# Rotor problem



## boomer (Oct 19, 2009)

Restoring my 68 convertible, I decided to convert the rear brakes to disc so i can get the car to stop. I purchased a kit from mbm with the understanding that it would fit the rear that i have. Well it didnt, the problem is the rotors dont fit the axle ends by about an 1/8 th of an inch. Contacted mbm in N.C and was told that the solution is to have the ends milled to accept the rotors. That just dosent sit well with me. Anyone else had or heard of this problem. wondering if it is common or just my rotten luck.Need to solve it so i can move forward. thanks


----------



## Rukee (Feb 8, 2007)

Instead of milling the axles smaller to accept the rotors, couldn't you mill the rotors open to accept the axles?


----------



## boomer (Oct 19, 2009)

I thought about that too, but then i have to do that each time i change the rotors. added cost each time. I just wish the kit fit the way it said it did.


----------



## Rukee (Feb 8, 2007)

I think it would be cheaper, easer, faster to mill the rotors, even if you did have to replace them down the line.


----------



## chevyboy91188 (Oct 31, 2009)

how far and hard are you going to drive it? the rotors should be good for at least 80,000 miles I would figure that would take at least 15 years to rack that kind of mileage up if it was just a weekender


----------



## daveh70 (Sep 4, 2008)

*I think I know what you should buy.*

I had a problem with my '67 GTO last season. I needed to replace the existing 2 piece hub-rotor assemblies. They aren't reproduced. Only these hub/rotor assemblies made at a few places. I bought a product from Year One, but it didn't fit my existing (original) 4 piston front calipers. Then I found a unit from Inline Tube that fit fine. It's a single piece hub/rotor. The part was ROT-02 at $85 each from them. I see the unit works for the 67-68 models. Maybe you should try that.


----------



## Rukee (Feb 8, 2007)

He's talking the rear brakes.


----------



## 66tempestGT (Nov 28, 2009)

how thick are the rotors? you would be milling a spot on them that is load bearing. if you make them to thin there they could rip apart. the edge of the axle doesnt do anything. i can understand wanting it to be a straight bolt on project but if there is metal to be removed the axle has some to spare.


----------



## Rukee (Feb 8, 2007)

Milling the center hole of the rotor slightly larger should not compromise the rotor in any way. Especially if you mill it to match the size of the axle hub.


----------



## 66tempestGT (Nov 28, 2009)

i dont agree. the part you are milling is the only thing connecting the friction surface to the hub. there is a reason the manufacturer didnt make them thinner there in the first place. he is talking about taking off 1/8 of an inch. how thick do you think it is now?


----------



## Rukee (Feb 8, 2007)

66tempestGT said:


> i dont agree. the part you are milling is the only thing connecting the friction surface to the hub. there is a reason the manufacturer didnt make them thinner there in the first place. he is talking about taking off 1/8 of an inch. how thick do you think it is now?


I think you are misunderstanding the milling that is going to happen. He's not talking making the thickness if the rotor thinner, just making the center hole 1/8" larger in diameter.


----------



## chevyboy91188 (Oct 31, 2009)

Rukee said:


> I think you are misunderstanding the milling that is going to happen. He's not talking making the thickness if the rotor thinner, just making the center hole 1/8" larger in diameter.


he is understanding the situation he is saying that the hat portion between the wheel flange and the friction surface of the rotor is made that thickness for a reason. the manufacturer may have not been able to make that portion any thinner due to the large torsional shear force that is placed on that cylindrical portion of metal. if you were to make that cylinder any thinner it may not be able to take that shear. 

but with 1/8" total needing taken off that would be the equivalent of taking 1/16" off of each side or taking 1/16" off of the radius. that isnt that much metal if we are talking about an initial thickness of close to a half inch but if the initial thickness is less than that you could get into issues without doing the proper stress calculations

if someone could give me dimensions, force numbers, and the material used I could do the calculations lol 

honestly the best thing would be just to shave the shafts because gap or no gap when you replaced the rotors again, the studs are what lines it up and holds it in place so the safest thing would be to do the axles.


