I broke down and purchased a 3.70:1 Yukon ring and pinion set. They do look a little nicer finished than other brands I've installed in that Yukon polished the bearing surfaces on the pinion gear. Still a lot of machining burs on the ring gear. And no spec anywhere for pinion depth. Instructions say use trial and error method and has a litany of pictures with acceptable contact patterns. At least that's not as difficult on a 9" Ford. But, I like to know when I select a final shim I am close to what the gear mfg. wants for the pinion depth. The Motive Performance Gears (which I now believe are also US Gear) gives pinion depth specs and state the final pinion depth mush be plus or minus 0.002" of that spec. OEM gears also have pinion depth specs. Removes trial and error.
A little disappointed at this point. I don't know yet if I will use this Yukon gear set or return it. Have to digest it a little more. It was a bit pricey for what I got.
It contains some calculations that will hopefully allow you to calculate the required pinion depth. Not sure if it will or will not for help you.
What's funny is the instructions has a disclaimer indicating the pinion depth setting is the responsibility of the manufacturers. Are you sure you don't have the settings? Sometimes they are right on the gears themselves.
Apparently Yukon has changed something. The only number markings on the ring gear were 37 and 10 indicating 37 tooth ring gear and 10 tooth pinion for a 3.70:1 ratio. There were also on both the ring gear and pinion gear the number 244 to indicate a matched set. Pinion depths for 9 inch differentials are small numbers typically in the range of 1.020"-1.030" so 244 couldn't be for pinion depth.
The instructions that came with this gear set were completely different from what you found at Yukon's website. The instructions with this gear set said for all 9" Ford rear ends start with a 0.022" shim, set the backlash between 0.006"-0.010", and then trial and error with shims and backlash adjustments to get the correct pattern. I guess that's okay. But the mfg. lap the gears so why not provide the pinion depth.
After closely comparing these Yukon gears to the Motive Performance series 3.89:1 gears I have, the Motive Performance gears are at least completely deburred. I'll probably go back with the 3.89:1 Motive gears I have. They were quite and setup very easily. I just wanted a slightly different ratio. Did Yukon change manufacturers recently to reduce cost? I don't know.
Yes very disappointing and I could imagine very frustrating for you at this point. The instructions I posted were for a pinion depth tool kit but it gave some Ford specs that I thought might be useful to you.
I have noted the pinion depth for an original Ford 9 inch rear to be 1.044 measured at the center of the axle. Not sure if it will help you but maybe it will give you a base line for a starting point with .022 shim recommended by Yukon.
You may also consider using the same shim set up you had with the 3.89 Motive gears as a starting point then set your backlash and see how the pattern looks.
I did some research online to see if others were having the same issue of where the mfg. pinion depth spec is located on the Yukun gears and seems others are asking the same question. Most of the responses to the question were to call Yukon. Go figure...
I suspect Yukon made this change to eliminate returns due to noise when customers stated the gears were setup per their specs.
I always thought when the mfg lapped the gears they also determined the optimum pinion depth during the process. Who knows anymore with aftermarket parts.
In the process I did find out USA Gear (not US Gear) is owned by Yukon. They sell their lesser quality gears through the USA Gear brand.
Interesting...let me know what you gear set-up you will go with. You mentioned you may stick with the 3.89's.
I will be going through the same ordeal is just a short time. I made more progress today with the cowl work. Much easier when you can just buy the cowl or patch panel.
Nice work. I wish I had more than a 2 car garage to work in. I've never been one to want to replace an entire panel when just a small patch needs to be replaced. My thought is leave as much of the original sheet metal there as possible. I'm old enough to remember when replacement panels were not available if the dealer didn't sell them. We use to make patch panels from doner fenders, quarters, etc.. Then good old body filler and glazing putty as needed to finish it. I don't understand why today so many jump to replacing an entire panel when a patch is all that is needed.
My plan is to recheck contact pattern and bearing preloads as I disassemble it. Hopefully I'll find something obvious wrong like the rear pinion bearing went bad. I might pull the pinion housing first to check the pinion bearings before going on to anything else. If everything looks good I am leaning towards reinstalling the 3.89 gears. I'll let you know what happens.