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TR6 Modifications to Datsun Aluminum Drums - TR-6

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davidk

davidk

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After looking for modified aluminum finned drums, I have given up and bought a used set of Datsun 280Z aluminum finned brake drums. I'm sure we can use a standard drum to figure out the machine work that needs to be done, but does anyone have the specific modifications needed to make the Datsun drums fit? Knowing the amount of material that has to come off the back of the drum would be helpful.

Thanks for your help!
 
A Google search turned this up on an online forum: <span style="font-style: italic">The machining that need to be done on the 240Z drums is really quite minor lathe job and should be done cheap at any machine shop willing to do a short time job. It's a matter of enlarging the center hole slightly to fit onto the TR hub then removing some material from the back edge of the drum to clear the TR backing plate.</span> I've also seen mention of possibly having to slightly enlarge the lug holes because of the "shoulder" on the TR lugs...and it's up to you if you want to drill countersunk holes for the retaining screws, as the drums will be held on quite well by the wheels alone.

So, if you've got the drums, it might be worthwhile and not too expensive to modify them to use. I'm actually surprised that they're no longer available new either for TR6 or 240Z, but then both cars are getting up there in years....
 
I have a suspicion that how much has to come off may vary depending on which drums you got.

Anyway, I found that I had to remove a lot to prevent interference with the original backing plate. Essentially, the drum is set up for a backing plate with a lip that fits in between two ridges on the drum. On my TR3A (which had 9" brakes from a later car), the lip on the backing plate is smaller and hits the inner ridge. I wound up having to machine away the entire ridge. Would have been easier with a lathe big enough to swing the drum, but it won't quite fit on mine so I had to use the vertical mill to remove the lip.

Never did finish the second one and it's somewhat moot now since my current TR3 has it's original 10" brakes.

Sorry for the lousy photo, it's all I could find in a minute.
 

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Don B, thanks for the link. Nice setup, but at this point, I'd like to make the aluminum drums work.

Andrew and Randall, most of the machining does seem straight forward, but it does appear that a lot of material will need to come off the lip to make them work.
 
I can help. I have a set of used finned drums and also a set of new Brembos for a 240z that I had machined. The new ones are not machined enough so I picked up the other set on ebay to compare. I'll have to look for them and take a couple of photos.
 
Peter, that is great. If you can take any of the inside depth dimensions of the drums that fit, as well as the width and depth of the lip, it would be most helpful to those looking to get this done.
 
I think that the backing plates differ in some way too. ISTR the lips are different depths, I've got a few so I will check when I get the chance.
 
Hang tight. I'll get there soon, but trying to get our wood burning set before cold weather hits.
 
This shows the two Alfin-style drums side by side. Note the different fins: one is squared and the other convex between the fins. Also one is to fit a splined hub (guessing here) with a center hole of 3.038". This one also is higher overall but the inside brake surface is still 2" wide.
 

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And a shot of the enlarged center.
 

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Now here's what I found. First, I have backing different plates. One is obviously lighter in weight with an overall diameter of 10-1/8" and probaly from a TR6. The heavier plate I think came from an earlier car, probably a 4A since that's what I have. This measures 10-3/16." It's not much different but the added diameter prevent either style drum from fitting.

So first thing:
1) Measure your backing plates (both)
2) I would add at least 1/16" to this measurement for machining the drum to allow it to spin smoothly around the backing plate.
The machining would then remove the material from the outward surface of the steel drum insert out to the measurement in 1) + ~1/16"

On mine the total width of aluminum is ~.340 - .375(3/8). This depaned of the thickness of the metal on your backing plates. One of mine is heavier and thicker than the other plate that I have.

Next is easy:
Enlarge the center hole of the Z drums to be the same as the original drums, i.e. ~2.725" but measaure yours first.
 
Now for depth of cut.

The shorter style Alfin drums that I have are new Brembo p/n 43206-E4100 drums that I had machined.

We cut ~1/2" (.546") depth which is close but still binds the drums when the wheels are torqued. So I need to finish cut a little more for clearance.

The biggest thing I can suggest to measure your old drums and backing plates to be sure you are working from the same page.


If anyone has a Jones for the large hole drums, I won't be using them and would sell for a fair price. They are used, alittle nicked up but appear to be good usable drums.

If I can be of more help, just ask.


Here's a good link https://www.gomog.com/allmorgan/datsunbrakedrums.html
 
That's great Peter! Thanks for your help. I'll be taking them to the machine shop tomorrow.
 
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