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BW Diff Rebuild: a Walk-Through

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I've scoured our forum looking for a thread on the topic and couldn't find any, so I thought I'd start one.

 

I pulled the hat off the one kindly donated to me by Ando76 and found a bit of a surprise inside. After sitting around my yard for a while plus however long before, it's got some terminal corrosion on the gears. This is quite a setback as the thing seemed to turn OK when I received it. I was only counting on a fresh pinion seal and maybe axle bearings/seals and away I go. It's very sludgy inside, carrier bearings were locked up which made it difficult to remove the axle flange bolts: you can't turn the axles so you can't line up the little window to put a socket through with a rattle gun. All this festiness could just be from sitting collecting moisture in the last year or so.

 

After pulling it down further, I split the centre and found some shims behind the cones, not uncommon but these were quite worn and heat-affected. It could have been setup tight for speedway use so I'll be checking the pre-load and spider mesh on it on assembly. The cones seem OK, bit of corrosion inside the taper where they sit but I think are salvageable. Being a 28-spline unit, the axles and centre are worth hanging on to, but i'm fraid the rest is toast. The calipers, discs, gears, bearings are all too far gone.

 

The brakes seem to be an early disc setup (from say an XC) with vented discs/iron calipers. The axle flanges have a different shape to my current arrangement and are possibly incompatible with my non-vented, alloy caliper type from an XF ute.

 

So my plan is to:

 

* Source some early 2.92 gears

* Strip my housing with the 3.27/open/25 splines

* Use that housing with the 2.92/LSD/28 splines

* Install new bearings and seals throughout.

 

Early gears refers to the size of the ring gear bolts: from what I've read, early one had 3/8" LH thread Vs later 7/16" (possibly XD-onwards?). I have the diff in the coupe with 2.92s so I could strip that out. First I might see what a diff shop charges or an old set, might be easier that way.

 

Some pics so far:b0567d978b7e8000f4a980cf27349b46.jpgdb04065be9b9a6e7e5874b0b5007dd9f.jpg

 

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excellent go full on in depth with this please! While there is alot of info on the web on BW I havnt found an end to end rebuild and set up guide. I have a 3.45 lsd I removed from an el rear diff to go into my XG so Im keen for a saturation of info.

 

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Good stuff n great idea.
excellent go full on in depth with this please! While there is alot of info on the web on BW I havnt found an end to end rebuild and set up guide. I have a 3.45 lsd I removed from an el rear diff to go into my XG so Im keen for a saturation of info.
 
Awesome mate!
OK disclaimer here: although I'm a mechanic and have the basics covered from the relevant TAFE modules I did 25-odd years ago, I am far from being an expert and will very probably fall short of doing a professional job.

Doing up diffs is a similar trade to auto and manual boxes, in that even within a specific area of a trade, you become further specialised in one or two particular types or brands of diff. So one shop might be good at setting up 9"s whereas another might mostly do GM 10-bolts and BW78s. I have only done up about 4 types of diff: Ford Transit, Falcon BW78, BTR M80 and Mercedes/MAN bus diffs. The Merc ones had drop-out centres, the rest were Salisbury type (ie: integral carrier).

I'm only going to cover the process of doing a driveway rebuild, and share my mistakes in the past along the way. I do have access to a press and a lathe so I'll be using these when possible.

If anyone has any comments, suggestions or corrections, please chime in.... this is a forum after all.

