Nasty sticking brake habit - Alfa Romeo Bulletin Board & Forums
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post #1 of 30 (permalink) Old 12-05-2017, 06:13 AM Thread Starter
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Nasty sticking brake habit

I have a 1969 1750 GT which has been built-up as a race-car . The brakes have been left pretty much as standard. Twin brake fluid reservoir, feeding clutch and brake master cylinder . No servo . Under floor mounted brake master cylinder , operated by long rod to brake pedal pivot.

The car has been stored for 2-3 years only covered around 200 miles in that period , having previously raced in the uk.

The car drives fine , but occasionally the brakes seize on . The last time was fairly scary , I was driving up a long winding hill in the dark , when the brakes began to bind and the car loses power . The harder I try to accelerate the more the brakes bind until we come to a dead stop . On a hill , in the dark , with tiny rear lights anything could have come round the bend behind me and failed to stop.

The brake pedal is now solid like pushing on a stone , eventually a hard stamp frees everything off and away we go . After cresting the hill , the car free wheels easily down hill and no amount of soft or hard braking can replicate the problem.

After the stop both front brakes were smoking and when I got home both front wheels were at high temperature. So suggests not one brake binding but both.

Any ideas as I have to drive the car 80 miles home Tomorrow and the plan is not to use the brakes!

thanks

Ian
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post #2 of 30 (permalink) Old 12-05-2017, 07:14 AM
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I had a somewhat similar problem with my '76 Spider autocross car after installing a new brake booster. When hot, the brakes would slightly drag, the pedal was very firm, and brakes/pads/etc. would get very hot during track laps. When cold, everything was free, but a short drive on the street with light braking would cause the drag to reappear. Even though brake booster and master cylinder are supposed to be "Plug-and-play" installation with no adjustment on a hanging pedal 105 chassis, my assumption was that some tolerances stacked up and a bleed hole (or whatever) in the master cylinder was being obscured and holding pressure when the brake pedal was released. I temporally inserted .020 in. shims between the brake master cylinder and booster and the hot brake "dragging" stopped. The final solution was installing a new master cylinder and everything then worked correctly.

I posted a query about this issue a year or so back, and Jim Neil "Papajam" responded that he had heard of a rare similar condition on early transaxle chassis Alfas.


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George Schweikle

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post #3 of 30 (permalink) Old 12-05-2017, 08:17 AM
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I had a similar problem with my 74 GTV. I can't recall if the pedal was hard but the brakes did stick in the closed position. This would cause me to stop and let them cool. When they had cooled, the pads would retract and I could drive without any problems. Until you discover the problem, use the brakes gently. First, I would recommend that you change your brake hoses unless they are really new. This solved the problem for me. Secondly, to determine if your brake booster is bad, remove it and check for brake fluid in the booster. If that is the case, rebuild the brake master cylinder and replace the booster.
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post #4 of 30 (permalink) Old 12-05-2017, 08:57 AM Thread Starter
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Thanks for your replies - there is no servo/booster fitted so that's easy to rule out . I will look to change the brake hoses but as both front brakes lock together , I will be looking to free up the master cylinder tonight
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post #5 of 30 (permalink) Old 12-05-2017, 01:55 PM
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Two possibilities I have experienced come to mind:

1. On an LHD car the exhaust must run close to the M/CYL, yes?
To me, it sounds maybe like that when things heat up and expand, the clearance between your pushrod and M/CYL piston disappears and some pressure is applied/retained.
I had this problem under the bonnet, with a servoed car, but the same principle applies - insufficient clearance. Even a brake shop missed that diagnosis.
Have you (or anybody) fiddled with clearances? Can you feel some slop when the brakes are off? What about when they get hot, does that slop disappear? Your under-floor pushrod is adjustable.

2. I installed my own re-bored under-floor M/CYL. After a while, the brakes began to not fully release, and it slowly become worse. Examination showed that the very outer end of the M/CYL bore had surface rusted, and the piston wouldn't return fully home, keeping some brake pressure on. A quick hone and application of some rubber grease took the problem away.

Last edited by Ranz; 12-05-2017 at 10:45 PM.
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post #6 of 30 (permalink) Old 12-05-2017, 03:53 PM
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I had the exact same problem on my 1969 1750.

Brake master cylinder pushrod was sticking.

Just replaced the MC and problem fixed.

Cheers,
Wazza.

"horsepower sells cars - torque wins races".
1969 MK1 1750 GTV
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post #7 of 30 (permalink) Old 12-05-2017, 08:12 PM
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Had the same problem on my '69 GT Junior RHD with standing pedals, also brought to a halt at the side of the road. The 1300 won't pull you along with sticking brakes......

Turned out to be rust in the master cylinder, I pumped 2 bottles of fluid through the system bleeding at the front wheels and the fluid came out spotless, but I wasn't convinced, so pulled the M/C - was full of syrupy rust, the new fluid had just made a path through the gunge. Stainless steel sleeve in the M/C and all was good again. The master cylinder is the lowest point in the system on the standing pedal cars and everything gathers in there, especially moisture.

The front brake hoses can also be culprits, but not both together at the same time, still it won't hurt to change them out either if they are a few years old. I've also switched my cars to Bel Ray DOT 5 silicone fluid and am very happy with the results.

