8.75 question

-
plymouth67 said:
So the 742 case in my Challenger has been a mystery for some time now. Originally it had 3.55 gears in it, they were pretty loud going highway speeds on the both drive and coast sides. I pulled it apart adjusted shims and, that made a difference on the coast side but not really on the drive side. I changed the ring and pinion and had a HELLof a time getting a good contact pattern and it just went together kind of funny. Fast forward to about 25 miles later and....got really loud so I climbed under it and could move the yoke all around. I pulled it out took it apart, threw the original 3.55 ring and pinion in the case because I believe the pinion on the other set of gears is machined incorrectly since there is .12" difference between them from the bottom of the large inner bearing to the surface the shim or the smaller outer bearing would ride. That was about the same .12" I could move the yoke in and out....not sure why it was ok 25 miles ago but, oh well. So...anyway....no matter what I did with the 3.55 I could not get the drive side pattern off the toe of the gear. Shims out...backlash back and forth...coast side is perfect...drive side...not so much, so of course when you drive it...its loud on the throttle and quiet on when coasting. The first size shims i tried was .040" and it's only has .010" in it now. This seems like a pretty big change to me and it did make a difference on the coast side... So my question is after I have wasted a half an hour of your time reading my ramblings is....Has anyone else ran into something like this? Could there be something in the case that is not right?
Click to expand...
What was your inch pound drag torque reading. A tight pinion nut on a 742 case does not mean you have proper bearing preload. If the bearings are tight you will have drag that should be measured with a dial reading inch pound torque wrench. Sounds like you have an incorrect assembly issue.
 
That gear set is branded as Hoosier or Yukon.

They usually set up like an OEM 742 ring and pinion with around 0.090" pinion depth shim.

What does your original pinion depth shim measure?
 
if they are Yukon gears your problem may be incorrect machining where the pinion preload shims are placed --- Yukon does not undercut this area and leaves a small radius instead ,, this will not allow the preload shims to sit flat and the bearing to seat against them and the shoulder -- i have mentioned this before in another post in 2018 and have tried to get a contact number for Yukon so they can correct this issue -- have had no luck -- talked with people at Randy's Ring and pinion and they told me "our guys just torque the nut down and go '' -- made me positive not to buy a differential from them -- --- pic posted shows area of concern. i had to get creative to install the couple sets of Yukon 3.55 gears i had --- this issue is only on Yukon 742 gears and probably on the 741 gears they produce
Maybe since Cass has more connections he can make a call to whoever makes the Yukon gear sets to correct the issues an

109_2272.JPG
 
DoctorDiff said:
That gear set is branded as Hoosier or Yukon.

They usually set up like an OEM 742 ring and pinion with around 0.090" pinion depth shim.

What does your original pinion depth shim measure?
Click to expand...
If I remember correctly the shims I took out originally were .030" I do know I shimed the one I bought from you up more the get the contact patch where I wanted it.
 
I have a set up bearing if you want to use it. Come by and get it if you want to. Or bring the pumpkin over and I'll help you. Just don't bring any viruses. with you.
 
Last edited:
Jadaharabi said:
I have a set up bearing if you want to use it. Come by and get it if you want to. Or bring the pumpkin over and I'll help you. Just don't bring any viruses. with you.
Click to expand...
Thanks for the offer...I may take you up on that but for now the kinda noisey old 3.55 is treating me just fine....think i may use another case i have and set up those 3.23 and when i do maybe i will swing by. Thanks
 
john-9 said:
if they are Yukon gears your problem may be incorrect machining where the pinion preload shims are placed --- Yukon does not undercut this area and leaves a small radius instead ,, this will not allow the preload shims to sit flat and the bearing to seat against them and the shoulder -- i have mentioned this before in another post in 2018 and have tried to get a contact number for Yukon so they can correct this issue -- have had no luck -- talked with people at Randy's Ring and pinion and they told me "our guys just torque the nut down and go '' -- made me positive not to buy a differential from them -- --- pic posted shows area of concern. i had to get creative to install the couple sets of Yukon 3.55 gears i had --- this issue is only on Yukon 742 gears and probably on the 741 gears they produce
Maybe since Cass has more connections he can make a call to whoever makes the Yukon gear sets to correct the issues an

