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Standing on the brakes
https://mail.slantsix.org/forum/viewtopic.php?t=64106		 Page 2 of 4
Author:  emsvitil [ Mon Sep 30, 2019 11:50 pm ]
Post subject:  Re: Standing on the brakes
A 4 wheel drum system doesn't need a proportioning valve, just a distribution block.
Author:  Dart270 [ Tue Oct 01, 2019 3:06 am ]
Post subject:  Re: Standing on the brakes
Essentially no old Mopars had proportioning valves, only distribution blocks that most people erroneously call prop valves.

Lou
Author:  valiant_200 [ Tue Oct 01, 2019 8:22 am ]
Post subject:  Re: Standing on the brakes
I thought the brass block with the brake light sensor (67 & up) was a proportioning valve.

Anyway, I had to replace that along with some lines when I converted it in the late 80's, as part of the upgrade.
Author:  SlantSixDan [ Tue Oct 01, 2019 9:05 am ]
Post subject:  Re: Standing on the brakes
Er-ruh…many old Mopars equipped with disc brakes have actual, real, honest-to-grapefruit proportioning valves.

Right column, lower paragraph

Right column

Left column

Lower half of page plus next page
Author:  valiant_200 [ Tue Oct 01, 2019 10:07 am ]
Post subject:  Re: Standing on the brakes
Referring back to this comment:
Quote:
FYI, the front disc master cylinders have a much larger rear reservoir (for the front circuit).
I am looking at both the 62 (with the 74 Dart disk system) and the 65 (dual drum system) right now. In both cars the master cylinders appear to be identical, which is to say that they are beefy, squarish units with a much larger rear reservoir, like an MC36412.

It is sounding more and more to me like I might have the incorrect M/C for this application. Therefore, I think the first logical step is to remove this possibility.

Referring to Page 234 of the Raybestos Application Manaul (attached), the two proposals on the table that I like are the RAYBESTOS MC36221 (67-70 Valiant with front drums), and the RAYBESTOS MC36338, (71-74 Valiant with front drums). Both are similar in physical appearance and look nothing like what I have installed now. To further confuse the issue, I see there is also an MC36439 that is specified for 73-75 Valiants with a V8.

But which is the better choice? It seems to make sense to try and match the bore size with the original Death Onion dimension of 1". On the other hand, MoPar decided to go with this different M/C from 71 to 74, and further change the formula for cars with V8's. There must have been a reason for that design change.

Although I have been able to find application data, I have yet to find any technical specs on these parts. What are the bore sizes for each? Does anybody know where to find that information?

Our path forward is we will replace the Master Cylinder with what we believe is the proper part. Then, if problems persist, we will take the further step getting a gauge and measuring the pressure in the system.

Continued thanks for helping me solve The Riddle of the Crappy Brakes.

Attachments:
Raybestos Applications for Valiant.jpg
Raybestos Applications for Valiant.jpg [ 63.36 KiB | Viewed 8265 times ]
Author:  DadTruck [ Tue Oct 01, 2019 10:57 am ]
Post subject:  Re: Standing on the brakes
Quote:
Our path forward is we will replace the Master Cylinder with what we believe is the proper part. Then, if problems persist, we will take the further step getting a gauge and measuring the pressure in the system.
personally, I would get a gauge and know the hydraulic brake pressure at each corner of the vehicle, then if that indicates a problem, take steps to resolve it.
as opposed to changing to a different MC because it looks different, for which you have no technical specifications on the alternative MC to support that it will be different, or better, or worse.

but to each his own,,,,
Author:  Charrlie_S [ Tue Oct 01, 2019 1:06 pm ]
Post subject:  Re: Standing on the brakes
Many years ago, I had a stopping problem on a race car, built by someone else. Put a pressure gauge on it, and found only 500 lbs line pressure, with as much pedal effort as I could manage. The mechanical leverage ratio was all wrong. Corrected that and got 1500 lbs line pressure. Then changed the hydraulic ratio by changing master cyl bore size (smaller) and WC bore size (larger). Hugh difference.
Author:  valiant_200 [ Tue Oct 01, 2019 1:19 pm ]
Post subject:  Re: Standing on the brakes
Quote:
Quote:
Our path forward is we will replace the Master Cylinder with what we believe is the proper part. Then, if problems persist, we will take the further step getting a gauge and measuring the pressure in the system.
personally, I would get a gauge and know the hydraulic brake pressure at each corner of the vehicle, then if that indicates a problem, take steps to resolve it.
as opposed to changing to a different MC because it looks different, for which you have no technical specifications on the alternative MC to support that it will be different, or better, or worse.

but to each his own,,,,
I like the idea of measuring the line pressure and will probably buy a gauge out of curiosity, if nothing else.

The physical evidence that I have the incorrect M/C cannot be overlooked, so therefore I am going that route as well.

I appreciate everyone's input so far. I would not have thought to look for a gauge on my own.
Author:  SpaceFrank [ Wed Oct 02, 2019 9:37 am ]
Post subject:  Re: Standing on the brakes
Please let us know how it works. I've been happy with the later 1-1/32" master cylinder in my 9" drum cars, but I'm a 225 lb. guy with a lot of lower body strength. Maybe I just like a firmer pedal.

