Chad Posted July 22, 2009 Report Share Posted July 22, 2009 I got a 98 4 chev tahoe, had soft brakes when I got it. I replaced the front with all new calipers/pads/rotors and did a full fluid flush up front. No change at all in braking performance. I noticed a signifigant amount of fluid came up out of the resivior when bleeding (enough to cover the engine and firewall) so I suspected the master had a bad seal. I replaced the master and also got new shoes for the rear drums and bled the rear as well as re-bleeding the front. Same squishy brakes. Still only stops about 1/2 as well as it should. I have an 97 tahoe too so I have a valid comparison. I also decided to bypass the brake booster by removing and capping the vacuum source just to eliminate posibilities, no change, still squishy but obviosuly much harder to stop with no assist. I also verified the ABS works, got up to speed on a gravel road and cycled it several times, ABS works exactly as it should, front and rear. I'm at a loss at this point, all the moving parts are new, fluid is fresh and been flushed propperly. I bench bled the master according to the insturcitons in the box and I'm confidant I did it right. It's exaclty the same as when I got it, but now lots of new parts. My only idea at this point is a bad solenoid in the ABS, but I don't want to try to track one down just on a hunch. Any suggestions? The old front pads had about 40% left, and the rear shoes about 50% left. Link to comment Share on other sites More sharing options...
Komeuppance Posted July 22, 2009 Report Share Posted July 22, 2009 Sounds like it needs more bleeding... How bout those brake lines?? Nice and squishy rubbers?? Might be a minute crack allowing air in, and reducing pressure. -Robert Link to comment Share on other sites More sharing options...
Komeuppance Posted July 22, 2009 Report Share Posted July 22, 2009 BTW... wrong forum NOOB!! Link to comment Share on other sites More sharing options...
Chad Posted July 22, 2009 Author Report Share Posted July 22, 2009 Yah, it wasn't stock, nor advanced, so I figured maybe it belonged here instead :confused0024: The lines "look" OK, but I should jack it up and have the wife stomp on the peddal while I watch the lines for swelling. There is no leakage or fluid loss BTW. The old fluid was 2/3 full looked dark and "origional", so I doubt it's been leaking and frequently topped off by the PO. Link to comment Share on other sites More sharing options...
Chad Posted July 22, 2009 Author Report Share Posted July 22, 2009 the soft lines dont' swell. they do move (try to straighten out) but far too little movement to account for this amount of "squish" feel Link to comment Share on other sites More sharing options...
Coke Posted July 22, 2009 Report Share Posted July 22, 2009 Slider bolts free? Calipers working as they should? Bled the master cyl before install? Link to comment Share on other sites More sharing options...
Shelby Posted July 22, 2009 Report Share Posted July 22, 2009 once in a while you have to do what may be call'd odd ball testing,, go to a u-pull it and get some master cyl brake line ends , leave enought line to cut roll mash what ever to close them off , but not too much as to hold much air , now start with the rear fitting ,screw the now block'd off fitting into the master , bleed it a little , now see what sort of petal you have with key off,, now turn the key on while holding pressure on the brake petal,, lissen for a CLICK as you turn on the key,also most times you can feel the ABS solonid as it operates , if you felt/heard the solonid then the abs solonid is working,, back to your petal is it hard , with the frt wheels off the ground the frt pads should apply as normal , in fact the petal should feell like a normal very high brake petal ,, operate the brakes a couple times did the vacuum assist work for 3 or more times,, and now you have a very hard petal, , now keep light petal pressure on the brakes and start the engine,, did you feel any change in the petal it should have gone down slightly and got softer as vacuum builds up , , now spin the frt wheel and have some one lightly begin to apply brakes,, stop when you feel the pads starting to stop the wheel,, how far did the petal travel should have start'd holding the wheel by 3/4 inch petal travel now to test the frt brake , replace the rear master line with normal line and install block'd fittinng in the frt , if it has 2 frt wheel lines you'l need to block both,, in factif the master has 4 lines,, you'l need to block each set for testing frt and rear ,, now the frt part of the master will not move,, but the rear section of the master cyl pistons will operate as normal,,that means if the rearbrakes have a problem the petal will be soft and low,, but if the rear brake system is in order the petal will be a full petal as normal ,, almost all petal height is control'd by the rear brake protion of the master cyl,, the rear system fluid pressure acts like a mechanical link to operate the forward portion of the master cyl piston,, this is because the fluid inbetween the frt and rear pistons will not compress so the pressure is apply'd to the frt piston at the same time it's apply'd to the rear shoes or pads , improper booster operation or shoe adj or air will cause the rear master cyl to continue to move untill such time as the pressure can move the frt piston or the two pistons touch and the frt one has to move many GM's had a hyd assist booster system this can have air in it same as power steering,, with like results , soft spongy petal , bleed it just like the power steering Link to comment Share on other sites More sharing options...
