diff pinion washer shims?

[sodafeld1]

Learning diffs on my hj75 1988 troop. I have replaced the crown and in the process of installing new bearing on the pinion. There are a few sized washer shim spacers available between the pinion and bearing in .05mm increments, 11 different sizes.
In otramm's video he reuses the factory shim as he says it is ok when not changing gears.
It would be a bit of pain if you have to pull the bearing off , then put back on when exploring which shim is correct for gear contact.
As I am replacing the gears,
Am I best off getting these shims in the different sizes?
Or the standard 1.05mm shim washer is ok to use as the baseline? ( The one I have from the old pinion.)

 

[sodafeld1]

mmm, looking at the manual, I think there is nothing else but try and see..that's what you pay for at the diff shop

 

[Malleus]

The thickness of the shims is based solely on the gear pattern, which is determined by the spacing of the pinion, relative to the ring gear. The only way to know what size you need is to print the gear pattern.

FWIW, this isn't done on the assembly line this way. The way it's done by the manufacturers is to measure the contact point (the theoretical pitch line where the two gears contact each other) on both the ring and pinion and then calculate the shim thickness required. A sample differential is printed regularly, in order to validate the measuring tools.

You can set up the gears this way, if you have the dimensions of the gears, including the distance from the mounting faces to the pitch lines, and a means of measuring the internal mounting locations of the gears, inside the differential carrier. It sounds difficult and involved, but it's really not. All gear manufacturers supply this information, so that their gears can be set up properly. The only real variable (actually, a set of variables) is the internal machining of the differential carrier.

You need to set the casting on a flat table, with the pinion centerline vertical, pinion input side facing down, and measure from the table to the face the pinion backface would sit, when installed, without shims. You have to orient the casting this way because the pinion seat is on the opposite side of the casting from the pinion input side (the side connected to the propeller shaft). You may have an inspection cover on the back side of the differential carrier that mates to a machined face. Do not use this face to measure from. It's tempting, because you can see both faces at the same time, but this isn't the datum used to set the gear centerline; it's uncontrolled as to distance from any datum.

You then need to turn the casting 90° and measure from the machined face on the ring gear side to both the ring gear mounting face (internal to the casting) and the pinion centerline. You can't measure the centerline directly, because it's not a real surface, but you can measure the bottom of the hole by measuring to a round bar placed in the hole (any size is fine) and then measuring the hole diameter. The rest is all addition and subtraction.

This is the way the assembly line measuring tools are designed. Printing is the easier method. It just takes longer.

 

[aztoyman]

Shops often keep a "setup bearing" on hand to speed up the process. They hone out the ID of a new bearing to make it a slip fit. It saves all the time of setting up in the press every time you try a shim.

To answer your question of using the original shim, yes it's typically a good starting point and sometimes you get lucky and you're good to go.

 

[sodafeld1]

The thickness of the shims is based solely on the gear pattern, which is determined by the spacing of the pinion, relative to the ring gear. The only way to know what size you need is to print the gear pattern.

FWIW, this isn't done on the assembly line this way. The way it's done by the manufacturers is to measure the contact point (the theoretical pitch line where the two gears contact each other) on both the ring and pinion and then calculate the shim thickness required. A sample differential is printed regularly, in order to validate the measuring tools.

You can set up the gears this way, if you have the dimensions of the gears, including the distance from the mounting faces to the pitch lines, and a means of measuring the internal mounting locations of the gears, inside the differential carrier. It sounds difficult and involved, but it's really not. All gear manufacturers supply this information, so that their gears can be set up properly. The only real variable (actually, a set of variables) is the internal machining of the differential carrier.

You need to set the casting on a flat table, with the pinion centerline vertical, pinion input side facing down, and measure from the table to the face the pinion backface would sit, when installed, without shims. You have to orient the casting this way because the pinion seat is on the opposite side of the casting from the pinion input side (the side connected to the propeller shaft). You may have an inspection cover on the back side of the differential carrier that mates to a machined face. Do not use this face to measure from. It's tempting, because you can see both faces at the same time, but this isn't the datum used to set the gear centerline; it's uncontrolled as to distance from any datum.

You then need to turn the casting 90° and measure from the machined face on the ring gear side to both the ring gear mounting face (internal to the casting) and the pinion centerline. You can't measure the centerline directly, because it's not a real surface, but you can measure the bottom of the hole by measuring to a round bar placed in the hole (any size is fine) and then measuring the hole diameter. The rest is all addition and subtraction.

This is the way the assembly line measuring tools are designed. Printing is the easier method. It just takes longer.

Wow, That is one of most technically well written replies I have read on mud! Reminded me of Crawford from 'Shop school for soul craft' book working as a tec writer..hopefully don't end up like the guy in thext cubicle to crawford.
I kind of can get my head around it, but a visual would reaffirm the writing very well. I like the honed out bearing technique even more so, very simple, like me.

Just seeing a new crown with the perfect factory tooth pattern from the box is an education for me.

Tempted to get another bearing and the range of shims, nail it proper, so I don't have to pull it apart again for awhile. Put all the energy into cleaning it up, spend money on those cogs..Can re use the bearing on future diffs too.
Thanks guys.

 

[sodafeld1]

Yikes! that's an expensive bearing on it's lonesome..

 

[Malleus]

If I can find, or make up a drawing for you, I'll post it when I get a chance.

 

[sodafeld1]

That would be wonderful, not only for me. It reminds me of chemistry at high school, reading the text, but when observed physically in action it is clear as day. Pics always helps.

talking about tyres is much more popular

 

[sodafeld1]

I guess this is something like what you mean..
bugger I already installed the crown..

 

[sodafeld1]

and if I yoyo toyota 90366-40004 I can get koyo 30308JR and koyo 30308DJ which are a fraction of the price.
May do this rather than remove crown again instead.

 

[sodafeld1]

Plot thickens when doing a yoyo, nearly every equivalent bearing is a little thicker or thinner by 1-3mm, so depending on bearing, shims shall definitely be required.
The kit supplied nsk which is 26.5mm deep whilst koyo is 25.25mm deep , some of the yoyo bearings are 23mm deep.
The honed bearing shall have to be either the same manufacturer or factored into the measuring.

 

[Malleus]

This fiddling process with the "slip bearing" is exactly why I recommended measuring. If you measure, you're done after measuring once. Using the try and fail method with a bearing is problematic, because, as you've found for yourself, no two bearings are identical and a thousandth makes a difference. In practice, the pattern you print will not be the running pattern under load, so there's a bit of wiggle room, that's defined by experience, but still, you want to measure the shims with the actual parts you'll be using. To do otherwise is guessing.

I found that same image of the gearset and dimensions. I like that webpage. What I couldn't find, and I wasn't surprised, is an image of my description. The reason is that repair shops don't build differentials the way the assembly lines build them, and the websites are made for repair shops. I'll see if I can whip something up, in my spare time.

 

[sodafeld1]

Very interesting