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BW Diff Rebuild: a Walk-Through

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Got the centre cleaned up, doesn't look so ugly now.

 

Removing carrier bearings:

 

There are little divots under where the bearings seat to presumably take a two-leg puller. I don't like pressing things apart if there are less painful methods of dismantling, so in this case and also with the pinion outer race, I like to grind them off.

 

Start by holding the carrier in the vice, vertically so one bearing is pointing up. Place a garbage bin under it and then break open the roller cage. Either grind or just rip it apart with a big screwdriver. Rollers will go everywhere except in the garbage so good move well done there champ.

 

Then, carefully grind a flat on the bearing cone. Gradually take off material until you start seeing a bit of bluing in the steel, which means the metal is getting paper-thin. Be very careful at this stage because you want to constantly make sure you're not grinding the carrier itself.

 

As the cone is an interference fit, there is tension from inside which if it's thin enough, will crack right through on its own. It did this for me on both ends of the carrier. You may even hear a little "tick" when it happens. The cones should then walk off with a couple of screwdrivers under them. Once they're off, you can see where you (probably) nicked the carrier a bit. Not the end of the world if you do.

 

 

You can see the little crack going across 458c0ccfe9d3ff355e33217784e294ba.jpg

 

Nicked it a bit, shouldn't worry it at all.

fd39402a327700a3561a3da7f0041b53.jpg

 

 

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anyone have a full exploded diagram of the BW78 or recommend the best service manual for them?
This may be of help for some to follow along with:
 
Pretty much sums up how to build the centre, as Thom explained. I haven't seen a 4-pinion LSD apart before so interesting the difference between them and 2-pinion.

He probably should have mentioned the shims when explaining the difference between the BW and GM posi but waited till the end (got side-tracked?). Wish he would mention it being an Aussie diff too... I guess yanks can't handle us doing things better

Anyway good video, cheers for posting

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On 04/06/2018 at 4:48 PM, gerg said:

Earlier type iron/steel calipers

 

b7da0e9cd4829a5c180a9aa04091a3b7.jpg

 

 

 

Same as the ones i'm rebuilding.  Came out my FC LTD, late XC/XD and (I think) HQ Kingy.

 

Nice write up, mate.  Always here for future reference. Thanks for posting.

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Same as the ones i'm rebuilding.  Came out my FC LTD, late XC/XD and (I think) HQ Kingy.
 
Nice write up, mate.  Always here for future reference. Thanks for posting.
Any bits you need (or anyone else) give me a yell. It's of no use to me now.

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Ok quick question about thoms method of reshimming. So if you took .04" off the end to get your desired cone to hohseing gap youd make your shim .04 + .01 to .015 = .055"?

 

Also any truth to the cones going soft over time and being no good for a reshim? (Sounds bullshit to me could imagine cooking /glazing them or hardening them but soft...)?

Picked up another diff outa an xh xr6 today for $50. Supposed lsd and 3.45 but turning one axle the opposing turn the same direction. Ill presure wash it and pop the rear off tomorrow for a squiz 

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33 minutes ago, TempesT said:

 but turning one axle the opposing turn the same direction. Ill presure wash it and pop the rear off tomorrow for a squiz 

LSD will turn in the same direction. should be good on this part of the question

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Ok quick question about thoms method of reshimming. So if you took .04" off the end to get your desired cone to hohseing gap youd make your shim .04 + .01 to .015 = .055"?


Do you mean 0.040" to stop it bottoming out? Where does the 0.015" come from? Is that for gear backlash? I'm not understanding where you're coming from there.

You have to be very careful to not shim up too much because the gears will be moved toward each other too far and bind, and as you tighten the two housings together, they won't quite meet and the carrier bolts will take the force and flex then break, not to mention the force on the gears themselves.

This is why you MUST dummy-assemble without the preload springs to check that your shims are providing enough clearance to allow complete movement in the cones and spiders. Once you're happy with the backlash (you'll know) you can go and assemble properly.


