Scare of my life.

[Fiddy B2C]

I took ole Fiddy out the other day just to knock around in the cold and heat the old girl up.  Driving along, I drop my cup and am bending over to retrieve it, and when I look up, there is a car stopped in the middle of my lane.  I’ve got about 25 ft to stop while going 40 mph.  So I hit the brakes, the back locks up and I’m thinking, wow I probably should have installed seat belts at some point...  Without panicking, I swerved to the right in the shoulder of the road and came to a stop right next to the car...a Fiat...  if I would have hit her, there would be nothing left of that car, but worse yet, it would have scratched the paint on ole Fiddy’s bumper.  Anyway, I need to do something about the rear end locking up and I’m thinking a proportioning valve is the way to go?  What are your thoughts on this and are there any recommendations where to find one that would work with an original set up brake system?

[Don Coatney]

Have you inspected the brakes on all 4 wheels? If not that should be the first step. A proportioning valve was not required when the vehicle left the factory. So with an all original setup why should it be required now? 

[Jeff Balazs]

Could be an adjustment is required? Seems to me that a Wilwood adjustable proportioning valve could be piped in. I have one on my truck but then I also have 4 wheel disc brakes.

Hth;

Jeff

[mechresto]

Fiddy

 Yes you can add a proportioning valve, but it shouldn't be necessary. 

With all things assumed to be in proper adjustment, braking pressure is equally balances to the 4 points of your truck.

Where the issue comes from is that when running empty, all your vehicle weight transfer is to the front of the truck, remember. ...these are work trucks, intended to be loaded....Thats where the brake bias was engineered to function.

 To get these beasts to brake like a passenger car...is another can of worms. The only way to go I'm my humble opinion, is with a dual MC, an adjustable proportioning valve and a lot of cussing, blood,sweat, and tears.

 Yes, you can add a valve to limit the rears on a single MC system but that's adding just one more component to an already failure prone set-up.

 I at one time had the drawings and the part numbers for converting to dual MC. But a vindictive ex wife saw to it that I no longer have any of it.

 

 

[Fiddy B2C]

Thanks for the advice folks.  I have inspected and adjusted the brakes, and mechresto, I agree that these beasts were designed with load in mind.  Driving the truck at 25 mph and standing on the brakes, she stops in a straight line, but the rear locks up, which stands to reason there is no load.  My solution to this problem...get a friggin cup holder and pay more attention...

[Don Coatney]

Loaded or unloaded the brakes should work the same. Ever see an advertisement or warning that the brakes do not work correctly unless the truck is loaded. Of all the Pilothouse era truck owners on this forum none have ever reported that the truck must be loaded for the brakes to work correctly. Once again I suggest you inspect all 4 wheels looking for contamination or incorrect adjustment.  

[mechresto]

Don

We're talking about the "oh crap" braking scenario...yes, under normal braking with all things adjusted and assumed to be working at 100% efficiency, the vehicle will stop normally. 

 What happens in a single system without proportioning, during the "oh crap" situation  is explained in this document, pay extra attention to the last of page 5 thru 8.

the-physics-of-braking-systems.pdf

[lonejacklarry]

The front did not lock up and you were still able to steer effectively?   If that is the case then I would agree with Don Coatney. 

 

[pflaming]

As a precautionary exercise, because of this thread, I'm going to do hard stop tests with my truck so I know how it reacts and fine tune any descrepencies. I now drive it very often and need to know. 

 

Edit, and yes I too need better seat belts and a coffee cup holder.

Edited January 20, 2018 by pflaming

[Jeff Balazs]

Fiddy;

I drive my 52 3/4 ton daily in relatively heavy and fast moving traffic here in SoCal. As you are already aware these trucks are from a completely different era of traffic and road conditions. I knew as I began my build of this truck that there were some serious upgrades required to handle the traffic conditions it now faced. Good reliable and predictable braking was at the very top of the list. Some people will tell you that the original brakes are more than adequate. I don't agree. The folks you share the road with these days have no idea and don't care if your pride and joy can stop as quickly as their new whatsit can. I get constant reminders of this almost daily.

I went to the extra effort of putting 4 wheel disc brakes in my truck and I am very glad I did. I have had to use them to their full capability more than once.

As a bare minimum I would suggest putting discs on the front  of any of these trucks that anyone intends to use in regular traffic. It isn't that expensive or complicated. And done carefully it may just save your day......

Jeff

[Fiddy B2C]

23 hours ago, lonejacklarry said:

The front did not lock up and you were still able to steer effectively?   If that is the case then I would agree with Don Coatney. 

 

The front did not lock up, but when the rear did, I eased up on the brakes and steered to clear the car in front of me...and mind you, when I stopped, there was a 6” curb about 2” from my right tires, and the other vehicle was about 4” from my left fenders...

[Plymouthy Adams]

1 minute ago, Fiddy B2C said:

The front did not lock up, but when the rear did, I eased up on the brakes and steered to clear the car in front of me...and mind you, when I stopped, there was a 6” curb about 2” from my right tires, and the other vehicle was about 4” from my left fenders...

 

here where I live they would refer to that as PECISION PARKING

[Fiddy B2C]

23 hours ago, pflaming said:

As a precautionary exercise, because of this thread, I'm going to do hard stop tests with my truck so I know how it reacts and fine tune any descrepencies. I now drive it very often and need to know. 

 

Edit, and yes I too need better seat belts and a coffee cup holder.

Please post the results of this hard stop testing.  I have read several places that identify that the rear brakes tend to lock up when even, hard stopping is applied.  During “non oh crap stopping,” the truck stops clean and in a straight line.  I’d like to hear how your truck handles.

[Fiddy B2C]

4 minutes ago, Plymouthy Adams said:

 

here where I live they would refer to that as PECISION PARKING

Hahaha,

any more precision parking exercises like that and my heart is going to give out....

