Round 3 of GTX Rear end rebuild - gear noise

[AR67GTX]

This is my fourth time to pull this rear for anyone who has followed my previous two threads. A 489 case with new Sure Grip and 3.55 Richmond gears. This is the second set of gears the mechanic has installed in it. This time I had a loud mechanic howl when ever I released the throttle. I only put about 10 miles on it since it was definitely all jacked up. At least I'm getting quick at pulling the rear out of this thing - 1 hour 15 minutes this afternoon. This little carrier I built is a lifesaver.

The drive side pattern looks pretty decent to me (I think) and it was quiet in acceleration and cruise.

But the coast side (where I was getting loud noise) looks pretty peculiar to me - the pattern covers nearly the entire face???

So, what would cause that? I did a quick check of backlash and it seems to still be at ten thousands.

 

[Mike67]

Your dilemma made me curious as my knowledge with setting up gears is shadetree at best....so I started doing some research, I did not know there were two types of mfg'ed gears. But I found this article very detailed and might provide you some answers in the setup section of the body...great illustrations too...
https://www.cartechbooks.com/techtips/ring-and-pinion-gear-selection-for-optimal-performance/

 

[moper]

So, what would cause that? I did a quick check of backlash and it seems to still be at ten thousands.

Improper setup.
Both the drive side and the coast side of all the teeth on the pinion and ring gears have exact spots that are meant to contact. There is only one "perfect", and it's not a big target. They have to be placed exactly there or they will be noisey. Sometimes it takes patience and lots of setups, and ignoring the case dimensions of the setup tools. The only way to verify that placement is the pattern and the backlash. Of those, the pattern is always the most important to get perfect. Your guy got part of it, and figured "good enough" on the pattern. With a new set of gears, you have one shot to get it right because they break in either right or wrong and then it's done. That's why it doesn't go in the car until it's perfect.
IMO - the gears will always be noisey on coast now even if he can find the right spot. I have never had any success in resetting a new set that was noisey and getting it quiet.

 

[Darthomas]

Pinion set too deep into the ring.
Normally wants to go that way anyhow when load is removed, and then it sings.
When pinion is not deep enough, or pinion is "loose" from bearings it walks away from the ring under load, and makes noise when the gas is on.

 

[AR67GTX]

Your dilemma made me curious as my knowledge with setting up gears is shadetree at best....so I started doing some research, I did not know there were two types of mfg'ed gears. But I found this article very detailed and might provide you some answers in the setup section of the body...great illustrations too...
https://www.cartechbooks.com/techtips/ring-and-pinion-gear-selection-for-optimal-performance/

Handy reference guide - probably the best one I've stumbled across. Thanks. However I didn't notice any discussion of issues that would explain the expansive pattern on the coast side. It's running from toe to heel and to crown. I'll be hauling it back over to the shop on Friday for another go at it.

 

[pwtjr]

This brings back bad memories for me. I rebuilt my 8 3/4 a few years ago. Had that thing together and apart so many times before I FINALLY got it.
I tried to go by the manufactures pinion depth recommendation, but it just wasn't happening. Can't remember the exact details now, but I do know they had my pinion depth way to deep by their recommendations. I seriously had this thing apart a dozen times or better before I hit the sweet spot.
Wish I could help more.
Good luck.

 

[AR67GTX]

Just to be sure - by saying the pinion is too deep, that means too far towards the rear of the car and the center of the ring gear - correct?

 

[gtxno1]

Darthomas is correct the diff must be set up correctly usually requiring special tools to do it what you can do is waste one bearing to do it the one that gets pressed on buy a new one take it to a machine shop and let them hone it so it just slides on the pinion now you can try the shims and get it perfect and even set the rolling pressure required when all done you can install the correct shim with a brand new bearing save the honed bearing for future builds very cheap tool lol BTW as long as you did not drive across the US you can probably just adjust everything to the proper specs and the noise will be gone buy some diff paint for the gears do not guess just do it right

 

[AR67GTX]

After taking more time to study this coast side pattern I think I mis-reresented it above. It appears the coast side of the gears may have been lapped by Richmond. I didn't notice that upon installation because there was so much yellow marker paste on them. I think the actual contact point is on the outer half or at the heel where the finish is lighter in this photo. It's probably not very distinct because I only drove it a few miles and probably only coasted a few hundred feet.

