m0sh_man Posted November 22, 2005 Report Posted November 22, 2005 ok my booster and master cylinder came off a car that was wrecked in the front and sat for about 3-6 months before i removed them, and put them on my car, all my metal brake lines have been inspected and none leak, However often when i press my brake pedal, it goes near the floor, and other times its very firm like it should be, When its soft, i press the brake a second time, and its firm like it should be. My conclusion is that the master cylinder is starting to go bad, but i want someone else to chime in before i pay any money out for a new one (yes a new/rebuilt one next time). matthew Quote
Pabz Posted November 22, 2005 Report Posted November 22, 2005 Ok, i think consensus on this issue is, Check vacuum to booster for leaks. then bleed the crap outta the breaks using a tube and jar. Could be the flexible rubber tubes that go to the caliper too. There is a procedure for checking the break booster. I will look it up when i get home. Quote
Supreme Cutlass Posted November 22, 2005 Report Posted November 22, 2005 Pedal on the floor is almost certainly a master cylinder problem. Quote
pwmin Posted November 22, 2005 Report Posted November 22, 2005 im assuming the rubber hose to the booster isnt mushy? Quote
m0sh_man Posted November 22, 2005 Author Report Posted November 22, 2005 well, replaced the master cylinder today (i did bench bleed it) im sure alittle air got into the lines, so im going to have to re-bleed the whole system, HOWEVER it fixed the problem, now the brakes start working at the exact same spot on the pedal travel every time, so i guess the master cylinder was the problem, i bought a reman'd one from napa for $43.99 had to get it for a 1990 lumina cause thats what my brakes are from (removed the PMIII crap) however i found out later that the 91GP had the same mastercylinder, so i guess i can just say 91GP like normal for now on. matthew Quote
Crazy K Posted November 24, 2005 Report Posted November 24, 2005 I have done the PMIII replacement on my evil 1991 CS convertable and am experiencing the same problems on my replacement unit, I used a donated 1994 lumina z34 booster, w attached Master Cylinder combination ABS unit, (plus the entire ABS wiring harness and abs PC) so i can eventually wire in the abs wires and have abs, as i already have all the hub sensors. I would prefer to rebuild the MC, any thoughts? Quote
m0sh_man Posted November 28, 2005 Author Report Posted November 28, 2005 ive got a couple PMIII units here at the house, both are untested units as my car had a wiring issue which caused them to not work properly (i think) i paid $100 shipped for just one unit that was said to be in 100% working order, ill sell BOTH for $100 shipped. matthew Quote
SigEpCutlass Posted November 28, 2005 Report Posted November 28, 2005 sounds to me like you really need to bleed you breaks dude. Quote
Supreme Cutlass Posted November 29, 2005 Report Posted November 29, 2005 sounds to me like you really need to bleed you breaks dude. He said that the master cylinder fixed the problem... Quote
rubenyc Posted February 23, 2006 Report Posted February 23, 2006 My '90 Lumina has the same symptoms, I think. It happened once about a week ago, then the car sat for half an hour and when I started it up again it was braking fine. However, I was driving home today and it happened again. Both times after highway travel, if that makes a difference... Pedal goes almost all the way to the floor and the car brakes just a little (scary stuff), when I let go of the pedal and then stomp it again it seems like pressure is back and I can stop the car normally. I'll try bleeding the brakes this weekend, thing is I need the car tomorrow. Do you think it's safe to drive it like this, or do I risk brake failure or something like that? I'm sure the front brake hoses are fine, I checked them recently. The brake lines seem rusty in places but they weren't leaking last time I looked. Anyway I checked the fluid, it seems fine, not low or anything so I don't think I have a leak. Just to make sure, a few layman's questions: my car doesn't have this PMIII system I keep reading about, does it? (1990, no ABS) The brake booster: I think that's up behind the pedal? I'll check the condition of the rubber hose. And is there any way to tell if my master cylinder is good or not...? Thanks! Quote
trainman Posted February 23, 2006 Report Posted February 23, 2006 A vacuum leak/ ruptured diaphram in the booster would cause a hard pedal, an internal leaking master cylinder would cause the soft pedal/to the floor pedal conditions. Remember, when you bleed brakes...start with the wheel FURTHEST from the master cylinder..eg.. RR-LR-RF-then LF. it's east to forget sometimes. Quote
Dark Ride Posted February 23, 2006 Report Posted February 23, 2006 Just to make sure, a few layman's questions: my car doesn't have this PMIII system I keep reading about, does it? (1990, no ABS) The brake booster: I think that's up behind the pedal? I'll check the condition of the rubber hose. And is there any way to tell if my master cylinder is good or not...? If your car doesn't have ABS then it doesn't have the PowerCrapper 3. Sounds like a Master Cylinder problem to me. The Brake Booster uses Vacuum from the engine to "assist" your braking. If you had a Bad Brake Booster, it would still brake, but the pedal would be hard to push. Mitch Quote
