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Hard brake pedal, no stopping power


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Are the first-gen W-body power brake boosters prone to defects? Are they a common problem?

 

Background:

 

I did a search on "Booster" and got a bunch of hits; it seems the power brake boosters on the first-gen Luminas are not overly powerful--but--I don't see anyone who has claimed to fix poor stopping power with a simple booster R 'n' R. Folks upgrade to a newer, larger booster for "better" brakes, but that's not what I'm dealing with--I think.

 

What I'm dealing with is an extreme case. I have two 3.4 Luminas, a '92 and a '93. Both of them have poor stopping power, (the '93 is worse than the '92.) Both of them have working rear calipers, both of them have functioning emergency/parking brakes, both of them have vacuum to the boosters and booster check valves that hold vacuum. Both have firm pedals--no indication of air in the system. I have pressure to all four calipers on both cars as verified by my brake caliper pressure gauges. A hard stop will warm up all four rotors on either car. On glare ice, both cars will rattle the ABS, and the car is steer-able while stopping. Therefore, I believe the ABS is functioning properly.

 

How bad is it? On regular pavement/good traction, I can use BOTH FEET and ALL MY STRENGTH on the pedal, and the car glides to a stop. I CANNOT get the ABS to engage, the brakes don't grab hard enough to skid the tires. Normal, non-panic stopping seems to take more-than-expected effort; but it's not death-defying. I have replaced pads and rotors on the '92 with Z-E-R-O change in stopping power--although that did get rid of the shudder/pulsing of the warped rotors. I have never changed the pads on the '93; although that's in-the-works.

 

By comparison, my Dad's '98 Monte Carlo will stop with the slightest pressure from my big toe. There is a H-U-G-E difference in braking effort needed to stop between the Monte and either of my Luminas.

 

I have a rebuilt booster on order; I guess I'll find out if that was the problem in a couple of weeks...

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is the vac line from the rear of the manifold to booster in good shape? that really firm pedal description is what my old Z34 was like when it came off.

 

other than that, it seems like you have checked everything and have a good knowledge of these things. maybe a new master/booster is in order. hopefully someone else will have more insight.

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Just how bad is it?

 

I know when I first got my car, it wouldn't stop. I could push down the brake halfway, and it didn't do anything at 10mph. Turned out it needed a new everything, new pads, new rotors; even though it made no noise at all.

 

Basically, if you feel a REALLY stiff brake pedal, you have a vacuum problem in the hose or in the booster itself.

 

If the brake pedal moves normally, but doesn't stop the car worth shit, lift the calipers and check specs on rotors and pads (ie my problem)

 

If the brake pedal goes down, then continues to sink (engine off, no booster power) then you have a master cylinder problem.

 

If all else fails, bleed ALL air out of the system and deal with your crappy brakes, or upgrade them.

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Start the car and run it for a few seconds, shut it off. Pump the brake pedal once, twice, three times. You should have assist, or a "pssh" sound coming from unde the dash (power booster atmoshperic valve opening)..you should have enough assist to pump the brakes twice easily without the motor running..the third time the pedal should start to get really hard.

 

If that checked out, start the car and get the vacuum in the booster again by reving the engine up and letting it deaccelerate (deaccelerattion produces max vacuum). Shut engine off and let it sit for a few minutes and come back. Perform the same test above with exception of starting the engine again. This will test to see if the booster is holding vacuum.

 

If either of these tests fail, find the vacuum hose on the booster (make sure the hose itself isn't in bad shape), pull the one way check valve out of the booster where the hose connects to it. You should be able to blow air through it one way but not the other. If you can blow both ways replace that valve as it's leaking and won't hold the vacuum very well.

 

If the check valve is ok the vacuum valve or the atmospheric valve could be leaking. At this point I'm taught to just repalce the master cylinder as it's cheaper - but you could rebuild the one you have if you are indeed sure it is causing the problem.

 

It is possible your master cylinder could be failing as well, but normally your pedal would be low, mushy, or go to the floor (as mentioned above).

