Sorry to bother you people (guys like me should not be allowed to be caretakers of these cars).

Picked-up the car that my uncle bought in 1990. He had raced it gently in the 90's and early 2000's. Mostly with POC in CA at Willow Springs and Laguna Sega etc...

Now it's with me in TX. In order to get it registered it needs to pass a simple safety inspection. But it's not going to pass without parking brakes.

To make the car quicker my uncle modified the rear brakes to allow vented disks, with 911 calipers. His notes read "911 vented rotors with specially adapted steel 911 Calipers". This is on the car now. Hence; no parking brakes.

In 2010 PMB had rebuilt the original 914-6 Calipers, and widened them to allow the use of handbrakes with vented rotors. These Calipers were never used and are looking shiny and new (we all know what PMB rebuilds look like (just awesome)). So I'm installing these now...... At least that was the plan.

I find that there is not enough space between the mounting bracket and suspension arm.
Hopefully the pictures make it clear that the 914-6 brakes protrude about 1.5" more to the inside compared to the 911 calipers (where the handbrake arm is located). That part is clashing with the suspension arm.

Could any of you recognize which part is wrong here?
Additionally... any suggestion how to resolve this (I prefer to keep vented rotors)?

PS: I have been told me that the rotor diameter is also too large. But that can be turned down a little.Click to view attachmentClick to view attachment

key word modified...

Are you sure you tried mounting the calipers to the correct side of the mounting ears? ... there should be plenty of clearance

That's what I thought.
Matt

So, you want to use the 914/6 GT calipers (modified 914/6 with spacers). These are designed to fit the stock trailing arms on a 914 or 914/6. You do need to use that (pictured) brake shield bracket between the caliper ears and the trailing arm. That sets the correct centering of the rotor within the caliper. It also pushes the caliper out a bit from the trailing arm. Yes it is a bit of a tight fit, but there is no way it should not easily fit unless the trailing arms have been modified in some strange way.

A 914-6 caliper is the same overall length as a 914-4 (or really close). Only the body is bigger to accommodate larger pistons. Make sure the caliper orientation is correct. They use 20mm vented rotors (M caliper size) and shouldn’t require any turning.

Take a pic of the 914-6 calipers on the trailing arm or at least how you are trying to attach them and we should be able to diagnose the problem quickly.

I don't know if this helps but my PMB V-calipers, stock /4 rear calipers with spacers and 911 vented rotors, needed 4mm removed from the OD of the 911 rotor and it needed thick washers (approx 2-3mm) between the arm and the caliper, plus slightly longer bolts.

I placed the pads on tight enough so that the caliper hung on the rotor and then I measured the gap for the thick washers.
IIRC the pads were tight and I sanded them a bit to make them fit, but this may have been the Alfa fronts.

Mark - good to see you back on the site.

That exactly how the 911 calipers are mounted (bracket and washers sandwiched in between).
I will remove a rotor, to see if that makes the difference.

See: http://www.914world.com/bbs2/index.php?sho...rotors&st=0

Find a local teener. Most inspections are just oil change places. I pull in and they go to the computer and input the vin and it passed safety inspection. (which is a joke anyway).

Here you go:
AUSTIN (Nexstar) — Texas drivers will save a trip to the auto shop after lawmakers voted to eliminate the annual vehicle inspection requirement for most vehicles this legislative session but a couple years away.

Texas Gov. Greg Abbott signed the bill into law Tuesday, June 13.

In 2025, those inspections will be replaced by an annual $7.50 fee — the same as the current inspection fee, but without the need to actually take your vehicle into the shop. Drivers in new vehicles that have not previously been registered will pay $16.75 upon registration. That money will benefit the Texas mobility fund, the clean air fund and the state’s general revenue.

Good info.
That’s nice to know.

As is normally the case, you people are correct. The calipers did fit after removing the rotors. Just barely with bracket but without the extra washers. I suspect that the diameter of the rotors need to be turned down a bit.
Diameter at the moment is 289mm.

I read on other threats that it should be 280mm.
Does this 280mm diameter sound about right?
Click to view attachment

914-4 rear rotor

Diameter: 283mm
Thickness: 9.4mm


914-6 rear rotor

Diameter: 286mm
Thickness: 10.4mm

The 911 rear vented rotor (I assume you are using) is 290mm diameter.
The 914/6 GT rear vented rotor (you are mimicking) is 286mm diameter.
With 914/6 GT rear calipers you have to trim 4mm; 2mm radius cut.
With 914/4 spaced rear calipers you have to trim 6mm; 3mm radius cut. Some 914/4 rear calipers will accept the 914/6 rear rotors but you need to be prepared to trim them to fit. Ideally you want the outer edge of the pads to meet with the outer edge of the rotor. If the rotor is too large then the pads will leave a ridge on the outer edge of the rotor which can cause problems.
When trimming rotors be careful not to damage the balance weights, if present, on the internal vanes. These look like heavy wire pinched on a vane.

911 Rear rotors at 285mm should work with that caliper "with" spacers in the caliper 1/2 (which is what we're seeing in the picture). Because there is no longer a 914-6/GT offset rotor offered from the factory, you will need to space the caliper back by 4.5mm (5mm with the dust shield mount included in your pics). This can cause interference with the control arm. The inner adjuster tube needs to be ground level to the welds to make room for this install.

@HansJan

Sounds like you've already got it figured out.

I had trouble with the rock shield bracket and had to extend it to mount on the opposite side of the caliper.

Also had a spacer to go under the rotor to get the correct clearance.

Here's some pictures.

Spoke's Widened 914 Rear Calipers

[quote name='Spoke' date='Sep 18 2023, 02:19 PM' post='3102562']
@HansJan

Sounds like you've already got it figured out.



Indeed, I have it working at the moment. The 911 rear rotors edges were not turned, but they fit. Just barely though. However, the rotors were faced-off too thin (16.5mm).

Eric (PMB) is sending new Rotors that are going to fit this car. Even though I hate to open the fluid lines again, the install of new rotors will also provide an opportunity to replace the racing pads for street pads, and the protective bellows at the end of the parking brake cables.

While this threat is coming to an end I need to roll the credits:
Uncle Martin (who built this car): What he has done to the suspension of this car is amazing. Simply an Engineering marvel.

Chris (Tangerine): His shifting solutions transformed this car. It removed all guessing from gear selection. I was told to replace the synchro of 1st gear. But that's no longer the case (car is no longer complaining about 1st gear selection before coming to a complete stop (very useful for Californian stops:)).

PMB/914Rubber/AA/Restoration Design/all other suppliers that keep us going: Please keep it up.

914world.com: The damage I would have done to this (and the previous) 914 without you guys....!?