Alfa Romeo Forums banner

1 - 20 of 38 Posts

·
Registered
Joined
·
1,609 Posts
Discussion Starter #1 (Edited)
I'm having a strange issue with my brakes suddenly not releasing. It doesn't seem to matter if its a hard stop, or if they are hot or cold. I started last Sat, as I was driving down the road. I came to a stop, and when I pulled away, the car was VERY sluggish. I pulled over and stomped on the brake pedal 3 or 4 times and all was good. I thought it was a bit strange, but it quite doing it for a couple of days. 3 days later I pulled up to a stop sign on my way to work, and the brakes decided they wern't going to release at all. It felt like all 4 were locked as I could not go anywhere. It was like I was doing a brake stand, except I couldn't spin any tires. The car wouldn't go forward or backward no matter how much gas I gave it (I didn't give it that much for fear of breaking something major.) I stomped on the brakes a bunch of times, and they released as if nothing had happened. They did the dragging thing again yesterday (at a bridge toll booth no less) and required me to pull off and stomp the brakes a few times again.
That said, the brake master cylinder is new as of last Oct, as is the brake booster (converted to single circuit single booster.) The flex lines are all new braided stainless steel ones that I installed back in March. The car hasn't done this before. When It does lock the brakes, the pedal is VERY firm. I did do a search for this before I posted. I did note the post about 2 down with just the rears dragging when hot. These are dragging hot or cold and then suddenly releasing like nothing ever happened.

Well it did it again. Got on the brakes and they wouldn't release. The fluid is new (bled the brakes 2 weeks ago), same stuff as before, Its not just one brake that drags, the car drives straight while dragging with no hands on the wheel. I'd kinda like to get this figured out as I was invited to go autoX with the local Porsche Club next weekend. (I'd drive the race car, but its all taken apart for various reasons.)

Any Ideas?

Thanks

Will
 

·
Trained (ex)Professional, , 1953-2018 RIP,
Joined
·
16,232 Posts
Since the fronts do not drag, that would seem to rule out the M/C and the booster. I'd suspect either the rear brake hose or the rear brake pressure limiting valve.
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #3
I don't know that the fronts don't drag. Thats the thing, I cant get it to do it anywhere I can jack the car up. I came home last night with them dragging, as I pulled into the driveway, I felt them release.

That said, I might have stretched the rear flex line when I replaced the springs. when I lowered the rear end down, I forgot to remove it. When I bled the brakes, they felt better than they ever have however.

thanks,
Will
 

·
Registered
Joined
·
167 Posts
very similar (same?) problem happened to me, it was the rear flex line. It looked fine from the outside but it had collapsed internally. It's easy and cheap to change it out and see if that fixes the problem.
 

·
Registered
Joined
·
1,255 Posts
This does sound really similar! I just finished changing my rear flex line 2 nights ago. It all seems to be fine now. See my thread here called "Rear brakes tightening up when hot"...there are also alot of other suggestions from other BBer's. Good luck.
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #6 (Edited)
The plot thickens. They did their thing on my way home from work today. I nursed it home with hopes of getting the car up on the jack before they let go. I was partially successful with that, however they released before I had the car up. I did find that the front brakes were MUCH hotter than the rears so it seems to be the fronts that are the issue. The pads are in good shape, so the pistons aren't getting hung up due to over extension. The pedal now seems to go from progressive, to hard depending on how stuck the brakes are. (For example, the wheels are locked, the pedal feels like a brick wall, when working correctly they feel right.) The remaining booster is routed into the front brakes rather than the rears (like a euro car.)
The brake flex lines are braided Stainless Steel lines that were new as of last Feb.

Thanks,
Will
 

·
Administrator
Joined
·
16,626 Posts
If you can reach a bleed screw when it occurs try cracking it open when the brakes are locked on/dragging.

If a bit of brake fluid spurts out (have a rag handy) and the brakes release then something is preventing the release of hydraulic pressure. Possibly a hose with an internal fault - acting like a one-way valve. I had an old truck with a front brake line that'd do that. A gentle application of the brakes would release normally but a firm application would cause the brake to lock 'on'. Disection of the brake hose revealed a flap of hose material that'd pass fluid to the brake but, if it flopped out a certain way it'd prevent the release of pressure.

If loosening the bleed screw for a moment makes no difference then it may be time to rebuild the calipers.

Only other guess is something that happened to one of my MGs (so I don't know if it applies to an Alfa). After rebuilding the master cylinder the brakes would sometimes lock on after a few repeated applications. I finally figured out that a gasket in the rebuild kit was the wrong size - too thin - which prevented the master cylinder's piston from fully uncovering a port inside the bore. Thus pressure could build up and not always be relieved.

Good luck - these intermittant things can be hard to track down. But keep at it - your brakes are kinda important!
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #8
Yeah, brakes are important. I need to get this figured out soon as I have well over 1300 miles of driving to do in the next 3 weeks, and the other car is all taken apart (hence the reason for all the driving.) I'm going to make a serious attempt to get it to do its trick on Friday when I have some time to really look at it. As I said, if I stomp on the pedal a few times, they release. It doesn't seem to matter if they are hot or cold, or weather or not I stand on the brakes or lightly feather them. I'm almost thinking it has something to do with the vacuum system (perhaps the valve in the intake is sticking or something.) I know its got to be something stupid and simple. I just can't get it to happen when I want it to.