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Start the car and run it for a few seconds, shut it off. Pump the brake pedal once, twice, three times. You should have assist, or a "pssh" sound coming from unde the dash (power booster atmoshperic valve opening)..you should have enough assist to pump the brakes twice easily without the motor running..the third time the pedal should start to get really hard.

I NEVER hear the "psssh" sound from the booster. I can pump the pedal with the engine off and the brake pedal never feels different as the vacuum bleeds out of the booster. The pedal is ALWAYS hard.

 

If that checked out, start the car and get the vacuum in the booster again by reving the engine up and letting it deaccelerate (deaccelerattion produces max vacuum). Shut engine off and let it sit for a few minutes and come back. Perform the same test above with exception of starting the engine again. This will test to see if the booster is holding vacuum.

 

If either of these tests fail, find the vacuum hose on the booster (make sure the hose itself isn't in bad shape), pull the one way check valve out of the booster where the hose connects to it. You should be able to blow air through it one way but not the other. If you can blow both ways replace that valve as it's leaking and won't hold the vacuum very well.

Yes, I have vacuum to the check valve; yes, the check valve holds vacuum.

 

If the check valve is ok the vacuum valve or the atmospheric valve could be leaking. At this point I'm taught to just repalce the master cylinder as it's cheaper - but you could rebuild the one you have if you are indeed sure it is causing the problem.

No doubt you mean to replace the booster, not the master cylinder. I have a booster on order; then it's a matter of working up the ambition to actually stuff the thing onto the firewall. I'm doing the '93 first--if it fixes the problem (and I'm 99 44/100 % sure it will) I'll order a second booster for the '92.

 

It is possible your master cylinder could be failing as well, but normally your pedal would be low, mushy, or go to the floor (as mentioned above).

Not low, not mushy, not on the floor. In all respects everything else in the brake system "seems" to be working based on temperature measurements at the rotors. Worst case is the boosters are SO bad that they're covering up other symptoms. I accept that if I can get the brake effort back to a reasonable level, I may notice other problems that aren't at all obvious now--but--that isn't really what I expect to find on either car. The only other issues I know of is that the '93 needs new rear brake pads and probably rotors; and front brake hoses based on the tearing of the outer rubber covers. That isn't a functional problem however--just a longevity problem. Simple maintenance. The pads/rotors and front hoses aren't the cause of the insane pedal effort problem, though; at least based on my experiences with the '92.

 

I'm going to remove and plug the vacuum hoses to the boosters and drive both cars. My expectation is that the '93 won't be much worse with the booster disabled; and the '92 will be a little worse but not "dramatically" different. I think the booster on the '93 is about 90% failed; the one on the '92 is about 75% failed.

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Four in the friggin' morning, I've been working on this thing ALL DAY; and now that it runs again, I have to get ready to fly to Baltimore in two hours so I don't even get a chance to test drive it...

 

As long as I was under the hood, I pulled the intake manifold and fixed some truly hard 'n' brittle vacuum hoses. Someone prior to me buying the car had slathered black RTV around the distributor-block-off-cap-thingie. Of course, it didn't hold; and that's--I guess--been my oil leak that I thought was the rear main seal. I was in no mood AT ALL to yank the rear head off, and perhaps I got it re-sealed via the Punch and Judy method, and perhaps not. I'll find out soon enough.

 

I'll be back in a couple of weeks with a driving report...

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  • 3 weeks later...

HO--LEE CRAP! WHAT A DIFFERENCE!

 

I now can come to an ordinary stop just by resting my foot on the pedal. A hard stop only takes one foot--and only moderate effort.

 

To answer my original post--I am now convinced that the power boosters in these W-bodies is a common problem. I don't have a lot of data to back that up--that is to say, both of my cars had partially failed boosters; and I've talked to others with "hard pedal--poor braking power" complaints. Also, there's all the posts about converting these cars over to the newer, larger diameter boosters--which, after driving my car with a fully-functional REGULAR-DIAMETER booster--seems very silly. I don't know what I'd do with more power assist, there's plenty already.

