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Posted by: zoomCat Jan 16 2022, 12:48 PM

I'm putting together a pair of rear calipers for a six, which the previous owner had replaced with 911 rears to get the vented disks. He didn't keep the originals, it was back in the 80's and nobody cared.
Here's what I've got so far:



On the left is a rebuilt stock 914/6 left rear. The plan is to add a spacer for vented disks.
In the middle is a 914/6 right rear, which I got years ago that already has a spacer. It will be rebuilt.
On the right is what I think is a right rear Ferrari 308 caliper, because the bleeder is in the wrong place. It can be a donor if absolutely needed. The rears the previous owner had installed are the first candidate for donors.

My question today is about the RIBE hardware.



On the left is the rebuilt stock, on the right is /6 caliper that had a spacer added. The fasteners on the left have sloped shoulders, while the other has more square shoulders, which I see on the front A and M calipers I've got.

What was original, either for the stock calipers or the GT calipers?
Is there any functional difference? Esthetically I'd like to get it all matching and correct before I send it all off to PMB, but that depends on availability.

Posted by: BillJ Jan 16 2022, 01:23 PM

Waiting on all 4 of my -6 calipers to arrive from PMB in a couple.days myself. You should ask Eric he will know right away. His expertise on the hardware for these is outstanding.

Posted by: gandalf_025 Jan 16 2022, 01:23 PM

This is a factory 6 rear that was rebuilt by PMB
and as far as I know they reused the original
hardware..

Posted by: gandalf_025 Jan 16 2022, 01:28 PM

This is a 914-6 gt rear caliper
rebuilt by PMB also. They supplied
the hardware for these.

Posted by: gandalf_025 Jan 16 2022, 01:50 PM

Then again, you could always make your own
hardware and spacers …. These worked well for
quite some time..

Posted by: 914Sixer Jan 16 2022, 03:34 PM

You normally used the hardware that came out of the donor
911 caliper to install spacers

Posted by: mepstein Jan 16 2022, 04:04 PM

I sent PMB some 914-6 calipers and rear M calipers and they sent me back 914-6GT calipers.
The non vented M calipers can be used on the back of a 912.

Posted by: BillJ Jan 16 2022, 07:47 PM

If you want to send those over to me since it was an error that would be fine

Posted by: Eric_Shea Jan 16 2022, 09:08 PM

Factory 914 six calipers had no spacers and used the “button” head M7x50 and 55 Ribe fasteners. (Caliper on the left)

Factory 914-6/GT “prototype” calipers used both the spacers and the fasteners from the new long wheelbase 911 S with vented rotors on the rear. Those fasteners were M7x60 and 65 “cap” head Ribe. (Caliper in the middle) This early spacer was machined not cast and they have rounded edges with machining marks on them. Remember, this was all new for ATE. Everything was solid rotors up to this point. They didn’t have a 60 or 65mm fastener on all previous calipers. These one off (41 off) prototypes used the 911 stuff all around. These cap head fasteners do not look like A-Caliper fasteners. They look like M7 versions of “M-Caliper” fasteners. M-Calipers used a “cap” head M8 fastener. A-Caliper fasteners are actually M9 versions of our 914-6 M7 button head fastener. M7 fasteners have Ribe R5 bit heads. A-Calipers, again, use an M9 version of our “button” head with a Ribe R6 bit head. Probably one of the more delicate fasteners to get apart because of the smaller bit head and larger M9x1 thread engagement. In contrast, the M8 M-Caliper fasteners use the M8 cap head with a much more robust Ribe R8 bit head. Much easier to remove without damaging.

The last caliper is a Ferrari 308 caliper. (Bleeder positioned under the handbrake arm). (Caliper on the right) These came from the factory with spacers installed. These would be a cast, more form fit spacer as identified by the casting line running around the spacers. By this time ATE spec’d the proper M7 x60 and 65 button head Ribe fasteners to use on these calipers as this was a production unit.

Hope that helps.

Posted by: Eric_Shea Jan 16 2022, 09:12 PM

And the 69 solid rotor 911’s and a 76 912E.

Posted by: Eric_Shea Jan 16 2022, 09:19 PM

This is a perfect example of a factory 6 caliper with the M7 button (crowned) head fasteners.

Posted by: Eric_Shea Jan 16 2022, 09:21 PM

This is a perfect example of a factory GT caliper. Low casting number. Shouldered “cap” head vintage 911 fasteners were used. If you know what you’re looking for you can see the rounded edges on the spacers as they come to the pad cavity.

Posted by: Eric_Shea Jan 16 2022, 09:23 PM

This is a perfect example of what “NOT” to do

If I recall, we fixed this. (If I’m not wrong, they’re probably now the correct GT calipers pictured above in post #12)

Wrong size spacers and wrong size aftermarket fasteners that had no strength and no right to be on a brake caliper.

Posted by: Eric_Shea Jan 16 2022, 09:34 PM

Perfect example of early 911 rounded spacers vs later Ferrari form fit spacers.

Posted by: PatMc Jan 17 2022, 08:09 AM

Might not be anything wrong with the fasteners (aside from the fact that they're too long and look like hell).

170,000psi fasteners are readily available in 1/4-28 thread. A 1/4-28 bolt of this spec will have a tensile strength of 8,340 lbs. We have 4 of those bolts in the caliper...so 16,500 lbs or so combined.

With a 38mm piston at 1200psi, caliper is trying to spread (or clamp) with a 2,100lbs of force.

