'73 up drum to disc conversion track width change

-
michiganpat

michiganpat

Well-Known Member
Joined
Sep 1, 2023
Messages
215
Reaction score
110
Location
Grand Haven, MI
Hey guys, just to confirm, did chrysler change the track width of drum brake cars in '73 when they went to the single piston slider calipers? I'm going to convert my '76 to disc this winter, and I was just wondering if the wheels will be pushed out even further than they are now. here's my car, 100% OEM stock with stock 5.5" wide SBP rallyes...195/70 on the front, 215/70 on the rear.

IMG_1356[1].JPG
 
Yes.
Dusters and Dart Sports always look weird when fitted with stock width wheels because of this. The bulging quarter panels make the rear wheels look recessed. The front track got wider with the front disc brakes and actually looked good while the rear wheels tucked way in looked like a big man with little feet.
 
So the front wheels should be in about the same spot as they are now when I go to disc? good. just trying to figure out what to do for wheels when I make the conversion.
 
Just an aside- a 65-67 B body 8 3/4 axle is a great upgrade, is literally a drop in (aside from drive shaft shortening), and actually puts the rear track almost exactly even with a disk brake front track.
 
michiganpat said:
So the front wheels should be in about the same spot as they are now when I go to disc? good. just trying to figure out what to do for wheels when I make the conversion.
Click to expand...
No they will not be in the same spot. That is what Kern Dog is telling you. They will stick out a little bit more.
 
Somewhat on topic… that’s a clean Duster! Nice ride!
 
H22A4 said:
Somewhat on topic… that’s a clean Duster! Nice ride!
Click to expand...
grandpa and I restored it back in '91 when I was 16.....he passed away 4 years later. when I first met my wife I told her "never make me choose between you and the car, because you won't like my choice".....
 
Hellrats said:
No they will not be in the same spot. That is what Kern Dog is telling you. They will stick out a little bit more.
Click to expand...
his reply was a bit confusing, because I asked if the drum brake track width changed in '73 to match the discs, as I thought the drum brakes were also redesigned (essentially the B body design adapted to the A's)...if you look at my duster the front tires are quite close to the outer edge of the fender already, wasn't sure if they were going to be pushed out even more with the discs.
 
YY1 said:
Just an aside- a 65-67 B body 8 3/4 axle is a great upgrade, is literally a drop in (aside from drive shaft shortening), and actually puts the rear track almost exactly even with a disk brake front track.
Click to expand...
planning on a Jeep Cherokee XJ rear end. car is a slant 6 and plan on keeping it that way, and the XJ rears are much easier to find around here than a nearly 60 year old B body housing.
 
I too am confused. He is talking specifically about 73--which is the factory single piston brakes. IS the track width wider with those factory disc brakes than with the lower option factory 73 drums?
 
I'm confused as well. How do you have a 1976 with SBP wheels? I thought by 74 they where all large.
 
Hellrats said:
I'm confused as well. How do you have a 1976 with SBP wheels? I thought by 74 they where all large.
Click to expand...
ALL A body drum brake cars are small bolt pattern. Disc brakes weren't mandatated by the NHTSA until Jan 1, 1976. my car was built in November 1975. so it looks like they adjusted the drum brake wheelmount-to-wheelmount distance to match the discs, since the TSB from 1973 does not differentiate disc from drum
 
I’m not sure that the TSB actually clarifies the question. It’s referring to the track width change between the 67-72 drum brakes and the ‘73+ disk brakes.

That change is well known, going from the 67-72 SBP drums to the 73+ disks results in a pretty large change as described in the TSB. But the TSB does not list different track widths for the 73+ cars, it only lists one. Of course, it only lists one track with for the 67-72 cars too, and I don’t believe the 67-72 drum and disk cars had exactly the same track width either. Although the 73+ disk track width is wider than both the drum and disk 67-72 cars.
 
Last edited:
72bluNblu said:
I’m not sure that the TSB actually clarifies the question. It’s referring to the track width change between the 67-72 drum brakes and the ‘73+ disk brakes.