 

First Guess--guys have partially-failed boosters just like I did, and replacing it with the new, bigger-diameter booster makes a HUGE difference--but so would installing a fully-functional regular-sized one. MAYBE the bigger booster isn't as prone to failure. MAYBE it's more reliable. If that's the case, I can see using the bigger booster. For my purposes, the CarQuest booster has a lifetime warranty--and I don't need more boost than I have--so I don't see any reason to shove in the bigger boosters. Others may disagree--all I can say is I'm NOT Arnold Schwartzenegger; I don't have leg muscles that look like canned hams--and the brakes work JUST FINE now.

 

I can't stress enough how much difference this made. Until now, I figured a booster either worked; or it didn't. I didn't realize they could partially fail so the amount of boost was reduced--but not totally gone.

 

I ordered another booster to repair my other Lumina; I didn't bother to get the extra-large version. I'll add more info later; and I've got some photos to post.

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notsoslimshady76

Hey, good for you man! If you had poor braking problems with the ABS, then I would definitely think it is the master cylinder. From my understanding, although PMIII has its own problems, the braking is still very good compared to my lowly vacuum brakes. Congrats

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Ok, more details and photos.

 

1. Not too hard of a job on my DOHC 3.4. I made it easier by also doing the intake manifold at the same time. There isn't a lot of clearance between the upper plenum and the locking tab; I couldn't find the tab at first. So I figured--hey--how tough can it be to pop off the upper plenum? Of course that led to the discovery that what I thought was a rear-main-seal oil leak was in fact the infamous "distributor shaft O-ring" oil leak. So then I pulled the lower intake figuring I could lift the shaft out that way. Nope, hits the rear cylinder head. I patched that leak by lifting the shaft about 1/16 of an inch (all the clearance there is between the top of the shaft; and the rear cylinder head casting) and packing non-hardening Permatex #2 gasket sealer underneath it--360 degrees all around. Then I let it settle back down and installed the retainer. (So far, so good. No leaks after two days. We'll see what happens in two years...) I re-used all the intake gaskets except the O-ring for the coolant passage. Of course, the air box came out, The top of the trans bellhousing area was black 'n' slimy from all the leaked oil, so I did what I could to clean it off.

 

ExhaustCrossoverAreasmall.JPG

 

I pulled the master cylinder and ABS as a unit by removing four electrical connectors, two nuts, and four brake tubes being sure to label the order of the tubes. Very easy. I moved the cruise control servo for clearance. Then, disconnect the booster pushrod from the brake pedal by popping one spring clip. Don't lose the washer. The pushrod slides sideways off the little post on the pedal.

 

2. Once the upper plenum is off, the booster lock tab is very easy to get at.

 

BoosterAreaOfFirewallsmall.JPG

 

LockTabCloseupOfFirewalsmalll.JPG

 

3. I made a "special tool" to twist the booster off the firewall. I used 5" of channel iron; angle iron or even suitably thick bar stock would work as well. Drill three holes--two the same distance apart as the studs on the booster, and one right in the middle that is tapped for whatever thread size you need to screw in a bolt with a ~3/4 inch hex head. I used a metric bolt 'cause it was handy. Then I cut off the excess threads on the back side, and welded the bolt into place.

 

FabricatedToolToRemoveBoostersmall.JPG

 

4. The new booster was not identical to the old one--but--it's what CarQuest lists for a '93 Lumina. Nothing trick, nothing fancy. Standard, ordinary replacement part. P/N 54-71286; $142.03 plus sales tax. That price includes the $12.86 core charge.

 

NewVsOldBoosterssmall.JPG

 

5. I shoved new pads in all the calipers (the cheap pads--$40 for all four wheels) verified that the calipers floated on the mounts; verified that the piston(s) weren't seized; verified that the park brake system worked; and verified that there were no leaks at the calipers. The front rotors were fine, I cut the rear rotors.

 

6. I installed new brake hoses at the front--the rubber jackets were pretty bad. Rear hoses were OK, so I left 'em alone. I used teflon/steel braided front hoses. They don't change the braking effort, but they do make for less pedal travel (a firmer pedal) I'm doing this on every car I own--at the point that a car needs brake hoses, I install the teflon/steel braid units. I don't take off good hoses just to put the teflon stuff on, though.

