4 to 6 conversion: rear brakes Options

[bossboy302]

Collecting the bits for my project, (4 to 6) rear brake question...
Are the rear 4 rotors the same thickness as 6?
If so, can the 4 rear calipers (with their parking brake) be used?
I am doing the 5-lug.

Thanks in advance

[mgphoto]

Collecting the bits for my project, (4 to 6) rear brake question...
Are the rear 4 rotors the same thickness as 6?
If so, can the 4 rear calipers (with their parking brake) be used?
I am doing the 5-lug.

Thanks in advance

Yes, but the rotors need to be cut down by 3 mm.

[Superhawk996]

The real reason to go to /6 calipers is due to the /6 weighing more - it got bigger pistons and a slightly larger efffective radius due to the larger OD rotor. Translation - more rear brake.

The /6 pressure regulator was also calibrated differently to account for the fact that the /6 could tolerate more rear braking due to the added rear weight.

/6 calipers are pricey and hard to find but are the way to go if you can swing it.

[mepstein]

Collecting the bits for my project, (4 to 6) rear brake question...
Are the rear 4 rotors the same thickness as 6?
If so, can the 4 rear calipers (with their parking brake) be used?
I am doing the 5-lug.

Thanks in advance

First, read this thread. It's the best 5 lug conversion thread written. http://www.914world.com/bbs2/index.php?showtopic=105728
Basically, If you just want 5 lug on the back, have your hubs and rotors drilled for 5 lug or buy 911 solid rotors (used on the 912) and shave 2-3 mm off the diameter. Use your 914-4 calipers.

You have some options. If you want a bigger rear caliper, you can use a 911 M caliper and 911T rotors. Add the 911 e-brake with this thread.
http://www.914world.com/bbs2/index.php?showtopic=4909

Or buy 914-6 calipers, 911T rotors and bolt them on. Still need 5 lug hubs made from 914-4 hubs.

PMB Performance has all the parts and know how.

You will need new bearings with any hub removal and replacement and always change your brake rubber soft lines if you don't know when they were last replaced. Again, PMB is the source.
(IMG:style_emoticons/default/beerchug.gif)

[mlindner]

Or if you are not in need of the parking brake, your front calipers can move to the rear with a 6mm spacer. Works great with SC front calipers.

[bossboy302]

Thanks all for quick replies...

Have done some reading before asking, but just wasn't sure about re-using the 4-cyl calipers, which I have.

Thus far have had trailing arms powdered, new bearings, etc, and have 5-lug hubs (non converted ones).

Definitely want the parking brake feature.

Don't think I need the full-on 911-type 'drum' parking brakes.

If I can find reasonably priced 6 calipers, I'll do that. If I can't, I can use the 4 calipers with trimmed rotors.

Also doing full-911 front conversion, new lines and hoses, and 19mm M/C. 155 h.p 2.2E motor, no track use.

Thanks for all the tips.

Hope to start a build thread after making fender flare decision.

[zoomCat]

Be aware that the 911 brakes on the front have a piston area about 30% larger, so your brake bias will be off. You’ll loose some ultimate braking potential, and the fronts will wear out faster than the rears.

It’s a system, changing just the fronts throws off a number of things.

Thanks all for quick replies...

Have done some reading before asking, but just wasn't sure about re-using the 4-cyl calipers, which I have.

Thus far have had trailing arms powdered, new bearings, etc, and have 5-lug hubs (non converted ones).

Definitely want the parking brake feature.

Don't think I need the full-on 911-type 'drum' parking brakes.

If I can find reasonably priced 6 calipers, I'll do that. If I can't, I can use the 4 calipers with trimmed rotors.

Also doing full-911 front conversion, new lines and hoses, and 19mm M/C. 155 h.p 2.2E motor, no track use.

Thanks for all the tips.

Hope to start a build thread after making fender flare decision.

[mepstein]

Thanks all for quick replies...

Have done some reading before asking, but just wasn't sure about re-using the 4-cyl calipers, which I have.

Thus far have had trailing arms powdered, new bearings, etc, and have 5-lug hubs (non converted ones).

Definitely want the parking brake feature.

Don't think I need the full-on 911-type 'drum' parking brakes.

If I can find reasonably priced 6 calipers, I'll do that. If I can't, I can use the 4 calipers with trimmed rotors.

Also doing full-911 front conversion, new lines and hoses, and 19mm M/C. 155 h.p 2.2E motor, no track use.

Thanks for all the tips.

Hope to start a build thread after making fender flare decision.

What are 5-lug hubs (non converted ones) ?
It's hard to find 6 calipers for anything under $1K. Not they aren't worth spending the money on.

