MTFCA Forum

I developed a knock on the first day of the national tour in Spokane, WA.
That put me in the trailer and sent me home.

Pulled the engine and this is what we found.
   
This is the first time that I have had a broken drum presented itself as a knock.
The drum is cracked across the face and one adjacent web is cracked.
The break stands proud almost 1/8"
The rods and mains are fine.

Bob, That sucks. At least it did not grenade on you.

OUCH. Why did this happen? Kevlar with adjustment or installation issues?

Very sorry to hear of this and see the damage. This probably won't make you feel much better, but Mark is right; you have a lot more to be thankful for than upset about.

BE_ZERO_BE wrote: ↑

Fri Aug 20, 2021 1:13 pm

I have been running kevlar bands for over 30 years.
On the tour I adjusted the Brake band.
I can not remember the last time I adjusted the Low band.
I know it has been at least five years since I last adjusted it.

Interesting break without an over adjustment situation.
I too, have had similar excellent service from kevlar in all my T's.
One either swears by them or swears at them.

Lucky you stopped when you did. It could have been a lot worse on the inside of the engine!
Transmission drums can fool you into thinking that they aren’t cracked. As others surely have found when you pull down an engine and check the drums and they look good. Closer inspection sometimes reveals small cracks in the webbing thats most likely been there for years.
Good luck and it’s another day in the life of a Model T.

If you need a drum give J&M Machine a call. They make them and they will last a lifetime.

It took just two posts before Kevlar was intimated with the problem. I too have been sing them since Custom Friction composite bands were introduced right at the start. I have broken a crankshaft since then, but never a trans drum.

Allan from down under.

It might not be the fault of the present driver. If this is an original drum, it could have started to crack many years ago, and then finally at just the time when the driver pushed down on the pedal, it cracked.
I learned a lesson about mine when it broke. When I had previously re-lined the brakes, I noticed the low drum was blue. Then one day, I was out for a drive, and when I started out in low, the car suddenly screeched to a stop. I couldn't even get out and push it. Fortunately my son was home and quickly came with the truck and trailer and a rolling floor jack. We jacked up one rear wheel and winched it onto the trailer. So, if there is anything suspicious about the drums when you have it apart, that is the time to replace the drum.
Norm

 
 
Here is a better photo of the brake drum.
 

It probably started a long time ago and finally progressed until it cracked on the working surface of the drum.

 
 
Here is a better picture.
The web crack occurred where it was drilled when the drum was balanced.
 

well, that's surprising...said no one ever.

Holy Cow

Looking at your drum, it also appears a majority of the web was removed. Was that also done to try and balance it?

That makes me even more want to stay with my unbalanced drums.

Wow Bob! You didn't just dodge a bullet, you dodged the whole magazine. Sometimes it's hard to know when to stop when balancing drums. I take some out of the web but have never drilled one like that. I guess there is a lesson to be learned from it.
Allan from down under.

Those lightening “dimples” do not follow any of the typical lightening guidelines that allow for the removal of material without significantly affecting the overall part strength, i.e. hole diameter no greater than 1/3 width of material, at least 1 diameter of material between holes. If done that way, through holes might remove more material while retaining more strength than the part shown. The lesson here is that balancing is good, but not done in a way that sacrifices significant part strength.

Eric

It's pretty clear why that failed the way it did. A drum that has had too much material removed from the face due to wear or re-machining would be more likely to fail, also. A drum in that condition could heat up very rapidly at the rim and thus be highly stressed. Removing any significant amount of material from the web area is not a good idea, since it reduces the mechanical strength, thermal mass, and thermal conductivity of the brake drum. If material must be removed, the surfaces should be left smooth and rounded, with no grinding makes, notches, corners, etc. The portion of the casting at the outer edges of the holes in the web that run under the rim should never be altered.

Per Mike Bender T Tips Video - add weight do not remove

https://www.youtube.com/watch?v=56jutHY ... 4j&index=4

Mark Gregush wrote: ↑

Sat Aug 21, 2021 12:07 am

That makes me even more want to stay with my unbalanced drums.

Done right , a balanced transmission is a joy. This "balancer" obviously dont know how it's done. The holes are a NEVER no,no. The webbing is way too thin also. I suspect the casting was way off center. First step would have been to lighten the opposite I.D.

Cant blame kevlar for this mess.

Some drums are a bit beyond balancing by removing metal. If the casting is poorly centred at the time of manufacture, it may require so much material to be removed that the part is compromised, as it was in this case. The best answer is to find another drum. The new ones are much better balanced, being CNC machined.

Allan from down under.