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Only comment I have is keep going!
I’m in the same boat as you, mechanic by trade but diffs and gearboxes/transmissions are a specialty area which I only know bits and pieces about.
If you need any info from workshop manuals let me know, I have half a library

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Crusty rollers (same for rest of diff)

 

61cb46d177d762035350cef565d76ab9.jpg

 

Internals need a cleanup/polish

 

47b47f75715d2dd4daf35376d977f3b2.jpg

 

XF alloy type brakes

 

6c129029f5c5aa44fb8ec2e7816cb96f.jpg

 

Earlier type iron/steel calipers

 

b7da0e9cd4829a5c180a9aa04091a3b7.jpg

 

Box of filthy diff guts

 

879d731387161d7a47b92d3dde790ace.jpg

 

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Great write up mate and a good heads up for blokes like me who have had a diff sitting in the shed for 5 years waiting to be installed. I’ll be sure to check out for signs of crusty bits inside any diff before installing it into my cars. Of course I’d be checking brake parts for corrosion but probably would have just checked diff oil level and put it to work, now I’ll give it a good going over beforehand. Thanks for sharing your knowledge

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Great write up mate and a good heads up for blokes like me who have had a diff sitting in the shed for 5 years waiting to be installed. I’ll be sure to check out for signs of crusty bits inside any diff before installing it into my cars. Of course I’d be checking brake parts for corrosion but probably would have just checked diff oil level and put it to work, now I’ll give it a good going over beforehand. Thanks for sharing your knowledge
Cheers, stored in shed should be a lot better off than out in the elements (that fucks anything) but always pull the hat off and check internals, carrier and pinion noise/free play, tooth contact (with some spray paint), tooth chips, any bits sitting in the bottom that shouldn't be there (I'll go into that one later ) as it's cheap insurance.

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those solid brakes are Eseries,(EA EB ED) or XG XH if you end up looking for kits for them. the others are pre XE, (if rotor comes off the axel when axel is still in Diff it will be XD .. others needed the axel removed. 

you've now convinced me to pull the back off My diff i bought.. because the brakes were all shagged from sitting outside.. i'd thought the super clean oil would mean the gears fine. but i now expect similar.

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Anything in particular I should be looking for in an lsd diff? I’m an lsd addict only commodores spin a single wheel
I'm pretty sure that if each axle spins independently by hand, the cones will have a hard time biting without any pre-load. If and when they do, they'll engage with a thump and could do so randomly, making for interesting handling and also risk breaking something.

So if you need a bit more pre-load, you need to determine where the wear has occurred. If either the cones or the housing have worn, the cones and side (axle) gears will sit further out from the spider gears, giving more backlash. You can shim between the side gear and the cone (equally each side) to move them further into mesh with the spider, and also get some pre-load back, but only up to a point. If the cones and housing are worn far enough, the outer face of the cone will bottom out on the housing, preventing the tapered part from engaging. Diff shops will machine the housing and cone to get clearance again, but this is out side the scope of a driveway rebuild.

If there is excessive wear in the diff centre gears, but the cones and housing are OK, then you have a problem. Shimming up will take up some slack, but then you're increasing pre-load in the springs to a point where you're stressing everything beyond what it can handle. I'm of the belief that this is what happened when I did up the last LSD centre that Chernobyled itself without me even driving like a dickhead. I shimmed the side gears/cones to take up the backlash but I think the prepaid was way too much. I heard a massive bang once going around a corner, wondered what the fuck it was. Turns out, it sheared all the 5/16" bolts around the hemisphere so that the 2 halves were only held together by the carrier bearings. When both cones are firmly engaged, the torque difference between the axles passes through these pissy little bolts and it was too much. The sheared halves of the bolts all came off and floated around the housing and somehow didn't jam anything (well not the first time)... I'll go into that later though.

So to get the backlash out without screwing up your pre-load, you can shim up the spider gears by doubling up the thrust washer (or maybe there are selective thickness ones?). I'm about to find out on mine. I don't think that open centre gears will transfer over to an LSD centre because LSD gears have a special slope built into the tooth profile that's designed to create end thrust under torque, pushing the gears apart and forcing the cones to engage. I think they wear out teeth more rapidly because of this.