View attachment 1715503104
Click to expand...
So I looked at mine and it has the radius you are talking about...I wonder if this caused some of the issue.
 
it probably is - the way i found out about this was i was in the process of determining the shim thickness for the preload on the bearings so i started with the original FACTORY Shim ,, as i tightened the nut i heard a snap -- took it apart and because the factory shims are so hard it cracked the shim --- so i looked closer and seen the radius -- tried softer aftermarket shims and they distorted over the radius outward which would not allow the bearing to seat . if you have a factory oem 742 gear look at the same area and you will see the undercut --- to solve the issue i carefully ground a chamfer on the inside of the bearing to clear the distortion of the shims caused by this radius. ---- wish i could get this issue to the manufacturer of Yukon gears ,, but being they are overseas in India i believe it would have to probably go thru one of the distributors such as Doctor Diff as he deals with overseas manufacturers.
 
john-9 said:
it probably is - the way i found out about this was i was in the process of determining the shim thickness for the preload on the bearings so i started with the original FACTORY Shim ,, as i tightened the nut i heard a snap -- took it apart and because the factory shims are so hard it cracked the shim --- so i looked closer and seen the radius -- tried softer aftermarket shims and they distorted over the radius outward which would not allow the bearing to seat . if you have a factory oem 742 gear look at the same area and you will see the undercut --- to solve the issue i carefully ground a chamfer on the inside of the bearing to clear the distortion of the shims caused by this radius. ---- wish i could get this issue to the manufacturer of Yukon gears ,, but being they are overseas in India i believe it would have to probably go thru one of the distributors such as Doctor Diff as he deals with overseas manufacturers.
Click to expand...
This would kind of explains why it seemed correct when I put it together and then 25 miles later the pinion was loose ...
 
exactly -- since the bearing is not properly seated due to this radius it will be loose -- not running true in the race -- when i assembled my units the pinion preload was not consistent and then when the shim split as i added torque to the nut ,, you could hear it snap i knew there was a problem. once i rectified the issue everything fell into place.
 
john-9 said:
exactly -- since the bearing is not properly seated due to this radius it will be loose -- not running true in the race -- when i assembled my units the pinion preload was not consistent and then when the shim split as i added torque to the nut ,, you could hear it snap i knew there was a problem. once i rectified the issue everything fell into place.
Click to expand...
Thanks...the more I think about how things went together the more I'm sure this is what is happened to mine. I looked at the pinion and it does have the radius and I noticed when I tore it apart the shims were kind of funky...like bent up some. I originally thought shims were bent somehow with the play I had in the pinion....
 
So as I drive my car more the 3.55's whine is just driving me nuts. So I dug out another case and I'm going to put this 3.23 back together that gave me problems in the beginning. I took @john-9 advice and my pinion gear has a radius that does not let the front small bearing seat against the pinion properly. I took a grinder and put a chamfer in the bearing so it slides down all the way now. I'm sure this is what caused the problem with this set when I put it in the first time. As soon as a couple things show up I will be ready to put this together and hopefully it will be quiet...

20200503_131227.jpg


20200503_131128.jpg


20200503_130831.jpg


20200503_130911.jpg
 
excellent picture of the problem area on the Yukon 742 ring and pinions ( probably the same on the Yukon 741 ring and pinion sets ) before you really get into your set up do a trial set up of the pinion with shims to make sure you have enough clearance on your bearing chamfer for the distortion of the preload shims caused by that radius.--- if all else fails do you know anyone that is a machinist and they could do a very small smooth undercut radius at that area to clear the bearing.
 
Ok, so I'm back to this now....think it's all squared away. Going to ask what you guys and/or gals what you think about my contact pattern.

20200512_175435.jpg


20200512_175352.jpg
 
Look like you need to remove a couple thousands from the back of the pinion bearing and tighten up the back lash a little to me.


Don't forget I have a set up bearing for 742 pinions if you need it.
 
You must log in or register to reply here.
-

Back
Top