I need to replace the shoes on my drive axle brakes. My understanding is I have Q brakes on my Dina.
I have heard that Q brakes require new drums at every shoe change. Is this correct?
Yea you do Q brakes only work good when the thickness of the drum is right and your geometry is going to be off with new shoes and old drums, Q brakes use a higher lift S cam they are not as forgiving as the older style brakes
Damn. That means my bus may very well be parked until 2027 to come up with the funds to fix the brakes.
Drums were $600 each plus truck freight in 2006. They were also hard to find back then. I imagine the price with shipping will be over $1,000 per drum, if not even more. I expect with shoes, misc parts, and labor I could be looking at upwards of $5,000 to replace the brakes on my drive axle.
I also need a new rooftop A/C unit, and I really should replace the steer tires in 2026. I replace the steer tires every five years and rotate them back to the tag axle. The steer tires I expect will cost a minimum of $1,500 mounted.
My MCI service manual has a section on Q brakes and it shows a table with maximum allowable drum diameter for re-use. It states the drum can be re-used as long as the diameter falls within the specification.
Quote from: thomasinnv on September 21, 2025, 07:13:56 AM
My MCI service manual has a section on Q brakes and it shows a table with maximum allowable drum diameter for re-use. It states the drum can be re-used as long as the diameter falls within the specification.
Must be a MCI thing,my Bendix Q training manuals (2001) say to replace drums because of such a close tolerance you cannot turn one, on the Q-2 system you replace all pins and the high dollar S cams,the Q brake is a good system I don't why the clearances had to be so close.I didn't read it but the instructor told us if a new drum was over 0.020 out of round don't use it
The post mentioning the service reminded me to check my service manual to see what it says about the brakes.
Quote from: belfert on September 21, 2025, 03:01:31 PM
The post mentioning the service reminded me to check my service manual to see what it says about the brakes.
When all else fails, rtfm lol.
Quote from: thomasinnv on September 22, 2025, 08:12:48 AM
When all else fails, rtfm lol.
The manual says nothing about if drums should be replaced when the shoes are replaced.
Quote from: belfert on September 23, 2025, 05:56:11 PM
The manual says nothing about if drums should be replaced when the shoes are replaced.
Service manual doesn't give you any specs for allowable diameter of the drum? I wonder if 'Q brakes' are the same across different manufacturers? Are they just like a brand name or type like meritor? I can snap a picture of the q brake section in my manual if you're interested. Maybe luvrbus can chime in on wether q brakes are the same on dyna and mci?
Quote from: thomasinnv on September 24, 2025, 06:15:48 AM
Service manual doesn't give you any specs for allowable diameter of the drum? I wonder if 'Q brakes' are the same across different manufacturers? Are they just like a brand name or type like meritor? I can snap a picture of the q brake section in my manual if you're interested. Maybe luvrbus can chime in on wether q brakes are the same on dyna and mci?
They can be different from OEM to others they are sized for weight and the DOT required stopping distance, The drums I replaced on the schools Dina where 16.5 x 7 inches, all the replacement drums I saw for the Q brakes have a "Q" in the parts number. The Dina is a good tough bus designed for the Mexicans roads and highways and you never know what they have, I never under stood the Roto chambers unless it was for stopping distance those chambers are expensive they cost more than the DD-3's
My rotochambers were replaced with standard brake chambers years ago.
Quote from: belfert on September 24, 2025, 01:25:51 PM
My rotochambers were replaced with standard brake chambers years ago.
I know I remember telling you could change those when you were bummed about the price
Quote from: thomasinnv on September 24, 2025, 06:15:48 AM
Service manual doesn't give you any specs for allowable diameter of the drum? I wonder if 'Q brakes' are the same across different manufacturers? Are they just like a brand name or type like meritor? I can snap a picture of the q brake section in my manual if you're interested. Maybe luvrbus can chime in on wether q brakes are the same on dyna and mci?
My understanding is that Q brakes are a style of air brakes originally made by Rockwell International (Now Meritor/Cummins.) I think others make Q brake parts now.
Yes, the manual has allowable tolerances for drum sizes. Of course, I don't have the correct tool for measuring the inside diameter of a cylinder.
Quote from: belfert on September 25, 2025, 01:59:46 PM
My understanding is that Q brakes are a style of air brakes originally made by Rockwell International (Now Meritor/Cummins.) I think others make Q brake parts now.
Yes, the manual has allowable tolerances for drum sizes. Of course, I don't have the correct tool for measuring the inside diameter of a cylinder.
Any machine shop should be able to measure them for you. Or any shop that turns rotors and drums.