Overall height of brake rotor?

RedBeard_83 · Jan 13, 2021

So I looked all in the brake threads to no avail. I need to replace my front brakes and have come across many options of course. My question is how do I measure my overall height of my rotor? Its either 4.95" overall height or 4.65" overall height . just need to know how to measure mine so I can get the correct parts. It is a an 86 1/2 ton swb with 1.25" front rotors and the rear brake shoes are 2 3/4 if that helps.

Keith Seymore · Jan 13, 2021

This overall height measurement of the rotor is not a traditional brake specification. I assume the "height" means the distance from the back friction surface to the wheel mounting surface?

You didn't say but I assume your truck is 2wd. Attached below are the brake worksheets that the engineers referenced in order to release the part numbers for production and service.

By your description of the front rotors and the rear brake shoe size you have the JB5 system. If you reference JB5 you should be able to order the correct parts (normally everybody recognizes the JB1/JB3/JB5/JB6/JB7/JB8 nomenclature).

K

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RedBeard_83 · Jan 13, 2021

Keith Seymore said:
This overall height measurement of the rotor is not a traditional brake specification. I assume the "height" means the distance from the back friction surface to the wheel mounting surface?

You didn't say but I assume your truck is 2wd. Attached below are the brake worksheets that the engineers referenced in order to release the part numbers for production and service.

By your description of the front rotors and the rear brake shoe size you have the JB5 system. If you reference JB5 you should be able to order the correct parts (normally everybody recognizes the JB1/JB3/JB5/JB6/JB7/JB8 nomenclature).

K

You must be registered for see images attach

You must be registered for see images attach

Truck is 2wd. This helps . rock auto is listing brake rotors by overall height and so is o'reilly autoparts .so was hoping someone could tell me how its measured . probably just gonna have to bring my rotors in and match them up . thank you @Keith Seymore . much appreciated.

Keith Seymore · Jan 13, 2021

After further though I'd guess you want the 4.95. That .3" difference between the two is just about the same as the .25 difference in the thickness of the friction surface.

K

RedBeard_83 · Jan 13, 2021

Keith Seymore said:
After further though I'd guess you want the 4.95. That .3" difference between the two is just about the same as the .25 difference in the thickness of the friction surface.

K

That's what I was leaning towards. Thank you for the help . Got a lot to do in the next couple weeks. Waiting on rest of parts to arrive then redoing the frontend with all new stuff and lowering the truck 3" frt and 4" rear as well as replacing brakes front and rear .

jkrom · Apr 17, 2023

sorry to hijack old thread, but I'm running into similar situation - all of the aftermarket parts places are using the "total rotor height" dimension to differentiate, but with no clear direction as to what that means.

@Keith Seymore , from my lurking here you seem to have the most knowledge on such things - My truck is an '85 stepside 305 / 3 on tree with manual brakes, is it safe to assume that's the JB1 RPO and likely the smaller 4.65" height?

Keith Seymore · Apr 17, 2023

Yes - if your truck is manual brakes it is the JB1 RPO. That's the smallest system we made.

K

Mike69 · Tuesday at 10:09 PM

Keith Seymore said:
After further though I'd guess you want the 4.95. That .3" difference between the two is just about the same as the .25 difference in the thickness of the friction surface.

K

By chance do you have a photo or further explain measurement. I dont quite follow

Ricko1966 · Tuesday at 11:24 PM

Mike69 said:
By chance do you have a photo or further explain measurement. I dont quite follow

He's using RPOs and build sheets,not measurements. Get your RPO off of your glove box door and look at the brake spec sheets he has puctured.

Overall height of brake rotor?

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