Thanks,
Will
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #9
I came out to the garage this morning to go to work and low and behold, the car would not move. The front brakes were stuck tight. The rears were free, but the fronts were completly locked. After stomping on the pedal a few times, they released and I was able to go to work. Anyone have this happen before? I'm going to try bleeding them tomorrow, and check for any crud that is blocking a line or something.

Will
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #10
So, after hours of checking everything, disconnecting the booster vacuum line, ect, I made some discoveries. First it locked the front brakes on me once, but released after I turned the engine off. I disconnected and plugged the vac. line and took it for a spin. The brakes were as they should be, didn't drag once, didn't lock once either. Upon return I pulled the fitting off the booster, inspected it and replaced it. Upon restarting the car, the pedal would build pressure then release it after a certain amount of pumps. I kept doing this until I heard a POP. No fluid leaks anywhere, but the brakes went back to feeling like they should and not building up pressure at the pedal. I then proceeded to go for a 40 mile drive, and the brakes were fine. The stopping power is down a little bit (still stops fine, just requires more pedal pressure.) and they didn't lock or drag once.

Anyone have any ideas? Did I pop the vac diaphragm?

thanks,
Will
 

·
Administrator
Joined
·
16,626 Posts
A quick test of the vacuum booster is to apply/release the brakes 4-5 times in a row with the engine off. This bleeds off any residual vacuum in the reservoir. The pedal should he higher than usual.

Next, with your foot on the brake pedal, start the engine. If the booster is working correctly, the pedal should drop to 'normal' as the engine's intake vacuum is added to the booster.
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #12
The pedal doesn't move. Its resting spot is against the full upright stop. It doesn't move from there after I pump the brakes with the engine off. Never has. The brakes have gone back to full stopping power, and they don't hang up. I drove around all day, some stop and go, and they were great.

Its like the car was telling me to change the oil. I did so and suddenly the brakes are fine. I dont get it. Instead it traded the draggin brakes for a rubbing exhaust that won't for the life of me go back to where I had it when it didn't rub no matter how much I space the pipe away (with everything loose). That however is off topic, and will end there.

Will
 

·
Registered
Joined
·
1,265 Posts
I'm having a similar problem at the moment, I'm thinking its the air valve (the little side piston that controls the where the vacuum goes) is the culprit an is sticking.
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #15
I still haven't fully figured this issue out yet. I replaced the front brake calipers, and went from having a semi-firm brake pedal and a car that would occasionally lock just the front brakes, but unlock them with a second push of the pedal, to having a mushy brake pedal with brakes that still lock and unlock just as they did before. I bled the complete system, and still don't have brakes that will stop the car in a panic stop. Is it common to have to replace the booster and MC after a year? I really don't like this boosted brake business, its unnecessary, unreliable, and expensive to be replacing every year.

Will
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #17
The brake light switch has been disconnected for a year. it died, I haven't bothered to replace it for the simple reason of having to deal with rebleeding the brake system again.

Will
 

·
Registered
Joined
·
1,265 Posts
I forgot to post my outcome!
Pull the booster off, remove the small diaphragm housing and the air valve piston (the small piston), clean it up, apply plenty of rubber grease and re-install. Solved the brakes locking on for me. Would be a good time to replace your light switch too. The mushyness is just air in the lines (although it took a lil bit of driving for the pedal to firm up as the pistons/seals settled after rebuild). It took me a while to twig to the fact that the 2l ATE's I replaced my dunlops with leaked air into the calipers when i was bleeding using one of those "One man bleeder" setups with the check valve in the line at the bottom. I got around it by using a length of timber to hold the pedal down while i did up the bleeder, removed lumber, undid bleeder, depressed pedal, lumber, bleeder.
 

·
Registered
Joined
·
1,609 Posts
Discussion Starter #19
I don't think there is any air in the system. I bled a full quart of brake fluid through it. As for the booster, I do hear a sucking sound at idle coming from the bottom part. It also seems loose on the booster. Can I pull the screws out and tighten the upper part onto the booster without making a giant mess? I can't remember if there is brake fluid there or not.

Thanks,
Will
 

·
Registered
Joined
·
1,265 Posts
I don't think there is any air in the system. I bled a full quart of brake fluid through it. As for the booster, I do hear a sucking sound at idle coming from the bottom part. It also seems loose on the booster. Can I pull the screws out and tighten the upper part onto the booster without making a giant mess? I can't remember if there is brake fluid there or not.

Thanks,
Will
Well. You could keep doing half a job on your brakes, or you could fix it properly. Technically, yes, you could pull the small diaphragm apart on the car, but it'd be a giant pain in the *** to get at and get tightened properly. Just pull it off and go through it properly.
 
1 - 20 of 38 Posts
Top