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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: plazomat]
#1692669
10/31/14 06:42 PM
10/31/14 06:42 PM
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Joined: Jan 2003
Posts: 25,720
Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 25,720
Rio Linda, CA
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MC may be too large but a smaller MC will lower the pedal even more.
Adding a prop valve or RPV won't help the stopping problem.
The INTERNET, the MISinformation superhighway
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: therocks]
#1692670
10/31/14 06:43 PM
10/31/14 06:43 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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Plaz you had 4 wheel drums that were OK for what they were & you wanted better & kept the rear drums intact & swapped to the alum dual MC/discs up front (as stated in your parts list) with no other changes & it's worse now, is that correct?. The alum MC can have a thicker flange/more recessed piston position (possibly deeper "thimble" also) & then there's the thickness of Andys adapter plate all of which contribute to a lower pedal. An adjustable MP will take care of that. This is pretty much identical to what I had/did on my drum/drum dart converted to disc/drum & it was fine even with the big bore MC but others definitely have had issues with too big of bore in the MC but 1&1/32" doesn't sound to big  . Keep us posted. You had manual brakes before so pedal ratio ain't an issue. I would get the pedal height up but sounds like something else is going on. If you have only plumbed in new discs up front which is how I read it (then problem is up front (mc/discs) not in the splitter valve or in the rear drums) & your proportioning might be off (if anything the discs would be engageing too quick) but that ain't the issue going on. I would get the front wheels off the ground & grab a helper to spin the wheel(s) (for a start).
live every 24 hour block of time like it's your last day on earth
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: cudaman1969]
#1692672
10/31/14 07:15 PM
10/31/14 07:15 PM
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Joined: Aug 2003
Posts: 643
Toronto, Ontario, Canada
plazomat
OP
mopar
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OP
mopar
Joined: Aug 2003
Posts: 643
Toronto, Ontario, Canada
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Thanks guys for all the insight - just wanna make this thing safe to drive again. Dayclona - would love to see your list - not set against power brakes, just didn't think it was needed..it is for a 1969 Plymouth B. I just like the look of the 2 bolt master, but if it has to go then so be it - I usually drive with the hood down anyway  Changing pads is quick and easy enough - what do you guys suggest for a pin type caliper - I think 2.75 piston - 72 ebody calipers. Rapid Robert - you are correct that the drums in fine working order just wanted better....all hardlines are plumbed and new. Pedal height - just to clear up what I mean. The pedal is physically at the right height, up tight against the brake light switch. It just does seem to grab until about half way down and then can't push it beyond 75% down - hard as a rock. Feels like brakes have no bite.. 
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: cudaman1969]
#1692674
10/31/14 07:24 PM
10/31/14 07:24 PM
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Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog
Striving for excellence
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Striving for excellence
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
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The responses are all over the map here. LOTS of opinions.
I don't see how pads could get glazed if they never got hot enough to stop the car.
When a "custom" situation like this gives poor results, maybe a wise move is to mimic a setup that the factory used. Once you have a matched set of components, you have a better chance of success.
Here is what seems wrong from my point of view:
Wrong type of master cylinder for the application.
Lack of proper front/rear proportioning.
Again, the OP has not given all the information. Maybe I missed it?
Vehicle, brake size, caliper bore size, master cylinder adapter size and type, brake pedal pushrod length as compared to the original. Again, once you deviate from a factory setup, every single component results in a "variable" that can cause trouble if it is not correct for your application.
Trying to help with such little information is not easy. If you want help, you need to give more details.
Are you listening?
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: plazomat]
#1692675
10/31/14 07:52 PM
10/31/14 07:52 PM
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Joined: Oct 2005
Posts: 8,853
Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 8,853
Ontario, Canada
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Quote:
Pedal height - just to clear up what I mean. The pedal is physically at the right height, up tight against the brake light switch. It just does seem to grab until about half way down and then can't push it beyond 75% down - hard as a rock.
So the whole time you push the pedal its filling up the system because you haven't used the valves as advised. Start there.
