Sticky brake pedal - Alfa Romeo Bulletin Board & Forums

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Old 02-10-2004, 07:49 AM
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Sticky brake pedal

My 1971 GTV is giving my brake problems I have never experienced before. The problem is that the brake pedal sticks in the down position, requiring a yank to release it. It only does this when the motor is running. When the car is off, the pedal comes up slowly, about a count to five.

The car is new to me and when I got it it had classic bad MC symptoms. The pedal would go to the floor and you could hear fluid flowing past the seals in the MC.

I replaced the MC with one from Centerline (CIFAM brand). The pedal is lower than I expected but hard. Other threads have discussed the shortfalls of some MC suppliers. I felt safe with Centerline as they were recommended. Is CIFAM OK stuff?

The PO had replaced the MC and mentioned that he cleaned up the booster. The booster and pedal box appear to have been cleaned and painted. Could this have been put back together wrong? (I am also having clutch problems.)

The only pedal return spring I can see is part of the booster visable up under the dash. There is a spring and cup (with a slot) concentric with the rod into the booster, that appears to push the pedal up. The cup is bearing on the yoke that pivots on the pedal, is this the right stop or is there a stop on the rod closer to the booster? What does a bad booster act like?

My suspicion of the pedal box is partly due to having clutch problems as well. The clutch barely disengages at the bottom of the stroke. In fact the car has to be shut off to be put it in reverse.
The adjuster at the pedal box is further out than the spec I found (5.25 inches). The slave moves as soon as the pedal yet the clutch fork only moves 7/16 inch (measuring at the furthest point away from the clutch). Is this sufficient? There is no return spring on the clutch fork, is this normal?

The clutch grabs fine, Is there a way to see the clutch plate to inspect for wear? What should I see?

So, the combination of the PO working in the pedal box/booster and me having wierd problems with both pedal systems makes me suspicious of that area. But the pedals seem well connected (not loose) and not binding.

Does the assembled genius have any advice or experience with these problems?

Thanks for your help! TD
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1969 1750 Spider
1971 1750 GTV
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Old 02-11-2004, 03:28 PM
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Sounds all the world to me that the booster is no good; the result of brakefluid contamination. Not sure on the pedal return spring and cup. Is there another place in the pushrod closer to the booster where the cup could fit? Does the brake pedal move freely if the pushrod is disconnected?
The first thing I'd do for the clutch is to bleed it. Ensure that the bleed screw on the slave cylinder is at the 12 o'clock position or you'll never get all the air out. Next, I'd look at the clutch pedal pivot arm. Have a helper push down on the clutch pedal while you look at the pivot arm that acuates the clutch master cylinder pushrod. If the weld on the arm has broken and the serrations are worn, the arm can slip on the pivot shaft and not fully release the clutch. I'd change the master, slave and hose if there's no air in the system and the pivot arm is OK.
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Series 1 Euro 1750 GTV
Series 2 USA 1750 GTV
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Old 02-11-2004, 09:03 PM
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I had a similar effect once on a booster for an old Girling (Volvo 1800) system. I (yes, I) rebuilt the booster and it would stick in the brakes engaged position if started while holding the brake pedal down. Tapping the booster (a separate unit from the MC in this application) would often cause it to unstick. Needless to say, I didn't try to drive this way. One good hard stop and I'd not have been able to release the brakes. On units with integral MC/booster, I suspect the brake pedal would end up stuck in the engaged position.

You might be able to test this theory by disconnecting and plugging the booster vacuum hose. I suspect it wouldn't stick then, and you'd have the MC question separated from the booster question.

Or so I think....

Michael
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Old 02-12-2004, 06:41 AM
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Thanks for the tips.

Regarding the brakes, I am starting to think it is the booster. I am going to install a new vacuum hose this evening and see what happens, ths hose seems like too simple a fix though.
If the booster holds vacuum can I assume it is OK? Any idea how much vacuum is normal?

Papajam, your comment on the clutch pedal shaft slipping is interesting. After bleading the MC and slave to a point of confidence, I have adjusted the pedal to MC rod out 1/2" past spec and now have some clutch action, very close to the floor.
The PO did some work in the pedal box area. Is it possible to put it together wrong?

The only diagram I have shows a big nut and bolt type cotter pin frequently used on bicycle cranks. I guessed there was one flat threfore one way to assemble. Do you have any additional info on this?

Thanks, TD
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1969 1750 Spider
1971 1750 GTV
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Old 02-12-2004, 09:07 AM
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I didn't intend to suggest a hose issue would fix the booster problem, but that disconnecting the booster vacuum would disable (or weaken) its response to the MC. If the brakes no longer stick with booster vac. disconnected (plug the manifold side, though) then it would seem likely to be the booster instead of the MC. I thought that is what you wanted to test.

On my 1800S car, though, the brakes work just fine un-boosted; the booster was really a afterthought for that system. The Alfa, on the other hand, I _think_ brakes poorly without the booster. I drove a Suburban whose booster had just sprung a leak and it took real effort to get it to stop. That booster was replaced immediately.

Michael
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Old 02-12-2004, 02:53 PM
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If I understand correctly, the clutch master cylinder pushrod is a half inch longer than it should be? If that's the case, that could be the problem. When the pushrod is too long, and this goes for brake M/Cs as well, the M/C piston can't return far enough to uncover the compensating port which allows fluid from the reservoir to enter the cylinder ahead of the piston. There simply may not be enough fluid in the pressure side of the system. You might want to try pulling the clevis pin from the pivot arm to pushrod. Then, while ensuring that the clutch pedal is about the same height as the brake pedal, shorten the pushrod so that the clevis pin can be installed with no pressure on the pushrod.
AFAIK, the pedalbox can be assembled only one way.
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Series 1 Euro 1750 GTV
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Old 02-13-2004, 07:07 AM
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Papajam, I think you are right.
My fiddleing around led me to believe there just wasn't enough fluid between the MC and slave. My solution was to hold the pedal down and wedge the clutch fork out, then "re-****" the pedal. This did increase the throw of the slave but when the pedal was released the extra fluid pressure seemed to be lost when the pedal reached the top of the stroke. (a hydrolic squirting sound from the MC).
This made me suspect the piston in the MC was moving too far or not far enough. By adjusting the rod in and out I have managed to get what seems like normal travel.
To further complicate things it seems like the clutch disc is sticking.
This car is a challange because I have not been able to drive it much. It has been stored for ten or more years. All new hoses.....
I'm hoping that driving will sort out a lot of the problems.

It does have a clean rut free body with new paint and interior!
Thanks for the advice! TD
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Trav

1969 1750 Spider
1971 1750 GTV
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