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Front brake upgrade with slip-on rotor


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Has anyone ever used a slip-on rotor on the front? I've been interested in making it happen since it would match the rears(T3 Q45 swap), and it would mean I could pull the rotors off without having to mess with the wheel bearings. I found a rotor that I think would do the trick. It's a front rotor for a 99-01 Ford Explorer and has 0.2mm clearance on the center bore and 0.6mm on the outer hub bore. The rotor is 26mm thick instead of the standard 28mm the Q45 front calipers are made for, but that's not an issue. The inboard face of the rotor would end up ~10mm further out than stock, but I don't think that's in an unreasonable spot. Thoughts? I'll attach the drawing of the Explorer rotor below.

 

Btw, the European Brembo site has a "search by size" option for rotors. Great tool for coming up with custom brake solutions. https://www.bremboparts.com/europe/en/catalogue/size?producttype=Disc&th=28&a=68&issizetolerance=True

brembo_explorer.png

Edited by calZ
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4 hours ago, LooseRocks said:

What exactly do you mean by "inboard face"?  The face in contact with the hub?

 

The surface that contacts the innermost brake pad. 

 

49 minutes ago, Neverdone said:

Are you currently running a Z31 front hub or some custom hub?

 

Those rotors are 5 lug is why I ask.

 

I have Z31 hubs that I used to mock up a wheel speed sensor add-on, but yes, I'm waiting on some 5-lug hubs from T3.

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The outboard face is 8 mm from OE  which means the center is 4 mm out.  Will that require new brake caliper mounting brackets that allow for the 4mm offset?  I suppose some spacers and longer caliper mounting bolts might work if having the caliper 4 mm away does not cause some weird stress issue for the caliper mounting brackets.  Might be wheel fitment issues for those that have wheels with minimal caliper clearance.

 

With no basis for a single grain of truth (not ME or have run any CAD stress sim) I can't imagine 4 mm being an issue for too much added stress on the caliper mounting brackets.  The wheel fitment might be the only stopper for people that already have their wheel fitment dialed with their current setup.  Would love to have over hub rotors though.  If you can figure out a formula that works with T3 current 300 MM BBK that would be awesome.  I don't really understand why the don't just make a deeper hat option so it can go over the hub.

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  • 4 weeks later...

I did this on my build.  Not only did it make no sense (to me) to have to dismantle the hub bearings to change the disc, the OEM setup also severely limits your options regarding disc choice.  I used floating discs, for example, which would not have been possible with the OEM setup.

 

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I did have problems with the TTT hubs however.  Once everything was assembled, I noticed the disc had a visible wobble when mounted on the hub.  I hooked up a dial indicator and measured something like .015" wobble at the outer edge of the disc.  Obviously that was FAR more than could be ignored...most OEM manufacturers specify no more than .001" runout of the disc:

 

Then I measured the runout on the TTT hub without the disc attached, and got a .002" wobble on the hub face.  I think that was the source of the problem, and the wobble just magnified on the disc face since it was much larger diameter.  I measured my 45 year old OEM hubs, and they measured perfectly true, no wobble whatsoever.  So after pondering things for a bit, I decided to just use the stock hubs.  Since I have staggered front/rear wheel/tire sizing, I couldn't really see any downside to having 5 lug in the rear and 4 lug in front.  This did involve getting new front brake hats machined, but fortunately at that time I had not yet ordered wheels.  I mean, I would rather have used the TTT hubs, but I knew the wobble would have been a major problem, not just with the brakes but I am sure it would have introduced a "shimmy" into the steering wheel as well.  Once I received the new brake hats, the discs ran perfectly true on the OEM hubs.

 

For the record, I do not blame TTT for the problem.  I have no doubt the hubs were manufactured true.  The way CNC parts are made, it would have been a far greater challenge to make them wobble than to machine them true.  I think I created the problem when I pressed the bearing races into the hubs.  Aluminum is very soft, and the bearing races are hardened steel.  Unless they are pressed into the hubs PERFECTLY straight, I could easily see them distorting the bearing bore or shaving a small lip, in which case they would not seat perfectly true and could easily cause a wobble.  I think that is what happened, and it is my fault, but I suppose it does raise some questions about the suitability of aluminum as a hub material.

Edited by Ironhead
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Those are some serious brakes Ironhead. Nice!

I remember Dave at AZC used to drill the stock rear hubs for 5 lugs and as part of the deal he put them on a lathe to true them, just in case someone had backed into a curb in 1973 while parallel parking. I would assume you could do the same for the TTT front hubs if desired.

