Review: 3.38 Diff, Axxis Ultimates, etc

Originally Posted by Bim Growl

So, Ed, can you explain the "proper" way to do this? I just plucked my old flanges out and pushed them into the new diff. Spun it with my hands for about a minute to make sure it all was smooth and threw it all back onto the car.

What's the "proper" way?

Output flanges just pop snap out and press in. No skill involved.

The input flange requires a bit of knowledge to set correctly since the tightness of the net sets up the lash between the pinion and ring gears.

Originally Posted by JCz04Bimmer

I coulda swore it was a gigawatt of power?! No seriously, Bim, it was something insane in terms of ft/lbs but there was a crazy technique that Ed did to get it right. He's going to have to chime in here.

The flange we're refering to was the input not the output (sides) The torque required was determined by the bearing preload. I wasn't around for when they actually reinstalled the input flange but if you go by how easily it came off, it probably wasn't anywhere close to Ed's imagination

Originally Posted by Elwood

The flange we're refering to was the input not the output (sides) The torque required was determined by the bearing preload. I wasn't around for when they actually reinstalled the input flange but if you go by how easily it came off, it probably wasn't anywhere close to Ed's imagination

I'll do a write-up on swapping input flanges later today when I have more time.


Ed

Originally Posted by slow323ci

Output flanges just pop snap out and press in. No skill involved.

Alright, so then I did do it correctly... I didn't need to swap the input flanges at all. Instead, I swapped the output flanges on the sides of the diff to fit with those on the rear axles. The input flange on the diff just bolted right up with what I already had on the driveshaft.

Thanks for the clarification slow. I did this about 6-8 months ago and haven't ahd any issues, so I kinda figured I did it correctly, but thought I'd throw it out there for conversation's sake.

Now I'm in need of some clarification. The flanges that the 3.38 diff originally came with did NOT match up with my car despite both being from a 330 car! I just got back from meeting with niL who was going to buy my differential because he cracked his input flange. He says that his input flange was exactly the same as mine. Originally we had thought that my car was the oddball because it was a 6spd but I'm starting to think that the flange that the 3.38 diff came with was the oddball. Is there possibly a difference in input flanges on convertables because I'm pretty sure that the diff I got came out of a vert. Can Verti possibly chime in here?

Thanks for any insight.

I posted some photos of the Brakefest here.

What do you do about the speedo being off? Or is it?

ahh! sounds like a great mod! i have a steptronic tranny in my 330 right now, but im doign the manual swap over this winter including the 3.38diff. im pickin up the manual tranny this week... damn so you think w/ the diff and manual tranny my car will be a lot faster than it is now?

Originally Posted by rjk85

ahh! sounds like a great mod! i have a steptronic tranny in my 330 right now, but im doign the manual swap over this winter including the 3.38diff. im pickin up the manual tranny this week... damn so you think w/ the diff and manual tranny my car will be a lot faster than it is now?

Bro, your car will be impossibly faster with the auto tranny out of their! Think about it this way, manual cars have a 2.93 ratio and go 0-60 in 6.4sec (bmw site). Auto cars have a 3.38 and STILL go 0-60 a really frickin high 7 seconds. Imagine if auto's had the SAME exact configuration and had a 2.93. The 0-60 on THAT would somewhere around 8.5seconds. So, yeah, the automatic takes a TON of power away The performance increase won't the THAt muc h but it'll absolutely cut off at least .5-1sec off your car. And also remember that manauls by definition can be driven better because of the amt of control u have over ur car.

Keep us posted about the swap!

Originally Posted by folsom330i

What do you do about the speedo being off? Or is it?

E46s use the wheel speed sensors to determine vehicle speed. Changing the diff ratio will not affect the speedo.


Ed

Swapping diff input flanges

Background:
The pinion bearings need some preload for optimal life, about 5000N (~1100lbs) the last time I checked BMW specs. Although that may seem like a lot, you are generating this preload with a large diameter fine pitch thread. Generating 10 times that load is easy. The input flange likes to be held on with a LARGE amount of preload, probably 10 to 20 times the bearing preload. To little load and the input flange will move around on the pinion shaft resulting in fretting, brinnelling, or other forms of wear on the mating splines which leased to spline failure. So, how do you get a huge load under the input flange nut (a.k.a. pinion nut) without overloading the bearings? A crush sleeve serves the purpose. A cylindrical sleeve is used under the flange and provides the majority of the reaction force when tightening the pinion nut. The sleeve is designed to bow outwards (barrel shape) to allow for movement until the bearings start to share some of the load. The trick is tightening the pinion until the bearings see the proper amount of preload. Unfortunately, it is impossible to determine bearing preload by using a torque wrench on the pinion nut since the crushing of the crush sleeve takes up such a large and unpredictable amount of the generated force. We can only find bearing preload indirectly by measuring the amount of torque it takes to spin the pinion shaft. Since you probably don't want to diassemble a diff to the point of just having the pinion in the case, you are best off measuring the torque required to spin the whole differential assembly prior to removing the input flange.