spoolinturbo Posted July 22, 2009 Report Share Posted July 22, 2009 proportioning valve to the rear brakes?? i did some research for you...and it seems that squishy brakes is a problem from the factory for pretty much all tahoes ever haha Link to comment Share on other sites More sharing options...
nathan89quest Posted July 22, 2009 Report Share Posted July 22, 2009 I had the same problem on my 98 chevy 1500. Replaced all of the brake hoses front and rear. My brakes work like new now. Just my .02 Nathan Link to comment Share on other sites More sharing options...
Shelby Posted July 22, 2009 Report Share Posted July 22, 2009 best way to find a swelling hose is to actualy hold it in your hand as the brakes are apply'd ,, swelling flex hoses is one thing we never found much while working on euro cars but block'd hoses thats another thing,, lots of internal wall colapses stoping pressure to the pads or holding it on them and not releaseing the brakes the girling system use'd 8 seperate pistons think of it as a double X system , it could have strange brake problems Link to comment Share on other sites More sharing options...
Turborusty Posted July 22, 2009 Report Share Posted July 22, 2009 GM was plagued with problems like that for a LONG time. Happened to my brother's Grand Prix GT. Dealer kept telling him it was ok.....went on for 3 yrs like that. Scared the poo out of me when I drove it. Then he got fed up one day and bought a new brake booster and master cyl. then they'd put you through tthe window if you weren't careful. Turborusty Link to comment Share on other sites More sharing options...
craig87 Posted July 22, 2009 Report Share Posted July 22, 2009 some of those are just soft from the factory. if it is air you can clamp the three flex hoses hold the pedal and relaease the clampsone by one until the padal drops. aslo make sure it has the right size rear wheel cylinders. I have seen those installed by backyard mechanics. thers shyould have been two sizes offered. as far as air in the abs you need a scanner to bleed it. i think a snap on can bleed it but i use a tech2 on them so i;ve never tried the snappy or otc on it. Link to comment Share on other sites More sharing options...
Chad Posted July 22, 2009 Author Report Share Posted July 22, 2009 with the engine off, I press the brake to empty the booster. Then the peddal has resistance, but does drop to about 1/2 of it's stroke before it becomes fully firm. I had my wife jam on the brakes while holding all 3 of the soft lines in my hands, no apparent swell, but I may choose to replace them anyway. The booster was bypassed and opperated the same minus the assist, so I know that isn't part of my problem. The master was bled very carefuly, watching for all the bubbles to come out as instructed/described in the literature that came with it. My 97 tahoe has never had this problem and stops on a dime, so I know something is wrong with this 98. The ABS was tested on gravel several times, the front and rear both oppeate flawlessly, I can both hear it and feel it in the peddal. I think I'll get new soft lines and also get/fabricate some line plugs to isolate the problem. I can get some universal lines and bend over and tig weld the ends. I may have gotten a bad master cylinder I suppose, especialy if this is a common GM problem... Link to comment Share on other sites More sharing options...
Chad Posted July 22, 2009 Author Report Share Posted July 22, 2009 and I'm not about to accept this as "OK", it's not unsafe but deffinalty unacceptable. Link to comment Share on other sites More sharing options...
Turborusty Posted July 22, 2009 Report Share Posted July 22, 2009 don't overlook the soft line on the rear between the body and the axle housing. Turborusty Link to comment Share on other sites More sharing options...
