Setting pinion preload GM 9.5"

[i6pwr]

I have a 14 bolt 9.5" SF from a trailblazer SS with 45K miles. I have a whine on decal and goes away if I tap the gas.

My question is can I tighten the pinion with the axles installed and accurately set the preload? I would think you can add a set amount of torque to compensate but not sure, just trying to eliminate the extra labor.

 

[mechtech2]

Who knows what's wrong? You may make it worse.

 

[Zaedock]

You would need to pull the shafts to get the most accurate reading, although the freewheeling shafts may still fall within the allowed tolerance. I would pull the cover and inspect everything. You may end up having to replace the crush sleeve and reset the pinion bearing preload - if that's actually what it is.

 

[Gotch]

Backlash "may" be the issue... Tightening the pinion will make it worse (moves the pinion away from the crown gear). Unfortunately, you'll need to pull everything, start with a fresh crush collar and then set the backlash and wipe. Depending on mileage you may want to replace the bearings as well.

I made up a tool to fit over the yoke to tighten the pinion. The crush collar can take around 300lbs/ft to crush...your brakes will NOT hold that much torque.

 

[punisher]

Yes, you can tighten the pinion nut and increase preload, and no you cannot accurately check preload with the carrier/ring gear/pinion seal in place.

Flat surface, in neutral, ck for any lateral play in pinion. turn it back and forth and feel how much slop is present.

Are you getting a noise on "coast" or when you downshift and engine brake?

 

[i6pwr]

Originally Posted By: punisher


Are you getting a noise on "coast" or when you downshift and engine brake?


During coast it's quiet but when the engine begins braking it starts to howl. The howl begins as soon as the braking effect begins, not during hard engine braking.

Everything in the case looks great, obviously it needs attention though.

 

[i6pwr]

Unless there's something you can see with the wear pattern that I can't without using the grease.

 

[punisher]

To be fair, your drive side heel looks a bit wonky, coast side looks acceptable. IMHO of course.

 

[i6pwr]

Originally Posted By: punisher
To be fair, your drive side heel looks a bit wonky, coast side looks acceptable. IMHO of course.

Then the pattern makes sense for a worn or loose pinion bearing?

Under load the pinion yoke would lift upwards opening the gap at the heel correct? Then that would explain the pattern under coast being further down on the heel if I understand it correctly.

I really want to tackle this myself, I feel I'm mechanically inclined enough but I do have sweaty palms just thinking about it considering what's at stake. Just hard to bear handing someone $4-600 mainly in labor.

The way I see it, if I need to pull the carrier, then I should replace the pinion bearings but do I need a press?

Given the wear pattern should I replace the gears? That's what I really don't want to do if they can still be used.

I understand the crush sleeve can be a bear, all insight welcome.

 

[i6pwr]

Coast side toe looks like the drive heel....am I seeing this correctly? Would this explain the howl and likely be a worn or loose pinion?

 

[mechtech2]

Don't forget about a bad pinion bearing, or side bearings [which also need preload].

Noisy rear ends are big problems. You can use heavier oil , or get the whole thing done right.
You or I have no clue what's wrong at this point.

BTW, I used to set up rear ends for Mercedes AMG.

 

[morris]

this may not help but. an easy way to check backlash. is to us cigarette paper as the thin reffance it should pass through the gears with out cutting. then use newspaper as the thick reff to be cut in two as it goes through the gears. this may not real accurate but i have seen it used and the gears lasted forever.
this is what i have found. 1.printer paper .003 in. 2. brown paper sack .002. 3. yellow envelope .005 in. 4. business card .009 in. these are aprox. best to check your own paper

 

[Gotch]

The easiest way to check backlash is with a dial indicator. This is also the most accurate.

All the suggestions thus far have merit, esp. mechtech2's.

However,you can't properly set preload on a pinion in a GM diff without a new crush collar... Your backlash will increase and the wipe will also be out to lunch.

This diff needs a major and complete overhaul or like mech said, throw some thicker gear lube in.

 

[i6pwr]

Well, I have an idea on what's going on but I agree...it's not guesswork when it comes to this. Either the pinion isn't set right from a worn bearing, increased backlash from wear or a slightly cocked pinion angle or.....what is coming to mind is that when I read of many, many stories of the TB SS rear producing a whine then I want to say the gear oil used could be a culprit.

There was a TSB on the SS rear stating the vette specific GM LS fluid at about $22/qt needed to be used. Even with this fluid others still hade whine on decel so I am thinking on trying some redline Heavy Shockproof and see what happens.

I had my hands all in this rear before I installed it, there was no slop in the pinion, carrier was good, spiders were good, backlash is within spec so before I start paying to have it rebuilt...which wouldn't hurt, I'm going to try this fluid tomorrow and see what happens. Some swear by it so what's to lose...I'll post the results.

 

[i6pwr]

I replaced the GM LS fluid with the Redline Heavy Shockproof and took it for a 5 mile drive. Granted the fluid didn't get very warm but the noise dropped dramatically so far. Coast was barely audible and could have been the tires.

We'll see tomorrow but so far it's working, may be just a bandaid but time will tell.