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Old 08-08-2001, 01:31   #1 (permalink)
olympic
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Rear disc brakes = reality!!

I managed to complete the rear disc brake conversion on the passenger side of my Topaz. Things went fairly smoothly but f**k was it alot of work!!!! Fabricating that caliper bracket was a genuine P.I.T.A. All the dimensions and even some of the contours had to be perfect.

The rotor has a very slight wobble to it when I spin it on the spindle. I think it's because I didn't get the centre bore on the rotor perfectly round. I'm going to take the remaining rotors to a local machinist to have the bore enlarged on a lathe and the lug holes drilled. It has to be perfect or the brakes will pulse or vibrate at highway speeds.

I started uploading pics to http://www.picturetrail.com/olympic (click on braking upgrades)but the site went down. I should have the rest up shortly.
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Old 08-08-2001, 09:06   #2 (permalink)
HO V6 XR5i
 
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Sweet

You are awesome man!! I can't wait for them to work out for you
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Old 08-08-2001, 11:47   #3 (permalink)
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I'm sure you'll want everything to be perfect especially with the speeds you'll be capable of on the highway! Nice work.
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Old 08-09-2001, 07:26   #4 (permalink)
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Re: Rear Disc Brake Mods

Checked out your latest pictures, just a few questions came to mind,
#1, was the stock SHO calp. ,a cast piece, as it looks in the
picture?

#2, what grade of steel did you fab the new bracket from?

#3, what is the reason for the two outside lugs (undrilled)
being left on?

Good job Olympic! Let us know how the machine shop work goes.
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Old 08-09-2001, 07:31   #5 (permalink)
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Re: Rear Disc Mods.

Sorry Olympic!

The first question should have read , was the stock SHO calp. bracket, a cast piece , as it looks in the picture?
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Old 08-10-2001, 02:32   #6 (permalink)
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Yep, the SHO bracket is cast iron. It's less than 1/4" thick where it bolts to the knuckle and about 1/2" thick where the caliper attaches. I used a high grade(expensive) 1/4" plate steel to fab my new brackets. I would have used thicker steel but then the bracket mounting bolts would not clear the base of the hub. The smaller piece welded to the top is 3/16". I was thinking the same thing you probably are. The 1/4" steel plate wont be as strong as the OEM cast bracket. But if you look at the rear pic of the assembly, you can see that the distance from the knuckle to the large holes that the caliper bolts to is less than 2". So you would need a tremendous amout of force to bend the new plate over that small a distance. Also, if you look at the physics involved here you can see that the force exerted on the bracket during braking will be acting in a plane which is parallel to the plane of the bracket. So the force will be trying to turn the bracket around it's axis(the spindle). Since the bracket is nearly 6" across, it seems impossible that it will bend in any way. The only forces that "might" bend the bracket are those that work perpendicular to the plane of the bracket. But since the SHO caliper is a full floating system, perpendicular forces are almost zero. The only way there would be perpendicular force on the bracket is if I had a warped rotor or the caliper sliding pins siezed up. I will ensure neither of those things happen on my car.

One more thing to consider is that the rear brakes only do 15-20% of the braking. So the components won't see anything near the stress that the front brakes will. I would not even consider doing this type of thing for the front brakes.

Hopefully I can drag my @$$ out of bed before noon(it's 3 am as I'm typing this!) and get the hubs and rotors to the machinist. I need him to:

-machine the hubs about 1/8" so they will fit inside the SHO rotor hat.
-enlarge the centre bore on the rotors so they will fit on the topaz hub
-drill the 4X4.25" bolt pattern into the rotors
-resurface the rotors
-drill a 1.75" hole in the custom caliper bracket where it will fit over the topaz spindle. I did the first one myself but it was alot of work since I dont have a drill bit that big. The bolt holes I can do myself.