When it gets "hard as a rock" is it possible you've totally compressed the cylinder in the m/c ?!?!?
What about the pushrod, what are you using and is it in full contact in the m/c with the pedal at full height? This can be an issue because the m/c spacer plate is a good 1/4" thick or more.
Keep in mind the pedal ratio here - if there is even a 1/8" of play in the pushrod it will take almost an inch of pedal just to take up that slack! On the flip side, are you sure that the pushrod isn't preloading the m/c ??
FWIW you want the pushrod in the m/c, bolt the m/c to the firewall then crawl in the car and install the pushrod to pedal bolt without having to move either the pedal or the pushrod to make it fit.
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: plazomat]
#1692677
10/31/14 08:25 PM
10/31/14 08:25 PM
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Joined: Dec 2007
Posts: 18,157
Mass
DAYCLONA
I Live Here
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I Live Here
Joined: Dec 2007
Posts: 18,157
Mass
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Quote:
Thanks guys for all the insight - just wanna make this thing safe to drive again.
Dayclona - would love to see your list - not set against power brakes, just didn't think it was needed..it is for a 1969 Plymouth B. I just like the look of the 2 bolt master, but if it has to go then so be it - I usually drive with the hood down anyway
Personally, I'd go with a 1 1/8" bore master intended for manual disc applications which the majority were equipped with 10" rear drums, and a proportioning valve, either factory or aftermarket adjustable....just my opinion
Mike
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: DAYCLONA]
#1692678
11/01/14 01:32 PM
11/01/14 01:32 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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The bigger the bore, the higher the pedal effort for manual brakes (and longer required pedal travel -- but long pedal travel can be caused by other 'errors' in the installation). Would be the same rule for PB also, but you might not feel the difference as the booster might mask it.
I put manual DB on my 68 Fury and used a MC from a mid-70s 1/2-ton truck with MDisc. Don't know the bore, but I know it's on the smaller end. Same pedal feel as MDrum but significantly improved braking.
I feel there's a typo or some add'l info missing in that chart above. 1-1/8 is the largest bore, and has always been used with PB (I don't know what that taxi reference is about). The heavier the car, the more crucial the bore size toward pedal effort. A 67-70 A-body could probably use the same bore for both PB and MB, but a heavier car will show excessive pedal effort if the bore is too big.
Edit - that chart is showing where a particular MC was used, bu tit doesn't mean that it's the only MC used for that car - 67-69 C-body is an example of that, a 67-68 could have 1 of 2 bore sizes for MB or PB.
Last edited by Fury Fan; 11/01/14 01:36 PM.
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: DoctorDiff]
#1692680
11/01/14 04:26 PM
11/01/14 04:26 PM
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Joined: Dec 2007
Posts: 18,157
Mass
DAYCLONA
I Live Here
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I Live Here
Joined: Dec 2007
Posts: 18,157
Mass
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Quote:
A 1 1/8" bore master cylinder was never installed on a factory equipped disc brake A,B or E-body.
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: DoctorDiff]
#1692683
11/01/14 06:55 PM
11/01/14 06:55 PM
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Joined: Oct 2005
Posts: 8,853
Ontario, Canada
Stanton
Don't question me!
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Don't question me!
Joined: Oct 2005
Posts: 8,853
Ontario, Canada
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Quote:
I would put in a correct MC for your application
Where's the fun in that ?!?!
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: DoctorDiff]
#1692684
11/01/14 07:25 PM
11/01/14 07:25 PM
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Joined: Jan 2003
Posts: 4,269
Morrow, OH
markz528
master
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master
Joined: Jan 2003
Posts: 4,269
Morrow, OH
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I have the same problem with my 67 Coronet. Have the 10 inch rotors and an adjustable proportioning valve and the DoctorDiff smaller (15/16"?) master cylinder. I have the Raybestos semi-metallic pads and 10 x 2 1/2 inch rear brakes.
It just doesn't have any braking power. Last year my daughter spun the car out at the track because the rear brakes locked up.
