Master cylinder interchange disc/drum-drum/drum

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Duster_71

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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
 
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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.
 
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
 
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).
 
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?
 
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.
 
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