs safely and it will not crush the sleeve any more than it already is . Is this good advice ? I would like to reassemble what I have and give it a test drive since like I said , everything seems to have no more play and this is a daily driver and my wife wants her truck back .
Worse case scenario is that it still growls like a grizzly in heat and it comes back to the garage for the new to me western rear end .

 

[folkenheath]

Well, is definitely a problem. However, depending on how loose it is, and how long it's been like that, your ring and pinion could be junk too now, and/or your bearings. Since everything could be turning in incorrect positions. I hope not though.

 

[496truck]

Well , got in there again tonight a little and found that the pinion nut was really loose . I could turn it by hand !
Tightened it up with a ratchet to see if there was still play and probably have it up to 80 ft lbs , and the play in the yolk is gone . I think I'm going to try tightening everything back up and fill it and see what that gives me . I wasn't able to find a 2.76 around here , one wrecker found one 1/2 way across the country for me and it would be $750 .
My question now is if I had backed off the pinion nut , I would have marked it as per GM recommendations and tightened it to an extra 3 in lbs of rotational force , but since the nut was loosened for me , how do I tell how much to re-tighten ?
I've read that I can tighten to 150 ft lbs safely and it will not crush the sleeve any more than it already is . Is this good advice ? I would like to reassemble what I have and give it a test drive since like I said , everything seems to have no more play and this is a daily driver and my wife wants her truck back .
Worse case scenario is that it still growls like a grizzly in heat and it comes back to the garage for the new to me western rear end .

Just tighten it up like I described earlier but only go to 8-10 inch pounds rotational force. You can leave the carrier in but remove the wheels and brake drums to eliminate any brake drag.

 

[Blue85]

Are the gears ruined? What does it matter? They're 2.76s so they have to go anyway.

If the pinion nut was loose, just tighten it back up. If the bearings are bad, replace them (but they might be fine). Figure out why the U-joint was loose (probably wrong size or thrashed straps) and correct. None of this takes much time or money and then you're good to go for a while as you find new gears or whole axles to swap.