Brake Performance

2170 Views 8 Replies 5 Participants Last post by Mark Cooper 916, Mar 31, 2015

ANW

Discussion Starter · Mar 22, 2015

Hello all,

New to the forum! I need some advice.

I have a 2000 gt veloce, 1972. With twin servo braking system.
I have just spent the last two weeks trying to sort out the braking system.

This has involved sorting several leaks, from poorly flared pipes and replacing a poor quality master cylinder.

However, I still feel as if the brakes aren't as good as they should be. During a test drive, when using the brakes firmly, the car will slow but not 'bite' ie I am unable to lock the wheels.

I have checked the temps of the disks just using my hands and the front ones are very hot, but rear seem only warm suggesting a problem there.

I am going to bleed the system again, just to check there is no air. Otherwise my only thoughts is the proportioning valve.

Has anyone any thoughts or had similar issues. I'd be very grateful for any help.

Cheers
Andy.

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dlbehrns

· #2 · Mar 22, 2015

kits

because the front rotors were really hot that tells me that the pistons are not retracting enough to release the pads from the rotor. I would do brake caliper kits. Pull one of the front calipers off and see if you can see any rust in or around the piston that pushes on the brake pad. When I pulled the oem calipers off my 72 after sitting for ?years they were so rusty I had to replace the calipers. what are the shape of the pads?
If it were me I would get caliper kits and see where that leaves you. If the braking isn't improved dramatically, replace the calipers.

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60sRacer

· #3 · Mar 25, 2015

Brakes from that era usually have a pressure limiting valve in the line to the rear. This device often gets cruded up. I installed a Tilton adjustable pressure limiting valve where this would normally go.

Robert

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ANW

Discussion Starter · #4 · Mar 25, 2015

The plot thickens but not the brake pressure

Thank you to the 2 previous posts, very glad to have experienced guidance on this one. I think this car is going to be the start of a long learning process for me!

I have been trouble shooting the system for about 2 weeks (on and off).

I found another leak! Poorly flared pipes to the brass t piece. Pipes now replaced although t piece has brass burr remaining on inside so I have had to replace that also. As nobody seems to stock them anymore I had to get my local motor factors to provide a 4 way Union 3/8 24tpi and then source a different hydraulic brake light switch (parallel thread). We ploughed through catalouges to source one. (I believe fitted to a hilman imp! Amongst other classics).
A nod must also go to all the alfa companies in the UK with guidance at this point.

So no leaks, and I've checked the distance between pads and disks. I think I can rule out calipers 'springing back'. Rear proportioning valve recently replaced by PO (although poor flares and burrs could be in there also so I may end up going back to this)

I also had a look at the bb, and spotted a thread written back in 2006. Very good info there.
So i power bled the system again (off a car tyre) at around 15psi. Pedal getter better.
I think I am going to go to my local alfa garage and get a proper bleed undertaken. The way the system is designed suggests that any air would travel to a high point around the servos.

This leads me to another thought, if you bled the system at pressure, would this cause the rear proportioning valve to shut off preventing air from going to the rear calipers?

Sorry for the long post, gaining experience, will keep you updated!

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ANW

Discussion Starter · #5 · Mar 26, 2015

Further discoveries

Hello,

I have revisited what was posted. Decided to check the gap between the caliper pot and the pads. Loose is an understatement, they rattle around. Am I correct in understanding this is called caliper spring back?

The rear calipers are presently off the car for a look tomorrow.......

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lotuseleven

· #6 · Mar 26, 2015

another thing to check, this one happened to me. The vacuum line that goes to the brake booster on my car was kinked, and there was no vacuum getting to the booster. This was a single-booster stepnose, so might not apply for a later car.

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Mark Cooper 916

· #7 · Mar 27, 2015

If you are finding an excessive gap between the pads and rotors, check the rotors for warping. This can knock the pads and thus the pistons back into the calipers.

This is usually manifested by a pulsing pedal and a initial low pedal when applying the brakes. If you have none of these tell tales, I would suspect air in the system.

Check that the bleeder nipples are at the top of the calipers. It is not unknown for a PO to inadvertantly swap calipers left and right. This will put the bleeder nipples at the bottom of the calipers and you will never expell all of the air with them like this.

105 series brakes are usually pretty good. Persevere and you will win!

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ANW

Discussion Starter · #8 · Mar 30, 2015

Thank you for the encouragement, since I have the calipers off I may as well check to see if the disks are 'true'. The good thing is that I'm learning lots as I go!

Thanks must go to PMB_performance for the thread on restoring 105 callipers. I would have never considered using grease to extract the Pistons (a lot safer than compressed air).

The question now is, looking at the pictures, the inner bore of the cylinder is nice and smooth but the top section above the inner seal is pitted. Does this matter? Will this cause problems with the piston moving in and out?

Thank you!

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Mark Cooper 916

· #9 · Mar 31, 2015

That pitting will have no bearing on the piston sealing. Just check that the outer surface of the pistons are clean and free from pitting. This is the sealing face.

The square section seal fits into the groove visible in your photo, and the piston slides on the ID of the seal. Check that the groove inner faces are also pit free.

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Brake Performance

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