Pinion Depth 12bolt

[Quickboat]

Trying to setup my 12bolt by first measuring the pinion depth. I put a shaft through two bushings mounted in the carrier main caps (same as when I setup for welding on new housing ends) and using a telescoping gauge measured the distance between the end of the pinion (flat face) and the bottom of the shaft. Then adding half of the shaft width should give me my axle center to pinion depth. The Motive gears I am running have 2.899 etched on the end of the pinion so after calculating the .028 shim (supposed to be a good starting point) behind the large pinion bearing, I would need to remove .037". That means even without any shims I would be needing to remove another .010" from somewhere. What am I missing? I checked to make sure all of the bearing races are seated and also the pinion bearing....?

[Quickboat]

I said the hell with the depth measurement (thanks for the help anyway.. lol) and just set it up with the .028" shim and .008" backlash and here is my pattern
any suggestions?

[Ron Sutton]

Thanks for the photos. That makes it easy.

The pinion teeth are not deep enough on the contact pattern with the ring gear. Keep removing pinion shims until you get the pattern centered on the drive side ... about 1/8" from the root of the ring gear teeth.

[Quickboat]

Thanks for the photos. That makes it easy.

The pinion teeth are not deep enough on the contact pattern with the ring gear. Keep removing pinion shims until you get the pattern centered on the drive side ... about 1/8" from the root of the ring gear teeth.

Can the backlash be judged here? Does it look good?

[Ron Sutton]

We can see the pattern, which is a component of both backlash & pinion depth. Obviously, we can't see the backlash, unless you shoot a photo of the dial indicator while you're checking it. You said you had it at .008" backlash, which is on the tight range of typical street set-ups (.008"-.012").

The pattern looks like it has too little backlash.

This is where I have to explain my strategy on setting up race gears ... and you can decide if that strategy works for you or not. I think NOT.

We set up all of our race gear sets on the LOW side of backlash. Frankly, at the very minimum, and sometimes less than that. The gear sets we run call for .008"-.012" backlash also. We set ours at .007"-.008" ... because any greater .. and our talented race drivers can FEEL the backlash when they apply, and lift off of, the throttle. This upsets the car a smidge on corner entry ... and they were already at 102% of what the tires could handle.

I know ... that sounds extreme. But when you're competing in a world of thousandths & drivers are train to feel everything ... you win races with how you treat every little detail.

I do NOT recommend this for the street. These tighter clearances can BUILD HEAT. We find .008" runs fine ... .007" runs a little warmer, which we do things to make it run cooler ... and .005-.006" run too hot on long runs & kill rear ends.

Sooooo ... I "assumed" you were running .008" backlash because you wanted to, for a performance reason. If not, the pattern shows you need to run less backlash. Try .010" & .012" & see how it looks.

ALSO ... I think I told you one part incorrect earlier. You DO want the pinion gear to mate deeper into the ring gear. Ultimately for street driving, you're looking for a pattern that is centered both ways on the drive side of the teeth. You need MORE pinion shim, not less, to achieve this. But let's get the backlash happy first.

Start by increasing the backlash to .012" ... run the pattern & post a photo ... and we will have a good idea of what to do on the pinion shim.

P.S. You are applying some load/drag to the gears when you're running the pattern ... correct?

[Quickboat]

Thanks again..
Yes I put drag with my hand on the ring gear. I will loosen up the backlash a smidge tonight and re-spin it. The Motive gear instruction sheet calls out .007 to .009" back lash so I split it at .008.
When determining preload for the carrier, I took the original carrier and shims and got the stack up on a surface plate then compared the new carriers stack up and determined it was .011” taller. So I removed .011 out of the shim total preload. Is that correct?

[Ron Sutton]

Thanks again..
Yes I put drag with my hand on the ring gear. I will loosen up the backlash a smidge tonight and re-spin it. The Motive gear instruction sheet calls out .007 to .009" back lash so I split it at .008.
When determining preload for the carrier, I took the original carrier and shims and got the stack up on a surface plate then compared the new carriers stack up and determined it was .011” taller. So I removed .011 out of the shim total preload. Is that correct?

If your gear calls for .007"-.009" ... and you're at .008" ... leave it ... and just shim up the pinion a little. You're not off far.

As far as measuring for carrier preload, that will get you a baseline to start at, but you should check it with a inch-pound dial torque wrench. Are you using new bearings or re-using the old ones?

[Quickboat]

If your gear calls for .007"-.009" ... and you're at .008" ... leave it ... and just shim up the pinion a little. You're not off far.

As far as measuring for carrier preload, that will get you a baseline to start at, but you should check it with a inch-pound dial torque wrench. Are you using new bearings or re-using the old ones?