Looking at the OEM M7 fasteners, 12.9 strength...they should also be 170,000psi. But the unthreaded shank is necked down smaller than the threads, and only about .020" larger in diameter than the shank of a properly made high grade 1/4-28 bolt.

Ate also used the same M7 fastener (differenent lengths) in the 42mm 84-89 911 rear, which at the same 1,200 psi would exert almost 2,600lbs of force.

Based on these figures, I'd say a 170,000psi 1/4" fastener would be more than suitable to hold a caliper together properly with 33 or 38mm pistons, and 42mm pistons too.

Posted by: BillJ Jan 17 2022, 08:14 AM

I told you Eric would know. Just chuckling in amazement at the depth of knowledge and understanding. Good stuff.

Posted by: gandalf_025 Jan 17 2022, 09:37 AM

You recall correctly Eric..
I bought these a few years ago at the Hershey Swap Meet
just as shown, they were sitting in a box with other calipers..
They were sent to you immediately and made
into the set above..


[/quote]

This is a perfect example of what “NOT” to do

If I recall, we fixed this. (If I’m not wrong, they’re probably now the correct GT calipers pictured above in post #12)

Wrong size spacers and wrong size aftermarket fasteners that had no strength and no right to be on a brake caliper.
[/quote]

Posted by: Superhawk996 Jan 17 2022, 11:47 AM

Setting aside the question of fastener tensile strength and suitability for application.

If they didn't have the tools and/or couldn't be bothered to trim the fasteners to the proper length, I have to wonder what else they couldn't be bothered to do properly when working on brakes.

I would never trust my life to workmanship like that.

Posted by: Eric_Shea Jan 17 2022, 09:51 PM

Those were a hot mess. Duly noted though that Home Depot fasteners are OK to use on brake calipers.

Posted by: zoomCat Jan 18 2022, 04:59 PM

Thanks for all the feedback, Eric in particular for the encyclopedic knowledge of the particulars. It looks like the 60 and 65mm button head fasteners on the Ferrari were never used on the 914/6 GTs, so I don't need to chase down a set of those.
I wouldn't hold up the build for that non-functional distinction, but it's amazing how you can become invested in some of the smallest details when you disassemble a car to every nut and bolt.
Now I just have to get the very rusty bleeders out of my donor M calipers. I suspect that the piston bores are not salvageable anyway.

Posted by: zoomCat Jan 18 2022, 06:39 PM

And for those who might be intested in what a dead inner adjuster looks like:



The adjuster on the left is now a very small paper weight, because it's too small to be a boat anchor. The other looks pretty good, at least to me, even though it does show signs of wear.

Posted by: PatMc Jan 19 2022, 08:50 AM

Grab a torch (even a propane plumbing torch is fine) and get the bleeders to glow a bit...as soon as the color goes away, give it a try. 95% of the time they come out...the other 5% they break.

As for bores, keep in mind, the bore is not the sealing surface....the piston is. In thousands of calipers I've rebuilt, I can count on one hand the amount where the bore was not serviceable after a good blasting.

Posted by: Superhawk996 Jan 19 2022, 09:18 AM

Just to be clear, I was not lobbying that these fasteners were OK to use.

Not just a question of tensile strength. Due to the nature of the caliper geometry, the fasteners are exposed to bending loads which is something you don't want but can't be avoided in this application.

Knowing that there are bending loads involved, surely don't want a full threaded shank in there where bending loads are imparted on the root of the threads that can act like a stress riser. Would also want a rolled thread vs. something with a cut thread form. Rolled threads being less of a stress riser . . . to a degree.

Likewise, don't buy your highly stressed SHCS fasteners at Home Depot. If it's critical enough to warrant a grade 12.9 fastener, I'm not getting it at Home Depot. I'll also add there are fastener grades above 12.9 and I honestly don't know what the Ribe fasteners are but assuming they are AT LEAST 12.9 but may be even higher.

For those that are interested Eric has a wonderful website on caliper rebuilds complete with a picture of the proper Ribe fasteners.

https://www.pmbperformance.com/brakehowto.html

Posted by: Robarabian Jan 19 2022, 10:27 AM

This was an educational thread. Can anyone remind those of us still learning the nuances of 914-6, how you tell the caliper difference between a 4 and 6 rear caliper by looking at it?

I figured out from this thread, the Ribe heads may be a tell, but any other way to tell at the SWAP meet?

Posted by: Superhawk996 Jan 19 2022, 11:59 AM

Piston diameter is 38mm for /6 and 33mm for /4 will be the easy giveaway.

Posted by: gandalf_025 Jan 19 2022, 12:24 PM

Bigger pistons, takes larger brake pads
and generally costs a lot more....

I'm sure there are threads here that
describe the appearance differences
in detail..

Posted by: Eric_Shea Jan 19 2022, 12:24 PM

Oh I know you weren't...

I should expound. Sites like this have an "amazing"... literally "astonishing" amount of information. The only problem is, it's the end-users job to sift through the mounds of rubble to find the gold. I can't think of "any" thread I've seen @http://www.914world.com/bbs2/index.php?showuser=22428 weigh in on where his advice is anything but solid gold.

12.9 for the Ribe and Verbus fasteners used on our cars.

Posted by: PatMc Jan 19 2022, 04:23 PM

Agreed.

I've always assumed they were 12.9 strength simply due to the fact that the later calipers using hex bolts are 12.9...and I'm pretty sure the non-button heat Ribe screws are marked 12.9 (at least some of them)...and they're the same size and everything else. The only thing that changes is the thread engagement (1x diameter rule doesn't apply in cast iron).