The time has come that I want to change out my 5 lug solid rotors to ventilated rotors all the way around.

Fronts: I am adding alumninum Brembos upfront (I have 3" struts). Will I be able to use the same hats and bolts that are on my solid rotors with the ventilated rotors? I also have 16x7fuchs, narrow body.

Will changing the rotors effect the front end alignment?


Rears: I am going to purchase a vent kit for my rear stock calipers from Eric which require 4mm to be turned off a stock 911 ventilated rotor.

If I take the rotors to a brake or machine shop and ask them to take off 4mm will that be precise enough info for them to know what to do? I presume taking 4mm off gives a little bit of wiggle room for clearances.

It will neither effect nor affect your alignment.


If you got that number from Eric, that's the right number. (although they'll probably take off 5/32" if it's an old shop...)
IIRC, the 'minimum' is 3mm so you've got a spare millimeter to account for production tolerances.

RE the front? Don't know what you mean about using the same hats....I am assuming you have stock front rotors and they don't have hats.

Hats are a separate piece that adapt a rotor to the hub. Sometimes the same rotor can be used on different applications that way.

Here is mine with a flat hat. The red pencil is aiming at the hat. Note that it is bolted on separately to the rotor

Click to view attachment

I believe Eric offers the machine surface for a fair price and it is probably cheaper and correct to have him do the machine work...you could probably do the machine work yourself if you have access to lathes. I took off about 0.15 mm on my rotors myself at work on a lathe and made sure they spun true to with in +- 0.005mm

If you have no expierience with lathes I would NOT recommend you try this yourself as it is dangerous for a beginner. Its a lot easier to just pay Eric for the services.

Paul,

Please tell me more about your front rotor hats. Are they custom made or where did you purchase them? What rotors & calipers are used?

I have Wilwood rotors that need a flat hat.

Thanks,

Eddie

My friend here in Japan bought some Wilwood calipers and brake kit for his Toyota celica GT and they came with those flat hats....all I can say is they are NOT flat. In fact they were poorly machined and were off about 0.4mm which caused some balance and noise issues on my friends car. I ended up fixing it by first surface grinding them truly flat to with in +- 0.002 mm and them turned them on the lathe at work to clean them up and took off the bare minimum of material so they spun completely true or with in +- 0.005. This made a huge difference.

You would be surprised how low tolerences are on mass produced parts. I know I was.

Similar experience.....These hats were cut on a water cutter!!!!! There was about .030" clearance between the locating lip of the hub and the hat. When I brought this issue up to the manufacture he claimed the bolts centered them. What a dumb jerk! They hopped up and down like a yo-yo and would have shaken my teeth out at speed. In addition, they were powder coated very unevenly. Eventually I cut a groove inside the hat and added some JB Weld to make the hole smaller (see the above pic). I then bolted everything together and dialed in the rotor on the lathe and machined all the hat surfaces true and concentric. Huge improvement and they run perfect.

My rotors are Wilwood and the hats came from a guy who is no longer in business for obvious reasons....

I suspect there are a bunch of 911 big brake owners who have had there tires balanced 10 times trying to resolve a shake issue without realizing it's their hopping big-ass rotors...very sad

I'm confused on what you're talking about with the front rotors too, the "stock" 914 4 bolt rotors are a once piece--i.e. the rotor and 'hat' are a single casting.

You'll need a 911 5 bolt hat for your project and I think a set of 5 lug rear stub axles too...

Your wheel clearance should be fine, alignment should be OK but I'd still realign the car after just to be sure...

Eric Shea should be able to walk you through all that...I'd recommend having him machine down a set of rear rotors for you too...

If you read the first post he's already 5 lug. He's just upgrading from solid to vented rotors.

Right...so 914/6 and re-drilled stockers are 1 piece rotor/hat combos too...with a 3" front end I'm assuming they're one of the two...

Yes - but was it 'done right' with 911 struts (as your post implies) or was it done with drilled and studded 914-4 rotors (as the original post seems to suggest) ?

If you are 'just' changing 911 solids to vented, yes, it's easy.

If you're doing it with 914/4 struts, you are changing -something-

Since the 5-lug wheels are a given, as is the desire to run vented rotors, IMHO the shortest path is 911 struts and hubs.

There has been talk of _4-lug_ vented rotors, but it seems a bit ridiculous to modify a 4-lug vented setup to 5 lugs, when the 911 parts are already a known, available solution. But this is why I tend to avoid 914-4 discussions - I just don't keep up on this...

So the answer to the question the OP did _not_ ask is: Yes, if you're changing to 911 struts, you will need to re-check your alignment. 911 struts and hubs is probably the cheapest and fastest way to get what you want.

Yes, my suspension up front is 911, from a 69 911 T with 3 in struts. I have true 5 lug studs with the solid 911 rotor and hat as separate pieces. I do not have converted 4 lug.

The rear are also true 911 5 lug hubs.

What I was trying to get at was...
It's my understanding ?? that hats are of different depths. I wasn't sure if my hat off the original 911 solid rotor setup will bolt right-up to the new ventillated rotors that I have on order...or do I need to find different hats, or possibly machine them.

I'll know the answer to my own question once it's all torn apart and the rotors arrive...just trying to see if I have all the parts for the front.

Thanks for all the replies...
Mark

Aha.
We don't call those hats - we call them hubs.

Yes, they come in different sizes. The best I can suggest is to compare part numbers from the solid rotor cars to the 914/6 which is '69T with vented rotors.

In any case - those hubs should be available through any of the reputable recyclers if what you haven won't bolt up without giving you spacing issues. You'll want new bearings and grease seals.

Thanks,
I guess I'll just see how it fits this weekend and go from there.