I am using all new components. I understand how to check the in/lbs of the pinion but how can I check the carrier preload that way?

[Ron Sutton]

We use drop out 9" Fords with floater style housing rear ends ... with hollow axles ... so it's easy. We just slide an axle into the splines of the carrier ... and thread a bolt into the outer end of the hollow axle (where a plug would normally go) and put the inch/pound wrench on.

When we do non-floaters, we have old axles with a nut welded in the center of the axle flange face. Hmmmm. There has to be several ways, but it will depend on what you have handy at your garage ... and I don't what you can do in your garage.

Any old axles you can weld a nut on?
Can you make a plate with 5 holes that goes over the end of an axle studs (to weld a nut to) ?

[Quickboat]

We use drop out 9" Fords with floater style housing rear ends ... with hollow axles ... so it's easy. We just slide an axle into the splines of the carrier ... and thread a bolt into the outer end of the hollow axle (where a plug would normally go) and put the inch/pound wrench on.

When we do non-floaters, we have old axles with a nut welded in the center of the axle flange face. Hmmmm. There has to be several ways, but it will depend on what you have handy at your garage ... and I don't what you can do in your garage.

Any old axles you can weld a nut on?
Can you make a plate with 5 holes that goes over the end of an axle studs (to weld a nut to) ?

I went with 33 spline axles so the old ones are useless, but I would have no clue as to what the in/lbs would be with the carrier tagging along anyhow.

[Ron Sutton]

The carrier bearing preload is about the same as the pinion bearings. 15 in/lb if used ... 25 in/lb if new. If not, you can set it up with no preload, then simply add .010" total shim ... .005" each side & that should give you "about 25 in/lb of preload.

[Quickboat]

I put a .032" shim (+.004 only choice) and that made the back lash .007" using the same carrier shims as before.

[Ron Sutton]

NICE !

That is a "good" pattern. It's not perfect, but its VERY close. The pattern is telling us to decrease the backlash a tick (.001") for a perfect pattern. BUT I would NOT do it in a street car. I am suggesting you keep the backlash at .007" & not go lower. It will build too much heat & howl.

In other words, you got it as good as it is going to get.

[badazz81z28]

I am using all new components. I understand how to check the in/lbs of the pinion but how can I check the carrier preload that way?

You need to set up the gears fully to check the contact pattern. The easiest way to do this is to get your self a non locking nut for the pinion for set-up. I used a set-up pinion bearing as well but if you have the right tools you can keep pulling your real bearing on and off again during set-up. Pick a shim like your .032. Install the pinion and install it completely in your housing and install the yolk and nut to proper pre-load (running torque with an inch pound beam wrench.

Now install your carrier. Again you need to achieve proper back lash with a dial indicator. Install enough shims so the differential is snug but you can still pull it out with your hands. Install the carrier caps, tighten bolts. Measure back lash.

Apply marking compound, insert an axle and rotate it with the axle putting some resistance on the pinion by holding the yolk slightly (allowing it to rotate, but with resistance). Check wipe pattern.

There are some good instructional pictures on the web to compare too.


Basically what you are doing is completely setting up the rearend like you would for real and checking it for proper set-up. Everytime you change the pinion shim, the side shims on the carrier are going to vary to maintain the same back lash. So it is labor intensive.

Here what I settled with, Zero noise and 2000+ miles and multiple runs down the track.


Oh yeah IMPORTANT! Follow the gear manufacture specs for back lash. It etched on the gear....DO NOT>>>DO NOT use a general spec.

[regal454]

Check out this neat tool from Ratech.

http://www.ratechmfg.com/pinion%20setting%20tool.htm

[Quickboat]

NICE !

That is a "good" pattern. It's not perfect, but its VERY close. The pattern is telling us to decrease the backlash a tick (.001") for a perfect pattern. BUT I would NOT do it in a street car. I am suggesting you keep the backlash at .007" & not go lower. It will build too much heat & howl.

In other words, you got it as good as it is going to get.

Guys I have showed this to are saying go for .003" more, do you agree to get it perfect? I am game if it is actually better for a performance application.

[Ron Sutton]

Are you saying "add .003" more pinion shim? You can try that & see what the pattern looks like. You don't want to end up too deep into the root, but you won't know until you do it & run a pattern.

[Quickboat]

I swapped with a .035" (+.003) shim and here are the results, the backlash went to .0085"- (.007-.009 is called out)..

[Ron Sutton]

Oh, that's nice. Good call.

[Quickboat]

Oh, that's nice. Good call.

Thanks for the help Ron.. I'll button her up!