 

LuminaBrakeHosesmall.JPG

 

7. After sealing up the hydraulic system, I flushed the brake fluid at all four calipers and the two ABS bleeders (6 bleeders total) until the fluid ran fresh 'n' clear at each one.

 

8. There is a molded rubber vacuum hose from the upper plenum to the booster. Mine was swollen near the plenum from gasoline fumes. My local Chevy dealer actually had one IN STOCK!!! The price wasn't horrible--$11.26; part number 10400822. They've sold 5 in the last year, so it must fit the 3.1, too. The old hose wasn't so bad that it leaked, I had good vacuum at the booster with it--but it was clearly on it's last legs. Since it was VERY EASY to replace with the plenum off, now was a good time to address it.

 

9. There were lots of hard plastic vacuum hoses behind the plenum; some of them shattered in the course of screwing with all of this. I used sections of rubber hose to patch the hard plastic tubing. Not optimum; but most of this work was done "after midnight" and the Chevy dealer was closed.

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Where did you get the braided front brake hoses at?

Summit. I'm getting good at inventing brake hoses for cars that aren't supported with "kits" already designed for them.

 

Ever tried to get teflon-liner brake hoses for a '66 Toronado?

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So do you just buy the hoses, buy the right fittings, and just go to town then?

Two hoses, two banjo adapters, bend the brackets so they don't rub on the strut's spring seat. More than twice as expensive as ordinary rubber hoses; in part 'cause they don't make a hose that has the banjo built-in.

another photo:

LuminaBrakeHose2.JPG

 

 

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I'm "95%--plus" done with the second booster; this one went on the '92. I did not pull the intake plenum or lower manifold this time. I have had to work on it over the course of three days.

 

First Day:

 

  • Drive the car in the garage
  • Lift it up
  • Pull the wheels off
  • Visual inspection of pads, rotors, hoses, and calipers. (they're fine)
  • Reinstall wheels temporarily so I can lower the car. I hate having to stretch over the fender to work on stuff.
  • Disconnect electrical connector at hood light, 'cause I hate staring into that light while working.
  • Yank out the air temp sensor connector, the entire airbox, and intake hose
  • Pull two speednuts, two vacuum hoses, and an electrical connector; move the cruise control out of the way.
  • Pop four electrical connectors, label and remove four brake tubes, and two nyloc nuts; pull master cylinder and ABS box out of the engine compartment. Set aside somewhere clean and safe.
  • Remove two plastic lock tabs and one speed nut, remove hush panel under dash.
  • Push the brake light switch tab off of the brake pedal post VERY CAREFULLY--see tirade below. Grab spring clip with needlenose pliers, but don't lose the outer washer when the clip comes off.
  • Remove vacuum hose from booster check valve. Install "special tool" to booster studs, twist booster off the firewall. I could feel the booster lock tab catch--but I did NOT have to pry on it--I twisted just a bit harder, and the booster lock tab popped free without any trouble.
  • With the booster loose, the pushrod comes off the brake pedal much easier. Don't lose the INNER washer from the brake post.

 

At this point, the booster is free of the firewall, but I ABSOLUTELY could NOT pull it out of the engine compartment because I couldn't get it past the metal and rubber heater tube. I closed up the garage and finished for the day. Overall, I thought everything went pretty good.

 

TOTAL TIME FIRST DAY: One and a half hours.

 

Second day:

 

I debated about how much coolant to drain before removing the heater tube that prevented me from getting the booster out of the engine compartment. In the end, I drained NO coolant out on purpose. About a pint spilled when I removed the lower end of the heater tube. I can live with that. With luck, I won't have to go nuts trying to bleed the air out of the cooling system.