So: gear teeth wear, cones should have the spiral groove still in them, housing should have an air gap between it and the end of the cone (visible through a small window). Don't pull the 2 housings together with these bolts. Squeeze them together in a vice or press and do up the bolts evenly.
those solid brakes are Eseries,(EA EB ED) or XG XH if you end up looking for kits for them. the others are pre XE, (if rotor comes off the axel when axel is still in Diff it will be XD .. others needed the axel removed. 
you've now convinced me to pull the back off My diff i bought.. because the brakes were all shagged from sitting outside.. i'd thought the super clean oil would mean the gears fine. but i now expect similar.
Cheers Dean that clears things up. Vented rotors definitely drop off after unbolting calipers. Yeah the ute that the 3.27 solid rotor diff came out of I thought was XF but it was picked clean of everything else so could have been XG.

Good move to pop the hat off. Best to be Irish and to be sure to be sure

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Cheers Dean that clears things up. Vented rotors definitely drop off after unbolting calipers. Yeah the ute that the 3.27 solid rotor diff came out of I thought was XF but it was picked clean of everything else so could have been XG.



XF utes and vans all had drum, right to the end of production. Wasnt until XG they swapped over to disc, and as Dean said they're solid disc. XF had vented on the rear, with similar (maybe same) calipers as XG/early E series.

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1 hour ago, Mr Polson said:


 

 


XF utes and vans all had drum, right to the end of production. Wasnt until XG they swapped over to disc, and as Dean said they're solid disc. XF had vented on the rear, with similar (maybe same) calipers as XG/early E series.

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XF calipers are the same as XE rear disc calipers, with bastard pins and slides. 

the EA EB ED series(XG and XH also has EA EB ED) had a similar hand brake setup as above but the mounting was completely different (aka Better)

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The one out of the wags.....

 

There's nothing really wrong with it save for the fact that it's 3.27 (too short) and it's a single spinner. It's quiet as a mouse and is clean as a whistle inside.

 

b51258a5595c1951ed3db78988793023.jpg

 

Oh except....

e428a8529cc81532b6a1db4d58c57671.jpg

 

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I'll weigh in a little bit, I've been successful rebuilding a few lsd's, my method is to measure the width of the cones then machine the flat face on the cones but not the housing after taking some material off measure the width and add that amount to the shims + 010- 015", at least 3 of the lsd's I've done this to have lasted more than 100,000ks, of course you can shim them up to a higher pressure but they won't last as long

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I'll weigh in a little bit, I've been successful rebuilding a few lsd's, my method is to measure the width of the cones then machine the flat face on the cones but not the housing after taking some material off measure the width and add that amount to the shims + 010- 015", at least 3 of the lsd's I've done this to have lasted more than 100,000ks, of course you can shim them up to a higher pressure but they won't last as long

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That method makes perfect sense. I assume you have to install the reverse jaws in the lathe chuck so the back of the cone has a step to butt up against, otherwise wobble city. Are they as hard as a dog's forehead (ie like a bearing cup)? Did you resurface the spiral bit or not worry about it?

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That method makes perfect sense. I assume you have to install the reverse jaws in the lathe chuck so the back of the cone has a step to butt up against, otherwise wobble city. Are they as hard as a dog's forehead (ie like a bearing cup)? Did you resurface the spiral bit or not worry about it?

 

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Yes reverse jaws, they machine quite well as they are cast iron I leave the taper alone

 

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Yes reverse jaws, they machine quite well as they are cast iron I leave the taper alone  
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Oh I didn't know that. I assumed they'd be a carbon steel or something silly like that. I'll have to remember that when putting mine together. What clearance (if you remember) was the cone face to housing end?

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Oh I didn't know that. I assumed they'd be a carbon steel or something silly like that. I'll have to remember that when putting mine together. What clearance (if you remember) was the cone face to housing end?

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I'll have to look up in my service manual but from memory it was something like 3-5 mm

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MIght be worth mentioning a few handy hints on how to get rid of the smell of fucking diff oil to. That shit stinks and doesnt go away!
Yep, we had a thing where if you got it on your overalls, you placed them in the big round filing cabinet and never thought about them again.

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