Re: Front Disk Brake Conversion not working as expected
[Re: RapidRobert]
#1084472
11/02/11 01:53 PM
11/02/11 01:53 PM
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Joined: Feb 2003
Posts: 7,982 Scranton, PA
Montclaire
master
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master
Joined: Feb 2003
Posts: 7,982
Scranton, PA
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Bottom line, use the right parts. Why would you use the 73+ spindles when the right stuff is available? There was an article in Mopar Muscle a while back, I no longer have the specs. They printed a chart with different variables between the earlier and later spindles and there were some differences, I think mostly with roll center. BUT, the test was not only skewed from the start with non-factory settings (lowered here, changed there, who knows if a stock setup would yield different results?), it also was very one dimensional - the factory ran these setups through simulations that measured everything seven ways from Sunday. One test will not find every gremlin, the same way that a standard alignment will not find issues beyond the basics.
The right parts are out there, use them.
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Re: Front Disk Brake Conversion not working as expected
[Re: 1970440RT]
#1084474
11/02/11 02:59 PM
11/02/11 02:59 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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Quote:
When I would add in one side of the fronts I would get a good pedal, but more travel when pressing the pedal. When I added in the other front side, the pedal would almost go to the floor.
(1) that's normal as you're adding another caliper to be filled. (2) I wonder how it would act if you plugged the side of the fronts that is good and hooked up the problem corner one. EDIT Yeah if it is strickly a M/C prob & you swapped it & there is no air downstream it should be high and tight with just that (problem) side also. Not a leverage problem
Last edited by RapidRobert; 11/03/11 12:11 AM.
live every 24 hour block of time like it's your last day on earth
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Re: Front Disk Brake Conversion not working as expected
[Re: Montclaire]
#1084475
11/02/11 03:13 PM
11/02/11 03:13 PM
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Joined: Dec 2006
Posts: 3,533 Indiana
Fury Fan
master
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master
Joined: Dec 2006
Posts: 3,533
Indiana
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Quote:
One test will not find every gremlin,
I read one of the brake conversion articles in a Mopar magazine that praised the conversion kit (one of the ones that uses a bearing spacer) because they had not had a single problem and had put over 5000 miles on them.
As a test engineer, I was torn between laughing or grimacing at such a paper-thin evaluation.
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Re: Front Disk Brake Conversion not working as expected
[Re: RapidRobert]
#1084476
11/02/11 04:38 PM
11/02/11 04:38 PM
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Joined: Dec 2006
Posts: 3,533 Indiana
Fury Fan
master
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master
Joined: Dec 2006
Posts: 3,533
Indiana
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Maybe we got the answer further up, I’ve read all the replies but not all on the same day.
Regarding the bore size vs front brakes - From my understanding, a small bore is for manual brakes, larger bores are for power brakes (to keep pedal effort within 'normal' for a human leg). There is probably also a slightly-larger bore suited for discs then, because I suspect that the fluid volume required to move 2 pistons is greater than to move 2 front wheel cyls. Also, the late-70s caliper bores are larger than the early 70s (at least as far as C-bodies go), which supports my hunch.
Using a small bore MC requires longer pedal travel/longer MC piston travel. There are also a few orifices/ports in there that I'm not fully versed with, but I do believe that if in the event of a pressure loss in teh front brakes (which run on the rearmost MC section) that the piston travels further forward and bump-stops the rear brake piston into action.
So climbing further out on the limb: Small-bore MC takes lots of travel, can barely push the fluid vol to activate the calipers, but then physically pushes the piston for the rear brakes – and they lock up (especially because pedal effort is so low in this configuration).
Then one front brake is capped off, reducing the fluid vol requirements, so the pedal feels better, and blocking them both off makes a rock-hard pedal – proving the MC has integrity. The difference mentioned earlier, between blocking 1 caliper vs the other, is a mystery to me, though. Different length of metal tube was my initial thought but then discarded as the fluid vol required is same for both calipers and pressure loss in longer tube would be negligible.
And as a bit of evidence – Almost 20 years ago I converted a 65 Fury from manual drums to power discs (c-bodies use a different pedal assembly for manual brakes, and you can’t tell the difference by looking down from the driver’s seat, you have to be aware of this difference). I used a 71 PDB booster /MC with my MB pedal. Braking was great but the pedal was very soft and felt like it had air in the lines. Bled them repeatedly, over several weeks, but to no avail. Blocked off the front hoses and got a rock-hard pedal, so I knew the MC was OK. None of the brake experts I spoke with had any good ideas. I didn’t drive the car very much, and the brakes were awesome, so I accepted it. I figured it out many years later as I learned more about C-bodies.
