I know of no way to measure the bore without removing the MC, taking it apart and measuring the bore with a caliper, which I have, but that's a lot of work and it has to be fully bled again. I'll do that last if I have to.
High pedal pressure with KH disc brakes
- Thread starter Bob Jasinski
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I understand completely.
Alright. I've seen people put them backwards.
I'm all for DOT 5. I will be using it if i do a complete brake job with caliper, master, and cylinder
The bore is the same from one end to the other.
It might be a little larger right at the opening but carefully pushing the piston in it could be measured
340sFastback
Well-Known Member
When I used to have KH on my car I ran EBC Red pads and they helped reduce leg effort (15/16 master cylinder, manual brakes, 10 inch rear drums, small bore rear wheel cylinders). The EBC pads needed some heat in them to start working well. So in the hot summer days when car was driven the most that is when they worked the best. I was able to get the KH brakes to work pretty good with those pads. But when all was said and done I wanted even less leg effort without using a booster. So I went big bolt pattern 11 3/4 Stage II and 10.7 rear disc Dr Diff kits which got me the even lower leg effort I was after using the same 15/16 master cylinder.
Hmmm. I wonder if I could get it far enough away from the firewall to measure without taking the lines off.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Just so you know;
My car has those HK front brakes & 10x2 drums on the rear, transplanted from a Duster/Demon;
A 15/16 master & same rear wc's.
Factory Mopar front pads, and whatever on the rear.
My car runs big & little tires,
I run braided front hoses, a regular rear jobber hose, Dot-5, and no proportioning at all.
I do run a booster;
I tried the smaller dual diaphragm, but didn't like it.
I swapped to the bigger single, off a 73>75 Dart, BadaBoom! Best feel/best stopping car I've ever
had.
Best of luck to you.
My car has those HK front brakes & 10x2 drums on the rear, transplanted from a Duster/Demon;
A 15/16 master & same rear wc's.
Factory Mopar front pads, and whatever on the rear.
My car runs big & little tires,
I run braided front hoses, a regular rear jobber hose, Dot-5, and no proportioning at all.
I do run a booster;
I tried the smaller dual diaphragm, but didn't like it.
I swapped to the bigger single, off a 73>75 Dart, BadaBoom! Best feel/best stopping car I've ever
had.
Best of luck to you.
I bled all four wheels again, no difference.
If you think everything is mechanically correct drive it a bit and try to get used to it. I never had any problems with the little extra pedal effort but I'm 6' and 190 lbs. and I grew up with these braking systems. One thing for sure it's not going to feel like a Honda with 4 wheel power discs.
340sFastback
Well-Known Member
A lot of times after pads seat and master cylinder seals settle in the brakes will work better. Why size rear wheel cylinders do you have?
Then (if bubble-free dot5), that much travel with finger/hand pressure (in your pic) shows you've made the most of minimizing effort with available pedal travel. If you have the room in the wheels, bigger OD rotors that allow the calipers to move out to have more leverage on the wheel is one way but a small vac or hydro (power steering pump driven) booster on the firewall is a lot more practical.
This 2019 military test of DOT 3, 4, 5, and 5.1 may surprise you. Seems they are now going back to glycol instead sticking with DOT 5: https://apps.dtic.mil/sti/pdfs/AD1091780.pdf
That's a very lengthy study, thanks for forwarding. Did you notice that the purpose of the study was "Brake Fluid Standardization for Anti-Lock Braking Systems (BFABS) Benchtop Testing Report"? This study is about finding a substitute for DOT 5 in vehicles that have anti-lock brakes. DOT 5 is hardly mentioned because DOT 5 has never been recommended for anti-lock brakes due to its incompatibility with the high vibrations that occur in antilock braking systems that causes bubbles to form.