[kencombs]

I'm planning my '56 build and brakes are on the list.  My take on the loaded/unloaded issue is this:

A proportioning valve will help with the unloaded  problem but at the cost of rear axle braking capacity when loaded.  But that may not be an issue for most as we don't often (ever?) load our trucks. 

I have a Mitsubishi tilt cab box truck, roughly equivalent to an American 3500 series in capacity.  They attack the loaded unloaded issue with a valve linked to the rear axle.  It reduces pressure to the rear brakes with the springs are not compressed by a load.

Disks up front will increase front axle braking capacity.

But, so would bigger drums.

At this point I think that will be my path.

A little back story to explain that choice.  Way back when, I had a '58 Ford PU with a 354 hemi and cast iron torqueflite.  Heavy front, light back.  Just a few days after completing the install I had to make a panic stop and experienced a similar problem as the OP. 

I had a 56 Chrysler as a donor, so I removed the 12" brakes from the front and adapted them to the Ford axle.  Only needed to turn the inner bearing area down to fit the Chrysler bearing and use a spacer behind the backing plate.  And redrill the backing plate to fit the spindle of course.  Searched the local parts store's racks to brake hoses that fit and had great brakes again. 

 

Long story short,  more powerful fronts, not less rear is my choice.

 

The stock  drums worked fine with 6.00x16 bias plies but just don't provide enough force to use the traction of modern radials IMNSHO.

 

[palmersparts]

Precision parking  without the help of computers, abs, 4wheel steering or any of that new fangled stuff they have com up with and used as marketing schemes in the last 50 years

[lonejacklarry]

18 hours ago, kencombs said:

  Just a few days after completing the install I had to make a panic stop and experienced a similar problem as the OP.  

 

The point of using the brakes is not to lock the brakes.  When the brakes are locked then you lose steering control and it actually increases the braking distance as the tire is sliding along on a patch of molten rubber.  The term is "lower coefficient of friction". 

 

If the brakes lock they are working fine except that you pushed the pedal too hard.  We folks that are old enough to remember brakes prior to anti-locking style drive accordingly.

Edited January 22, 2018 by lonejacklarry

[kencombs]

2 hours ago, lonejacklarry said:

 

The point of using the brakes is not to lock the brakes.  When the brakes are locked then you lose steering control and it actually increases the braking distance as the tire is sliding along on a patch of molten rubber.  The term is "lower coefficient of friction". 

 

If the brakes lock they are working fine except that you pushed the pedal too hard.  We folks that are old enough to remember brakes prior to anti-locking style drive accordingly.

Of course your correct, but the point is:  The rears locked way before the fronts even got close to maximum braking.  That is/was due to two things:  One, the rear was very light relative to the front and Two, the front brakes were much too small for the added weight and wider tires than original.

[lonejacklarry]

5 hours ago, kencombs said:

 ...and Two, the front brakes were much too small for the added weight and wider tires than original.

 

I'm sorry, Ken, but I am not following this.  

[Don Coatney]

52 minutes ago, lonejacklarry said:

 

I'm sorry, Ken, but I am not following this.  

me 2

[Jeff Balazs]

Before I put my truck back on the road I spent quite a bit of time adjusting the front to rear balance of my disc brakes. I did this on dry and wet pavement and tried to get fairly accurate measurements. To begin with my rear discs actually locked up before the fronts. With the Wilwood adjustable proportioning valve I have it is possible to fine tune this. Makes a huge difference in how quickly I can stop the truck.....and how straight and predictable the stop actually is. I think a lot of modern vehicles while good still have a tendency to lock up the fronts first. I really don't likes this bias and feel like there is no point in having 4 wheel discs set up this way. I have the bias set so I can feel the rears working almost as much as the fronts and honestly it is almost impossible to lock them up. But man does it slow to a stop quickly.

Jeff

[kencombs]

11 hours ago, lonejacklarry said:

 

The point of using the brakes is not to lock the brakes.  When the brakes are locked then you lose steering control and it actually increases the braking distance as the tire is sliding along on a patch of molten rubber.  The term is "lower coefficient of friction". 

 

If the brakes lock they are working fine except that you pushed the pedal too hard.  We folks that are old enough to remember brakes prior to anti-locking style drive accordingly.

 

I guess I just need to get older, maybe 74 isn't old enough to understand. The Ford example I gave was in the late sixties, long before antilock.

 

Seriously, let me try to explain it another way:

a good braking system should allow one to  lock every wheel at exactly the same time, not one, two or three but all four.  If they won't do that it makes it impossible to modulate the braking the all 4 to near lockup without actually sliding the tires  Most older trucks will lock the rear wheels long before the fronts are near max braking.  If you keep the rears rolling, you're not near the max braking of the front.

 

So, more brake power up front or less in the rear is the answer.  Actually more front and rear but still with a front bias, with today's tires would be optimum.  My 225/75 radials stick a lot better than the 6.00 x 16 originals!

Edited January 23, 2018 by kencombs

[48Dodger]

Are the brake lines original or fully replaced?

If the rears truly locked up before the fronts, and its an original set-up, I believe that the system might be polluted.

Otherwise, if its a modified system, it might need an adjustable port valve.

 

48D

[pflaming]

On 1/22/2018 at 5:52 PM, kencombs said:

I guess I just need to get older, maybe 74 isn't old enough to understand.

 

79 and chasing 80 doesn't help any. Right wrist carpal  tunnel and right shoulder went viral on me Tuesday. Neurologist scheduled for next week. Got to quit this hobby. 

[John H.]

Hey Jeff Balazs,

        Can I ask what set up you used for your disc brake setup on that 3/4 ton? Sounds very interesting.