MTFCA Forum

Does any one sell one piece brake cams for a 26? I just bought a set from Lang's and the cam lobes are separate parts pinned onto the shaft.

Here is a picture of one of them. I really don't like the way it is made. It looks like an accident waiting to happen!!

The 26/27 brakes were not meant to be service brakes, they are parking brakes. OP: I do not see any difference between the lever which is pinned to the shaft or a cam being pinned as long as they are tight on the shaft, you could shear ether one if one put enough force on them. If you don't like them might I suggest looking for good original ones.

I agree with Mark. I wouldn't worry about it unless there is something very obviously deficient in its assembly, and you're the only one that can conclude that, not us.

I would agree other than the diameter of the shaft is larger at the lever end. The shaft appears to be only 7/16" in diameter at the cam end. Subtract the 3/16" pin diameter and your left with 1/4". Divide that by 2 and you have only 1/8" of material left on each side to hold the forces that are applied by the hand brake lever. That is what concerns me. The parking brake is also the emergency brake!

Sounds like you have come to a conclusion, then.

I agree that he has decided.
If you want to think of it as an emergency brake, fine. I have yet to even consider reaching down to grab the handle using it as such when making a panic stop. Don't matter if 21 or 30 in tires, skidding is not stopping and your transmission brake should be able to do that much. With the Model T steering you should have both hands on the wheel in an emergency more esp if rolling backwards. Now if you have it hooked up to the parking brakes, different story, well sort of.

I can not see how that could be safe. Meaning a smaller diameter round shaft in round hole pinned. I will give the benefit of doubt if the item has been proven in an independent lab on the shear/clevis strength test to the item it is replacing. Now pull like hell in an emergency situation and see what happens over time. As some of you comment, "In Henry's day" well, I do not believe he would have done that when it comes to public safety. When it comes to safety, only better, proven methods of material construction/techniques should be used. Saving dollars to meet the demands at an affordable price is not in the interest of any hobby. One person gets hurt, that is one too many in my opinion.

I am with Scott C.

My $.04 worth,

Hank

I wonder what keeps the pin in place? Had I the need to fit these, the shaft would be chucked in the lathe, a deep groove machined at the cam and shaft interface, and a substantial weld used to fill the groove. All the while it was fitted I'd be looking for some good original forged pieces. Assemblies such as this are akin to the two piece, pressed together spring shackles.

Allan from down under.

I agree with Scott the design is poor. Having had a pinion bearing grenade, shuck two teeth off the pinion gear, and leave me freewheeling down a hill towards a parking lot and waterfalls in a state park, you can bet I was pulling on those parking brakes/ emergency brakes for all they were worth! They were in poor shape and didn't do much, and ultimately the driveshaft turned enough for a few teeth to catch, and we slid to a stop! Rollback wrecker ride home, rebuilt the rear end, which already had new thrusts back in the fifties, and the parking brakes will now stop it if they need to! I think if those are the only ones to be had, I would have them tig welded at both ends and cut the bushing back a bit if necessary for the weld to clear. With the larger shoes and better lining, there is more stress on those cams than the 1925 and back.

I'm not responding to this to defend the design...it is what it is, and it is inferior to a one-piece or two piece welded assembly. The responses thus far running against it, however are not addressing the stress area, though, so are clearly just "gut reactions" to the design.

Well enough.

Has anyone thought it through and asked themselves about the lever that actuates it and the stresses it sees relative to the cam? And has ANYONE heard of that properly assembled lever failing? In the many years on the forum, and touring I haven't heard of a single instance. And brother, I've seen some crummy rivet jobs.

I don't pooh-pooh safety, but this is a parking brake. Drive line failures, whatever other panic use is deemed necessary, it was never more than a parking brake, and until someone shows me the stress analysis that shows that joint failing before all the other riveted joints in the system from the brake lever back I'm not losing sleep over it if it was my car. For the tortional stress it will see, if it is properly fitted (and no one other than the part's assembler knows that, I suppose) that is a robust joint.

only 1/8" of material left on each side to hold the forces that are applied by the hand brake lever

This is not true. The cam itself is adding significant hoop strength to the assembly. If on the other hand, you were looking at a roll pin there, there would be great cause for concern. Given the available "oomph" available on the handbrake, even with a safety factor, anyone that thinks they're going to shear that solid pin with the forces available, I believe are mistaken. If it only went 1/2 way through, like a set screw...UH-OH, but that's not the case here.

Why not just make it in one piece like the original and be done with it?

