15/16" MC more travel than I would like.

[rustytoolss]

just installed DR Diff 15/16 MC, brakes have more travel/soft than I would like. I'm sure adjusting rear may help some. I did install 2.75" calipers a while back (I'm sure that's not helping) If I were to replace the 15/16 wheel cylinder with 7/8" wheel cylinders would that help much ?
I have also thought of drilling another hole in the brake pedal to change the ratio (a bit) could help some. I've done this before . I know it will not change the PSI / will just change the travel somewhat. Thoughts
Going to rebleed to make sure that there is not any air still in the system.

 

[MIKESPOLARA]

You need to go larger on the master bore size.
Power or manual? Manual go to 1" bore, power use 1 1/8"

 

[diesel_lv]

Power or no power. I've got a 15/16 MC from Dr Diff manual brakes on my '67 Coronet. Great feel and hardly any travel when the rears haven't blead back. I haven't installed the check valve for the rears yet, but hoping once I do, they won't bleed back and occasionally need pumping.

 

[hunt2elk]

I replace the 15/16 rear cylinders with 7/8, but I don't think it is necessary.
I have an almost new 1 1/32" aluminum cylinder from Cass if you end up not liking the 15/16".

 

[MIKESPOLARA]

Power or no power. I've got a 15/16 MC from Dr Diff manual brakes on my '67 Coronet. Great feel and hardly any travel when the rears haven't blead back. I haven't installed the check valve for the rears yet, but hoping once I do, they won't bleed back and occasionally need pumping.

Bleed back? In hydraulics that's called air in the system

 

[beanhead]

"I'm sure adjusting rear may help some."

It makes all the difference...definitely tighten them up before deciding on drilling/modifying anything, you may not want to once they're functioning properly.

 

[rustytoolss]

Forgot to say by my brakes are manual 15/16MC, 2.75 Calipers, 15/16 Wheel cylinders. I need to check out for any possible air in the systen, check rear brake adjustmenr also., before getting all upset. It seems like I don't have enough stopping pressure. I don't think I could slide the tires on a panic stop. And like I said before more pedal travel than I would like. If it were stopping better/ I would be OK with the travel.
Was thinking if need be, I could install the 11.75 Rotors.

 

[rustytoolss]

Power or no power. I've got a 15/16 MC from Dr Diff manual brakes on my '67 Coronet. Great feel and hardly any travel when the rears haven't blead back. I haven't installed the check valve for the rears yet, but hoping once I do, they won't bleed back and occasionally need pumping.

so are saying that I may/should install a residual valve in the line going to the rear brakes ?

 

[Don Frelier]

The pedal should be firm almost as soon as you press on it. ( Right near the top )

 

[diesel_lv]

Bleed back? In hydraulics that's called air in the system

No, I talked to Cass, there is no residual pressure valve in his master cylinders. He said that the rear drum springs push the rear wheel cylinders causing them to need to be pumped. Have been to the shop n no air in system. Cass said to install a 10lb residual check valve downline on the rear brakes before the rear "T".

 

[Billccm]

I have the Dr Diff conversion 15/16 master manual brakes. Lots of pedal travel, but stops good. Takes time to get used to it. Dr Diff has rear wheel cylinders that you can try. This also reduces rear lock up.

 

[MIKESPOLARA]

No, I talked to Cass, there is no residual pressure valve in his master cylinders. He said that the rear drum springs push the rear wheel cylinders causing them to need to be pumped. Have been to the shop n no air in system. Cass said to install a 10lb residual check valve downline on the rear brakes before the rear "T".

If you have to pump and the pedal comes up you have air or a bad master, usually air. I run without residual valves all the time with drum brakes and that does not happen in a good bled system

 

[diesel_lv]

If you have to pump and the pedal comes up you have air or a bad master, usually air. I run without residual valves all the time with drum brakes and that does not happen in a good bled system

Air doesn't go away. I can pump them and then firm pedal n it stays firm for 200 miles of driving,then turn off and on n it's still firm. A week later, it's gotta be pumped almost every stop for 10-20 miles n then all of a sudden it stays firm again. Local brake shop, all they do, said no air in system, no leaks anyplace.

 

[rustytoolss]

As for me I just got my 15/16MC from Dr Diff and took my first drive today. The car does stop better, but not as good as I had hoped for. Could still be some air in the system (pedal feels spongy, I expected long travel ) and my rear brakes may need some adjustmet. I was just expecting more stopping PSI. But like I said only the first drive. I also my need to make some adjustment to my rear ADJ brake valve. I'm sure it will get better when I check things out a bit more.

 

[hunt2elk]

I run the aluminum 15/16" aluminum master cylinders from Cass, his 11.75" front rotors, and 7/8" rear wheel cylinders on both my B-bodies. My 70 Duster is the same except I had to add a prop valve in the rear line because of rear wheel lockup, I suppose because it is a lighter car. I had a valve from Pirate Jack that still wouldn't solve the problem. Ended up with one from Willwood and that gives me the adjustment I needed. They claim theirs has the more hold off than any other brand made, and they are right.
If you end up wanting to try the 7/8" rear cylinders, I have 4 brand new NAPA brand I would make you a really good deal on...