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Well i'm not ready to change to 5 lug yet due to lack of funds but i know i will want it eventually. And i need new drums and shoes but i also know eventually that i will go to discs and i dont want to replace all of that stuff and then throw away used but good drums and shoes...so i was wondering if i could go ahead and do the rear disc conversion without doing a 5 lug conversion. I know where im getting my rear disc conversion kit and it comes with the mounts, calipers and used 5 lug rotors. So i was wondering what rotors would i have to shop for to get 4 lug rotors that are the same size as the 5 lug

Thanks, Grant
 

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There are lots of problems with doing what you want with the parts you can get. Assuming the rear disc set-up you can get is from an sn95 car, there isn't an OTS 4-lug rotor that will fit. The rotor diameter is wrong for the sn95 brackets and the axle register hole is too small for the axle (assuming you redrilled sn95 axle to 4-lug). If you used your 4-lug axle, the brackets are still wrong both in height (discussed above) and in off-set (designed for the longer sn95 axle). It might be better to look for an 87/88 T-Bird Turbo Coupe housing with discs (gears are 3.55 for the MT; 3.73 for the AT), or a 93 Cobra rear disc set; both are 4-lug, 10-11/64" vented rotors with 45mm single piston calipers, similar in appearance to but very different from the sn95 rear disc pieces.
 

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North Racecars Brake Solutions

I went with the $549 kit to simplify things and not have to collect a bunch of parts. I am also swapping to a 86 Lincoln Mark 7 Master Cylinder. The rear brakes are from 88 Turbo Coupe. I am staying 4 lug forever.
Instructions and part #s: North Racecars IRS Cobra Disk Conversion Instructions
Your putting down pretty good power and not having a 4 lug issue. Why are so many so hot to jump ship? Somebody at work was just asking why I am keeping the 4, well cause it works! That is a nice/cheap rear kit, been thinking of rear disc myself.

Of top How did Mike Post do for you? He has a good reputation, taking mine to him hopefully mid March.
 

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Your putting down pretty good power and not having a 4 lug issue. Why are so many so hot to jump ship? Somebody at work was just asking why I am keeping the 4, well cause it works! That is a nice/cheap rear kit, been thinking of rear disc myself.

Of top How did Mike Post do for you? He has a good reputation, taking mine to him hopefully mid March.
He knows what he is doing.......no complaints. I am gonna need a new tune myself as soon as I get this all back together.
 

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How noticible was the braking performance when you upgraded to disc on the rear?
 

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How noticible was the braking performance when you upgraded to disc on the rear?
I was wondering the same thing.

Going by memory from some book I read it said the 60-0mph stopping distance was roughly 15 feet shorter with 4 lug rear disc on a foxbody with stock 4 lug front brakes,compared to the stock rear drum brakes.
 

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If you have a correctly functioning power drum system, and solely switch the rears to discs, you won't really feel an improvement, except in your head. The rear brakes are only around 30% of stopping and the drums are adequate for that. The only place you would really see a benefit is heat dissipation like in repeat track runs or road course racing. I changed mainly for the looks, but also upgraded front calipers, rotors, master cylinder, & booster to make sure I stop at the end of a 1/4 run.
 

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How noticible was the braking performance when you upgraded to disc on the rear?
I "tested" the stopping distances before and after my rear disc conversion 15 years ago. Stock type pads and all season 15" tires on the 86. Front brakes were converted to the 87+ 11" with 60mm calipers (the 73mm came next). Test was on an open section of road with a cone set-up at the stopping zone; measured with a 150 foot tape used in construction. This unscientific test resulted in less than a 10 foot difference; call it no difference due to measuring and other errors. I was disappointed and thought going to the 73mm front calioper would fix it; not even close.

Why you might ask. What I didn't know or understand back then is that the Fox chassis brakes are biased about 75/25% to the front (this has nothing to do with the prop valve). When switching to rear discs, this bias does not change; the rear still contributes 25% to the effort. Evidence of this the the service life of rear drum shoes or disc pads - they last forever. What you do get out of the switch is better heat management (if that is of concern), less fade when the brakes are wet, and maybe the kool factor. When I did that test above, the drums clearly needed some cooling time after two-three stops, whereas the discs were good (or better) to go.
 
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