70 Challenger Front Drum to Disc Upgrades

[71383bee]

After a year of driving the 70 Convertible I'm considering upgrading the front to disc brakes.  The car has the standard 10" 4 wheel non-power assist drum brakes.  I see several "kits" from Dr Diff, Scarebird, and others and the area I get confused in is with regard to the master cylinder.  Some say I can use the stock 4 wheel non power drum setup with no changes.  Others say I need to go to a larger diameter bore MC and use a prop valve.  I thought disc brake cars need a prop valve so that makes sense.  What I don't understand is the bigger bore. 

The car has its original MC that I really would like to retain the stock look as much as possible so I'm not really interested in changing to a modern MC unless I have too.  I am not interested in going to power assist.  I do need to rebuild the MC though so I am open to swapping if it still looks CLOSE to stock.

Has anyone done a similar upgrade and can offer some advice?  The rear 10" drums are fine.  I am familiar with doing these. 

What I am after is to retain the non power setup as much as possible with a focus on just swapping the front drums to disc. 

Thanks,

[340Challman]

You will definitely need a disc master and a prop valve. You will not lose your "original" look as long as you get a remanufactured disc master. You will look as original as one sitting on the dealer lot in 1970. Have fun. I'm re-doing my front brakes as well. Switching to the 11.75" rotors with the 73-74 spindles that have the bigger inner bearing. I'm going with the Dr. Diff kit. It is very complete. Good luck.

[asapRT]

I'm working on mine as we speak...I added factory disk brakes spindles, calipers, hoses, added slotted disks though....Easy change over..

WAITING ON....
MUST GET>>>>
1... I found ordered Master cylinder 2229171 being rebuilt

2... Found a 18628 booster sent off to be rebuilt... I do have an extra 18628 needs to be rebuilt... Hard to find..1 year only.

3... Ordered proportioning valve with lines

[GoMangoBoys]

I bought the factory front disc brake setup from a 73 B body I believe.  It is a long story, but at one point I had acquired a 72 spindle and a 73 spindle.  I discovered that the difference is that on the 73, the inboard bearing is larger.  I then acquired a set of 73 spindles since I preferred the larger bearing.  The caliper brackets are the same for both years.  I bought new rotors and bearings from Rock Auto for a 73.  I also bought a stock brake booster from Rock Auto and a master cylinder from Mike Ross, a former forum member.  I still need to get a proportioning valve.  I don't know what to buy for that.  Our car is not yet on the road.
I would love it if someone can point me to a good choice for a proportioning valve.

[EV2RTSE]

This article has a lot of good info for anyone considering a disk brake swap and is worth taking the time to read whether using stock or aftermarket parts.

https://www.moparaction.com/2016/03/16/disc-main/

73 B-body stuff is mentioned as a no-no. I have read on other forums that some have used 73-B stuff with no issues, but the author of the article is a member of the SAE, I'd follow his advice IMHO.

[MoparLeo]

You need to understand the difference between disc and drum brakes and how they work hydraulically.
Disc brakes use a caliper with a very large piston(s) that displace a lot of fluid to function. As the brake pads wear down, the piston continues to move outward to compensate for the worn pads. The fluid level in the m/c drops because the fluid in moving down into the caliper and continues to do so with normal pad wear. This piston is normally 2" in diameter or more and over 1 1/2" thick. And basically only moves one way.
The drum brake system uses wheel cylinders and an adjustable brake shoe system. The wheel cylinder pistons are very small. Avg. 1" +/- and retract when you release the brake pedal. The fluid in the m/c remains fairly constant. As the shoes wear down self adjusters(most systems have these and can be added if yours doesn't) keep the shoes in close proximity to the drum surface so the shoe doesn't have to travel very far to contact the drum. So the wheel cylinder pistons, which displace very little fluid, don't have to move very far so the m/c doesn't need as much capacity to function properly.
Do yourself a favor and avoid rebuilt master cylinders unless done by a reputable rebuilder. In almost 40 years of being in the automotive repair business rebuilt master cylinders had a poor reputation for failures and you never want the m/c to fail for obvious reasons.
The Disc-o-tech article is an excellent one to use factory parts to update your system.

https://youtu.be/WxT9vLO6pOc

[GoMangoBoys]

Well,  I am really glad that I decided to weigh in on this thread to "help out".  The way that I helped in this case is by telling what not to do.  I would rather be lucky than good any day!  I am embarrassed to admit this, but closer inspection looks like I have a 73 B body spindle on one side and a 73 E body spindle on the other.  This fiasco all started when someone gave me a free set of spindles that he said were 72 B body.  They turned out to be one 72 and what I thought was a 73 B body.  This was based on looking at the inboard bearing size.  I then bought a pair of 73 B body spindles off of Ebay.  It looks like I used one of the pair and one of the original freebies.  I tell you, they LOOK identical.  But when I measure the distance from the top ball joint arm to the center of the spindle, the 73B is 1/2" longer.  As luck has it, I have a set of spindles that I picked up at Chrysler Carlisle that I was going to use on another car that DO have the larger inboard bearing and the shorter geometry.   It will be short work to bead blast and paint them, then swap them out for the mismatched pair.  Like I said, I'd rather be lucky than good.  Thank you @EV2RTSE  for setting me straight.

