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Question after adding 4 wheel disc brakes

stock orange

Jr. Member
Joined
Apr 30, 2010
Messages
73
After adding 4 wheel disc brakes to my 72 build I have noticed that the front axle is about 4 inches longer than the rears.
I have 33x15 BF goodrich tires and custom made wheels that where made look stock only wider.
I have a chevy brake kit up front and a 1977 Cadillac Seville disc set up in the rear.

Is this a common problem? I would rather not have to add spacers to the rear wheels.

Thanks in advance
 

Apogee

Contributor
Bronco Guru
Joined
Nov 26, 2005
Messages
6,033
Adding disc brakes to the rear should increase the track width by the difference in hat thickness of the rotor (~1/4") and the drum hats (~1/8"), so approximately +1/8" per side. Up front, I didn't think the disc track width was much, if any, different than the drum brake track width, approximately 58.5" WMS to WMS. My rear is about 58" on my '77 EB IIRC, so I'm curious how you're getting a +4 inch difference on yours, but I suspect is has something to do with your custom wheels...do they all have the same width and backspacing?
 

SHX669

Bronco Guru
Joined
Jan 9, 2009
Messages
1,997
Do you have 1 1/2" wheel spacers on the front or a full width front axle ?
 

broncodriver99

Bronco Guru
Joined
Jan 27, 2008
Messages
4,780
Loc.
Glen Allen, VA
WMS to WMS shouldn't have changed much if at all because of a brake swap. The front axle is, was, should be wider than the rear from the factory and no matter the brake setup.
 

toddz69

Sponsor/Vendor
Bronco Guru
Joined
Nov 28, 2001
Messages
10,080
The front axle is, was, should be wider than the rear from the factory and no matter the brake setup.

I know some vehicles in the past have had a slightly wider front axle, but I've never known the Bronco to be one of them. Track width front and rear has always been quoted as 57.4" stock with identical wheels at all 4 corners. Curious why you think the front axle *should* be wider?

Todd Z.
 

broncodriver99

Bronco Guru
Joined
Jan 27, 2008
Messages
4,780
Loc.
Glen Allen, VA
My understanding is most all vehicles have a wider front track. Maybe it isn't the case in newer cars, I don't know, but it was common practice for a long time. It was usually in the .5"-1.5" range difference. It was done for a lot of reasons. I believe the Bronco is about .5" difference front to rear.
 
OP
OP
S

stock orange

Jr. Member
Joined
Apr 30, 2010
Messages
73
Adding disc brakes to the rear should increase the track width by the difference in hat thickness of the rotor (~1/4") and the drum hats (~1/8"), so approximately +1/8" per side. Up front, I didn't think the disc track width was much, if any, different than the drum brake track width, approximately 58.5" WMS to WMS. My rear is about 58" on my '77 EB IIRC, so I'm curious how you're getting a +4 inch difference on yours, but I suspect is has something to do with your custom wheels...do they all have the same width and backspacing?

I am heading to the shop tomorrow and will check the measurements
thanks
 

Attac

Contributor
Sr. Member
Joined
Jun 29, 2015
Messages
865
Pictures would really help a lot.. One of a tape running from axle flange to axle flange as well as one from rotor to rotor. Need to determine if the axles were right to begin with first. Did you check to make sure of the backspace of the wheels you took off were all the same. I have seen different backspaces ran from front to rear on rigs before.
Chuck
 

Hozr

Bronco Guru
Joined
Oct 15, 2011
Messages
1,434
Loc.
Oly, WA
I don't see how the axle width's could have changed by swapping to disc brakes. Has to be an issue with the wheels
 

SteveL

Huge chevy guy
Joined
Jun 24, 2001
Messages
11,613
Loc.
Hawthorne ca
We narrowed a full width to eb size with a wah. I think that's about how much we cut out of the passenger side axle tube
 

73bronco

Sr. Member
Joined
May 10, 2007
Messages
936
The bronco body tapers bigger as it gets to the rear. Rear is something like 66" wide and the front is around 61" if I recall correctly. Maybe you're seeing the difference in where the tires are in relation to the body? Axles should be 58.5" in front and 58" out back.
 

Apogee

Contributor
Bronco Guru
Joined
Nov 26, 2005
Messages
6,033
F150 axles are 65" wide...so if the OP was talking about a 6" difference, that could be a great explanation. I don't know how to come up with a 4" difference readily without something custom going on.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
47,355
According to magazines and factory data sheets of the day (well, at least "marketing" data sheets) the Bronco had at various times, either identical front and rear track widths, or wider fronts by a slight amount.
Literally almost every new year update in the magazines quoted a different track width. Which tells me that their sources were varied and perhaps not always accurate. Unless Ford actually did change them regularly. Just does not seem logical.
However, when have I ever thought Ford always used logic when putting Broncos together!

I have also read here on the forums where people have claimed that the GM disc brake conversions change the track slightly. Not sure, as I've never measured them side-by-side myself. But it sure does not seem like they would have changed much.
Changing to Ford full-size discs with knuckles might change something, but not sure about going with '76/'77 EB knuckles.

We should definitely get some measurements to add to our database thread that we have yet to create in any coherent way.%)
Good segment to start the ball rolling with.

Paul
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
If you have a lift and don't correct the track bar the axle will shift off to one side making that side a little wider. A chevy disc conversion will widen the front track about 3/16" a side
 
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