The next project for my 914 is converting to 5-lug suspension. I have the front struts and rear hub from a 1972 911 to start with.

The rear will have vented rotors. I have some questions about doing this part of the conversion.

Two questions:
1) Will I need longer studs in the rear? Before adding the spacer, a lug would catch with 11 rotations on a stud. After adding the spacer, a lug catches with only 8 rotations.

2) When I add the spacer, the rotor is no longer centered perfectly on the hub. How do I center the rotor on the hub?


911 Hub
Click to view attachment


Hub with spacer
Click to view attachment


Hub with spacer and rotor. 911 rotor has been cut by Eric Shea. Thanks E.
Click to view attachment


With the spacer, the lug only catches with 8 revolutions, down from 11 in its stock state. Is this enough or do I need longer studs?
Click to view attachment


With the spacer, the rotor lip that centers it on the hub now misses the hub because of the spacer. How do I center the rotor now? Do I use just the 2 little hold-on screws to center?
Click to view attachment


One of the calipers that will be used.
Click to view attachment

The spacer always goes on after the rotor. Unless you need it to space the rotor to match the calipers.

As far as stud length goes, my guideline is to use open end lug nuts and as long as the thread is at least flush with the outside of the nut, i call it a day.
If not, i use longer studs.

This spacer goes under the rotor. It is to make up the difference in the width of the caliper 1/2 spacer.

Just install the spacer and use longer hold down screws... I have the same spacers on my car.

Mark the holes on the 911 hub onto the spacers and drill them through.

This is a great kit! Thanks for offering it Eric!

I like this idea. The current studs are 45mm. I see 66mm studs on PP. These will give plenty of room using lugs w/o the top cover and allow a small wheel spacer if I so desire.

Where is the best place to buy wheel studs?

944s use 50mm studs. I was thinking the exact same thing as Andy. Throw an open ended nut on there and see if you're showing thread. If so, good to go. Otherwise, throw some 50's on there. Bruce Stone usually has some used ones laying around.

I did the open lug test and there was about 3/8 inch of the nut uncovered.

So I went with the 66mm stud. This will give plenty of room for perhaps a spacer in the future.

Click to view attachment

Click to view attachment

The rule of thumb that applies here is "thread engagement should be equal to or greater than the diameter of the fastener". Therefore, you need 14mm of thread engagement on a typical Porsche wheel lug. Many speed event sanctioning bodies require open lug nuts so the thread engagement can be easily verified.

The Cap'n

Couldn`t have said it better myself

Does that make it "lug-centric"? Or are they anyway? I'll be doing a 5 lug conversion soon myself, so this is the start of probably many questions.
Cheers, Elliot

This is my favorite Elliot:

http://www.914world.com/bbs2/index.php?showtopic=91963

Also, read up in here:

http://www.914world.com/bbs2/index.php?showtopic=105728

It will help with making a determination on what level is needed.

I opted to stay with re-drilled 914 hubs instead of the 911 hubs.

I am running into a problem centering the rotor. The rotor is a cut-down 911 vented rotor.

To center the rotor with a 911 hub, the idea was to use the rotor hold-down screws to also center the rotor.

But on the 914 rotor, the hold-down screw holes are not in the same place as the 911 rotor.

See the pics. The 914 hub has the hold-down screws centered about the axle. The 911 rotors are offset and not centered about the axle.

Any ideas on how to center the rotor?

The only thing I have come up with is spacers around the studs to take up the slack between the studs and the stud holes in the rotor.

I made a couple of spacers out of 10mil brass sheet and put a spacer on 2 lugs. There was no play in the rotor but the rotor has .01 inch end play as measured on the edge of the rotor.

Not too bad but the spacers are pain in the ass.

I think I'll try removing the spacers and center the rotor by measurement and using lug nuts keep it in place while I drill and tap hold-down screw holes to match the 911 rotor.

Anyone have any other ideas?

wheels can have 1-1.5mm radial runout, lateral is what is important.


Just tighten the lug nuts down on the rotor ,Indicate the radial runout adjust with soft hammer, drill and tap your holes for CS screws.

For a permenant solution, install the rotor on the hub with 2-3 lug nuts, they should center the rotor as they tighten onto the rotor face.

Use a new sharpie to mark the location of the 911 holes. Use a 5mm drill and drill two new holes in your new hubs. You might even want to start those holes with the rotor still in place. Then tap with a 6x1 tap.

Remember, if you have spacers under the rotor hat, you'll need to grab 4 new (longer) M6x1 screws commonly available in the HD or Lowes "metric drawers".

Couldn't you do the hole on the spacer first with the short screw and then tap the new holes for the 911 rotor into the spacer after you have secured the spacer in position?

Then you wouldn't have to fuss with it everytime you remove the hub?

I am just throwing out another idea as I am contemplating this upgrade also!

I just finished one side using this method. I held the rotor with 5 lugs and adjusted the fitment until I had about .005 inch of play.