Looking at my service manual a similar contact area on the coast side (towards the heel) says to increase the pinion shim (pinion too shallow). The CarTechBooks guide Mike67 posted says the backlash should be increased to move the coast pattern back to center - but that will move the drive side contact towards the heel which I'm not sure is going to help things much since it looks pretty centered now - unless I'm mis-reading it too. Alternately, the pinion shim thickness could be increased (pinion again to shallow) to shift the coast pattern towards the toe.

So, I'm a little confused - the consensus of most comments in this thread and my previous thread was that the pinion is probably too deep? Sounds like it may be too shallow? Not sure I would want to open the backlash up any more.

My differential guy has been talking to some guys at our local speed shop and we discussed that I let them look at it and see if a fresh set of eyes can come up with something we are missing.

 

[gtxno1]

Stop guessing apply the paint check the pattern there is no gray area pretty simple

 

[AR67GTX]

Fortunately there was enough lead paste still in the gears that I could coat a few teeth. Problem is that this Lucas Gear Lube really clings to everything and is extremely slippery - so the pattern is not the best and may have to use your imagination a little. The coast side is definitely off on the heel - which is a lot different than when he set it up.

The drive side looks pretty good - pretty much as set up.

Here are photos from right after the set up before I ran it.




So the pattern on the coast side has definitely slipped but the backlash appears unchanged. So what could cause that? I noticed it revolves real easily now. I'm not sure if it's the lube or maybe something has lost it's preload.

 

[moper]

I'm guessing the pinion depth is wrong, and the carrier bearings were not adjusted properly.

 

[AR67GTX]

Guess I checked the backlash too hurriedly the other night. Today it's about .018 inch and now I notice it has play in/out at the pinion - about .005 to .007 inch I think - hard to get a solid mount and reading up there with my mag base/dial indicator. But I can also feel and see the movement. So, it looks like the pinion is loose which sort of explains why the drive side of the gear contact looks good but the coast side has gone way off and backlash increased. So, about 10 miles of easy driving on it - wonder if that has hurt the pinion bearings or pinion any??

 

[gtxno1]

Everything must be checked bone dry no gear lube of any kind on anything a little engine oil on the bearings only, when checking and making adjustments. You can Inspect the bearings closely to see if they are useable

 

[gtxno1]

Inspect the pattern in one direction only the driving forward direction

 

[Darthomas]

The in out movement and easy turning shows that the preload is no longer there,
but you may be fortunate.
Quiet on the drive side neans the contact pattern (and shim selected) is correct.
Noisy on coast means the pinion moves toward the rear of the car, deeper into the ring.
Lock the yoke up in whatever you use, and get out the socket and breaker bar.
Betcha can get that nut tighter, and if you re-torque it, you may find that there is no more end play, and it would then be quiet on coast.
Good luck.

 

[Jeradaktyl]

I came here because I have the exact opposite problem...lol hope you find an answer

 

[AR67GTX]

I bolted a length of perforated angle steel to the yoke and leaned on the nut a little with an 18 inch breaker bar and piece of pipe on the end without moving it. I'm kind of suspecting a bearing shell wasn't fully seated but if so I would think the pinion nut would initially move without too great an effort. I'll carry it back over to the shop guy in the morning and let him figure it out.

Since it was quiet on the drive side I have hopes that when he gets the pinion tightened back up and the backlash in spec it will be OK. I can live with a slight whine on coast - the torqueflite planetary gears whine anyway when it downshifts into lower gears. Probably drown it out at lower speed.

 

[Mike67]

Well if you can't get it fixed....just keep the hammer down, coasting/braking are a bit overrated you know!!!

 

[AR67GTX]

My rear diff mechanic let slip the shortcut he took causing this problem - re-used the crush sleeve with a shim behind it to crush it slightly more. Pretty disappointed in that - taking this thing out and putting it back in with this heat and humidity is getting tough at 65. Waiting on a new crush sleeve now.