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View Full Version : Brakes: 11" Drum Swap, Front To Rear



JoeHall
08-29-2017, 08:40 AM
I need to replace the 11" factory rear drums on the 63GT, which I am installing Fairborn flanged axles in. Since the car originally came with disc brakes, it has Avanti style 11" rear drums, instead of 10". I have several good, 11" finned front drums and would like to avoid buying new rear drums if possible.

MY QUESTION: once the hubs are removed from front drums, are the drums themselves (minus their hubs) interchangeable, front to rear? In other words, can I remove the hub from an 11" front drum, then use that drum on the rear? Either way, with flanged axles, the drum will have to be hub-less, so removal of the hub is a non-issue. Question is, front to rear interchange of bare drums.

Thanks in advance.

Joe H

jclary
08-29-2017, 09:00 AM
My "backyard tinkerer" mind thinks it is "do-able," but, like any mechanical rotating part, I'm wary about concentric repeat-ability, and balance? Even if the measurements allow it without additional machining, are the tolerances close enough that will allow the drums to be removed & put back on without balance/vibration issues?

rkapteyn
08-29-2017, 09:28 AM
Yes you can use them.
The 11"rear finned brake drums are the same as front 11" drums .
Check the size of the center hole.
Robert Kapteyn

thunderations
08-29-2017, 10:33 AM
With that question being answered, let me ask another. Can the 11" front backing plates with all the hardware be bolted to the rear axle to replace 10 or 9 inch rear brakes? I'm putting Turner discs on the front of a 64 Daytona 113" wheelbase chassis that will be the frame for my 50 Champion convertible and it would be nice to update the rears to 11" if that would work. Thanks in advance for any advice, Ken.
This whole project is to build a retro Studebaker using the most modern Studebaker mechanical parts available under one of the most iconic Studebaker bodies ever made.

Yes you can use them.
The 11"rear finned brake drums are the same as front 11" drums .
Check the size of the center hole.
Robert Kapteyn

41 Frank
08-29-2017, 10:46 AM
The one problem I see with doing that Ken is the front backing plates have no provision for the rear emergency brake cables to mount to them.

With that question being answered, let me ask another. Can the 11" front backing plates with all the hardware be bolted to the rear axle to replace 10 or 9 inch rear brakes? I'm putting Turner discs on the front of a 64 Daytona 113" wheelbase chassis that will be the frame for my 50 Champion convertible and it would be nice to update the rears to 11" if that would work. Thanks in advance for any advice, Ken.
This whole project is to build a retro Studebaker using the most modern Studebaker mechanical parts available under one of the most iconic Studebaker bodies ever made.

thunderations
08-29-2017, 11:26 AM
Very true, Frank. Guess I might compare the front and back plates real close and see if the front can be modified to accept the EB cables. I'm not sure how much better 11" rear brakes are then the 10" when you consider adding the front discs that will be doing the majority of the braking. Might be smarter to just leave well enough alone and concentrate on the rest of the build. The 11" front drums could be a big improvement for someone wanting to upgrade their drum brake system from 9's or 10's.


The one problem I see with doing that Ken is the front backing plates have no provision for the rear emergency brake cables to mount to them.

WCP
08-29-2017, 12:46 PM
Joe, the 11" castings are identical, front and rear, but the machining is not. I had a set of NOS 11" front drums and considered them for the rear of my Daytona, but realized the re-machining would be less doable than modifying Dodge truck drums from Napa. On the front drums the braking surface needs to be narrowed and the relief for the backing plate "labyrinth seal" needs to be machined deeper. I didn't like the idea of trimming the backing plate lip.

StudeRich
08-29-2017, 01:31 PM
And Then there is the aforementioned Center Hole Size issue!

wdills
08-29-2017, 02:38 PM
WCP, please tell us more about the dodge truck drums and their modifications.

bensherb
08-29-2017, 03:44 PM
The center hole is a non issue since nothing on the Stude is hubcentric anyway.