I don't think there were different wheel cylinder bores for 9" brakes, but I could be wrong there. I know I've read about different bores for larger drum brakes.
Author:  SlantSixDan [ Wed Oct 02, 2019 12:47 pm ]
Post subject:  Re: Standing on the brakes
Quote:
I don't think there were different wheel cylinder bores for 9" brakes, but I could be wrong there. I know I've read about different bores for larger drum brakes.
For '73 the 9" front drums got a larger wheel cylinder bore, which shows you the lengths Chrysler would go to pinch every last tenth of a penny. The 9" drum brakes were passably adequate in 1960 traffic on the lightweight 1960 Valiant. They were questionably adequate on the larger, heavier 1963 Dart, and their inadequacy grew less and less arguable as the cars got heavier and the traffic got denser.
Author:  SpaceFrank [ Wed Oct 02, 2019 2:14 pm ]
Post subject:  Re: Standing on the brakes
Quote:
Quote:
I don't think there were different wheel cylinder bores for 9" brakes, but I could be wrong there. I know I've read about different bores for larger drum brakes.
For '73 the 9" front drums got a larger wheel cylinder bore, which shows you the lengths Chrysler would go to pinch every last tenth of a penny. The 9" drum brakes were passably adequate in 1960 traffic on the lightweight 1960 Valiant. They were questionably adequate on the larger, heavier 1963 Dart, and their inadequacy grew less and less arguable as the cars got heavier and the traffic got denser.
Good to know. If there are multiple available wheel cylinder bores for 9" drums, that could also be a factor. From a brief survey of RockAuto listings for 9" drum Darts across that year break, it looks like the fronts increased from 1" to 1-1/16" while the rears stayed at 13/16".
Author:  SlantSixDan [ Wed Oct 02, 2019 2:31 pm ]
Post subject:  Re: Standing on the brakes
Pretty sure the '73+ front wheel cylinders won't fit the '72-down backing plates. Anyway, a larger wheel cylinder bore would make for an easier pedal, not a harder one.
Author:  valiant_200 [ Wed Oct 09, 2019 1:24 pm ]
Post subject:  Re: Standing on the brakes
OK, I replaced the master cylinder with an MC36338, (71-74 Valiant with drums) and the stopping power is back to mediocre again, up from terrifying as noted before.

One frustrating note on all of this. Although the brakes are now OK for traffic as long as you are not a tailgater, one of the brand new drums I put on it seems to be really bad out-of-round. I am experiencing pedal pulsing coming to a stop and something is making the front end shimmy between 35 and 40 mph. It is very annoying but, since we are in the middle of Cruisin' The Coast, the big car show of the year here in South Mississippi, it will have to wait for a while to be inspected.

Aftermarket parts are so marginal for our cars now. Another annoyance is the aftermarket turn signal switch I installed in the steering column a couple of years back, which fails to completely cancel, causing my left tail light to not work. That is a subject for another forum, but it is annoying nonetheless.
Author:  Dart270 [ Wed Oct 09, 2019 1:35 pm ]
Post subject:  Re: Standing on the brakes
If you are going to drive this car long distance or in any kind of traffic, I highly recommend installing front disc brakes. There are many variants available (with the later upper control arms and spindles - also available new). Check out doctordiff.com, although there are other suppliers. This will be MUCH safer than the best 9" drums and you will enjoy driving the car(s) more as a result. Another benefit is 4.5" bolt circle, which opens up huge possibilities for good tires and aftermarket (or stock style) rims.

Lou
Author:  valiant_200 [ Tue Oct 15, 2019 10:28 pm ]
Post subject:  Re: Standing on the brakes
Quote:
If you are going to drive this car long distance or in any kind of traffic, I highly recommend installing front disc brakes. There are many variants available (with the later upper control arms and spindles - also available new). Check out doctordiff.com, although there are other suppliers. This will be MUCH safer than the best 9" drums and you will enjoy driving the car(s) more as a result. Another benefit is 4.5" bolt circle, which opens up huge possibilities for good tires and aftermarket (or stock style) rims.

Lou
I have several Valiants. The Vert is no doubt my metal spirit animal. I have owned it for 35 years. I drive it as often as possible and miss it dearly when it is off the road. My second favorite is my guinea pig, a blue 1962 Valiant 200 which I saved from certain death and, therefore, have felt free to modify.

Curious about disc brakes on an early Valiant, I built a stock 74 Dart disk brake system into it.

While there is no doubt that it improved my stopping power, it also introduced a new problem. The larger bolt pattern up front, which you and others have presented as an improvement, turned into a nightmare of searching and improvising to make work. Of course the problem is the rear axle remains a 4 inch bolt pattern and the change up front causes a mismatch. I got around this problem by buying an adapter and carrying one spare for the large bolt pattern. If a small bolt pattern rear tire goes out, I bolt the spare to the adapter and I'm on my way.

The mismatched bolt pattern also precludes any possibility of custom rims.

I like to keep my cars pretty close to stock and that means steel wheels just like the factory gave `em. It used to be that 14 inch steel wheels were common as raindrops, but the 14" whitewall tire is an endangered species these days and the rims are even harder to find. What I thought would be a simple search sent me plumbing the depths of the internet. After an exhaustive search, I finally found three rims from a 74 Dart in a junk yard in Indiana. The shipping was almost as much as the rims themselves.

Not that I don't want better brakes. I recently investigated a Wilwood power brake kit that I saw installed on a 65 Valiant at the Mopars At The Marina event during Cruisin' The Coast. The kit I found also changes the bolt pattern and worse, with its 3+ inch hub diameter, it removes any possibility of using stock rims.

I will check out the website you suggested. Meanwhile, I am refurbishing a 10" drum brake setup from a 71 Duster that I have sitting around. Maybe some badass drums will make a difference in stopping power and retain the 4 inch bolt pattern so I can continue to annoy people with my steelies and wheel covers. :P
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