Is my diff contact pattern good?

[MatRacer]

Hi,

I swapped my 3.73 ratio for a 3.15. Came with what is shown bellow with the shims I had. Backlash is right on at 0,003''. Preload is good.





The coast side is pretty centered. It's a used gear set. I think it is acceptable, even if i'm on the toe side a bit. I roated the diff by the input with a drill and loaded the diff by hand (with gloves) on the output flange... I wanted other opinions, since its my first diff setup...


Thanks!

[SkiFree]

I do not believe its acceptable. It is still a bit on the tight side and it will cause issues as the diff warms up under use.

I have seen patches exactly like that result in metal flecking off the gears by the end of a single race season.

Good luck, hope that helps.

[MatRacer]

It is still a bit on the tight side

Backlash?

According to this: https://www.bmwtechinfo.com/repair/main/057en/index.htm

I would be good...

In the rear axle section, specification at page 2, the backlash should be between .0024 and 0.0043''.

[Wanganstyle]

Backlash?

According to this: https://www.bmwtechinfo.com/repair/main/057en/index.htm

I would be good...

In the rear axle section, specification at page 2, the backlash should be between .0024 and 0.0043''.

Skifree has association with this company called Ireland engineering; they have been playing with differential setup since the 2002 days

Since you posted for advice and don't want to Take it I'll also give my advice.

Too tight. Will EAT gears

[MatRacer]

I wasn't sure he was talking about backlash...and was showing from where I had taken my information...English is not my first language...I was also confuse with the fact that I had read somewhere that Metric Mechanic was talking about 0.003 to 0.0035''...

I know Skifree is very knowledgeable...and thanks for pointing it out...

Allright thanks for the advice! Was hoping for your advice also...! :)

So what would be an acceptable amount off play? 0.004-0.006''? I guess increasing the backlash would also help to bring the contact toward the heel a bit...

Thanks again!

Mat

[Wanganstyle]

I wasn't sure he was talking about backlash...and was showing from where I had taken my information...English is not my first language...I was also confuse with the fact that I had read somewhere that Metric Mechanic was talking about 0.003 to 0.0035''...

I know Skifree is very knowledgeable...and thanks for pointing it out...

Allright thanks for the advice! Was hoping for your advice also...! :)

So what would be an acceptable amount off play? 0.004-0.006''? I guess increasing the backlash would also help to bring the contact toward the heel a bit...

Thanks again!

Mat

To give extremes:

Too tight = eat gears
Too loose = slam and break gears.

Best to reference an oem BMW unit you have on hand that is known good with your tool of measure; the tolerances are pretty tight on BMW diffs. Left shims are usually between ~1.6-1.8mm from the factory and right ones between 1.4-1.6mm. This is a total delta of about 0.4mm so you really need to be dead on for it to be happy (gear relationship acceptable and bearing load acceptable)

[MatRacer]

T

Best to reference an oem BMW unit you have on hand that is known good with your tool of measure

Good point! I have a 4.10 on the shelf, will check it! Thanks!

[MatRacer]

My 4.10 has 0,005''... Will aim for around that

[MatRacer]

Found back the Metric Mechanic document I was writing about: http://www.metricmechanic.com/pdf/Differentials.pdf

At the page 8, they are talking about their diff setup...which would appear to be on the tight side...

''We’ve developed a method for expanding the case
so these bearing can be shimmed and pre-loaded to
the proper 9 to 11 inch pounds of rolling torque
and still be able to set the back-lash on the ring and
pinion to .0030” - .0035”. ''

WTF is the expending case thing...

Anyway, I will order shims and set to around 0.005''

[Wanganstyle]

Found back the Metric Mechanic document I was writing about: http://www.metricmechanic.com/pdf/Differentials.pdf

At the page 8, they are talking about their diff setup...which would appear to be on the tight side...

''We’ve developed a method for expanding the case
so these bearing can be shimmed and pre-loaded to
the proper 9 to 11 inch pounds of rolling torque
and still be able to set the back-lash on the ring and
pinion to .0030” - .0035”. ''

WTF is the expending case thing...

Anyway, I will order shims and set to around 0.005''

Why don't you take given advice and ONLY follow BMW factory instructions?

BMW TIS.

No other letters of the alphabet needed

[MatRacer]

I do take advice and thanks for taking time to provide some!
I try to read as much as I can when I attemp something new for me.

Was pointing out what I had found and why I was thinking I was Ok...

FYI, TIS is one of the documentation I read...and 0,003 would be good... So Thanks again for the advices

Mat

[tinkerputzer]

I'm confused for OP since the TIS backlash spec is .0024-.005" and his is within that range. Are you guys saying the TIS should only be followed for street application? If you guys say .003" is too tight what is your preferred range?

Also i bet OP's 4.10 that measures .005" is far from new so i wouldn't assume zf shipped it with .005" backlash.

[MatRacer]

I'm confused for OP since the TIS backlash spec is .0024-.005" and his is within that range. Are you guys saying the TIS should only be followed for street application? If you guys say .003" is too tight what is your preferred range?

Also i bet OP's 4.10 that measures .005" is far from new so i wouldn't assume zf shipped it with .005" backlash.

Thanks for understanding me... haha.

The 4.10 was on a auto 325i that was just mint. never drove to the limits. First owner was an old lady and second was a straight 50 years old accountant...but still 150 k miles on it...

[TobyB]

So, "tight": the pinion's too close to the crownwheel, as in the tooth pattern's too
close to the root of the ring gear?
Because to me, looking at that pattern, seems like the pinion's far enough away from
the ring gear- in fact, it looks well out there.

Or "Tight"- pinion's too far forward towards the diff pumpkin? Too far 'back'?
Because the pattern DOES seem to be quite a ways in there.

I'm seriously asking, not snarking, because I've only 'set up' a few 168's-
and that was mostly a quick check to make
sure the gears weren't falling off each other entirely, then toss 'em in the
race car and see how long they lasted....

t

[tinkerputzer]

So, "tight": the pinion's too close to the crownwheel, as in the tooth pattern's too
close to the root of the ring gear?
Because to me, looking at that pattern, seems like the pinion's far enough away from
the ring gear- in fact, it looks well out there.

Or "Tight"- pinion's too far forward towards the diff pumpkin? Too far 'back'?
Because the pattern DOES seem to be quite a ways in there.

Well both can effect backlash and contact pattern. Pinion depth relates more to centering the contact pattern on the tooth. Carrier side to side placement is more about backlash but to some extent how high or low on the tooth the contact pattern is. It is a balance, but as long as you reuse the original shim from underneath the inner pinion race, along with the same gear set, in the same case, pinion depth should be fine. It's just a matter of dialing in the proper amount of backlash with the carrier shims.

Contact pattern can be tricky to read as it depends on what you use to read it and how much resistance you put on it. In OP's top pic there are a few teeth that have a nice contact pattern, it gets a bit light toward the outside but if you look close you can see it's there.