Converting my 69 dart to manual front disk and I am going with a kit that does not include a M/C. Looking on Rockauto they have 15/16" bore MC for power disk brakes. Does it make a difference? i assumed that as long as the bore size was not more than 1" it would work fine on a manual disk brake car.
Am i right about that?

Check with Dr. Diff . . . I used his 2 bolt master cylinder and adapter block on my 70 Sport Satellite - manual disc, works great, pedal is high and hard - easy to stop the car !

I used the 2 bolt one with the conversion plate from Dr Diff on the 340 Dart. 15/16" bore...
Liked it so well have since bought two more...one for a 72 Duster and one for a 65 Coronet...

Got my Dorman 15/16th on Amazon. Resolved poor braking performance with non power brake disc brake E Body.

at your parts house look in the rear piston "thimble" & for a manual brake app it needs to have the circular recess about halfway down for the neoprene nub on the end of the manual brake pushrod to lock into. A PB app does not need the recess but is fine with it, not so with manual brakes, must have. then as you are doing, get the right bore.

Dr. Diff recommended the Raybestos MC36406 to me back on '08 and I've been very happy with it.

I was looking at that one as well but it lists for power brakes but I want manual. That was what prompted my question. Are you using this mc on a manual brake car?

Just an FYI, the original bore size for '69-'70 disc brake A bodies was 1". And the same master cylinder was used for both manual and power disc cars.
They increased the bore size in 71 but IIRC manual and power disc cylinders also were the same 71 on parts.

I would be interested to know if the manufacturers make all their mc compatible with manual brakes if they can also be used on power brake cars but not vice versa.

I run all 70 C body disc masters.Mine has been on my 65 for 20 years.used it on my kids 62 300 with power and for drums.Mine is manual and disc.have done a few others and all worked good.Rocky

I use the 1 1/32" MC on my 3600 pound manual front disc car, I tried the 15/16" and it gave a low/soft pedal with no noticeable improvement in braking.

they are all about max profit/minimum inventory (which makes sense) like a carb kit will contain extras for several variations. You would think they would make all rear pistons (but of different diameters for all the apps) with the groove to be used for manual or power apps. there has to be a reason why both types are mfr'd.

Manual compared to Power. It depends on the set up. Some power setups will change the mechanical linkage ratios. But in your case, its not too useful bit of information.

Your decision should be based on:

• Whether the master cylinder will retain your pushrod.
• Whether the master cylinder has a large rear resevoir for the disks.(Some are just drum brake masters with the residual valve removed from the rear outlet).
• Total area of pistons that need to be displaced. Less or smaller pistons will need less volume from the master cylinder to move the same distance.

Cnxt's rules of thumb are good. A smaller master cylinder diameter will require less force to develop the same pressure. The downside is it will have to move further to displace the fluid needed to move the caliper's pistons.

Assuming your conversion is to a stock type caliper -
here's my work in progress crib sheet for the A-bodies.
Feel free to add, question or correct (especially if you have a documented source).

years___Application_____________p/n_______Bore
1966... Fixed Ft calipers, Manual................1"
1966... Fixed Ft calipers, Power..................1"
67-70.. Fixed Ft calipers...........2808600.....1"
71-72.. Fixed Ft calipers...........3461178.....1 1/32
73-74.. Floating caliper, Manual..3580146.....1 1/32
73-74.. Floating caliper, Power.. 3580112........15/16

1976?...............................____4647..........15/16

Let us know what you did when you finish.

I have used the 15/16 MC many times and always it stopped better than power brakes.

I know most of us are used to a relatively short pedal travel, but I prefer a bit longer throw. I've seen guys run their stuff big enough that the pedal acted like a toggle switch. Plus, it had a bit more effort.

Longer throw makes for better brake modulation if you drive it hard.

That depends.
Its not a good a rule of thumb. It needs to be like Goldilock's porridge... just right. Yes if its too hard to apply the force, then more throw can help. But definately don't want too much. That's disconcerting!

Most race drivers prefer to control by modulating force rather than distance the foot travels. For example see Carroll Smith, Tune to Win, 1978, pages 111-12.

My own experience has been that this applies to street and autocross as well. I prefer to modulate using the heel and ankle rather than moving the leg from the knee. Heel rests on the floor.

Obviously if the required force can not be easily applied, the smaller piston may be needed. Sometimes all it needs is a change of pad compounds to ones with more bite. This usually comes with increases in pad wear, but its worth it.

Good info!

"Are you using this mc on a manual brake car?"

I am. When I bought it, the listing said it was for manual disc brake A-bodies.

It is much easier to modulate, for example, 300 psi of brake pressure over 2" of travel than 1/2". Too little travel gives you the on/off effect. Too much can wear you out, but I find more is better than less.