That change is well know, going from the 67-72 SBP drums to the 73+ disks results in a pretty large change as described in the TSB. But the TSB does not list different track widths for the 73+ cars, it only lists one. Of course, it only lists one track with for the 67-72 cars too, and I don’t believe the 67-72 drum and disk cars had exactly the same track width either. Although the 73+ disk track width is wider than both the drum and disk 67-72 cars.
Click to expand...
That's a good observation. In 1973 the parts manuals have different, new numbers for the drum brake steering knuckles. It's very possible the wheels were pushed out in a similar way as the disc brake equipped wheels. Looking at the OP's car, one notices the track difference, front to rear.
 
YY1 said:
Just an aside- a 65-67 B body 8 3/4 axle is a great upgrade, is literally a drop in (aside from drive shaft shortening), and actually puts the rear track almost exactly even with a disk brake front track.
Click to expand...
No, not entirely true.
The B body axle had the spring mounts at 44” center to center. The A body is 43”. I’ve heard of dudes just spreading the leaf springs to mount a B axle but to me, that is a hack move for dudes that don’t have a welder.
 
Kern Dog said:
No, not entirely true.
The B body axle had the spring mounts at 44” center to center. The A body is 43”. I’ve heard of dudes just spreading the leaf springs to mount a B axle but to me, that is a hack move for dudes that don’t have a welder.
Click to expand...
for what it's worth, Jeep commanche trucks have I think 42" center to center, and spring under axle stock, and width is (depending on sources) 59.5 or 60".....may be able to use offset shackles and not even have to cut/weld perches....
 
michiganpat said:
for what it's worth, Jeep commanche trucks have I think 42" center to center, and spring under axle stock, and width is (depending on sources) 59.5 or 60".....may be able to use offset shackles and not even have to cut/weld perches....
Click to expand...

That a pretty cool little tidbit there.
 
S'cuder said:
That's a good observation. In 1973 the parts manuals have different, new numbers for the drum brake steering knuckles. It's very possible the wheels were pushed out in a similar way as the disc brake equipped wheels. Looking at the OP's car, one notices the track difference, front to rear.
Click to expand...

The 73+ drums used a redesigned B-body knuckle starting around November of ‘72 for the ‘73 model year, they used large upper ball joints and the larger 73+ wheel bearings too.

That said, I honestly don’t know for sure if the ‘73+ drums had the same track width as the ‘73+ disks. Based on what I’ve seen I think the 73+ drums have a wider track than the 67-72 drums. But I’m not sure if it’s actually the same as the disks.

Kern Dog said:
No, not entirely true.
The B body axle had the spring mounts at 44” center to center. The A body is 43”. I’ve heard of dudes just spreading the leaf springs to mount a B axle but to me, that is a hack move for dudes that don’t have a welder.
Click to expand...

Or better yet just move the perches to 42” and get a set of DoctorDiff 1/2” offset hangers/shackles. I mean, if you’re gonna move the perches why not right? Max out the tire clearance for the stock wheel tubs and run some more tire!

But yeah, the B-body 8 3/4’s are not just a “bolt in” operation either way. Leaving the perches at 44” and side loading the springs and losing tire clearance while you’re at it is shade tree hack job stuff.
DionR said:
The NVMA specifications only list one front track width for a '74 as well.

[/URL]
Click to expand...

I like these specs, but I’m not entirely sure how accurate they are for different option groups. Like the ‘70 specs list the rear track at 55.6” and the ‘74 lists it at 55.4”, but the width difference between a 7.25, 8.25 and 8 3/4 is quite a bit more than that.
 
That TSB states a 3.6” difference between the front and rear track? I knew the front was wider but that is a stupid example of engineering.
I have put the 68-70 B housing in Dusters a few times and it really evens it all out nicely. 3.6 inches??? What the heck ???
 
Well michiganpat it sounds like you will be letting us know. Don't forget to update the thread with your out come.
 
You must log in or register to reply here.
-

Back
Top