Master cylinder interchange disc/drum-drum/drum

[Duster_71]

Hello all,

I'm working on a 74 Duster with manual drum brakes all the way around and need to replace my master cylinder. It does not appear as though there are many options left out there and I want to make sure I get the correct(functional) one. How can I look at mine and determine the bore size? It seems that the common ones out there are Cardone 10-1573M with 1.031 bore and 10-1516M with .937 bore. There are other brands Centric and others that I really can't make any sense out of when it comes to the bore size, can anyone provide some insight?

v/r
Ron

 

[BillGrissom]

Many on rockauto list the bore size. Manual or power relates only to the MC and not related to what you have at the 4 wheels (drums or calipers), other than many people need a power boost for disk brakes and most all cars sold today have a booster. Personally, I don't fool with the old cast-iron MC's. You can buy a 2-4 bolt adapter plate on ebay ~$30 to allow using a newer 2-bolt aluminum MC. You can even buy as a kit w/ MC for ~$95 (Dr. Diff or such, forgot). Many here use an MC for a mid 80's Dodge truck (~15/16"D). I use one for a 95-99 Breeze w/ ABS (7/8"D). Best if 2 ports on driver's side w/ dbl-flare ports (not bubble-flare started ~2000). The smaller the bore, the easier the pedal effort, but more pedal travel.

 

[Duster_71]

Many on rockauto list the bore size. Manual or power relates only to the MC and not related to what you have at the 4 wheels (drums or calipers), other than many people need a power boost for disk brakes and most all cars sold today have a booster. Personally, I don't fool with the old cast-iron MC's. You can buy a 2-4 bolt adapter plate on ebay ~$30 to allow using a newer 2-bolt aluminum MC. You can even buy as a kit w/ MC for ~$95 (Dr. Diff or such, forgot). Many here use an MC for a mid 80's Dodge truck (~15/16"D). I use one for a 95-99 Breeze w/ ABS (7/8"D). Best if 2 ports on driver's side w/ dbl-flare ports (not bubble-flare started ~2000). The smaller the bore, the easier the pedal effort, but more pedal travel.

Thanks BillGrissom, Now, could i switch to the newer master cylinder w/adapter plate and use it with my manual drum brakes until I'm ready to switch the front to disc brakes and should i be able to use my current peddle push rod with any bore size? Or would it be possible to replace my manual drum/drum master cylinder with a cast disc/drum master with no issues?
v/r
Ron

 

[BillGrissom]

Yes, I still have drums all around, but prepared for front disks by installing a newer MC w/ booster in my 65 Dart (avatar). Many here use a manual MC w/ disks and are fine w/o boost. The pedal rod in my 64 Valiant (no booster) fit fine in the Breeze MC. The rubber bushing at the end locked tight in the piston. Search for my post w/ photos. The pedal wound up in exactly the same place. I super-glued a bellows to the new MC as a dust shield. Most 1960's manual MC's come w/ a new pedal rod & bellows, as you can see on rockauto. If re-using your pedal rod, you will need a new rubber bushing for the end. I recall buying at one of the specialty places (Dr. Diff) or perhaps ebay.

The biggest change when you convert to front disks is to install a pressure proportioning valve in the rear circuit, to reduce pressure. You can buy an adjustable one for ~$30 on ebay (or Summit). Without that, rear drums will lock up first, causing spin-out on turns. If you also install rear disks, you might skip the p.v., assuming you size all the calipers correctly (hard do do w/o an R&D team).

 

[Duster_71]

Yes, I still have drums all around, but prepared for front disks by installing a newer MC w/ booster in my 65 Dart (avatar). Many here use a manual MC w/ disks and are fine w/o boost. The pedal rod in my 64 Valiant (no booster) fit fine in the Breeze MC. The rubber bushing at the end locked tight in the piston. Search for my post w/ photos. The pedal wound up in exactly the same place. I super-glued a bellows to the new MC as a dust shield. Most 1960's manual MC's come w/ a new pedal rod & bellows, as you can see on rockauto. If re-using your pedal rod, you will need a new rubber bushing for the end. I recall buying at one of the specialty places (Dr. Diff) or perhaps ebay.

The biggest change when you convert to front disks is to install a pressure proportioning valve in the rear circuit, to reduce pressure. You can buy an adjustable one for ~$30 on ebay (or Summit). Without that, rear drums will lock up first, causing spin-out on turns. If you also install rear disks, you might skip the p.v., assuming you size all the calipers correctly (hard do do w/o an R&D team).

Thanks billgrissom, shouldn't I be able to us the factory disc/drum proportioning valve when I upgrade the front brakes? Did you use the factory proportioning valve (drum/drum) with your current set up and were you able to use your regular lines or did you fab/buy new ones?

 

[BillGrissom]

Sure, but search for all the posts on that. A "correct" p.v. costs ~$75 vs ~$30 for an adjustable one. The "correct" one has a fixed ratio, which may not be optimal for your radial tires, etc. But, adjustable is only helpful if you do adjust it via skid tests in a wet parking lot.

A drum/drum car does not have a p.v., just a distribution block in early cars plus a pressure-imbalance switch in later cars (~1968+). I did re-use my dist. block as a tee for the fronts. Install a p.v. after the imbalance switch.