I am going to replace the calipers with the larger 76 Volare calipers. Not sure what else to do, but right now the brakes stink!
67 Coronet 500 9.610 @ 139.20 mph
67 Coronet 500 (street car) 14.82 @ 94 mph
69 GTX (clone) - build in progress......
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Re: Disc o tech - blues....my 4 wheel drums were better.
[Re: DAYCLONA]
#1692687
11/01/14 07:50 PM
11/01/14 07:50 PM
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Joined: Feb 2010
Posts: 1,645
Phila. Pa.
Mattax
top fuel
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top fuel
Joined: Feb 2010
Posts: 1,645
Phila. Pa.
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Quote:
Mike,
I've seen that chart before but don't know where it came from. It may have some errors. Here's what I found for Master Cylinder bores from Chrysler factory info (which may have errors too, but at least its from a good primary source).
The chart you posted indicates 1968-69 B-bodies used master cylinder p/n 2883058.
Chrysler's Master Technician Booklet from 1969 agrees, (Master Cylinders for 1969 model year)
However the Plymouth 1968 Service Manual shows the following specifications.
All models with Drums 1"
Kelsey Hayes equiped 1"
Bendix equiped 1"
Budd equiped 1 1/8"
That noted, the Master Technician's booklet from '67 states the Bendix equiped cars have master cylinders with 1-1/8" bores. page 13, Master Cyliner Information Are they both right? Is one wrong? Maybe, I don't know. Probably some more digging, and searching with the restoration crew would be needed.
Quote:
These are often called the "Texas" valve for obvious reasons. They are the ones I mentioned from a 73-76 A body.
Frank - wrong link/picture. Those are later combo valves. The Texas shaped valves look much more like the state! :LOL:
Quote:
I know a combination valve is in order but will that fix the feel of the brakes?
It will not fix the problem you describe. Get whatever E-berg recommended. If he recommended a proportioning valve, then just get one and plumb it into the rear line. A proportioning valve reduces the increase in hydraulic pressure to the rear wheel cylinders once the system pressure reaches a set point. For example, if the set point is 300 psi, then from 0 to 300 psi all four brakes receive the same hydraulic pressure. On a harder stop from higher speed, lets say you apply more force on the brake pedal, and the pressure from the master cylinder produced is 400 psi. If the proportioning valve is set up for 50% reduction, the front brakes will get 400 psi and the rear wheel cylinders will see only 350 psi.
Quote:
I guess I need a residual pressure valve in the rear lines as well - will that fix the pedal height?
Many master cylinders come with a the residual valve on the front port (for the rear brakes). If there is no residual valve, the springs on the shoes will squeeze alot of the fluid out of the wheel cylinderss and back into the master's resevoir.
Quote:
Brakes are bled I guess - no spongy but low and hard as hell pedal.
Read MTSC booklets on brakes to see Chrysler's recommendations on bleeding. Gravity was Chrysler's prefered method for the front discs. If you hae any doubts get a helper and do the drums with the pump shut method, and make sure the bleeders are open at least a half turn.
Quote:
Brakes just suck - low but hard pedal and I gotta stand on it to stop the car..
As others have said, could be a number of things. Troubleshoot possible faults before changing parts. A few points that may be helpful
* Recognize that duo-servo drum brakes are self energizing. They require less pedal effort than equivalent disks (unless the lining's overheat and lose friction which doesn't happen in everyday driving).
* Lining material can make a difference. Some linings have more initial bite than others. Some of the modern high performance oriented linings may say 'street' but don't really bite until warmed up. Also, many of the newer high performance linings require bedding in that transfers material from the pad to the disk (or drum). This is what AndyF was talking about. On old school and some current organic and semi-metalic linings this is not really an issue, but on many of the new performance linings, it is. Finally, any grease, oil, etc, will mess up a lining quick! Brake cleaner is your friend!
* Final thought, make sure the rear drums are adjusted properly - just a few clicks shy of dragging. At lower speeds they a contribute a lot and will effect the initial pedal feel for sure.
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