stumpmj
stumpmj Dork
Sept. 19, 2011 9:49 a.m.

So it's come to my attention that engineers at Mazda didn't konw about galvanic corrosion in the late 80's. I'm disassembling an FC RX-7 as my donor car and I can't remove the front rotor from the hub. The rotor is iron (naturally) and the hub is aluminum so the two have corroded toghether. The rotor wraps around the fron and the full lenght of the sides of the hub so I have almost no access to the hub.

My goal is to remvoe the rotor without damaging the hub. I used a 5 lb sledge hammerwith the upright clamped in my vice and I was able to pound one of the rotors loose. I broke the bench that my vice is (was) bolted to trying to removing the second one. Any thoughts on how to get the rotor off of there?

I also broke a bolt that corroded in the rear hub so I've got that going for me too.

Aeromoto New Reader
Sept. 19, 2011 10:04 a.m.

Oxy/acet rosebud torch. Get the rotor nice and hot, the corrosion should burn off.

Tom_Spangler Reader
Sept. 19, 2011 10:05 a.m.

BFH

oldtin Dork
Sept. 19, 2011 10:07 a.m.

Have you used the blue wrench yet (torch)? The different heat dissipation of the two metals should give the big hammer an extra boost.

belteshazzar SuperDork
Sept. 19, 2011 10:38 a.m.

is there much danger of damaging the wheel bearings? I've often used the biggest hammer I could find.

hotrodlarry Reader
Sept. 19, 2011 10:40 a.m.

A friend of mine had a rx-7 with the same problem. I want to say he took the hubs off the car, went to the local big truck shop and they charged him $30 to press both rotors off.

44Dwarf Dork
Sept. 19, 2011 11:18 a.m.

sazall..cut down the rotor as far as you can then proigate the crack with screwdriver and BFH this way you lessen the chance of damaging the wheel bearings.

stumpmj
stumpmj Dork
Sept. 19, 2011 12:06 p.m.

Perfect. I'll try the sawall trick first.
If that doesn't work, I'l take the dust cover off (which is also corroded in place since it's steel and the hub is aluminum), take the hub off the upright and try and press it off. If that doesn't work, I'll get a stronger bench, bolt the vice back down, and use my 25 lb hammer instaed of the 5 lb one I was using. If that doesn't work, I'll add heat and then use the 25 lb sledge.

I've spent way more time on the donor than I have on the Locost itself at this point. Grrr....

bravenrace SuperDork
Sept. 19, 2011 12:11 p.m.

If you have heat available, that's what I would do first, because it WILL solve your problem.

stumpmj
stumpmj Dork
Sept. 19, 2011 3:25 p.m.
bravenrace wrote: If you have heat available, that's what I would do first, because it WILL solve your problem.

I'm just nervous about damaging the wheel bearing/seals. I'm also concered that the alumium hub will wick heat out of the rotor and prevent the relative movement from happening. Plus, all I have is a little MAP gas torch. No real heat.
Wait, does welding a bead all the way around the rotor count as adding heat? Worthwhile strategy?

mndsm SuperDork
Sept. 19, 2011 3:40 p.m.

Why worry about the bearings? Are they new? Those kinda things are generally REALLY cheap.

MG_Bryan New Reader
Sept. 19, 2011 3:49 p.m.

Since your bench broke and you don't have a torch, can you bolt the upright back on the rx7 and just hit it harder?

Twin_Cam SuperDork
Sept. 19, 2011 3:58 p.m.
Tom_Spangler wrote: BFH

The solution to all life's problems. Including stubborn brake rotors. Just make sure you wear ear plugs, or your ears will ring for days.

fasted58 Dork
Sept. 19, 2011 4:01 p.m.

p oil then heat em n beat em

mtn SuperDork
Sept. 19, 2011 4:10 p.m.

Just had this problem with my Miata. Took three hours to get a single rotor off.

Take off the caliper. Find two long bolts, 4 nuts, and a bunch of washers. Stick the bolts through the holes that are meant for the calipers. Put 2 washers on the bolt, then the first nut all the way down to the washer, and the second just to the tip. Put a wrench on the nut closest to the bolt head, and then start tightening the bolt down with another wrench. Here is a video describing it: http://www.youtube.com/watch?v=mtsTJCRljAs

mtn SuperDork
Sept. 19, 2011 4:10 p.m.

Oh, also, blast the hell out of it with PB blaster first and let it soak a while.

RexSeven SuperDork
Sept. 19, 2011 5:22 p.m.
mndsm wrote: Why worry about the bearings? Are they new? Those kinda things are generally REALLY cheap.

Yeah, the bearings are cheap, but they are a ginormous PITA to replace because Mazda made the front hub/bearing assemblies on the FC RX-7 "unserviceable." New 5-lug hub assemblies are about $450 each and are no longer available in the 4-lug pattern if that matters to you.

I tried Mazdatrix's technique on removing the bearings from my front hubs, but they would not budge, so I paid a shop $100 to spend close to an hour heating the hubs with a welder and whacking the bearings out with a BFH and a BFChisel. The new bearings went in smoothly with a bearing installer kit I rented from AutoZone, but you have to install them while the hub is hot or else it gets much harder to install them. The rear bearings are no easier, but at least they last longer.

OP: Is your car a 4-lug or 5-lug car? The 5-lug cars have a screw that holds the rotor in place and also an extra hole that you can put one of the retaining screw into to pop the rotor off. The stock screws are a soft brass that strip/deform easily, so try using a steel bolt with the same thread pitch.

mad_machine SuperDork
Sept. 19, 2011 5:59 p.m.

+1. Try the bolt into the hole trick. A LOT of cars have the threaded holes there just for that.. and most people don't know it. I actually started a fight on a hyundai forum about it. (hyundai tibs have them... but nobody agreed with me)

Aeromoto New Reader
Sept. 20, 2011 10:34 a.m.

If the assy is that corroded, you'd think the bearings would be trashed as well.

mad_machine SuperDork
Sept. 20, 2011 12:54 p.m.

Not really, Aeromoto. I have had rotors corrode onto hubs in very short order.. like in 50,000 miles from being driven off of the lot new. Bearings were fine.. just the chemistry at work between two dissimilar metals

stumpmj
stumpmj Dork
Sept. 20, 2011 1:27 p.m.

Like the bolt and nut trick! I'm trying that tongith when I get home. I didn't have time yeterday. THe wife put me to work on the house instead...

stumpmj
stumpmj Dork
Sept. 21, 2011 12:02 a.m.

OK rotor is off! I used 44dwarf's method but slightly modified. Instead of a sawzall I used a cut off wheel on my grinder. Pics can be seen here: Build log

44Dwarf Dork
Sept. 21, 2011 6:41 a.m.

Great!
I developed that method after need to replace the front rotors on my GEO at 185,000.....Yup stock uncut rotors lasted that long the bearings were fine but i didn't want to pound on them with that kind of mileage the rotor had grown around the hub by a least 1/4 inch.

Do your self a favor clean the inside of the rotor hat with brake cleaner then paint it with some 2 part paint (left over from car or tractor etc.) let it dry good while you clean up the hub then coat it with anti-seize then assemble this will slow down the rust and encompassing growth.

mad_machine SuperDork
Sept. 21, 2011 8:03 a.m.

I just remembered.. there was a time I used the bolt method to remove some rotors.. and succeeded in breaking off the top of the hat.. leaving the rest of the rotor in place.

thankfully I had weakened it's grasp on the hub enough that a deadblow hammer was able to pop it off

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