14 Bolt SF Build

[mr98z71]

Hi Guys, It's been a while since I posted since I was so busy buying parts so my truck! Anyways, I am building a 14 Bolt SF 9.5" rear for my 1998 Gmc Z71. I am going to be putting in a Detroit Locker with some 4.88 both front and back (obviously) and some disc brakes out back. My question is now, I was reading in the GM Service manual and it says that you find pinion shim thickness using a tool (which I don't have) or you can install the amount of shims according to the number the pinion gear has stamped on it. How accurate is this? I just don't want to press my new bearing on my pinion just to find out that my contact pattern is way out of whack.

Also, When setting the pinion preload, this is done without the carrier installed (so basically only recording the pinion resistance) right?

Thanks in advance for the help!

 

[jps4jeep]

If you are going to tackle this yourself, I highly suggests making a set of "setup" bearings. basically press off all your old bearings and using a die grinder or even a dremel, slightly enlarge the bearings ID so that you can press on the bearings by hand ratehr than using a press and splitter everytime you need to make an adjustment.

The "tool" you are refering to is a pinion depth finder, unless you plan on setting up several diffs, really not worth the purchase, unless you have the $80-$100 to burn.

The number on the pinion is the target depth for the pinion from the bearing center line (centerline of the carrier) to the bearing face of the pinion gear. This number is not the thickness of the pinion shims. With out the tool, my method of getting you in the neigborhood is to drop a prepped pinion into the housing with no shims. I lay a staight edge across the bearing cap face and measure to the face of the pinion. I take this number add the thickneness of the pinion from rear to front face, then subtract the number that is on the pinion from that. This is simply a starting point for my shims and is not the finial shim pack. I will prep the pinion with bearings and shims in the thickness. drop in the carrier with shims and setup bearings, torque to spec, paint up the gears and read the pattern. From this I can determine if the pinion needs more or less shim thickness, the carrier needs to be moved left or right based on where the toe and heel of the pattern is appearing on the drive and coast side of the gear. Once I get a pattern I like, I take it all apart and reassemble with final bearings, recheck my pattern and run it. On average a gear set up will take me several hours. IIRC my first setup took me close to 12 hours with more than 6 or 7 tear downs and reassembally till I got it dead nuts on.


Lastly, here is a chart similar to what I use to read a gear pattern.

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[great white]

Very well described.

 

[jps4jeep]

I was going to edit above, but I would like to add to my previous post, some pinion target depths will be from the bearing face of the pinion as mentioned and some will be from the rear base of the pinion. Really all depends on the manufacturer, easiest way to know is if the number is small, it is from the bearing face example: 1.023, you will not need to account for the pinion gear thickness.

If the number is larger like 3.700, then you need to account for hte pinion gear thickness.

 

[mr98z71]

good to know, Ill see if I can't tackle that this week someday.

 

[axisT6]

Read this.

http://www.gmfullsize.com/forum/showthread.php?t=190110

I wrote this for the 10 bolt, but it applies to your axle as well. The best way to check pinion depth IMO is by using gear paint. Read the write up. It will help.

 

[mr98z71]

Thanks for the reply, I worked on the axle today for 8 hours and this seems to be the best pattern that I can get (50 thou on the pinion with 7thou backlash).

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The Yukon manual tells me to increase shims to bring the contact towards the root of the gear, I went all the way up to 80 thou but the contact pattern was only a slim line towards the center of the gear. 30 thou shim make it look like this:

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[axisT6]

That 0.030" shim looks close man. You have to look at the WHOLE mark on the tooth, not just the dark spots.

Try this:

- Reinstall 0.030" shim.
- Install pinion tight enough that you get 1 to 1.5 free spins out of it.
- Install carrier.
- Thin out the gear paint a bit more with gear oil until you get a chocolate sauce like consistency.
- Paint at least 4 teeth on the coast side.
- Run the pattern by putting a wrench on one of the ring gear bolts and moving it up and down with gusto.

You have a clearer pattern doing this and you will also find that a 0.030" shim is indeed close but on the shallow side. Do the above and post a pic.

 

[mr98z71]

Im not sure what you mean by the 0.30 is close, it seems to be riding on top of the gear. Anyways, my final assembly was with a 64 thou shim (factory was 33) and my paterns look look this:

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[axisT6]

Like said, you have to look at the WHOLE mark, or the whole area where the paint was disturbed. Have you run the gears with yet?