Also any truth to the cones going soft over time and being no good for a reshim? (Sounds bullshit to me could imagine cooking /glazing them or hardening them but soft...)?


I just skimmed a bit off mine and they machined beautifully, so I reckon Thom's assertion that they're iron is right. Iron is one of the most stable metals around so unless they're some sort of heat-treated weirdo alloy shit, I reckon they'd be fine.


Picked up another diff outa an xh xr6 today for $50. Supposed lsd and 3.45 but turning one axle the opposing turn the same direction. Ill presure wash it and pop the rear off tomorrow for a squiz 


That's normally a good sign that it's a limo, or a seized open centre that a p-plater has been doing commo burnouts with.

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Sorry i read that again and i wrote it like a dogs breakfast.

Yes the .04" is a hypothetical amount taken from the end of the friction cone to stop it clashing against the housing (lets assume it leaves that gap between the cone and end of housing back within tolerance). I interpreted thom saying he adds about .01 to .015 additional to the shim. So he would add about a .055" spacer between the cone and spider gear?

As for my diff i got today i should have written that i need to test the break away to check the lsd heath (and rotate it to check ratio) I found some numbers in another thread to check break away.

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On 05/06/2018 at 6:57 PM, Thom said:
On 05/06/2018 at 6:54 PM, gerg said:
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

Hey thom can you check that in your service maunual?

Also ever had any issue taking the same ammount off the cones small end counter sunk surface (reducing the spline area for the axle)?.

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I'm not Thom but I just did this and will post pics. The back face of the cone has a slight taper into the splines, and after taking off 0.040" (1mm) the taper was gone. So up until you go that far, you're not removing any material from the splined area.

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Machining the cones:28b8f62e2d4ad978dd9991dec22144eb.jpg

Housing end of face, 0.040" off, same for the end lip of the cone. Always do exactly the same for each side.

aca75784ff76c77acb05287590c7d883.jpg

 

As the gears and cones had some wear marks between them, I decided to clean up the surface where they mate and found some 0.8mm (0.032") shims that were a bit big in the ID, so I skimmed the face deliberately leaving a step in the middle to locate the shim. Took 0.020" off the thrust side, shims measured 0.032". Subtracted, that gave 0.012" of shim up from where it was.

 ec7e284bcbde9d142c400a0580aef239.jpg

 

 

Shim in place

1245c2fcb3f15c42bccdab4009baf2a0.jpg

 

Now I know why the standard hemisphere bolts have tiny 5/16" double hex heads. I tried to fit these nice new grade 6 bolts but couldn't fit the socket on where the bolt head area is spot-faced. So in with the old ones.

 

3b203bd047150fe942b1188bb5f79107.jpg

 

 

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Top stuff
Thom you might know this, those spring keeper plates have those tabs out the side that to me seemed to be a wear indicator (ie bigger gap = more wear). But as I got to putting the other end of the hemi on, the housing didn't have a window for the corresponding tab. So the plates went in 180 from that picture, in a spot that has no window. Can you work out what those tabs do?

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Thom you might know this, those spring keeper plates have those tabs out the side that to me seemed to be a wear indicator (ie bigger gap = more wear). But as I got to putting the other end of the hemi on, the housing didn't have a window for the corresponding tab. So the plates went in 180 from that picture, in a spot that has no window. Can you work out what those tabs do?

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I'm not sure what they do, maybe limit travel? But the 4 pin centers don't have them

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I'm not sure what they do, maybe limit travel? But the 4 pin centers don't have them
Yeah that makes sense, as the cones wear and the gears spread, there's a chance that the locators could jump off the cross-pin and everything would turn to soup.

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Top stuff Greg!

Anyone have a source or shims?

This is the only retailer i found, his kit comes with spider gear shims and one to sit under the spring ( 4 pin).

www.mobilediffrepairs.com/store/p25/HOLDEN%2FFORD_LSD_SHIM_REPAIR_KIT_NEW.html

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