8 3/4 742 case setup questions

[oldbee]

I think 'Fran' is thinking factory gears. Worked at Chev. dealer for awhile/LONG while ago and they all had markings to help you with pinion depth. I don't think aftermarket gearsets have that marking on pinion. You have to start from scratch for the depth measurement.

 

[Fran Blacker]

Your right O'bee about factory gears. After market gears I believe have number expressed in inches. Problem is to figure out how correlate the numbers so they mean something. The factory doesn't give an inch measurement for pinion depth. I've looked on internet and found numbers but wouldn't quote them.

 

[vintage chromoly]

Your right O'bee about factory gears. After market gears I believe have number expressed in inches. Problem is to figure out how correlate the numbers so they mean something. The factory doesn't give an inch measurement for pinion depth. I've looked on internet and found numbers but wouldn't quote them.

Isnt the distance that's marked on the back of an aftermarket pinion gear the depth from the back of the gear to the centerline of the carrier bearing?
Couldn't one just measure from the cap surface in the housing to the back of the pinion gear with a depth mic?

 

[Fran Blacker]

Factory uses the face of the pinion.

 

[vintage chromoly]

Factory uses the face of the pinion.

None the less, with an aftermarket pinion like I'm using, why couldnt I use my depth mic to set the centerline of the carrier to the rear of the pinion gear?

 

[Fran Blacker]

you could, I've done factory gears not after market. Like to hear more how your step up goes. Still wonder why no shim on pinion.

 

[vintage chromoly]

I'll know more tomorrow on the shim.
I'll keep updating so maybe someone else might find this thread helpful.

Thanks for all the interest and help fellas!

 

[Cranky]

The factory uses the MD method or mounting distance for setting pinion depth and to get that dimension, you measure from the rear bearing seat or face to the ring gear center line. Best way imo to figure out what the PD (pinion depth) with gears that are not marked is to measure the thickness of the gear head and subtract it from the MD figure. For example, using the Dana 60, the MD is 5.000". If the thickness of the pinion gear head is 1.875", subtract this from 5.000", then your pinion depth is 3.125". Aftermarket gears are marked + or - in inches and are set according to the 3.125 standard dimension for the Dana. The 8 3/4's MD is 4.350" for the 1.750" straight pinion (42 case) and 4.344" for the 89 case. If you get a set of gears that are not marked, you use the mounting distance method to set them up or just use the pattern method. I like using my setup tool because it's faster and easier than sticking it all together, checking the pattern and then tearing it all apart again if it's not right. Sometimes it's a PITA as it is just getting the shims on the pinion to read what it wants....

 

[vintage chromoly]

Thanks cranky!

 

[vintage chromoly]

Picked up the pinion and gear.

There is a .090 thick shim behind the bearing. It was "glued" on with hardened gear lube and my friend thought it was part of the pinion gear.

I have the old pinion bearing and it slips on and off easily.

Waiting on fedex to bring my parts today.

 

[vintage chromoly]

Case (doctor diff) said .090 is where he starts when setting up a 742. Looks like Ill start there and see what the pattern looks like.

 

[Fran Blacker]

The factory uses the MD method or mounting distance for setting pinion depth and to get that dimension, you measure from the rear bearing seat or face to the ring gear center line. Best way imo to figure out what the PD (pinion depth) with gears that are not marked is to measure the thickness of the gear head and subtract it from the MD figure. For example, using the Dana 60, the MD is 5.000". If the thickness of the pinion gear head is 1.875", subtract this from 5.000", then your pinion depth is 3.125". Aftermarket gears are marked + or - in inches and are set according to the 3.125 standard dimension for the Dana. The 8 3/4's MD is 4.350" for the 1.750" straight pinion (42 case) and 4.344" for the 89 case. If you get a set of gears that are not marked, you use the mounting distance method to set them up or just use the pattern method. I like using my setup tool because it's faster and easier than sticking it all together, checking the pattern and then tearing it all apart again if it's not right. Sometimes it's a PITA as it is just getting the shims on the pinion to read what it wants....

Ton of great info! Saw the info online but no explanation.

 

[Cranky]

Isnt the distance that's marked on the back of an aftermarket pinion gear the depth from the back of the gear to the centerline of the carrier bearing?
Couldn't one just measure from the cap surface in the housing to the back of the pinion gear with a depth mic?

Yes you can....but what kind of depth mic do you have? Also, keep in mind that the split line of the carrier bearing fits can vary as much as + or - .005". You can measure both the cap and the saddle to see if they vary or not and make any necessary adjustment but if you're using a standard type depth mic, the spindle is flat and the bearing fit is round so it would be best to have a depth mic with a ball spindle for the most accuracy....but you can get pretty close using the regular depth mic then check the pattern. Also, some aftermarket pinions are just marked with a + or a - symbol and you subtract or add to the what the pinion depth is supposed to be for whatever rear you are working on but the majority of aftermarket gears are marked with the intended PD. http://www.technologystudent.com/equip1/microm2.htm

 

[dvw]

Use the .090 shim, slip on pinion bearing set the backlash and check the pattern. You'll be hours ahead. Then if necessary add or subtract pinion shim based on the pattern.
Doug

 

[crlush]

i have had the shims stick from the oil to the pinion and you have to use a razor to get it off, when you look at it doesn't look like there is one there.

 

[vintage chromoly]

Ok, so far I've rebuilt the sure grip, pressed on the carrier bearings, pressed in the races in the case and installed the ring gear.
I bought some ARP ring gear bolts and ARP cap studs.
I mocked up the pinion gear with a .090 shim and I'm .050 too close according to the depth number scribed on the back of the pinion gear.
I measured the thickness of the factory gear and the motive gear. The motive gear is .050 thicker, so I'm going to mock up with a .040 shim and see where that puts me.
Any suggestions on gear lube and viscosity?
Here are some pics:

 

[vintage chromoly]

Had my helper with me painting th case while I have this apart:

 

[vintage chromoly]

Pattern I've got now.
What do you guys think?
I'm thinking, I'm good.
Coast:

 

[vintage chromoly]

Drive:

 

[vintage chromoly]

.010 lash.