[bossboy302]

Ohhh....I probably got the nomenclature wrong, I mean the splined flange that the wheel bolts to.

[mepstein]

Ohhh....I probably got the nomenclature wrong, I mean the splined flange that the wheel bolts to.

You can re-drill a 914-4 hub for the 5 lug pattern but unfortunately a 914-6 or 911 part won’t just bolt on.

[bossboy302]

Hoping these would work...

https://www.pelicanparts.com/More_Info/UR91...ASABEgKWuPD_BwE

[mepstein]

Hoping these would work...

https://www.pelicanparts.com/More_Info/UR91...ASABEgKWuPD_BwE

They should. I didn’t realize that conversion part was being made but looks great. If you are using 914-4 calipers, it’s easy to buy solid 911 rear rotors at flaps and have your local mechanic turn them down. I bought my mechanic lunch in exchange for the service. Took him 5 minutes. Cheaper than buying 914-4 rotors and having them drilled.

[bossboy302]

IIIII...like it!

That is my hope. I thought better than drilling new holes in the 4-cyl stuff.


My local tech prefers Peroni...

[mgphoto]

Collecting the bits for my project, (4 to 6) rear brake question...
Are the rear 4 rotors the same thickness as 6?
If so, can the 4 rear calipers (with their parking brake) be used?
I am doing the 5-lug.

Thanks in advance

You want to make sure that the holes to locate the brake disk and hub line up, if not the disk can cause an out of balance situation.

[mepstein]

Collecting the bits for my project, (4 to 6) rear brake question...
Are the rear 4 rotors the same thickness as 6?
If so, can the 4 rear calipers (with their parking brake) be used?
I am doing the 5-lug.

Thanks in advance

You want to make sure that the holes to locate the brake disk and hub line up, if not the disk can cause an out of balance situation.

I don’t believe that’s true. The two holes hold the rotor to the hub but have nothing to do with balance. If you don’t bolt the rotor to the hub, bolting the wheel on will keep the rotor in place.

[mgphoto]

Collecting the bits for my project, (4 to 6) rear brake question...
Are the rear 4 rotors the same thickness as 6?
If so, can the 4 rear calipers (with their parking brake) be used?
I am doing the 5-lug.

Thanks in advance

You want to make sure that the holes to locate the brake disk and hub line up, if not the disk can cause an out of balance situation.

I don’t believe that’s true. The two holes hold the rotor to the hub but have nothing to do with balance. If you don’t bolt the rotor to the hub, bolting the wheel on will keep the rotor in place.

The screws center the disk to the hub, several mm play between the lugs and the disk.

[technicalninja]

Those flanges allow the 914/6 rear rotors to use both of the rotor retention screws.
I just bought a pair of flanges (rock auto as everyone else was out of stock) and a pair of rear 914/6 rotors from PMB and I was worried they would not fit.
They fit perfectly!

I'm guessing the 911/912 solid rotors are the same as the 914/6 rotors as I will have to have these shaved down on the OD to fit the 914-4 rear calipers.

[mepstein]

Collecting the bits for my project, (4 to 6) rear brake question...
Are the rear 4 rotors the same thickness as 6?
If so, can the 4 rear calipers (with their parking brake) be used?
I am doing the 5-lug.

Thanks in advance

You want to make sure that the holes to locate the brake disk and hub line up, if not the disk can cause an out of balance situation.

I don’t believe that’s true. The two holes hold the rotor to the hub but have nothing to do with balance. If you don’t bolt the rotor to the hub, bolting the wheel on will keep the rotor in place.

The screws center the disk to the hub, several mm play between the lugs and the disk.

But the wheel is lug centric. It’s going to make a bigger difference than the rotor.

[technicalninja]

Not having one of the screws installed doesn't throw the balance off that bad but what is does do is it turns the rotor in a non-concentric path which can cause weird ass brake judder. It doesn't take much offset to create serious judder.

This is far more noticeable on something like a Honda (front rotors) which uses these little bolts everywhere. Most late model rotors are hub centric anyway but the ones that aren't judder like a bitch if both centering screws are not present.

The Honda centering bolts are direct copies of the Porsche bolts and can be used if real Porsche hardware is not available.

[Chris914n6]

Rear rotor centers from the backside on the outer edge of the hub. There is a bit of rotational play but once the wheel is torqued down nothing moves. Not an issue.

The -6 vs -4 rotor diameter is 3mm diameter, or 1.5mm radius. Someone anal made the claim that it needs machined and it's been parroted since. Plenty of clearance on the -4 caliper for a -6 rotor.

-6 rotor securing bolts (available at Lowes etc) don't line up with -4 hubs.