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Sat Aug 02, 2025 11:59 am

It would seem that my 1970 notch has the newer version front calipers and I'm having issues understanding what going on. They lock on and stay on until I crack the bleeders. Can someone tell me what the center pin in the piston bore does?

Sun Aug 03, 2025 6:52 am

Background.....the late type 3 uses the same rotor and caliper as the EARLY type 4 cars.

Putting aside the differences in pad thickness and caliper offset/spacing from early to late.....the biggest VISUAL difference is that early rotors do not have what is called a "hub-centric" cuff cast into the center of the rotor.

Here is the late rotor (not yours). Notice the ring around the center on the wheel side of the rotor.

https://www.autohausaz.com/pn/13660884-411407075B?...20QAvD_BwE

Now look at this one. This is the one you have.

https://www.autohausaz.com/pn/12872314-411407075?u...9EQAvD_BwE

The earlier rotors....yours....with NO "hub-centric" ring....were also thinner. Without the ring they also flexed more.

So, on hard cornering or high speed sweeper curves....the earlier rotor....yours....flexes and an sometimes squeel, but has a habit of cocking the pistons slightly in the bores. Over time it can cause leakage and wear.

The pins and the little clutch in the back of the piston is designed to keep the pistons straight in the bore. Ray

Sun Aug 03, 2025 8:25 am

The soft lines to the front calipers are probably collapsing. If they’re over 10 years old they should be replaced. They swell from the inside and act like a one way valve. Which is your problem.

Sun Aug 03, 2025 10:39 am

So....to fix my issue, I replace the rotors, hoses, calipers....

Is there any standard measurements for the caliper bore ?

I'm kinda curious to see how worn the bores actually are...

Sun Aug 03, 2025 1:42 pm

Dfasty wrote: The soft lines to the front calipers are probably collapsing. If they’re over 10 years old they should be replaced. They swell from the inside and act like a one way valve. Which is your problem.

Yes, I dealt with that back in the early 90's when the internet wasn't around. My 70 Fastback had new rotors (with the hub centric ring that Ray says shouldn't be there on the 66-early 71 rotors), and new calipers. I replaced the master cylinder first thinking there was something in it that causing a problem (according to Bentley), then I replaced the hoses which had internally collapsed. Since then, whenever I do a brake job on a type 3, I replace the hoses right after having the calipers rebuilt or replaced (done at the same time, since I have the system open). Replacing the hoses allows the fluid to flow BOTH ways in the system.

OP, your first clue about opening the bleeders is telling you the hoses are bad. They aren't flowing fluid back to the master cylinder. Also, your brake pistons should be 42mm in diameter (Ghia calipers are 40mm, and are commonly sold as type 3 replacements). These don't really wear over time, but the seals can wear. Just something to think about. As for the pin, it was to help keep the piston from cocking in the bore when the car was in a turn, putting a load on the rotor (flexing). As time went on, that pin got eliminated.
I hope this helps.

Wed Aug 06, 2025 8:32 pm

Well.......I got some new hoses today. I put in some new quasi seals in the calipers, cleaned everything up, put a buff on my pistons and installed some new dust boots. After a quick bleeding session I now have brakes that work both on and off. No drag at all.

Thank you guys for helping me with the information.

Much appreciated

Fri Aug 08, 2025 5:37 am

GODOG wrote: Well.......I got some new hoses today. I put in some new quasi seals in the calipers, cleaned everything up, put a buff on my pistons and installed some new dust boots. After a quick bleeding session I now have brakes that work both on and off. No drag at all.

Thank you guys for helping me with the information.

Much appreciated

What are "Quasi" seals?

Ray

Fri Aug 08, 2025 11:23 am

Quasi seals is a loose term used in hydraulics for the square cross section o rings used in a "one direction" rod seal.

Fri Aug 08, 2025 12:46 pm

GODOG wrote: Quasi seals is a loose term used in hydraulics for the square cross section o rings used in a "one direction" rod seal.

Ah....I think you mean "quad seal", also called an "X" ring.

The square profile o-rings in the caliper are usually called square profile or "lathe-cut" rings. Many o-ring manufacturers recommend that whenever possible, replace square profile rings with quad-rings/q-rings/X-rings as they are more aggressive at sealing than a square profile.

Ray