Procedure:

1. Determine the "spinning torque" prior to disassembly. Run one of the driveshaft-input flange bolts into the input flange until it bottoms out. Use a stack of washers or a socket under the head of the bolt if it sticks through the flange too far. Use an in-lb or in-oz dial torque wrench and the appropriate sockets/adapters to see how much torque it takes to keep the pinion (and the rest fo the diff guts) spinning once started in motion. Ignore the initial spike in torque and watch for the constant number after the spike. Write down that value on the side of the diff case. Do the same thing for both your old diff and the new one. You should put the new flange on the old diff so the next guy an use it.

2. Pry out the pinion nut lock plates and remove the nuts (30mm socket). To keep the flange from spinning, have a buddy thread a couple driveshaft bolts into the flange and counter with a pry bar. Keep the nut with its original diff.

3. Pull off the input flanges. The flanges will come off with hand pressure. If not, use a rubber mallet. A 10 ton 3 leg puller is not necessary.

4. This is a good time to replace input flange seals if necessary.

5. Put your original flange on your new diff with the new nut using Loctite 272 (high strength, requires heat to remove). Snug it down and check the spinning torque. If the spinning torque is low, tighten the pinion nut a little more and check again. Repeat until the spinning torque is correct. DO NOT OVERTIGHTEN THE PINION NUT. Overtightening causes the crush sleeve to crush too far resulting in either overloaded bearings or insufficient pinion nut torque and a loose input flange. You will have to replace the crush sleeve and start over.

6. Install a new pinion nut lock plate. Use a socket or punch to drive the plate all the way down. Stake the lock plate into the grooves to keep it fom spinning.

7. Repeat steps 5 and 6 using your old diff and pinion nut and new flange.


Ed

P.S. The reason I though an obscene amount of torque was necessary to get the pinion nut off was because of the last time I rebuilt a diff. I helped a buddy rebuild a Ford 8.8 using new gears/bearings/etc. Getting a new crush sleeve to start collapsing requires a HUGE amount of torque (200-300 ft-lbs).

Thanks Ed.

You might want to add this to a new thread in the DIY section!

Originally Posted by teamdfl

E46s use the wheel speed sensors to determine vehicle speed. Changing the diff ratio will not affect the speedo.


Ed

Making a change after the speed pickup, differential, final drive on the trans etc. will not affect speedo readings, at a glance a tire height change will, correct?

Originally Posted by ILLCOMM

Thanks Ed.

You might want to add this to a new thread in the DIY section!

Very nice Ed

Originally Posted by ILLCOMM

Thanks Ed.

You might want to add this to a new thread in the DIY section!

Not to get off topic...but when was the last time you saw a new DIY posted on the tech section?

Originally Posted by folsom330i

Making a change after the speed pickup, differential, final drive on the trans etc. will not affect speedo readings, at a glance a tire height change will, correct?

Yep, the only thing that affects the speedo/odometer is the effective tire diameter.



Ed

Sorry Ed for the stupid question...

I had already taken the input out to replace the leaking seal before I came to the revelation that I should have consulted my Bentley book before hand..
Once opened I then learned there is NO indication as to what the torque spec could be or information about the spinning tq to establish proper spec.

Bentley is stating to dike mark both the nut and input pinnon surface to properly reinstall nut to spec. I hope the tread count was the same, (still this was an after thought on my part, to late.)

I read on a different site someone indicated about 11-14 inch-lbs is a good start.

Outside of completely rebuilding this unit what would you recommend?

I could remove the back cover and use a dial indicator to check for proper gear lash after I get a good starting reference for rolling tq on the input nut.

Sorry to use this tread as a question but you guys seemed to be right in the middle of my problem.

Excellent site too btw.


Shane Stubbs
New M3 owner / hit a curb drifting doing repairs and upgrades

That sucks to hear that you had to change your input flange. That is wierd. I got my 3.38 from Bavarian Auto Recycling. My input flange was correct but the output flanges were incorect. Obviously I had to swap those out but everything on the input side lined up. I wonder why that is?

anyone ^^^?