Beyond the e-brake cable the spindle and rear axle flanges are different sizes and bolt patterns. You might be able to fudge the mounting holes, but welding them up and driling new holes would be the way to go. There might also be a difference between the backing plate mounting surface to wheel mounting surface measurement front to rear that would need to be addressed. It could be done but you'd need to swap the e brake parts over and probably graft the cable mount from the rear backing plate into the front backing plate.

If having the drums/wheels hubcentric instead of lugcentric is important to you it can be done relitively easily with some simple machining if you have the capabilities, probably not cost effectve if you have to pay a shop. Here are some hubs I did for mine.
6659766598

WCP
08-29-2017, 07:29 PM
Wayne, the drums used are Napa 440-1169. The modification required removing 1/8" from the brake surface inner edge. These drums are supplied balanced and fairly inexpensive. I removed the centering rings from the Fairborn axles and new rings machined to suit the smaller drum bores. The dimensions used for the rings as follows:OD 2.840+/-.002" and ID 2.580+/-.002" and depth or length of 0.25". Radius inside bore edge 1/16D". I later noted that an OD of 2.838" would be better, as I had to tweak the drum bores to slip over the installed rings. I heated the rings with a propane torch and slip them onto the axle bosses. If you go this route, be sue to check the bore diameters. Mine measured 2.833 & 2.840".
The stud holes are 0.653" vs 0.634" for the NOS 1558903 Stude drums. The backing plate relief is 11/16" deep vs. 7/16' for the Stude front drums so no problem removing the 1/8" from the brake surface edge.
As posted above, the brake surface of the 1558903 is 2.5" and needs to be trimmed to 2 3/8" and not 1/4" (bad memory). This results in a relief of only 5/16" and contact with the backing plates

rkapteyn
08-29-2017, 07:44 PM
Ask Phil Harris!
He is an expert on this and gives good customer service.

JoeHall
08-29-2017, 11:34 PM
Thanks much for the above info. My flanged axles came from Ted H., and he had ran them in a car on the track. They may be earlier or later, because the flange that centers the drum is stepped, at 2.605" then 2.750. It has an adapter ring fit over the inboard, 2.750", and the adapter's OD is 3.105". So with my axles, to use the NAPA drums, I'd need an adapter ring with an ID of about 2.753 and an OD of 2.833 to 2.840". That is a very thin adapter ring, and not sure if it can even be made. Will ask the local machinist.

bensherb
08-30-2017, 01:34 AM
A ring with a .040" wall thickness, no sweat. Is this ring to resize the hub to fit the wheel/drum to make them hubcentric?

You could also replace the existing ring wth one of the size you need, or turn it smaller so the extra resizing one would be thicker. With tight tolerences or thin resize rings, fitting the ring then turning the entire assembly to the desired size as a unit works best for me.

2.840" is big, the bore of both my front and rear disk rotors, and my wheels is only 2.700", and it's way bigger than my stock Stude wheels; I had to leave .005" clearance in order to get the wheels and rotors to fit over the hub without pounding them on, so they are 2.695"

WCP
08-30-2017, 11:14 AM
Joe, the bosses on mine measured 2.580" and 2.583" and the rings were for 3 1/8" drum bores.

JoeHall
08-30-2017, 05:25 PM
Last night I read every related thread on this forum I could find, then today spoke to my favorite local machinist. All I need do is decide which drums I want, then bring those drums, backing plates, and flanged axles (with bearings mounted) to him, and he will take care of the backing plate hole and the drum center hole. What I must determine beforehand, is the amount of material he needs to remove from the backside, in order to clear the backing plate lip. So I plan to calculate that this weekend, then take the parts to him next week.

