Axle flange offset??

[Tonker1]

Hi,
I planning to install a complete new Wilwood disc brake system on both the front and rear of my 1973 Dodge Challenger. Currently I have:
stock front discs
stock rear drums on an 8  3/4 rear diff

For this they require me to measure the axle flange offset to determine which brakes will be suited to my purpose.
1. What steps are necessary to get the axle flange housing and the axle flange to a state where I can measure them?
2. They would also like to know whether I'm using a press-on green bearing or snap ring bearing? I'm not sure what either of those are.
3. While I'm asking about Wilwood brakes, is there any particular difference on Wilwood brakes between slotted and drilled or smooth discs for street use?

I have read around and gathered ideas on how to go about it, I would like to be more certain before I start fiddling with brakes which I need for the time being.
Cheers,
Tonker1

[Chryco Psycho]

1 - pull the drum & measure back to the axle retainer flange & add 1/4 for the thickness of the retainer & backing plate
2 - the right side axle should have a crown adjuster nut to set end play , if it does you have tapered axle brgs with the pressed on retainer ring .
3 - I would always choose slotted & drilled rotors over solid , they are abetter design & give up nothing

[Tonker1]

Thanks, Chryco,
I just wanted to clarify on your measuring solution.
1. lift of drum, but not entire brake
2. put tape measure as far back into brake as possible and measure from back of brake to front of axle flange
3. than add 1/4inch for backing plate and retainer.

I also wanted to know if the backing plate and retainer are exactly 1/4inch, because the three available sizes for the axle flange offset on the Wilwood website are 2.36, 2.50 and 2.72 (although it doesn't specify, I assume that is in inches?). The close measurements doesn't leave much space for it to be inaccurate and being in Australia I'd like to make sure before I commit money overseas!

Also, where is and what does the crown adjuster nut look like, to make sure I don't miss it?

I've done quite a lot of other work on cars, its just this is the first time I've worked on brakes and I want to get it right.

Thanks again

[Chryco Psycho]

I do not have anything here to measure or take a picture of so I am sorry but I cannot help with that .
The backing plate & retainer plate"should be .125" thick so together it "should" be 1/4 inch .
The directions I gave you are correct , you have interpreted what I was saying correctly , you should be able to measure to the retainer plate through the hole in the axle flange .
The other way to do it is to remove the axle & the brake backing plate , slide the axle back into the diff & measure again from the retainer out to the axle flange  but you have to add the thickness of the backing plate you removed .
 

[Tonker1]

I'm yet to check the axle flange offset, I've been resolving a some more pressing issues so now I'll be able to take the Challenger to the work shop and have front and rear seatbelts installed (I would personally install original style belts except Australian road rules have a requirement on knew to register vehicles, which is modern seat belts with an engineers installation certificate). I'll get to measuring in the next two weeks when I get it back form the shop and I'll let you know how it goes.

Cheers for the help

[Tonker1]

Axle flange offset confirmed on my '73 Chall as 2.72" using a green type bearing!

Ideally what I was looking for was front and rear:

• 4 piston callipers
• Drilled discs
• Slotting not necessary but preferable
• With a park brake, doesn't matter if front or rear
• Both kits to be sourced from the same company

From Wilwood I can source front brakes that match my criterea, and I could for the rear if I had a different axle flange offset. They have no provision for a park brake on the callipers in the kits for 2.72", there is however for offsets of 2.36" or 2.50". A park brake is a necessity for two reasons; firstly, I live on a steep hill, secondly, for road registration in Australia a mechanical park brake is required which operates separately from the hydraulic fuel lines. So:

1. Could the axle flange offset be changed using axles of different length or year?


Finding disc brakes which suit my criteria is easy for the front but finding any rear disc conversion kits post 1972 is difficult. SSBC is a good example of this as is Summit Racing, so is Strange Engineering and Baer doesn't even stock old Dodge.

2. What happened between 1972 and '73 which causes so many companies not to supply rear brakes?
3. Was there some massive change to the mount setup of the rear drum?
4. Do you have any recommendations on high quality disc brake suppliers?


Cheers

[Chryco Psycho]

Having never actually looked at the flange offset closely there is no reason why axles could not be swapped if they are different in 70-71 or made to spec by Strange , Mark Williams ETc the use the more common offset . All the offset would change is the depth the drum sat over the shoes & to match a change in the backset of the backing plate carrying the shoes .
 Doctor Diff has a conversion available & is great to deal with , Brad used a custom rotor with his set up . this would be my first call although if you have a rear sway bar it looks like it will interfere just like the SSBC caliper does . Scarebird is another source , all they make is the mount system but they use common readily available parts & may have an upgraded rotor that will fit .

[Tonker1]

There is a rear mounted sway bar on my Chall. Assuming there is an interference with the sway bar from the disc system I order, the stock bar will have to be replaced. The replacement sway bar is obviously going to be far stronger than the stock one, so to maintain even dynamics across the car I'd need a new front sway well.
Would the Hotchkis rear sway kit have suitable clearance?
Also, would that make car feel strange to drive, using Hothckis sway bars with completely stock suspension and steering components?

Cheers

[Chryco Psycho]

the problem with replacing the rear bar is most are hung on the axle [Bad ] instead of the frame [good ] & have weak mounts to the frame , Hotchkiss has good front bars , not sure on the design of the rear bars but with the wide calipers they occupy the same space as the sway bar .