I drilled the holes by starting out with a drill just the size of the hole in the rotor. This gave a centered hole through the spacer. Then I used the 5mm bit to drill through the hubs and tapped with 6x1.

There is just a bit of runout and I can adjust it by loosening the screws and retightening.

Bought longer screws at Home Depot for $0.99 a piece. What a ripoff.

One more question:

Does the spacer assume that a rock shield will not be used?

There seems to be a fitment issue when the rock shield bracket is in place under the caliper mounting tabs.


W/O the rock shield, the caliper is perfectly centered.
Click to view attachment

With the rock shield bracket, the caliper is a bit askew towards the inside of the car.

Yes.

I'll expound now that I'm not on the iPhone.

You have two options as I see it:

1. remove the dust shield. Not a no-no. The factory recommends removing them for sports purpose vehicles to help keep the brakes cool(er).

2. remove the spacer and use the dust shield with distance washers under the caliper mounting ears. Again, not a no-no. Ferrari uses varying sizes of distance washers under their rear calipers of the same make. You may run into clearancing issues with the lip on the inner adjuster tube that runs through the arm (see SoCalAndy's recent posts on this in his thread).

3. (I lied... there's another option), you can still purchase 914-6/GT rear rotors from Germany. They will cost $250.00... each.

What is a distance washer?

I was thinking about cutting the brace on the vertical portions and extend the brace to attach on the top of the caliper mounting tab instead of below the tab.

In order to keep the rock shield and not offset the calipers, I extended the shield bracket to mount on the back of the caliper.

Click to view attachment

The caliper needed to have a bit of its webbing filed to fit the bracket on the back.

Click to view attachment

Shield and bracket before mounting the caliper.

Click to view attachment

The caliper is nicely centered on the rotor now and the rock shield is securely mounted.

Click to view attachment

I'm looking at the same issues. Your solution is great, but I have a question. The pictures don't show this; where the calipers mount ( and center) without spacers before you made the longer bracket ?

My setup uses 2 washers between the control arm and the caliper; the bracket could replaces at least one of the brackets"

Jim,

In your situation, wouldn't the shield mount effectively act as "one" of your washers?

Jerry is using spacers under his rotor. You're going the route of under the mounting ears right?

Having the shield mount as your last (or first, depending on how you look at it) spacer should keep the original geometry the same.

Jerry, why did you end up grinding the caliper and not the (already modified) shield mount?

Thanks Eric, I forgot he used a spacer under the rotor, That makes sense. I'll use the dust shield bracket as one of my spacers. Everything else has fit well. After reading up on reseting the venting distances; should I wait until the tranny is back in and bolted to the CVs; or, can it be set now.

I wouldn't set the venting clearance until the CV's are in and the stub axle is torqued to spec. Once you are torqued up your hub and rotor will be solid enough to set the clearance.

Are those SC or Carrera rear rotors? Looks like the latter by the pics. Doesn't look like the pads are going to fit in there.

SC. If the rotor fits the groove the pads should fit.

I would strongly suggest against using a used stud on a car. New ones are not that expensive and you have no idea of how a used one was used. Was it over torqued? In an accident and the wheel bounced off a curb?

For small dollars, you can go a long way to ensuring your safety.

I could have grinded the shield mount. Didn't think about it.

SC as Eric mentioned. I got the rotors from Eric and I was able to coax him to cut the rotor diameter to size. I couldn't find a shop around me who would do that.

On final install, the pads fit very nicely. Had a little issue getting the adjusters to pop out (it was over a year since the calipers were restored).

The one thing that I didn't like and still don't about the vented rotor adaptation is the rotor itself is not self centered now.

Because the spacer goes between the rotor and hub, the rotor no longer contacts the edge of the hub and loses the centering.

The mounting screws hold the rotor in place but do not provide very good centering. There's still a lot of play in the rotor concentricisity. I used a run-out gauge to center the rotors then tightened the rotors with the mounting screws.

Thanks ! Worked good. Had to glue the washers to the bracket in order to keep it together.

Got a While Your There question; I have a pair on new E-brake cables, will the old ones pull out after unhooking the ends that terminate at the e-brake handle ?

Jim,

I just did this, they should pull out after you unhook the cables inside behind the driver's seat. my problem was that they were rusted to the caliper solid! I had to cut the cable etc. I have not yet gotten to the point of setting the venting and bleeding them, i'm doing the front now first, and new master cylinder. good luck!

[quote name='Philip W.' date='Feb 25 2014, 05:35 PM' post='2003108']
Jim,

I just did this, they should pull out after you unhook the cables inside behind the driver's seat. my problem was that they were rusted to the caliper solid! I had to cut the cable etc. I have not yet gotten to the point of setting the venting and bleeding them, i'm doing the front now first, and new master cylinder. good luck!


Thanks Phil. As I suspected. I have a small leak at the MC but haven't got to it yet.