Single Ended vs Double Ended Slave Wheel Cylinder

Bruce A. Frank

Bruce A. Frank

Member
My previous s120 Travelall May have not had the original 44 axle under the front end. For that matter my current s120 May also not have its original one either.

My previous binder had double ended wheel cylinders and the non-assisted brakes worked very well allowing my 5'2" wife to drive the truck daily with no complaints about stopping power. My latest s120 front Dana 44 axle has single ended wheel cylinders and requires just about all the foot pressure I can generate to stop in a reasonable distance .

I do not know if the single ended cylinders are the culprit or not. I am contemplating converting to a double ended cylinder. Any thoughts about if there is a problem with single ended cylinders vs double ended ones? Also, are there substitute cylinders, or am I on my own?
 
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I think brake systems with the double sided wheel cylinder are "self energizing" brakes. What happens is that the back shoe pushes the front shoe into the drum. My old b160 had the single puck wheel cylinders you describe and it was equipped with a hydrovac power brake system.
 
I am going to have to pull the drum and take a closer look. It didn't register that the wheel cylinder might be the problem when I had the drum off last time.

My impression at the time was that it looked strange. I did not pay attention to the coupling between the shoes as I was looking at other things. But, after some thought the shoes cannot be mounted to a solid point at the bottom as the movement caused by the cylinder has to translate from the primary Actuated shoe to the secondary Shoe (my name for them...seems logical to phrase it that way).

I did get the impression that the single ended slave cylinder was not in the normal position on the backing plate. As if a new mounting hole had been created to mount it. When it warms up a bit, I'll take a look again.
 
A photo would be the best. Single action cylinders I've seen were usually in single servo setups. It also depends alot on the shoes, where the lining on the shoe is, and how long on the material is on the shoe. They weren't as good as dual servo brakes in reverse, but the problems you're describing reads like there's other things going on.
 
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Well, after doing a lot of research online I discovered that the Ford f100 pu had a similar production period in the early '60s where the front wheel cylinders were the single ended. And they did not work well. The solution was to install the 1964 model double ended cylinders in place of the single ended cylinders...a bolt in operation.

Another poster noted that the oem rear cylinders were double ended and then could be used for the front cylinder replacement. Additionally, by converting to double ended cylinders on the front, stopping power was dramatically improved. And, the trucks with single ended cylinders on the front and the double on the rear wheels (as it came from the factory) tended to lock the rear axle. Once the fronts were replaced with the double ended cylinders, the rear lock-up tendency was eliminated and the rear brake shoes went much longer between replacement.

The double ended wheel cylinders installed front and rear solved breaking problems on the f100 Ford trucks...producing faster stops with dramatically reduced tendency for rear axle lock-up.

Now, don't know yet whether the '56 s120 has a bolt up replacement or if the rear cylinders would fit, but I do have a pair of the oem rear cylinders that I found on closeout for $6 each (wish I'd bought 4). May be able to get into the wheels tomorrow. I'll take pictures!
 
What you are saying makes sense to me. By going to a double ended cylinder, if it's the same diameter, the pressure on the shoes is doubled.

If you can get some time with a good parts book, here's what I'd do. Find out what year IH went to double ended cylinders. Then get those cylinders and a set of matching shoes. The reason for matching shoes is that they May provide better breaking balance.

While in the parts book do check the bore diameter of the mc for the double system vs. Single. Just a side note, if the system brakes evenly now and there is plenty of pedal distance from the floor, a mc with a smaller bore will give you a higher pressure in the wc's evenly all the way around.
 
There's a confusion here between servo action and hydraulic cylinder action. Servo action is the taking advantage of the rotating brake drum's tendancy to drag the front(primary) shoe with it, and applying that force to the rear(secondary) shoe. With a single anchor at the cylinder end with a single acting cylinder(one rod), and a floating link between the front primary shoe and the rear secondary shoe at their bottom or tail end, the secondary shoe's braking effect is amplified from the action of the front primary shoe acting on it through the floating link. The secondary shoe will do about 75% of the braking for that drum, and why they have the longer lining. However the servo action is not there in reverse rotation(backing up), that's why they're single servo.

