How to Rebuild your OBX Differential.

 

As we all know the belleville washers in the OBX diff seem to be cheap and prone to cracking. They won't stop the diff from working if they crack but they will no longer preload the axle and things are likely to be very noisy...

These washers really need to be replaced. When I say they are poor quality I mean it... I have heard of them arriving DOA cracked all the way through. I tested them with my 2lb sledge by smacking one of the originals and it broke on my first medium impact swing. I could even see the grain in the metal where it cracked! I tested a replacement by smacking it 10 times in a row with increasing force and only slightly bent it.

Here is a step by step process for replacing OBX belleville washers:


Here is a picture of the inside of the OBX with the upper worm gear, inner gears, and washers disassembled:



Step 1: Place the thinner of the two gears inside the center retainer.



Step 2: Place the stacked washers inside of the gear. They should be stacked like this )()()(




Step 3: Place the thick gear over the washers (it will stick up past the top of the inner retainer if assembled properly to provide preload)



If you are talented you can put them all in at once. They will fit inside of the gears like this (notice the preload is there because the two gears are held apart by the belleville springs):




Step 4: Put the center worm gear back in.


Step 5: Put the top back on the diff

Note the dowl pin...


It aligns with this notch..


From the top it goes in the back side of the hole that is not like the others (around 5 o'clock in this picture)



Step 6: Put the bolts in and torque them down to 25 ft*lbs (lubricated with oil)

Some people have recommended tightening the M8 12.9 bolts tighter specs and some looser. I based this on a few sources:

Engineer's Handbook
Machinetoolhelp.com
dodgeram.org
dansmc.com


NOTE: Tightening bolts dry will increase the number by 20-25% so 25 lubricated is about 29 dry anyway and lubricated bolts will tighten much more evenly...

I suggest putting the diff in a vice. The side opposite the ring gear has a nice spot to clamp to on most of differentials. The Neon diff pictured can be held very securely this way.

Some people have experienced axle fitment problems after pressing on the differential bearings. This occurs because the differential housing is made of a softer metal than he stock diff. After the bearings are pressed on the holes are distorted. This can be solved by using a brake cylinder hone to enlarge the hole slightly if the axles are too sung. I also found that if you try a different clocking of the axle some fit looser than others. This should be fixed and remedied after the bearings are pressed on but before installing the diff into the tranny. I simply found a place where it fit loosely and installed the axle that way.

People also sometimes have a poorly tapped hole. I didn't but if you do just run a tap through it to clean up the threads and you should be good to go.

FWD Washers should be stacked )()()( and RWD washers should be stacked ())(() with the two thinner washers in the center.. The RWD washers should be stacked in this manner in order to hold them together since they aren't fully enclosed like the FWD washers are.

Note that some FWD diffs are now coming with 5 washers. My washers are the same overall height as the OBX washers so they can be stacked )()(). The overall goal with the washers is that they get ~.8-1.5mm of preload. The bolts are a 1.25mm pitch so you can tell the preload based on the number of turns on the bolts. 

From the time that the washers become snug to the time when the case is fully clamped by counting turns on the bolt. One full turn is 1.25mm.  This means we want .5 to 1.25 turns from when the washers start to compress until the case is fully clamped down.


BTW: If you tear it down and wonder how it works I think this article By Dave Coleman of Sport Compact Car does the best job that I have seen of describing it:
SCC Quaife Article

 

Let me know if you have questions or comments.

If you want/need a set of washers just choose the correct drop down for your application below or send me a PM or email me rich_bryant_is@yahoo.com and I can hook you up!.


Recently I heard that some suppliers are saying that "aftermarket washers are too strong to compress properly and shouldn't be used." This is amusing since belleville washers vary in spring rate and you can put in whatever you want depending on their specs... If the washers are made of steel (stainless, high carbon, chrome vandium, etc) then they all have a very close spring rate. The overall spring rate is then determined by the dimensions of the washer... Mine are slightly stronger but have no problem compressing as needed and have proven durability. Afterall Belleville washers are made to compress the only thing that would stop them from compressing would be not enough force (and 9 12.9 bolts easily have the clamping force to compress them.) If they were too strong I would have had complaints about wear and clamping problems. If they were too strong then I would have changed them to something that wasn't!! With over 100 sets sold I have yet to have someone report such a problem.

The problem with the stock washers is that they are brittle and break. This implies that they would actually be less flexible than a proper belleville with the same dimensions. As similar metals become stiffer they also become brittle. They are a poor quality washer plain and simple.

As for the bolts they are stamped as (and appear to be) 12.9 from OBX but they have poor quality control on their assembly and often overtorque and/or strip them so I suggest replacing them.


 

 

 

 

----------- Sales Section -----------

 

 


Complete OBX Rebuild Kits


I am offering washers along with new high quality 12.9 M8 bolts to replace the originals. The bolts often come overtorqued and sometimes stripped out! I highly recommend changing both of them while the diff is apart. I already have the information for several applications.

If your specific application is not in the dropdown lists just email me for more information. There are slight variations in the kits so I will need measurements from the washers and bolts to ensure that the correct parts are included. Once I have those measurements I will add them to the dropdowns for automated ordering.


FWD OBX Bolt/Washer Kit:



Note:  In some cases OBX provides slightly different bolt lengths in their differentials with no other design changes.  I am be providing the longer version of the bolts for added clamping.  Never fear, all of the bolts that I provide have been tested to make sure they are not too long for the given platform.

 

FWD Bolt/Washer Rebuild Kit with shipping to the USA ($32 shipped Priority Mail):

OBX Kit Platform

 

FWD Bolt/Washer Rebuild Kit with shipping to Canada ($37 shipped Priority Mail):

OBX Kit Platform

 

FWD Bolt/Washer Rebuild Kit with shipping to Europe/Australia ($40 shipped Priority Mail International):

OBX Kit Platform

 

 

RWD OBX Bolt/Washer Kit:

 

RWD Bolt/Washer Rebuild Kit with shipping to USA ($36 shipped Priority Mail):

OBX Kit Platform

 

RWD Bolt/Washer Rebuild Kit with shipping to Canada ($41 shipped Priority Mail):

OBX Kit Platform

 

 

RWD Bolt/Washer Rebuild Kit with shipping to Europe/Australia ($44 shipped Priority Mail):

OBX Kit Platform

 

 

Washer Only Kits

For those that prefer only the washers I am also selling them without the bolts.

Washers with shipping to the USA ($17 shipped First Class Mail with no tracking):

OBX Washer Platform

 

Washers with shipping to Canada ($19 shipped First Class Mail with no tracking):

OBX Washer Platform

 



Rich's OBX Install Tips:

After you have the bearings pressed the axle holes sometimes distort slightly and need to have about .005 honed out of them. I have heard that people have had good luck with wheel hones cylider hones but I haven't tried one...

Some people have reported problems with the differential not being machined correctly for c-clips. I actually recommend simply taking a dremel or die grinder to them with a grinding stone. A carbide cutter might be a bit too harsh for this since we don't want it bouncing and creating burrs in the wrong places.


My axles were too tight from the start because the axle holes had too little clearance. I had them machined before I started and then they shrunk agian when the bearings were installed (live and learn)... I was able to turn my axle relative to the diff until I found a clocking that allowed it to slip in so I just went ahead and used it but you will want to test it before install to make sure it is ok.



More than 100 people have now used my replacement washers in turbododge, Neon, Honda, WRX, and other cars with no reported problems.

Additional Turbododge OBX Info



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Thanks,

Rich