 

  • Remove one bolt securing heater tube--it's half metal, and half rubber--to the bracket near the throttle body. Pull throttle cable and cruise control cable out of the little split-circular holder.
  • Remove clamp at upper end of rubber heater hose (above master cylinder area)
  • Squeeze spring clip at lower (metal) end of heater hose. Pull the metal end of the hose free of the intake manifold. Remove and set metal/rubber hose aside. Verify the rubber O-ring is still on the lower part of the hose, and that it's in good condition.
  • Spend about half-an-hour inventing new swear words trying to maneuver the booster past the fuel hoses, throttle body, vacuum hoses, the studs welded to the strut tower that secure the cruise control servo, the metal heater pipe that's secured to the firewall, and--ESPECIALLY--the four brake tubes that seem to grab the booster like bony fingers from the grave. The booster WILL come out--but it's NOT FUN AT ALL and I had to turn it completely around so the long and gangly pushrod end came out first. If you own the special tools to disconnect the two fuel hoses--that's probably the way to do it!
  • Pull the #5 plug wire out, so you can see to get a plier behind the plenum to release the spring clamp holding the molded rubber vacuum hose to the plenum nipple. Remove hose. Rolling the engine forward on the mounts might be a good idea--if you have the tool to do that. I didn't bother.

 

At this point, all the dis-assembly is D-O-N-E. "Installation is the reverse of disassembly..." ;)

 

My '93 had a severely-rotted vacuum hose from plenum to booster. So I bought another new hose to put on the '92. In fact, the '92's hose looked pretty good. Still, it'd be a NIGHTMARE to replace this hose with the booster in place, and it's not-too-bad with the booster removed. I put the new hose on using a thin smear of silicone grease to ease the hose over the plenum nipple, and then I installed a worm-drive clamp instead of the spring clamp.

 

I also saw that the larger-diameter hose that connects to the cruise control servo was in bad shape. The cruise worked, but the hose was cracked in about a million places. I'm sure this is the one that goes inside the car, to the brake pedal vacuum switch. At any rate, I was in no mood to trace the entire hose back to the source. I cut the hose where it joins the wiring harness just before being routed into the interior of the car. It's 9/32 hose, I found about a foot of 5/16 fuel hose and spliced it in with a short section of 5/16 metal tubing. If the cruise control dies later on, this'll be the problem and I'll dick with it then.

 

I broke another of the hard plastic vacuum hoses, it was spliced together again with a short piece of small-diameter rubber vacuum hose.

 

Slide the booster pushrod over the brake pedal stud BEFORE twisting the booster onto the firewall. Saves a bit of cussing.

 

I had a bit of trouble getting the new booster properly aligned on the firewall. Seemed like only one or two of the four lock tabs were engaging. I re-aligned it, felt around the back side of the booster with my fingers, and then got peeved, grabbed a bigass breaker bar and cranked the booster onto the firewall. DONE. HA. SO THERE.

 

I had a hell of a time with the brake light switch. It lit the brake lights ALL THE TIME. There's an adjustment procedure that involves pulling a metal spring clip on the brake switch, while pushing the brake pedal down. I did that a hundred times and it did nothing useful. Eventually, I bit the bullet, and dropped the steering column down so I could access the brake switch--I pulled the switch COMPLETELY OUT and re-set the adjustment. THAT OPERATION SUCKS in part because you're pulling more interior trim panels AND it was totally un-planned-for on my part. I spent as much time dicking with the brake switch as I did installing the booster.

 

TOTAL TIME SECOND DAY: About five hours--I kinda lost track, but half of that was spent working on my back (Prostitution Mechanics) while laying on the interior floor swearing at the brake switch, swearing at the steering column, and swearing at the two little green lock-tabs on the two electrical connectors on the brake switch. Should have been about two or three hours instead of five.

 

Lesson To Be Learned: DO NOT SCREW UP THE BRAKE LIGHT SWITCH ADJUSTMENT when you replace the booster.

 

There's nothing left for the third day except to bleed a little air out of the cooling system, bleed the brakes, and torque the lug nuts. I haven't done that yet, but it shouldn't take more than an hour.

 

TOTAL TIME FOR THE JOB, the second time I've done this = 7.5 hours, including repair of several vacuum hoses and the brake light switch R 'n' R. It "should" have been about 5--5.5 hours.

 

GM Flat rate is probably about an hour and a half--which is why I don't do this for a living.

Edited by Schurkey
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  • 1 year later...

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