I think this is a related situation.
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Re: Front Disk Brake Conversion not working as expected
[Re: Montclaire]
#1084477
11/02/11 04:40 PM
11/02/11 04:40 PM
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Joined: Jan 2003
Posts: 75,020 U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,020
U.S.S.A.
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Quote:
Bottom line, use the right parts. Why would you use the 73+ spindles when the right stuff is available? There was an article in Mopar Muscle a while back, I no longer have the specs. They printed a chart with different variables between the earlier and later spindles and there were some differences, I think mostly with roll center. BUT, the test was not only skewed from the start with non-factory settings (lowered here, changed there, who knows if a stock setup would yield different results?), it also was very one dimensional - the factory ran these setups through simulations that measured everything seven ways from Sunday. One test will not find every gremlin, the same way that a standard alignment will not find issues beyond the basics.
The right parts are out there, use them.
How does spindle height cause his soft pedal issue ?
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Re: Front Disk Brake Conversion not working as expected
[Re: Fury Fan]
#1084479
11/03/11 08:09 AM
11/03/11 08:09 AM
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Joined: Jun 2006
Posts: 135 Pittsburgh, PA
1970440RT
OP
member
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OP
member
Joined: Jun 2006
Posts: 135
Pittsburgh, PA
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Sorry, should have clarified,
If I blocked one side of the front brake system ( didn't matter which side - after further tests ) I would have a decent pedal. When I hooked both sides into the distribution block is when I would get the overly long pedal travel.
I can't explain the results as fluid can't be compressed. How would the isolated rear brake system produce a great pedal, while adding the front lines would give me excessive travel? The signs point to trapped air but after switching masters, that theory is disproven.
I don't recall the actual bore size of the Ehrenberg Master but it is at least 1 1/8", possibly 1 1/4". ( Not 1 15/16" as I originally posted ). The Eberg master is what I have on the car now and is working but with an unnaturally hard pedal with only a little bit of travel.
Last edited by 1970440RT; 11/03/11 08:10 AM.
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Re: Front Disk Brake Conversion not working as expected
[Re: 1970440RT]
#1084480
11/03/11 10:24 AM
11/03/11 10:24 AM
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Joined: Jan 2003
Posts: 75,020 U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 75,020
U.S.S.A.
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Quote:
Sorry, should have clarified,
If I blocked one side of the front brake system ( didn't matter which side - after further tests ) I would have a decent pedal. When I hooked both sides into the distribution block is when I would get the overly long pedal travel.
I can't explain the results as fluid can't be compressed. How would the isolated rear brake system produce a great pedal, while adding the front lines would give me excessive travel? The signs point to trapped air but after switching masters, that theory is disproven.
I don't recall the actual bore size of the Ehrenberg Master but it is at least 1 1/8", possibly 1 1/4". ( Not 1 15/16" as I originally posted ). The Eberg master is what I have on the car now and is working but with an unnaturally hard pedal with only a little bit of travel.
The long pedal is caused by the small bore of the master and the large piston area of the 2 front discs , the more piston area the longer the travel to move the fluid to push the pistons , when you block off the front of the rear lines , as you know the fluid can't be compressed if there is no air you greatly shorten the amount of pedal travel , the problem is the master cylinder you are using , and make sure you have the rod from your power booster set correctly .
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Re: Front Disk Brake Conversion not working as expected
[Re: 1970440RT]
#1084482
11/03/11 02:59 PM
11/03/11 02:59 PM
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Joined: Mar 2003
Posts: 4,848 Memphis
HemiRick
master
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master
Joined: Mar 2003
Posts: 4,848
Memphis
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Thats a symptom of a master cylinder push rod adjusted to far and its not letting the master cylinder plunger come back far enough....Fluid can only return to the master when it's all the way back.
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Front Disk Brake Conversion not working as expected
[Re: Fury Fan]
#1084486
11/03/11 04:32 PM
11/03/11 04:32 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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yes check the booster pushrod free play from the round nub to the bottom of the piston recess & want ~.060" or a bit less and take off the lines from the M/C and stick a drill bit deep into each cone and you'll feel the RPV if it has one as it's just a piece of neoprene on a spring & you'll feel the springiness. Cant have a OE type RPV on the disc side they hold too much pressure
live every 24 hour block of time like it's your last day on earth
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