FWIW I have an engineer friend who was telling me not to use AL front hubs, as the AL expands at different rates than the steel bearing races and he has seen quite a few spun wheel bearings in Mustangs with AL hubs. Suppose that's only a problem for the serious road racer types. I have AL hubs, so if I have problems, plan is to switch out to something else entirely...

Edited by JMortensen
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2 hours ago, JMortensen said:

Those are some serious brakes Ironhead. Nice!

I remember Dave at AZC used to drill the stock rear hubs for 5 lugs and as part of the deal he put them on a lathe to true them, just in case someone had backed into a curb in 1973 while parallel parking. I would assume you could do the same for the TTT front hubs if desired.

FWIW I have an engineer friend who was telling me not to use AL front hubs, as the AL expands at different rates than the steel bearing races and he has seen quite a few spun wheel bearings in Mustangs with AL hubs. Suppose that's only a problem for the serious road racer types. I have AL hubs, so if I have problems, plan is to switch out to something else entirely...

 

Most of the aftermarket CNC parts are made of aluminum, not necessarily because it is always the best choice, but because it is vastly cheaper and easier to machine than steel parts.

 

I suspect your engineer friend is onto something.  Not only from my experience with the TTT hubs, but because I have never seen an OEM car come with aluminum hubs, even considering high-end performance models from Porsche or whatever.  Considering hubs are unsprung weight, aluminum is not significantly expensive, and it is easier to machine than steel, I think if it was the way to go with hubs we would have seen them on production cars for some time now.

 

Also, the TTT hubs are so much thicker and beefier than the stock steel hubs, I would wager the weight difference is negligible if there even is one.

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Bad news: Q45 caliper won't fit without either cutting and rewelding the mounting ears or making some monstrosity of a caliper adapter to mount them to the front. The sliding design makes an adapter to put them near the original spot a non-starter. 

 

Good news: 1990 Z32 NA calipers are made for the exact width of the Explorer rotors and are a fixed design, giving more room for mounting.

 

Bad news: I picked up a Z32 caliper, and the 240z mounting ears don't allow for quite enough room for the Z32 caliper, meaning I can't get it close enough to the center of the rotor. 

 

Barring finding a rotor with slightly more diameter or going custom, I'm basically left with 3 options that I'll list in reverse order of practicality:

 

1. Make a ridiculous caliper adapter that ties into the two stock ears and the top side of the forward ball joint bolt, putting the calipers in a leading position. 

 

2. Trim the tops of the ears off, drill and tap new holes further down, and make a dead simple adapter to put the caliper right where I want it.

 

3. Give up on my stupid, stupid dreams of a non-permanent modification consisting of OEM wear parts and go back to a proven brake option.

 

Thoughts or ideas? Option 2 would be relatively simple, but I'd have to talk myself into hacking up good parts. 

Edited by calZ
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Option 2 wouldn't even take any welding, I'm just trying to avoid something that's not easily reversible. The option 1 adapter would be doable, but it would be pretty complex and not cheap to machine. I had thought about making these available to buy or at least give out the drawing, but it's looking like it might be more of a one-off. 

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Would an adapter like what is used for the z32 front brake conversion not work? I would think it's basically this except maybe you have to move the caliper further outwards (or maybe it's further inboard because of the rotor hat height)

 

10906520_822538207807812_8718560194380573914_n.jpg

Edited by ZHoob2004
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My memory is kinda fuzzy, but I seem to recall that the Z32 calipers weren't the best. The iron ones were heavy, the aluminum ones were flexy. I seem to recall people adapting them to S30s and other people saying: "Why didn't you just get some Wilwoods, they're less flexy and perform better?"

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A major driver behind this was to maintain a factory brake bias and make things match front to rear. There are plenty of big brake kits already available with Wilwoods and custom hats. That's not what I was trying to do. 

 

 

16 hours ago, ZHoob2004 said:

Would an adapter like what is used for the z32 front brake conversion not work? I would think it's basically this except maybe you have to move the caliper further outwards (or maybe it's further inboard because of the rotor hat height)

 

The Odyssey rotors in those kits are further away from the upright, so the caliper is mounted completely outboard of the stock ears rather than in-line with them. I might be able to find a different slip on rotor that works in a similar location, but then wheel clearance becomes an issue

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  • 3 months later...
  • 7 months later...

I picked up a full set of brembo calipers front and rear from a 944 turbo. They appear to be very close to what Z Car Garage is using in their kit. I also grabbed some front rotors off of an LS430, 2001 I think. Acuras use a similar rotor also. I'll start a thread when I start my project but it may be in the spring.

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