[71383bee]

Thanks for the great replies guys.  I appreciate all of the insight and for the education on disc brake function vs drum. 

The kit I was really interested in was from Scarebird.  It proposes retaining my stock drum spindles and uses an adapter plate with rotors from a lincoln and calipers from a 1990 Chevy Celebrity.  I would get the kit with the modified rotors and the monster caliper they offer  It sounds wild but makes sense after I read the install and talked to them a bit.  They claim I don't have to change my MC at all or add a prop valve which is why I am questioning it a bit.

https://scarebird.com/index.php?route=product/product&path=64&product_id=158

Another thing I want to point out is I really would like to retain my stock 14" road wheels.  A lot of the kits out there push me to upsize to a 15" wheel which I'm not interested in doing at this time. 

[MoparLeo]

So you want to upgrade the brakes without upgrading the wheel size ?
15" was a factory size and 15" tires are more plentiful than 14 "
The 15" allows a larger rotor and more cooling air available for the brakes.
The Smallest size wheels you can get on a modern Challenger is 18". Braking system technology has evolved and improved in the last 40+ years.
Best way to keep 14' wheels is to stay with the factory brake setup. Parts at Rock Auto or anywhere else.
Are you just wanting to hide the new brakes for some reason ? If you are concerned with resale, which doesn't matter til you sellit. All the parts are bolt on. You can save the old parts for the next guy. If you are concerned with showing the car, any judge that knows these cars will see the incorrect brake conversion easily.

[GoMangoBoys]

We are running the 14" Rallye wheels with our disc brake conversion using factory parts.  They fit fine.  It is true that there are more tire choices in 14".  We were on the fence about 14" vs 15", and decided based on getting a good deal on 14" wheels at a swap meet.  I bought TA radials in a 225 width.

[GoMangoBoys]

@71383bee
I saw these for sale today.  Just add a set of rotors and calipers from Rock Auto.
https://www.ebay.com/itm/254986183954?hash=item3b5e5c6512%3Ag%3AS4QAAOSwpeBfBRLB&LH_ItemCondition=4

[71383bee]

So you want to upgrade the brakes without upgrading the wheel size ?
15" was a factory size and 15" tires are more plentiful than 14 "
The 15" allows a larger rotor and more cooling air available for the brakes.
The Smallest size wheels you can get on a modern Challenger is 18". Braking system technology has evolved and improved in the last 40+ years.
Best way to keep 14' wheels is to stay with the factory brake setup. Parts at Rock Auto or anywhere else.
Are you just wanting to hide the new brakes for some reason ? If you are concerned with resale, which doesn't matter til you sellit. All the parts are bolt on. You can save the old parts for the next guy. If you are concerned with showing the car, any judge that knows these cars will see the incorrect brake conversion easily.

Hello Leo.  I appreciate your input.

The issue mainly is being driven by availability and cost.  The car currently has 14" rallye's.  If I upsize to 15" rims I'm looking at likely over 2.5k in cost for tires, rims, trim rings and centercaps.  This is just the wheels. still dealing with older drum brakes! 

This REALLY started with me looking at the suspension and realizing I need a COMPLETE rebuild.  So I have about 2k invested in that.  I figured i might as well upgrade to disc while I am at it so I am looking into what is involved.  At some point I need to stay STOP and new wheels and tires is that point. 

Thanks for the EBAY ad on the spindles.  It is intriguing.  May just pull the trigger on that. 

[71383bee]

@71383bee
I saw these for sale today.  Just add a set of rotors and calipers from Rock Auto.
https://www.ebay.com/itm/254986183954?hash=item3b5e5c6512%3Ag%3AS4QAAOSwpeBfBRLB&LH_ItemCondition=4

Thanks for the ad Go Mango!  I pulled the trigger and ordered the spindles.  I can get the rest of the front end parts from rockauto or NAPA as suggested.  Now all I need to figure out is the MC.

I believe I have a power assist disc MC from a 71 B body lying around.  Will that work?  I assume I need a prop valve too.  Any ideas on that? 

[MoparLeo]

Too bad you went for that add. It is for the 72 type rotors that are the small bearing type for the more expensive 2 piece rotors. That is the system that you want to upgrade from, not to. 73 and up are what you want.

https://classicbodyparts.com/product/1962-74-mopar-b-e-body-spindle-with-disc-brake-brackets/

[71383bee]

Too bad you went for that add. It is for the 72 type rotors that are the small bearing type for the more expensive 2 piece rotors. That is the system that you want to upgrade from, not to. 73 and up are what you want.

https://classicbodyparts.com/product/1962-74-mopar-b-e-body-spindle-with-disc-brake-brackets/

Those are nice too...

The ad says to use the 73 style rotors so that is why I thought it was safe.