----------



## Rukee (Feb 8, 2007)

chevyboy91188 said:


> *he is understanding the situation he is saying that the hat portion between the wheel flange and the friction surface of the rotor is made that thickness for a reason. the manufacturer may have not been able to make that portion any thinner due to the large torsional shear force that is placed on that cylindrical portion of metal. if you were to make that cylinder any thinner it may not be able to take that shear. *
> 
> but with 1/8" total needing taken off that would be the equivalent of taking 1/16" off of each side or taking 1/16" off of the radius. that isnt that much metal if we are talking about an initial thickness of close to a half inch but if the initial thickness is less than that you could get into issues without doing the proper stress calculations
> 
> ...


...again, we're not milling that section thinner!!! NO way!!!

Only opening the center hole slightly LARGER, by 1/8". Not a big deal.


----------



## crustysack (Oct 5, 2008)

I agree with rukee, the hole needs to be bigger not the inside surface of the cone. and that hole can be as big as you want, all the load is transferred to the axle by the wheel bolts not the edge of the inside of the hole-


----------



## chevyboy91188 (Oct 31, 2009)

so the rotors mount on the inside of the axle flange? not on the wheel mount surface. so the order from the differential to the lug nuts is rotor, wheel mount flange, wheel, then lug nuts? how about an explanation of how they are put together


----------



## Rukee (Feb 8, 2007)

Order = axle flange, rotor, wheel, lug nuts.
The currant rotors won't mount flush to the axle flange because the center hole is 1/8" too small to go over the center axle hub. The company told him to mill the hub of the axle smaller, he could do that, or mill the center hole of the rotor slightly larger.


----------



## crustysack (Oct 5, 2008)

so heres the pic to clear it up- although not a 68 gto - basically all disc brakes are the same- a pic is worth bla bla bla


----------



## chevyboy91188 (Oct 31, 2009)

I see what you mean, then heck id mill the hub if its just that center hole. you could do it yourself even without a lathe or mill


----------



## 66tempestGT (Nov 28, 2009)

yeah if thats the problem its not much of a problem.


----------



## jetstang (Nov 5, 2008)

The current size of the axle is for the brake drum center. Rukee is right, just mill it out and it should work fine. The lugs hold the brakes on, so any additional clearance isn't really an issue as the lugs align the rotors, not really critical to have the hub perfect, and not a stress point.


----------



## Too Many Projects (Nov 15, 2008)

I don't see in his posts where you guys came up with the 1/8" dim but if it is the center hole that is too small, yeah, have the rotor machined. 
Personally, if it were mine, I would be sending them back COD shipping with instructions to either send rotors that fit the application AS ADVERTISED or pay for the machining themselves.....


----------



## boomer (Oct 19, 2009)

Thanks to all for the advice. My machine shop guy says he can take a sliver off both, no big deal, no extra charge. 
After measuring with a good set of calipers it works out to about a 1/16th " total not the 1/8 we originally thought. so its not as big a deal as i thought it would be. I would like to do as mitch said but i would also like to move past this and finish the car someday. I am not happy with the fact that they dont fit as advertised or with the company making it the responsibility of the installer to correct their mistake but in the interest of saving time and probably more aggrivation i will just get it done.


----------



## Too Many Projects (Nov 15, 2008)

boomer said:


> Thanks to all for the advice. My machine shop guy says he can take a sliver off both, no big deal, no extra charge.
> After measuring with a good set of calipers it works out to about a 1/16th " total not the 1/8 we originally thought. so its not as big a deal as i thought it would be. I would like to do as mitch said but i would also like to move past this and finish the car someday. I am not happy with the fact that they dont fit as advertised or with the company making it the responsibility of the installer to correct their mistake but in the interest of saving time and probably more aggravation i will just get it done.


I completely understand your reasoning and in reality would probably do the same, but it's because we just fix their crap that they keep sending it out to the next guy. At the least, they would endure a good a$$ chewing on the phone and bad press on the World Wide Web....:lol:
Pypes exhaust is gonna get an irate phone call tomorrow after the ordeal I went thru to get their product to fit on my Camaro. It's still half/assed and I haven't driven the car to see if it hits anywhere....


----------