The ones I have on a couple of large drum housing look to be machined forgings.
Seems to me there was talk in the past about 2 piece 26/27 cams but this is all I could find.
Read the 2ed post;
http://www.mtfca.com/discus/messages/50 ... 1428792374
Ironic I would say.

After you post number 2, read post number 6. That one tells the whole story.

My thought are some one took the time to make them, if you piss him off from his design there will be no more. That cam is for a Parking Brake not an emergency brake, But if you are using them for an Auxillary brake I would use a different cam. I did not make these and have nothing to do with who ever did but it reminds me of years ago when I was rebuilding my Fordor, trying to find the pot metal regulators for the windows. I had one made then seen that some one was repopping them, they where not perfect but useable some one got on the Forum and raised a big stink about them and the guy decided to not make them any more. So what I am getting, at be glad some one is making them and if you do not like them make your own and find out what some of these people go through just to keep this hobby going. Just my two cents worth!

Joe

right on, on each point.

It is not good to use the rear wheel brakes for "emergency" unless you also use the low pedal. Reason is that pulling back the lever puts it into neutral if you pull it while you are in high gear. I like to put auxiliary brakes on the rear wheels which are activated by the brake pedal. Then when you push the pedal hard you are using both the aux. brake and the transmission brake. The parking brake lever also activates the aux. brake so by pulling the hand lever you are activating all three sets of brakes. This should be enough to slide the wheels and that's all the braking you get unless you install front wheel brakes.
I agree that the pin is not as strong as the solid shaft and cam. But if you have the aux. brakes installed, you should only need the lever if the transmission brake fails when you are rolling backward and if you pull the lever quickly after that occurs, you should not have a problem.
Norm

Isn’t the lever on the other end just held by the same pin?
I think the 26 -27 had one pin, earlier 2 pins.

Greg

The entire emergency brake system needs to put in focus to determine the weakest link. I can't see the possibility of the pin in the cam shearing given its position and on the other end a lever arm that's only 2 1/2 inches long. Yes the hand break arm is much longer "lever" but it is pulling on another 2 1/2" lever arm connected by a rod with clevis pins in yoke ends. Each lever arm and yoke end has a loop at the end of its neck. So the question is what breaks first: a loop or pin? Think about how much force you could apply to a wrench that's only 2 1/2 " long.
(Note not sure about the lever its T-864 - I just used it for the example and that is a used old designed cam)

I think the original handbook says differently about it being a parking brake....?



Just a side note: The distance of the pulling arm (Forged Steel) 3/4" and the hand/emergency brake handle(Forged Steel) 3/4" area is not as much forces due to diameter vs fulcrum. That lower 3/16" pin at the cam has a multiplier of about 4 @ 7/16".


Interesting discussion,

Hank

Wow!! Some of these responses are not what I thought that I would receive. I asked an honest question and voiced an honest concern. I did not insult anyone. Any way, here is an up date on what I have found. I had a hardness check done and the results were, the original tested at 8 and the reproduction one tested at 20. So, the new one does test significantly harder. I think that is a positive. I removed the pin and pulled the lobe. The shaft is splined, while the lobe is not. The pin is also slightly splined. So, it appears that the posted issue from the past has been addressed by the supplier. I now, do think that they are safe to use.

I will be the first to admit when I am wrong. But I did give the benefit of the doubt as stated, and the design is what stumped me. Since the majority of us have had issues with parts, ie, Hyatt Bearings, driveshafts, ring and pinion, etc, we all get a little concerned. With new folks coming in, they need to know facts from fiction. So first my apology to the person who made it if I insulted you by my concerns. Second, Thank You Scott Clements for taking one apart and investigating with time to test it.

All the Best to All,

Humbled Hank in Tin-A-See

And the hardness of the pin was?? That's a critical piece of this assembly.

So, with no stress analysis yet, our "gut" feel is that it's fine. The information is available on the interweb, including Ultimate Strength of materials, and calculators which can have a safety factor dialed in. I'm betting I'm not the only one who checked, but I'm betting also that it isn't many, either. It may still be useable after reassembly, but can state confidently that it's integrity is now compromised from when it arrived new, sealed in a bag. So now we feel better about the design, but have a compromised part. Huh.

If there is a desire to install the strongest part, either weld this thing or throw it away. Those pinned and knurled parts were plenty strong tortionally as new, but a separated and reassembled knurl is quite compromised and now the pin is doing much more work (and it's press fit is now compromised as well).

At least we all know how the thing is assembled

And to the guy who makes these things: Thank you. I don't own a car that these fit and probably never will, but the point is that you are supplying the hobby with a part that no one else is, and I appreciate it.