Pinion Depth on 8.75 741 case

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805moparkid

805moparkid

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i was wondering what factory pinion depth was on a 741 case?? i looked all thru my Plymouth service manual but nothing
 
Pinion depth is usually marked on the gear, it's specific to the gear set you're installing. Gear sets are usually matched for this very reason. It's the relationship of the pinion hear to the case. You have to measure it with a pinion depth gauge like this one.

If you took you diff apart, there should have been shims between the pinion and pinion bearing. These are what's used to adjust the measurement either further down in the case away from the ring gear or further up in the case closer to the ring gear. If you're re-installing the same gears, keep the shims and you should be in the ball park.
 
rmchrgr said:
Pinion depth is usually marked on the gear, it's specific to the gear set you're installing. Gear sets are usually matched for this very reason. It's the relationship of the pinion hear to the case. You have to measure it with a pinion depth gauge.

If you took you diff apart, there should have been shims between the pinion and pinion bearing. These are what's used to adjust the measurement either further down in the case away from the ring gear or further up in the case closer to the ring gear. If you're re-installing the same gears, keep the shims and you should be in the ball park.
Click to expand...

well see thats where im in the dark, i didn't take it apart. but they are matching ring and pinion. there is one shim so i guess i'll start with that.
 
805moparkid said:
well see thats where im in the dark, i didn't take it apart. but they are matching ring and pinion. there is one shim so i guess i'll start with that.
Click to expand...

Regardless, you'll still want to measure it.

Summit/Jegs have cheap ones that do the same job as the MW, but they're not as easy/intuitive to work with.
 
rmchrgr is correct on this one. If you have no gears to begin with then you will need the pinion depth gauge or you will have to press the pinion bearing off and on experimenting on shim size.
 
You can also get an extra inner pinion bearing, and make the inner diameter slightly bigger, so it slides onto the pinion shaft easily. Then you have to set up the rest as the shop manual says, and check the tooth pattern. If it's off, install more or less shims, until you reach the correct tooth pattern, and then press on the new bearing, and reinstall everything else according to specs.
Antoon
 
TheDeputy said:
You can also get an extra inner pinion bearing, and make the inner diameter slightly bigger, so it slides onto the pinion shaft easily.
Click to expand...

I built a diff a few years back and did like above, got an extra bearing and ground it out a few thousandths so it slid on and off easily. Don't want to grind away too much though. I cringed at taking a grinder to a brand new $30 Timken bearing but it worked great.

There are actually 'checking' bearings available now for this exact purpose. Check Randy's, MW, Ratech, DTS etc. Not sure who sells them. I got my extra at a transmission supply house before they were available.
 
ok well i got it in and it made noise so it out on the bench again... im still at the original WHAT is the measurement for this case with 3.91's? (original gears for the case but used)
 
805moparkid said:
ok well i got it in and it made noise so it out on the bench again... im still at the original WHAT is the measurement for this case with 3.91's? (original gears for the case but used)
Click to expand...

There is no measurement for a particular case, pinion depth is the measurement of gear mesh between the ring and pinion in relationship to the case. Did you find any markings on the gears? All factory gears should have the pinion depth scribed onto the base of the pinion gear. That is what you're aiming for. Again, gears are matched during the manufacturing process to ensure smooth operation.

Clearly the one shim was not correct. You need to get a shim pack and as stated above, you need to measure pinion depth. However you do it, it will not be correct until you get that measurement right.

Also, did you check you backlash? Spec should be around .008 in. or so.
Bearings pressed on correctly/all the way? Did you use yellow checking paste to see your mesh pattern?

This is not really a procedure where you can just kinda wing it.;)
 
rmchrgr said:
There is no measurement for a particular case, pinion depth is the measurement of gear mesh between the ring and pinion in relationship to the case. Did you find any markings on the gears? All factory gears should have the pinion depth scribed onto the base of the pinion gear. That is what you're aiming for. Again, gears are matched during the manufacturing process to ensure smooth operation.

Clearly the one shim was not correct. You need to get a shim pack and as stated above, you need to measure pinion depth. However you do it, it will not be correct until you get that measurement right.

Also, did you check you backlash? Spec should be around .008 in. or so.
Bearings pressed on correctly/all the way? Did you use yellow checking paste to see your mesh pattern?

This is not really a procedure where you can just kinda wing it.;)
Click to expand...

ok this is what i was wondering...

and no... on the gears/pinion there is a part number, ratio and then random letters... and nothing in my factory service manual about it either...

i reset the backlash to .008" (in 4 places) so that is better now... (was .013 my bad) after torquing

pattern was mostly towards the (toe?) inside/center of the ring gear on both drive and coast...

and thank you rmchrgr for your patience with me...
 