For drum choices, I can use the 1970s Mopar mentioned above, or the 1960s FoMoCo I found on another thread here. For FoMoCo, the drum center hole is smaller, and will need to be enlarged to fit the 2.750 axle flange. For the Mopar, a ring spacer will need to made to adapt the larger drum hole to the smaller axle flange. I will re-read all related threads, but believe the amount to remove from the backside is similar, no matter whether Mopar or FoMoCo.

I already have a FoMoCo drum on hand, bought about a year ago, after reading another thread here. So will probably explore the possibilities with that one first.

bensherb
08-30-2017, 05:57 PM
For FoMoCo, the drum center hole is smaller, and will need to be enlarged to fit the 2.750 flange on the axel.
.

Or take .050" off the axle and the Ford drums will fit, without machining, next time too. ;)

JoeHall
08-30-2017, 09:24 PM
Guess I am gonna go with the Mopar drums, since they fit a kajillion Mopar vehicles, 1970s-1980s. Will get them at the local NAPA, at about $63 each. Reading of others' experiences here, will need to remove about .125" from the backside, but will double check before taking them to the machinist.

JoeHall
09-01-2017, 12:21 AM
After further reading and research, and a few more hours in the garage with dial calipers, I am going with Bendix PDR-0124 drums. Overall, they are the easiest to adapt. They have a smaller, 2.43" center circle, which can be easily enlarged to fit the 2.750" axle flange, without a need for adapter rings. Further the depth is such that, with 1/16th inch removed from the friction surface, there'd be sufficient clearance at the back-plate lip, but I am going with 3/16" just for insurance. Those are the only two mods required to fit them to the Fairborn flanged axles.

The Bendix PDR-0124 drums fit miscellaneous full size FoMoCo, from 1957-1968, and are easily found on the internet and at FLAPS. I already had one on hand from last year, and just ordered a second one from Summit tonight, for $49. They do not have fins, but I could care less. Will post again when the project is complete and the car is back on the road.

JoeHall
09-11-2017, 09:21 PM
After further reading and research, and a few more hours in the garage with dial calipers, I am going with Bendix PDR-0124 drums. Overall, they are the easiest to adapt. They have a smaller, 2.43" center circle, which can be easily enlarged to fit the 2.750" axle flange, without a need for adapter rings. Further the depth is such that, with 1/16th inch removed from the friction surface, there'd be sufficient clearance at the back-plate lip, but I am going with 3/16" just for insurance. Those are the only two mods required to fit them to the Fairborn flanged axles.

The Bendix PDR-0124 drums fit miscellaneous full size FoMoCo, from 1957-1968, and are easily found on the internet and at FLAPS. I already had one on hand from last year, and just ordered a second one from Summit tonight, for $49. They do not have fins, but I could care less. Will post again when the project is complete and the car is back on the road.

The deed is done, and the FoMoCo drums were an easy fit. I had the 2.430" center holes enlarged to match the 2.750" axle nubs, with .005" clearance. However, when I picked them up from the machinist, he said it woulda been easier for him (cheaper for me) to have simply turned the axles down to fit the 2.430" center hole in the hubs. Live and learn.

Only other mod to the FoMoCo drums was to have the machinist remove .250" from the friction surface, on the back side. That was overkill, in that, it probable only needed .100 or so removed to clear the backing plate, but I could not be certain without the flanged axles and backing plates actually mounted. So erred on the side of caution and removed a little extra. Of course I left the outer lip alone, and it lands about even with the back side of the brake backing plate. As is, the shoe sits in the middle of the friction area, with about .150" on each side.

Now, just gotta finish what has turned out to be a total brake job on the car, from A to Z, including conversion to dual MC. Thank goodness for my local machinist, and Jim Turner. Jim now has flex lines to come off the MC and plug into front and rear lines, an ingenious idea that will make the plumbing go a lot easier. I plan to keep the OEM brake reservoir, and connect it to an 'L' fitting, tapped into the side of the MC, with a crossover hole drilled through the reservoir divider inside. I can't wait to see how the EBC, "Green Stuff" pads work out!