Dual servo, with a double acting hydraulic cylinder,(2 rods), the servo action is in forward or reverse.

Service on the 2 systems, single or dual, is similar except on single servo, a feeler gauge is used for a major brake adjustment procedure which requires shifting the anchor pin up or down to center the shoes. You will probably find a slot for the feeler gauge in your single servo drums.

IH or Ford, it doesn't matter. I have the period factory service manuals for both my fords and IH's, and they're pretty much the same. I would love to see any Ford service bulletins regarding brakes from that time period, 58 to 65. Maybe some web links would be great

I don't believe there is any advantage of one over the other in forward direction as they both use servo action; it comes down to drum diameter, shoe size, and wheel cylinder size for stopping power. You might want to bone up on wheel cylinder sizing to account for weight shift when changing to different wheel cylinders.

More than likely your truck just had years of no maintenance or incorrect maintenance to get to the current hard stopping sitch.

Basics like are the contact pads on the backing plates smooth for the shoes to slide on? Are the cylinders even moving, not bound with internal rust. Are the front shoes correctly centered and checked with a feeler gauge(.010") after all is cleaned and free to move. The devil is in the details.
 
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Actually I do understand the servo action, but since this vehicles brakes had recently been overhauled, I assumed that there was more to the efficiency of the braking with the double ended cylinder.

Yes, there is a slot in the drum. The clearance for the full arc of the front shoe should be the same and that is set by adjusting (rotating) the eccentric pin at the top of the backing plate where both shoes rest?

You have reminded me of this information. I do now remember having to adjust my front brakes with a wrench on that eccentric. Fact, the fiat 600 I drove while in high school required the same adjusting process.

So, what I will be looking for is that the shoe should be arc'd to closely conform to the drum and the clearance must be the same between the front shoe and the drum for the length of the lining...adjusted, primarily, with the eccentric.

A final point, the old fiat also had a separate eccentric cam at the mid point of the shoe.

Here is a picture of the shoes on the backing plate plagiarized from the Ford site. It doesn't show the top eccentric due to the size of the picture, but it May help others understand.

picture.php


I was working on my s120 today and I am now aware that the clearance for the front shoe is very different along its arc as viewed through the drum slot. Thanks for refreshing this knowledge! I had really forgotten this information!
 
Here's a page for the adjustment/anchor pin deely Bob:



the eccentric at mid-point would probably be for a twin leading shoe or lead/trailing shoe depending on the wheel cylinder action. I've included that picture also in case someone has an old truck with that setup. My 48 has the twin leading shoe and they are extremely easy to foul up the settings as the "expert" who assured me they were professionally overhauled did when I bought it.
 

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Greg,

I just today, due to over 3 weeks of the flu since going to visit family during Christmas, began again to get into the brakes on the s120. Right off the bat I discovered the problem.

The eccentric adjustments at the top of the backing plates on both wheels were adjusted so that the front shoe was too close to the drum at the top. When the wheel cylinder pushed the brake shoe forward only the very top of the shoe contacted the drum. So, the servo action was almost non-existent.

The rear shoe was making full contact during braking and has worn very evenly heal to toe. But, since the front shoe was not engaging the drum the "servo" action was not augmenting the power of the brake. That is why I felt the brakes were so under powered requiring very high leg pressure on the peddle to stop the vehicle.

The trailing edge of the front shoe, when the brake peddle was depressed, was more than a quarter inch from the drum (so far that I actually couldn't see it through the drum slot). The brake adjustment at the bottom could not adjust the shoe to engage the drum because the top of the shoe was too close.

I am saying things that you already know, but I am adding detail to help those not familiar with the single servo system.

While things were apart, though the old shoes were in pretty good condition, I decided to install new shoes on the front axle. Several people have said that these old shoes were no longer available. Well, I had no problem getting shoes at very reasonable prices.

Clearly the mechanic who previously worked on the vehicle was unfamiliar with a system using a single servo. If you guys had not reminded me about this, I would have likely continued to treat the adjustments of the system as if it were a double servo.