The first rotor that I modified myself is basically ruined(out of balance.) So I though I would have to buy a new one. But as luck would have it, 89 SHO's used the same rotors on all 4 wheels. So I still have 3 to work with. Hopefully atleast 2 are not warped beyond repair. Once the machining is done and I finish the second caliper bracket I should be able to bolt everything back into the Topaz and get some more pics. Then all that's left to do is hook up the brake lines and e-brake cables. Then on to the front brake upgrade!! :)

quote-"#3, what is the reason for the two outside lugs (undrilled) being left on? " I'm assume you are talking about the tabs that stick out of the new bracket? Those are the mounting tabs for the dust shield. I left them undrilled because I'm not sure if I will install the shield. I think it will look better without them.

On a side note, I place an order with www.shonutperformance.com for a new clutch, front and rear crank seals and oil pan seals. I was going to wait until I was ready to order a Quaife TBD but I might as well get these parts now so I can atleast get the engine buttoned up. SHOnut also informed me that my SHOshop y-pipe(from the group buy)is slated for delivery in late august. I knew it would take a few weeks since over 40 people signed up for that group buy! I have also heard that there can be a long wait(months) for a quaife TBD since Quaife wont produce them until they have 25 orders. Oh well, that'll give me time to go nuts on the rest of the car. i.e-front brakes, subframe connectors, strut tower brace, etc.
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Old 08-10-2001, 11:55   #7 (permalink)
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Re: SHO Brake Mods To Topaz

Glad that we're on the same page Olympic.
4140 or 1045 grade hot rolled steel is what I would use to fab. the calp. brkt.( or maybe S.S.!)
Perhaps the cast stock brkt. was just less exspensive to manufacter than a machined part.
Have you touched base with Mark, or the SHO guys re: this new mod?
I being a utility machinist at Stelco Steel in Hamilton, am very interested what you have acomplished, so far.
Press on my friend! Thanks for your reply!
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Old 08-11-2001, 00:19   #8 (permalink)
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The factory uses cast iron because it suits it's purpose perfectly. It's cheap and strong. It's doesn't yield under stress like mild steel will. S.S would have been nice but I dont have the equipment to work with that.

I took the rotors and hubs to the machinist today. He's a local farmer who does machining on the side during the summer and full time in the winter. He does good work for cheap. He's busy with baling hay right now so he said it would be tuesday or wednesday before he could get to my stuff. I dont mind waiting be cause the other shops in the area woul probably be 2 to 3 times more expensive. Also, the bigger shops usually can't be bothered with small work orders like this one.

Once he has the work done, all I have to do is finish the second caliper bracket and bolt everyting back on the car. I should be able to get to that next weekend.
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Old 08-11-2001, 07:54   #9 (permalink)
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Brake Mods Topaz/SHO

Your spot on re: the cast bits, hey... did you forget where I work? :) Perhaps we can refine the next set of calp. brackets etc. eh?
Glad to hear about the progress that your making, I'm still on the mend here.
Mark S. is checking out your project, as I'm writing to you!
Good stuff!
Press on my Friend!
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Old 08-12-2001, 04:19   #10 (permalink)
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Like you said, great minds think alike! I was thinking, once I get all 4 brakes swapped I'd look into developing a bolt on kit of some sorts. The hubs and rotors I could get modified by my local machinist. But the caliper brackets would require someone with CNC machining capabilities. Basically, they'd have to create an exact copy of the Taurus bracket. The only difference is that they would drill the spindle hole and 4 bolt holes to fit the Tempo knuckle. Pretty simple if you ask me. Maybe if I ordered 10-15 sets of brackets it would bring the price/bracket down to a reasonable level. I would definitely be in for a set. I just did it myself to see if it could be done. I didn't want to spend hundreds of dollars on a 1-off set of brackets only to find out it doesn't work.

I'm still not sure what's going to be involved in hooking up the brake lines or e-brake cables but it shouldn't be too complicated. I'm hoping that I can just swap the rubber brake hoses from the Taurus. The front brake swap is going to be a do or die situation. I'f the Taurus knuckle cant be adapted to fit on my Topaz I'm S.O.L. The rear disc upgrade is kinda pointless without bigger rotors up front.
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