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post #8 of 30 (permalink) Old 12-05-2017, 10:59 PM
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Alfasti - DOT 5 Silicone fluid can be dangerous in these cars with rubber m/CYL seals. Check out 60sRacer's post in another thread just today:

"It's not just the hoses. The really important parts are the seals in the MC and the caliper pistons, and in the boosters if you have them. I once put a silicon fluid in a completely refurbished brake system. In just three days the seals had hardened and were useless. I found out when I tried to back out of the garage and crashed thru the boxwood hedges, with no brakes at all. All the seals on an Alfa are rubber, and not at all compatible with silicon brake fluid.

"However, its my understanding that DOT 5.1 fluids are compatible with "all brake components", whereas DOT 5 fluids are labeled as "containing silicon and NOT compatible with some brake materials." In addition, I think most new brake component seals, including OH elements for Alfas, are compatible with all brake fluids now.

"You need to read the small print on the labels very carefully. At least in the US, they must be properly labeled. AFAIK, there have been several serious accidents that resulted from this problem.

Robert"

Take care.
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post #9 of 30 (permalink) Old 12-05-2017, 11:53 PM Thread Starter
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OK that covers it then thankyou for your answers . New brake master cylinder with stainless steel sleeve will be fitted.

The symptoms appeared after three months of inactivity , so I guess rust and gunk is causing the brake master cylinder to stick.

I will change the brake hoses at the same time.

I spend last night getting a little grease into the outside of the cylinder bore and around the piston seal to hopefully ease things a little

rgds

Ian
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post #10 of 30 (permalink) Old 12-06-2017, 12:06 AM
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Ahh yes, I should have mentioned that I switched my cars over to silicone DOT 5 fluid after a total rebuild of each of their respective the braking systems, so no trace of the old fluid remained. I'm meticulous in cleaning everything in Methylated spirits before assembly, so no trace of any other material remains in the system. I leave the new seals and washers in silicone fluid for a few days prior to the rebuild to see if anything alters their appearance or density / texture. So far no issues with brake washers either made in the UK or Spain.

I flushed the hard lines on some cars and replaced them on others. Thus far no problems and that was more than 20 years ago for the first of the Giulietta's, currently running 4 of them on silicone, all new projects are automatically rebuilt with silicone fluid - I get USA made Bel Ray DOT 5 from my local motorcycle shop. Never had a problem with it, but that is my experience, others may differ.

Dad's 1930 Triumph Super 7 Tourer with original hydraulic brakes was converted to silicone in the '80's using the original Lockheed Master cylinder & aluminium wheel cylinders and hard lines but new flexibles. ran trouble free for years. I converted the '68 Nissan Silvia to DOT 5 silicone nearly 10 years ago, also trouble free. My experience with Bel Ray DOT 5 is a positive one.

As an aside, an experiment by Mercedes Benz South Africa proved that 0.04% of mineral oil contamination in brake fluid can render all the washers and rubbers useless - assembly is best done with very clean hands and surgical gloves which I rinse in spirits regularly during assembly and change often if I touch any suspension parts where there are grease points.

Ciao
Greig
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post #11 of 30 (permalink) Old 12-12-2017, 09:55 AM Thread Starter
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Made it home , only one brakes on up a hill in 80 miles . Winter brake rebuild now planned.
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post #12 of 30 (permalink) Old 05-18-2018, 03:38 PM Thread Starter
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Still nasty sticking brakes

Well that didn't work then . I had the brake master cylinder rebuilt new stainless steel sleeves . A couple of set backs with leaks from the banjo seals but finally got the car going today all refitted.

Ran great . steady 70 mph on an open dual carriageway then it starts again brakes come in ,lock up and we grind to a hault. Next theory is a brake caliper dragging and overheating then cooking/expanding the brake fluid.

Any ideas ? I am planning to strip the calipers and rebuild them
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post #13 of 30 (permalink) Old 05-18-2018, 06:26 PM
I would recommend getting rebuilt calipers from Rock Auto. They're cheaper than the rebuild kits and even include the pins and retainer springs.

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post #14 of 30 (permalink) Old 05-19-2018, 08:32 AM
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I had heard of Rock Auto and originally thought they were some cheap operation with correspondingly questionable products. However, I just bought two rebuilt rear calipers and am very pleased. They had the correct angular orientation of the pistons and some form of protective coating on the castings. I assume they can offer their bargain prices because they have, or have access to, a large brake caliper rebuilding operation.

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Originally Posted by gprocket View Post
I would recommend getting rebuilt calipers from Rock Auto. They're cheaper than the rebuild kits and even include the pins and retainer springs.


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George Schweikle

1976 Spider (Dedicated Autocrosser, "SPICA, No Carbs")
1991 Spider Veloce (Retirement cruiser)
Scuderia Non Originale
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post #15 of 30 (permalink) Old 05-19-2018, 11:56 AM
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Can't see this being a caliper. Used to happen to my 1750 but that was due to boosters, but apparently in this case they have been removed.

Has to be something retaining pressure in the system. I assume the hoses were actually replaced when the master cylinder was rebuilt ... I guess the only thing left in the system is the calipers, but the fact that both fronts are hot surely indicates pressure in the system and not a caliper issue, ie. unlikely that both front calipers would seize at the same time.

Why not remove one pad at a time, and with a large screw driver inserted in place of the removed pad have somebody push the brake pedal and watch the piston move and then replace pad and move on to the next piston until you have seen them all move.

I still think it is master cylinder related ... maybe a previous owner rebuilt the master cylinder wrong and now it has been rebuilt with the rebuilder putting things back in the same incorrect order.

BTW as it is a race car, has a balance bar been installed and there are 2 master cylinders? If so check that the balance bar is not catching on something ... had that with a non Alfa race car, that held the brakes on ...
Pete

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