914 rear brake conversion to 911 type brakes.

[914Chap]

Hi,

Does anyone have any experience or knowledge of converting 914 rear brakes to 911 rear brakes? I am having a problem getting the disk offset to match that of the calipers. I am currently trying to use solid 911 rear disks along with 911 calipers without spacers. The calipers fit the mounting bracket as they are 3 inch spacing and the disks fit over the 914/6 hubs. Unfortunately, the caliper center line does not align with the disk center line, the caliper being offset approximately 6mm too far towards the center of the car. I could look to machine 6mm from the inside of the caliper mounting lugs to offset the caliper towards the disk, but would rather not if there is an alternative simpler or better solution.

Any suggestions or advice would be appreciated.

Cheers Jonathan.

[jwhillracer]

I was going to recommend PMB's "Vintage Brakes" Alloy 914/6 rear calipers that I have on my 914/6, but I've just looked up to find a link, and they're NLA!
A great pity, as with alloy "S" calipers on the front, and the PMB calipers on the back with 911 vented discs, my car stops as a 914 always should have!
Looks as though you will have to persevere and machine your calipers to fit..........

Another Jonathan

[KS]

I'm looking at developing a bolt-on four-pot caliper conversion for 914s with Chris at Carbon 12. Won't be any time soon, but I'll keep you posted...

[914Chap]

Thanks for the suggestions and input. I had spotted the PMB's 914/6 caliper option and it could have been a good way to go but at least the 911 brakes use the internal drum option for the handbrake. The original 914 calipers which I have rebuilt have driven me mad attempting to bleed them only to find the handbrake mechanism still has a very minor fluid leak, if there is such a thing on a brake caliper!!
I have only 1 option left to me other than machining the calipers, it would appear that some 914 front calipers have a different offset to others, but I am not sure if these have the 3 inch bolt spacing required or if they have the offset that I need. Hopefully someone out there may have the information I need on these calipers??
The offset I need, between the inside of the caliper mounting flange and the center line of the disk is 30mm.
In case anyone is interested in this modification I am planning on using the handbrake adapter cables from Tangerine racing which I have acquired, and hopefully this will give me a reliable and efficient handbrake.
I will update this on how it works out.
Cheers Jonathan.

[defianty]

Please keep us updated Jonathan. I'm running M calipers on the front of my GT conversion but am going to use the original 2.0L calipers on the rear. This will be sufficient but it's in the back of my mind that the next big upgrade down the line will be the brakes.

It's worth tapping into the knowledge over on 914World and I have heard the Eric Shea of PMB is very approachable, so it may be worth reaching out to him. I'd like to know the reason they're not doing the 914 GT calipers anymore seeing as there's a growing demand for them these days.

[rhd racer]

Hi Jonathan


I have run a few set ups, but you will have to bear with me as the 911 ones were all over 10 years ago....

1. Early 911 steel calipers - vented discs front and rear (pretty sure they were E calipers and discs). Required just 2 washers on each bolt to centralise over the disc

2. M calipers - 3.2 calipers front and rear, matched to 3.2 discs. Again, a 2 washer spacer per bolt

3. The Wilwood 4 pot conversion ran SC discs and bespoke spacers on the rear which
I made and are still on the car. This allowed me to get rid of the washers, and deal with a much wider bolt spacing than the 3" centres on the rear trailing arm. The Wilwoods required a narrower disc hence the move to the SC ones.

I must admit, I found it easy, as long as you match the caliper to the disc that they are designed to run with. It is more work to get the handbrake in.

Hope that helps
Wayne

[rhd racer]

Oh, I should mention that was with a full 5 lug conversion using early 911 stub axles etc. Not sure if that brought the offset closer, as not sure what you are running. Call me if you need to talk through.

Cheers

[914Chap]

Hi all,

Just an update on where I have got to on the 914 rear brake conversion. It would appear that as I am using original 5 stud 914/6 rear hubs I have ended up with the disc center line in a different position to those who have done this with 911 rear stub axles. For those who might consider the 5 stud conversion or the upgrade to 911 brakes, using 914/6 flanges and stub axles means I can use the standard drive shafts. This may or may not prove to be a good thing, time will tell. Others who have used the 911 parts will have resolved connecting the 911 stub axles to the 914 drive shafts some how? I will leave that to someone else to explain.

However, as a result when I have put the 911 discs on the center line of the disc is not where it ideally needs to be! Neither the caliper nor the internal drum line up correctly with the disk. However, I have managed to resolve this so far by machining a 6mm plate to fit between the radius arm and the back plate of the hand brake drum. This seems to have worked a treat, the drum is now aligned to the inside of the drum/disk.

Now I just need to align the 911 caliper with the disk. This requires 7mm to be machined from inside the mounting flanges of the calipers, which I hope to have done in the next week or so when there is room on the CNC miller!! I need to get the calipers halves split as we don't have a long enough cutting tool to reach past the whole caliper body. This shouldn't take too long on the scale of things.
I could have used spacers inside the disc rather than machine the calipers but this would have pushed the wheels further out which are already close to the standard arches, and would have also pushed the drum further away from the hand brake back plate creating further problems.

While I wait for the machining work on the calipers I still have to complete the installation of the modified cables and brackets for the hand brake which need to be welded to the underside of the radius arms. I also plan to weld the handbrake shoe stop to the drum back plate rather than welding them to the radius arm. Hopefully, I might get this all done in the next couple of weeks and will post a note on how it's worked out.

Thanks again for all the suggestions and advice above. Cheers all. Jonathan.

[rhd racer]

Good progress Jonathan. Yes, I welded the brake shoe stop / locators to the backing plate too.

On the 911 parts issue, I found an Audi CV joint which converted a 914 drive shaft spline to the 6 bolt SC output flange. For years I ran these on the outers, and then standard 914 CVs on the inners. I used Recoprop in Luton, who paired up what I needed in just a couple of days (PCD vs spline). Very helpful chaps.

As the car got more powerful as it was developed, the inners CVs became a weak point and I upgrades the outers CVs to the early 911 style with 2 bolts / 2 roll pin, and did the same at the gearbox end. I then had some longer driveshafts made to match the two - ie 911 early splines but the longer 911 length.

Luckily, at the time bits were plentiful and sensibly priced!

Good luck with it - I will hopefully come and see you sometime this summer.

Cheers
Wayne

[davep]

Are you using the 914/6 rear brake rotor or a 911 variant? The 914/6 version is the correct one to use unless you want vented rear rotors in which case you use the 914/6 GT rotor.
The brake shield support bracket or washers of an equivalent thickness are required to ensure the caliper is correctly located on the arm.
Probably the best calipers to use would be the 911 rear or maybe the early 914/4 front caliper; brake front & rear bias may need to be adjusted. These stand the best chance of an acceptable offset; late 914/4 calipers are probably a poor choice.

[914Chap]

Hi, I am using 911 solid rear disks as these have the machined inner surface for the 911 handbrake mechanism. I presume neither the 914/6 or the 914/6 GT disks have the inner handbrake surface? I did look to try to find out if the offset of the 914/4 caliper would work better with the 911 disk rather than the 911 caliper I have, but not managed to find out if they would work or not. I guess I may have to sort out the bias when I finally have a set of working brakes all round, as I just have a 'T' piece at the rear instead of the bias valve at the moment.

Cheers Jonathan.