Big bolt pattern and disk brake conversion

[DumpsterFire]

What's the best way to go about upgrading? Do 73 to 76 control arms just bolt in? There's a few parts cars around and if that's the best way I'll go buy control arms off them. Or is it better to buy one of the kits.

 

[Professor Fate]

Yes, the later big ball joint upper control arms just bolt in.
"The best way" depends on how much you pay for them and your ability to rebuild them.

 

[DumpsterFire]

If they just bolt in I'm going grave robbing.

 

[abodyjoe]

Disk Brake Conversion Info

 

[DumpsterFire]

Is there any differences between the disk and drum cars? I imagine the knuckle might be different

 

[Professor Fate]

EVERYTHING is different.
If you're going to the boneyard, grab EVERYTHING for the conversion- UCAs, spindles/knuckles, caliper adapters, calipers, rotors, proportioning valve, master cylinder, lines... even if you don't use it all, you have reference for how it all goes back together.

 

[DumpsterFire]

EVERYTHING is different.
If you're going to the boneyard, grab EVERYTHING for the conversion- UCAs, spindles/knuckles, caliper adapters, calipers, rotors, proportioning valve, master cylinder, lines... even if you don't use it all, you have reference for how it all goes back together.

Everything between drum and disk cars is different?

 

[Professor Fate]

Yes, that's what I said. Everything is different except the lower control arms.

 

[Kendog 170]

Grab LCA's with swaybar tabs on them too.

 

[abodyjoe]

Is there any differences between the disk and drum cars? I imagine the knuckle might be different

did you read through the link i provided? it explains everything needed.

everything from the lower control arm up gets replaced. can reuse the lower arm.

 

[DumpsterFire]

did you read through the link i provided? it explains everything needed.

everything from the lower control arm up gets replaced. can reuse the lower arm.

I'm talking about on 73 to 76 cars. Are the drum and disk cars different

 

[Professor Fate]

Grab LCA's with swaybar tabs on them too.

'73 and up have the sway bar tabs in the wrong place for an early A, but they would still be good trade bait.

 

[Professor Fate]

I'm talking about on 73 to 76 cars. Are the drum and disk cars different

YES THEY ARE DIFFERENT! As stated, and as outlined in his link.
Different upper control arm, different spindle/knuckle, obviously different caliper and adapter and rotor, different master cylinder, different proportioning/distribution valve, different line routing... Different!

 

[abodyjoe]

I'm talking about on 73 to 76 cars. Are the drum and disk cars different

body wise, no. suspension attachment points, no. if thats what you are asking. bolting on a large bolt disc set up is as easy as it gets.

 

[DumpsterFire]

body wise, no. suspension attachment points, no. if thats what you are asking. bolting on a large bolt disc set up is as easy as it gets.

What I'm seeing is that 73 to 76 control arms and knuckles are different based on if it's a disk brake car or not. This is correct right? So when looking at donors a drum brake car is useless

 

[abodyjoe]

What I'm seeing is that 73 to 76 control arms and knuckles are different based on if it's a disk brake car or not. This is correct right? So when looking at donors a drum brake car is useless

spindle, lower ball joints and upper arms.

the link i provided above walks ya through all that.

 

[4mulas]

Read the link @abodyjoe posted.

Also use the search feature on this site. Endless pages of big bolt pattern disc brake conversions

you need upper arms
Spindles
Caliper brackets
Master cylinder
Rotors
Calipers
Pads
Hoses
Proportioning valve
Bearings
And more!

 

[DionR]

EVERYTHING is different.
If you're going to the boneyard, grab EVERYTHING for the conversion- UCAs, spindles/knuckles, caliper adapters, calipers, rotors, proportioning valve, master cylinder, lines... even if you don't use it all, you have reference for how it all goes back together.

Pretty sure the '73+ drum brake UCA is the same as a disk brake UCA. I don't see a different UBJ, so seems like that is correct.

The '73+ drum brake spindle got the bigger inner wheel bearing, it is different than the '72 and older and certainly different than the disk spindle. But I think they standardized the UBJ in '73 so the UCA is the same disk or drum.

 

[Professor Fate]

Pretty sure the '73+ drum brake UCA is the same as a disk brake UCA. I don't see a different UBJ, so seems like that is correct.

The '73+ drum brake spindle got the bigger inner wheel bearing, it is different than the '72 and older and certainly different than the disk spindle. But I think they standardized the UBJ in '73 so the UCA is the same disk or drum.