The brakes work so spectacularly well now, I have abandoned my intention to add a vacuum booster to the system. The stopping power now is as good as power brakes (but, I am going to install a split/dual master cylinder for the safety factor).
 
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No reason that this year and model should not have auto adjusters for the brakes, but there are none listed...so obviously they cannot be installed!!!!

Well, I took the brake shoe number and referenced which vehicles they fit. A whole list of ihc 4x4 light trucks popped up so I selected a model that had features similar to my s120 and ordered the left 'n right kit for the front axle. If they fit, I'll let you know what worked.
 
Ok, here is the info on adding brake self adjusters to my '56 s120 Travelall. First is the finished installation. Flash and non-flash just to show a little different detail.

brakeselfadjusterlf.jpg
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brakescompletenoflash.jpg


Now, I ordered an adjuster overhaul "kit" to get the parts by backwards referencing the shoes on ihc vehicle models that used the same shoes (12" drums). That did not exactly work. All the parts for this type of adjuster were there, but the cable length was incorrect. All these small parts are available individually at most good automotive parts stores.

I took some measurements and concluded that I needed a cable approximately one inch longer than what was in the "kit". The correct cable turned out to be 12.5" from the outside of the hook to the outside of the eye.

brakescablelngth.jpg


This "two cables per pack" was what I bought.

brakescorrectcable2perpk.jpg


I adjusted the brakes "loose" to test the self-adjusters. Backed up and applied the brakes to actuate the adjusters. Then I lifted the front axle and found that the shoe clearance was exactly where it is supposed to be.

As I said, there is no listing for auto-adjusters for the '56 s120. Don't know why my reverse-reference search with the shoe part numbers didn't work. But, it was straight forward to get the correct parts (the cables).

Now, there is one little problem with what you see here. The manual adjuster has to be flipped over to put the star wheel close to the back shoe. The adjuster slot in the backing plate does not line up with the star-wheel in this configuration. You can see the adjustment slot (difficult because in this picture the dusty rubber plug is still in the slot) just below the left end of the spring above the adjuster barrel. The adjustment wheel can be reached from the forward slot by using the long end of the brake adjustment tool. If that is unsatisfactory, you could do as I am going to, create a new adjustment slot in the backing plate with a drill and a dremel tool cutting wheel.

The backing plates on my vehicle are mirror image left to right. It would be a fair amount of work, but if you don't want to alter the backing plate, swapping the backing plates left to right and right to left appears that it would put the adjustment slots in the correct position for the self-adjuster configuration.

One last observation, this cable length works for me, but I see that the adjuster tab, that engages the star-wheel, sits high on the wheel. Most configurations I have looked at show that tab closer to the horizontal engaging the star near the mid point (3:00 o'clock?). The power to turn the star wheel is provided by the spring attached to the sheet-metal bracket. There May be some mechanical advantage lost with engagement that high on the wheel. The new star wheel adjuster turns smoothly in my case. A cable 1/16" to 3/32" longer might provide for better function and movement of the star wheel. Still, it is inexpensive to experiment and optimize the mechanism. If the cable lengths are not correct, all that happens is the auto-adjusters don't work. The brakes still work just fine...just requiring manual adjustment.
 
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After pulling the wheel off the other day, in prep for drilling a new slot in the backing plate to accommodate the repositioned brake adjuster star wheel, I realized that the slot in the drum itself provides excellent access to reach the adjuster. It is certainly not ideal, as you have to dismount the wheel from the axle to reach that slot in the drum. Just an observation!

Since there seem to be a lot of people into restoration and repairing their old internationals who haven't had much vehicle repair experience, this might be useful. Once the self-adjusters are installed, when manual brake adjustments need to be made, it May be necessary to reach through the backing plate slot with a thin screw driver to push the self-adjuster finger away from its engagement with the star wheel. With the finger engaged, you May not be able the turn the star wheel backwards to loosen the brakes. Hold the finger away with the screwdriver and at the same time turn the star wheel with a brake tool.
 
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