95oldsVan Posted February 24, 2006 Report Posted February 24, 2006 Another test for others who need to be sure.Before you start the car,pump the brake pedal a few times until its very hard.Then hold the pedal down firmly and start the car and see if the pedal wants to go down to the floor or sinks way down. If so,the MC is most likely the culprit.You can also check to see if theres any fluid leaking from between the Booster and MC itself.Sometimes you have to unbolt the MC from the booster and pull it FWD a little bit and see if fluid is seeping past the rear seal. If so,then its rebuild time. Quote
92LuminaRS Posted February 24, 2006 Report Posted February 24, 2006 I've always bled the brakes with the car running since their power brakes... Is that bad? Quote
rubenyc Posted February 24, 2006 Report Posted February 24, 2006 OK, I think I'm just going to refresh my fluid first. A friend seems to think that old brake fluid could cause this problem after long driving/braking (both times that it happened to me I had driven the car all day on short trips). It's worth a shot I guess, before I replace the master cylinder. Quote
Crazy K Posted February 24, 2006 Report Posted February 24, 2006 good thought, old fluid that has absorbed moisture has a lower boiling point, and the engine heat could be casuing it vaporize... but, if you press the pedal hard enoguh,, does the pedal slowly sink, for example when the car is cool and off? safety first, you know..... Quote
rubenyc Posted February 24, 2006 Report Posted February 24, 2006 I just went outside and tried it, the car is cool since I haven't used it for hours. I can press the pedal very hard and it DOES NOT sink to the floor. That's a great test. So I guess that means it's just my fluid then. :-) Thanks! Quote
Crazy K Posted February 24, 2006 Report Posted February 24, 2006 well, it simply means it's possible.. if it had sunk cold... well you know... good luck! Quote
Crazy K Posted February 24, 2006 Report Posted February 24, 2006 actually... what type of car do you own? duh! it may not be the mc itself, it may be from brake drag at the rotors... if you have the older 93 down, or 94 lumins rear brakes, they can cause alot of brake drag too. so it may not be an engine heat problem... Quote
rubenyc Posted February 24, 2006 Report Posted February 24, 2006 It's a 1990 Lumina 3.1. I have the old brakes on it but they are somehow working fine. No/little drag (AFAICT) and even the parking brake sets and releases as it should - it wouldn't have passed Dutch inspection if it didn't, and I just had it inspected last week. Both times that the brake-pedal-to-the-metal thing occurred I had been running the car several times that day, had been driving at highway speed for like 20 minutes and then noticed the pedal sinking as I drove into town. This morning I drove on the highway for 30-40 minutes after a cold start, then into town, and noticed nothing out of the ordinary. Well, I'll replace the fluid soon (probably this weekend) so we'll see if that cures it. UPDATE: I figured out when it happens exactly. All is fine on the highway, but when braking over a long distance from 75 MPH to 0 for a traffic light entering my town, after that is when the pedal goes deep. So you must be right Crazy K, it must have something to do with the fluid heating up. I also noticed that if I put the car in Neutral at traffic lights once I'm in town, IOW not hold the brake, it "cures itself" slowly but surely. I guess that makes it cool down. I have new fluid and will change it tomorrow. Quote
95oldsVan Posted February 24, 2006 Report Posted February 24, 2006 Kee us posted...if fresh fluid doesnt cure the problem,it would sound like the MC may need replacing.Do check behind the MC by pulling it forward off the booster(dont take the lines off,just the 2 bolts that hold it on) and see if theres any wetness of brake fluid in the back of it.If so,you def got a slow leak in it. Quote
rubenyc Posted February 27, 2006 Report Posted February 27, 2006 Alright I didn't get to replacing the fluid yet (doing that Thursday), but I did find out something else. I responded about it in this thread. My left rear wheel is making noise. At first I thought it was the suspension, but I noticed it stops when I brake. Took the wheel off and found that the inner brake pad was VERY loose, like I could move it back and forth, up and down. I'm pretty sure that's what's clicking when I drive the car at low speed. It seems like just an annoyance, but then I thought, could it be the caliper (which in turn might have something to do with the loss of pressure?). The brake works fine otherwise, wheel spins freely but with a slight touch of the rotor once every turn (I guess that's what causes the pad to move and click). By the way, ever since this noise got louder (about 3 days ago) I haven't experienced any excessive brake pedal travel. Quote
rubenyc Posted March 2, 2006 Report Posted March 2, 2006 We put fresh fluid in it today. Pedal feels good and solid now and yes, there was some air in the lines. I've only had this car for two weeks so I'm guessing the previous owner messed up trying to bleed the brakes. There's still that clunky noise coming from the left rear brake though. Ah well, so begins my quest into the scary world of W-body rear brakes... 8) Quote
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