I understand that DOT 5 brake fluid discussion with some people is like discussing religion, but since I have had very good results with DOT 5 in other vintage cars, I am sticking with it. The main reason I want it in my FS is that (as I mentioned to RRR) is I have a lot of $$$ invested body and paint on this build and absolutely do not want a couple of pints of "paint remover" DOT 3,4 bolted to the firewall. What does surprise me is that I have read here on FABO (and Tom Condran's book) that conversion from drums to disc KH brakes is pretty much straightforward with the right parts and that a booster is not required. As far as going with bigger rotors, I've had such a difficult time find the small bolt pattern rotors I have now, and had to cut the hat with a lathe to avoid rubbing the seals, I'm going to stick with these until I figure out exactly what the problem is. I'm also experimenting with different brake pads, and if I have to, I will add a booster.
I've been very busy this week getting taxes done and getting ready for visitors this weekend and next, and still have not been able to confirm the bore of the master. It's a new Raybestos MC36406, supposedly 15/16" bore, but I'm trying to find a way to measure the bore without opening the lines. The master was bench bled, but it does have those two loops under the master (new lines from Inline tube) that some say are difficult to bleed. The rears are new Dorman W78734, 15/16" bore. The brakes do work well, and stop evenly, but you really have to push hard. I'm 6' 200 lbs., and not short of leg power, but it just isn't fun to drive, and that's my issue.
I'd be more inclined to look at compounds and surface finish. Initial braking the drums should be helping and they are self enegizing. Additional braking force shifts forward. See if you can narrow down when its occuring. Can you lock up all 4 on dirt or some othe poor traction surface?
My experience with NOS Mopar replacement pads and smooth rotors was lack of bite. Had some really good braking the long out of production Raybestos and just about as happy with Porterfield's street compound. R4S IIRC. Others have driven the car for autocross and everyone likes brakes. The 16:1 manual steering not so much. LOL.
My experience with NOS Mopar replacement pads and smooth rotors was lack of bite. Had some really good braking the long out of production Raybestos and just about as happy with Porterfield's street compound. R4S IIRC. Others have driven the car for autocross and everyone likes brakes. The 16:1 manual steering not so much. LOL.
Kendog 170
Let the boy go !
Good tip.
Don't do it if you live in Michigan. You'll never get them to release.
I'm still working on my brakes and continue to have problems, one is the pedal travel, the other is the amount of pedal pressure it takes to stop. This post is about pedal travel, it's still too much. Just bled the system again, first with a vacuum bleeder and second with my lovely wife in the car stepping on the pedal while I open/close the bleeders. This is probably the 5th time, the pedal remains the same, it goes down too far but does get firm. I'm starting to think I may need a longer rod from the pedal to the master. I am using the original rod that came with the manual drum/drum from the factory. I have KH discs in the front and stock 10" rear brakes, new wheel cylinders, drums and shoes, set as high as I can and still rotate the wheel by hand. The m/c is the dual pot MC36406. Could it be this MC has greater travel than the original single pot master and I need a longer rod?
if the MC has a smaller OD than 1" it will travel farther than the 1" but with less force to stop the same.
if the master is larger than 1" it will travel shorter BUT require more leg force than the 1" to stop the same
How much travel do you have from pedal in natural return state to firm pedal?
if the master is larger than 1" it will travel shorter BUT require more leg force than the 1" to stop the same
How much travel do you have from pedal in natural return state to firm pedal?
It's a 15/16" MC. This is where it starts to get firm, a bit more when my foot's on it.
that looks about like my 67 with 1" master and KH front disk
I'm really starting to think it was a mistake to go to the KH disc brakes. All these years I've been reading about this "upgrade". Now I'm finding its a pain to get right. My FS came with 10" drums all around, the standard Barracuda was 9" around, so it already had bigger brakes from the factory. The pedal pressure is too high as well, these aren't self energizing like drum, so I see having to add a booster too, Not looking forward to cluttering up the engine bay and making it harder to adjust the valves.
You're call, you can always sell off your Disk parts and go back to Drum? But I think there is really something wrong in your system OR your expectations. I can stop my 67 Dart with manual factory front disk and rear 10" drums with minimal effort. In a panic situation might use 2 feet but I doubt I would be able to react that fast.
Perhaps if you could test drive someone else car with the same setup and see if it feels different to you that would give you some data to make an informed desicion.
As for disk being better... I had my front drum fade once in a need to stop fast or hit the car in front of me situation and it was a heart dropping feeling. I was lucky that I had 12" to spare!
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