I've heard that, too- but have never actually seen a big ball joint drum A body in the flesh. A few small ball joint drum cars (small bolt circle). They may exist, but until I actually see one I'll stick with what I know so far. Either way, the spindle isn't going to work for him.
Again, the parts are all different for a disc setup! (except the lca)

 

[DumpsterFire]

YES THEY ARE DIFFERENT! As stated, and as outlined in his link.
Different upper control arm, different spindle/knuckle, obviously different caliper and adapter and rotor, different master cylinder, different proportioning/distribution valve, different line routing... Different!

Different caliper?I don't think you're getting what I'm asking. So I'm going after 73 to 76 a bodies for parts and find a drum brake car. Are the control arms and knuckle any use to me with trying to convert my early a body to big bolt pattern and disk.

 

[abodyjoe]

Different caliper?I don't think you're getting what I'm asking. So I'm going after 73 to 76 a bodies for parts and find a drum brake car. Are the control arms and knuckle any use to me with trying to convert my early a body to big bolt pattern and disk.

upper arm maybe. spindle no.

 

[DionR]

I've heard that, too- but have never actually seen a big ball joint drum A body in the flesh. A few small ball joint drum cars (small bolt circle). They may exist, but until I actually see one I'll stick with what I know so far. Either way, the spindle isn't going to work for him.
Again, the parts are all different for a disc setup! (except the lca)

Here is an UCA I know came off my ‘74 Duster with disk brake spindles. The spindle is a ‘73 drum brake spindle off my '73 Duster project car. Fits together well, UBJ is the same.

Funny thing is, I have the drum brake spindle because we converted the ‘73 to disks back when the car was my son’s. And I am almost certain we didn’t change the UCA’s when we did it. I know I had to do a LBJ, but only because I mushroomed the stub. So even the LBJ should be the same disk to drum.

So now you have seen a big ball joint A-Body drum spindle.

 

[72bluNblu]

YES THEY ARE DIFFERENT! As stated, and as outlined in his link.
Different upper control arm, different spindle/knuckle, obviously different caliper and adapter and rotor, different master cylinder, different proportioning/distribution valve, different line routing... Different!

No, the UCA is not different on the '73 up cars. At least not past November of 1972. It's in the TSB. The drum brakes were swapped over to a B body based unit with the modification to the hub for 5x4". So the spindle is different from a disk car, but the UCA uses a large ball joint just like the 73+ disk spindles.

https://www.hamtramck-historical.com/images/TSBs/1973/05-03-73C page1.jpg

https://www.hamtramck-historical.com/images/TSBs/1973/05-03-73C page2.jpg

Here is an UCA I know came off my ‘74 Duster with disk brake spindles. The spindle is a ‘73 drum brake spindle off my '73 Duster project car. Fits together well, UBJ is the same.

View attachment 1716277481

Funny thing is, I have the drum brake spindle because we converted the ‘73 to disks back when the car was my son’s. And I am almost certain we didn’t change the UCA’s when we did it. I know I had to do a LBJ, but only because I mushroomed the stub. So even the LBJ should be the same disk to drum.

So now you have seen a big ball joint A-Body drum spindle.

This. '73 up drum cars were SBP and LBJ.

 

[DionR]

What's the best way to go about upgrading? Do 73 to 76 control arms just bolt in? There's a few parts cars around and if that's the best way I'll go buy control arms off them. Or is it better to buy one of the kits.

So the partial answer to the OP's question is, the UCA's can be useful off the parts car you found. You could use the LBJ, but only if you are going really low buck or they are in really good shape.

You can use your current LCA, only difference between any of them is the sway bar mount if they have one.

My list would be any '73+ UCA and LBJ, disk spindles and the associated brake stuff. Should be all you need.

Dr Diff sells a kit for $720 and includes the spindle and brakes, adapters for the small UBJ and new LBJs.

Mopar 11.75" Front Disc Brake Kit (Stage 2)

11.75" front disc brake kit includes all new hardware. The package fits '62-'72 B-bodies, '67-'76 A-bodies and '70-'74 E-bodies.

www.doctordiff.com

Or you could buy reproduction spindles from him and grab the UCA's off the drum car you found.

Mopar Reproduction Disc Brake Knuckles for A/B/E Bodies

Reproduction forged steel disc brake knuckles fit '62-'72 B-bodies, '70-'74 E-bodies and '67-'76 A-bodies.

www.doctordiff.com

I get used UCA and new spindles myself, but I am a cheap SOB. You could end up spending some sweat equity to get the UCA though, not unusual that the bolts rust to the bushings and force drastic measures to get them out of the car. Plus the work of replacing the UBJ if they are worn.

 

[DionR]

I forgot about the caliper adapters. They should be easier to find if you go 10.95" rotors, and DR Diff sells ones for the 11.75" rotors if you are ok with 15" wheels.