weird gear tooth contact pattern?

Hi folks!
I have a problem with a used 9" gear set.Looks like whatever i do,there's always
the same weird contact pattern.

No matter what shim and backlash i get toe contact one the acc side,while
the coast side can be adjusted/shimmed correctly to the middle.
It started with a cross pattern,where the acc was too much toe contact
an the coast side too much heel.
Decreasing(less)backlash helped to bring the coast side fine to the middle,
but whatever i do the acc/driven side looks like too much toe contact!

Whats up with that funky cross pattern?
I had that in the past,but was able to "middle that out" to be acceptable.
This time:No chance!

Are these gears shot?Maybe they were run with a wrong pattern for too long?

Thanks a ton,
Ollie

 

Are the ring and pinion a matched set, or are they from different rears? Just a thought. It seems that you know how to read a standard gear pattern chart, so you're 1/2 way there.

Bob

 

This is an original Mustang 9",Bob.But who knows whats done to it in the past?
Just had the customer on the phone and he said there was always "some whining noise".
You know,they cannot describe that like we do..
All i can say that the diff was 2 minutes away from case crack!The pin worked its way almost an 1/8 to each side,killing the diff case.
Healthy 390/toploader package,LOL!

thanks,
Ollie

 

those gears are 40 yrs old and lead a hard life, I'd guess they're worn out

 

What's the ratio? Some gear sets are "hunting". The same teeth mesh together every few revolutions. 3.00 and 3.50 are two 9" ratios that I can think of. If the gears are separated they have to go back together with the same teeth meshing, or the pattern is impossible to get right.

Other ratios like 4.11 are "non-hunting". The pinion teeth meet every ring gear tooth, so assembly position doesn't matter.

 

Ollie,

Have you checked the pattern all the way around the ring gear? I just had a early 4 pinion carrier out of the 64 galaxie I'm building for a customer, very long story short, the carrier itself was bad! I could not get a decent pattern at first, rotate around to another spot on the ring gear and check pattern and it was acceptable. Checked another spot and it was close, but not something I'd prefere to put in a customers vehicle. I put a dial indicator on the flat backside of the ring gear and rotated it around to find the carrier/ring gear was out a total of .011"!!

After dis assembling the carrier completely and checking everything out, I found that the carrier itself was no longer true, and the ring gear actually came back to with .003" by itself. I had another carrier laying around, measured it before assembly and found it within .0015" true. I thought for shits and grins I'd put the ring gear and bolt it onto the carrrier and check the set for true and it was only out .0018". The carrier was stout enough to actually take some of the warpage out of the ring gear. I did place the high side of the ring gear to the low side of the carrier, not sure if that did anything for the measurement but it was how I assembled it. I put the back together and was able to get a decent pattern all the way around .

I'm not sure what the factory tollerances are for the carrier/ring gear assembly, but from what this showed me .011" of runout was way too much!! Not sure if you have this going on or not, just thought I'd let you know what I just went through.

 

Ratios of 3.00, 4.00, 5.00 and 6.00 are the "Non-Hunting" Ratios, always hitting the same teeth every revolution. 3.50 could be considered either I guess, It doesnt hit the same every revolution, it hits every other revolution of the ring gear. "hunting" ratios are the ones that mesh different teeth every revolution. It is better to setup back on the timing mark with a Non-Hunting ratio, but it can be done.

Do you have any pictures? This would help diagnose your issue.

 

Wow,thats a lot of tips!
This is actually a bone stock 3.00 9er out of a 67 stang 390/4sp.
I guess non hunting,but thanks for the tip.Will carefully look out for that in the future.

@Half Evil:
Yeah,i call it "the mountain".Had that almost always with the summit motive gears!
But then my carriers were somewhat true.Since i found that out,i polish the back of every ring gear to mirror finish and bolt the ring with extra torque.Still i don't like motive gear,but they bring them so what can you do?
Here the carrier might be as bad as yours there.It was totally shot and on the edge of a case crack!The pin moves an 1/8 in the carrier!
I installed a 4 pinion carrier out of a bronco that i had layin around.Shimmed it a bit closer,so that might be OK.

Just talked to him and tommorow i try a like new 2.5 that i have here.The guy wants
extra long legs.Why?The german Autobahn.No speed limit,everybody goes 100mls and way more!So thats the trend..LOL..
Guess he'll never understand when he sees me in my lil tricked out Monza doin 55 at 3500rpm,hahaha..
I will shoot a pic of how it goes with the different gears tommorow.
Good to know theres help out there!
thanks a ton,
Ollie