Just get the gear imprint in the marking compound from the pinion gear in the center of the ring gear teeth. If you do that it will be right, no matter what the specs are.
 
If you got the pattern centered, it ain't gonna say nuthin. All you'll hear is tirespin. lol
 
ok so i got it back together and took it for a spin... holy crap what a difference 3.91's make! it is so much faster!

no noise on accel (slightly more than part throttle)
no noise on decel (foot off pedal)

noise at coast and very light throttle pressure (very light like set your foot on the pedal)

i set the preload on the pinion so that it was very easy t turn but still some resistance (used bearing) maybe to soft even for used bearings?

backlash was .008 on all 4 checking points

using 85-140 gear oil with LSD additive

pattern was like "B" in the picture...
 

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805moparkid said:
ok so i got it back together and took it for a spin... holy crap what a difference 3.91's make! it is so much faster!

no noise on accel (slightly more than part throttle)
no noise on decel (foot off pedal)

noise at coast and very light throttle pressure (very light like set your foot on the pedal)

i set the preload on the pinion so that it was very easy t turn but still some resistance (used bearing) maybe to soft even for used bearings?

backlash was .008 on all 4 checking points

using 85-140 gear oil with LSD additive

pattern was like "B" in the picture...
Click to expand...

Sounds like youre in the ballpark but theoretically, there sould be no noise. The measurement to be taken when you get the pinion sinched down is to verify the turning torque. Some guys can do it by feel but thats after doing A LOT of diffs. To do it right, you need an inch pound torque wrench. New bearings should be between 25-40 in. lbs, used bearings are usually 20 in. lbs. If you rotate it back and forth the yoke should have a good amount of resistance. Pinion nut torque is like 220 ft lbs.
 
The bearing preload has no bearing (no pun intended) on pinion gear depth. All that does is apply preload to the bearing. And of course as you know, tapered roller bearings must have some preload. How bad is the noise? If it's not bad, I say drive it like you stole it.
 
rmchrgr said:
Sounds like youre in the ballpark but theoretically, there sould be no noise. The measurement to be taken when you get the pinion sinched down is to verify the turning torque. Some guys can do it by feel but thats after doing A LOT of diffs. To do it right, you need an inch pound torque wrench. New bearings should be between 25-40 in. lbs, used bearings are usually 20 in. lbs. If you rotate it back and forth the yoke should have a good amount of resistance. Pinion nut torque is like 220 ft lbs.
Click to expand...

ok so maybe i just dont have enough preload on the bearings... went i set it i just made sure it was easy to spin but not loose...

and the pinion nut it locked down...

StrokerScamp said:
The bearing preload has no bearing (no pun intended) on pinion gear depth. All that does is apply preload to the bearing. And of course as you know, tapered roller bearings must have some preload. How bad is the noise? If it's not bad, I say drive it like you stole it.
Click to expand...

well see thats what im thinking... with the pattern being where it was i guess i might just not have enough preload on the bearings...

changing the preload shouldn't make the backlash change right? also because they are worn gears should they be set up a little tighter than .008"??
 
Changing preload will not change ANYTHING but preload. Once the bearing is seated in the race, it cannot go any further. All you can do is tighten the nut down more and apply more preload. The pinion ain't goin anywhere. It certainly wouldn't have an affect on backlash. That's the adjustment for the ring gear. .008" is fine. I would leave it alone.
 
If you don't know the history of the gears, it's possible that if, they were not set up right by the first owner, or are old Zoom gears, you may never get rid of the noise.. Pattern "B" is perfect, if there're only slightly noisy at coast, turn up the stereo..

once had a customer come in with a set of 5:12s, when you took your foot off the gas, you'd swear there was a cop with a siren behind.. gears were damaged, and wouldn't shut up no matter where we set it..
 
inertia said:
If you don't know the history of the gears, it's possible that if, they were not set up right by the first owner, or are old Zoom gears, you may never get rid of the noise.. Pattern "B" is perfect, if there're only slightly noisy at coast, turn up the stereo..

once had a customer come in with a set of 5:12s, when you took your foot off the gas, you'd swear there was a cop with a siren behind.. gears were damaged, and wouldn't shut up no matter where we set it..
Click to expand...

these are chrylser gears but i think that you might be into something with original pattern
yea they get pretty loud on that very light pedal
 
If it's too loud to put up with, you can try giving it a touch more pinion gear depth. Maybe like .010". Noise on coast indicates too much contact on the outside of the ring gear.
 
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