Shelby Posted July 22, 2009 Report Share Posted July 22, 2009 if you have any leak down or petal movement at all with the line fittings block'd like i was talking about it says the piston seals are leaking internaly , rare but does happen vacuum boosters have what they call an atnospheric valve internaly , works much like a cruise control it gives you that sensitive feeling when your applying the brakes,, if it leaks the boster will push thru , it's also what makes the booster hard as a rock,,the entire diaphram holds pressure and pushes the assy forward against the master cyl,, with a leak the assy pushes against a spring and that gives untill it bottoms out , very much like the pri and secondary pistons in the master cyl frt and rear compartments many many years ago the booster assy's were repairable,, not fun but doable Link to comment Share on other sites More sharing options...
Zack_Morris Posted July 22, 2009 Report Share Posted July 22, 2009 Working at Sears as a mechanic for 4 years, I can't tell you how many times we had a full size Chevy with soft brakes. We had one in particular that nothing worked at fixing his soft brake pedal issue. We had it for 2 weeks and replaced the ENTIRE brake system with new parts from GM, hard lines and all. Still soft. There were also ones that would come in with pedals that felt like they had STi brakes. That's a GM for ya. Link to comment Share on other sites More sharing options...
PDX87Starion Posted July 22, 2009 Report Share Posted July 22, 2009 aslo make sure it has the right size rear wheel cylinders. I have seen those installed by backyard mechanics. thers shyould have been two sizes offered. Yeah make sure those rear drums are working correctly. Lots of parts and springs have to be correct and the shoes could be backwards or something. Have you stopped hard in gravel to see if the rears are even working? Link to comment Share on other sites More sharing options...
Zack_Morris Posted July 22, 2009 Report Share Posted July 22, 2009 (edited) Have you stopped hard in gravel to see if the rears are even working? I also verified the ABS works, got up to speed on a gravel road and cycled it several times, ABS works exactly as it should, front and rear. The ABS was tested on gravel several times, the front and rear both oppeate flawlessly, I can both hear it and feel it in the pedal. I'd say so Edited July 22, 2009 by Zack_Morris Link to comment Share on other sites More sharing options...
Chad Posted July 22, 2009 Author Report Share Posted July 22, 2009 Working at Sears as a mechanic for 4 years, I can't tell you how many times we had a full size Chevy with soft brakes. So of those that you succesfuly repaired, what fauts did you find? Link to comment Share on other sites More sharing options...
Chad Posted July 22, 2009 Author Report Share Posted July 22, 2009 the first time I hit the brakes hard on gravel, the rears loked up, the second and every time thereafter, they trigger antilock and drag but dont lock. I can also hear them bedding in Link to comment Share on other sites More sharing options...
Zack_Morris Posted July 22, 2009 Report Share Posted July 22, 2009 So of those that you succesfuly repaired, what fauts did you find? None. Calipers didn't leak, master cylinder didn't lose pressure, brake booster didnt lose pressure, hoses were replaced, wheel cylinders didn't leak. 99.9% of full size Chevy trucks and SUVs have soft brakes and that's just how they are. Link to comment Share on other sites More sharing options...
Guest Posted July 22, 2009 Report Share Posted July 22, 2009 Those things are known to have brake problems. The ABS pump is notorious for going out. Do what my customers do...call the local GM junk yard and tell em your problem, they'll tell you what you've got. Link to comment Share on other sites More sharing options...
Tman Posted July 22, 2009 Report Share Posted July 22, 2009 ok heres what you need too do get you some brake line pliers (you can use vice grips but i dont like to) I HAVE LINE LOCKS SIMILIAR TOO THIS http://toolmonger.com/wp-content/uploads/2...-hosepliers.jpg anyways place line lock on all 3 hoses then hit brake pedal see if its mushy still if it high and hard then you know the issue is in one of the wheels but if still mushy then its in master cylinder or abs unit Link to comment Share on other sites More sharing options...
Chad Posted July 23, 2009 Author Report Share Posted July 23, 2009 Thanks for the tip, that was better than trying to put in plugs which would then only need to be re-bled. I ended up calmping all 3 soft hoses with C-clams just after the fitting and tried the brake peddal, rock hard, engien running and when 'off' too... I relased the rear clamp and it was real soft so I readjusted the drums till they were good and tight (hard to get the drum on), ran it on jack stands and verifeid that they drag just a little but not enough to be a problem. with the 2 fronts still clamped and the rear re-adjusted, it was still quite hard so I'm confidant I got the rears adjusted propperly now. Now I released one front clamp at a time and it went soft both times. I got some new soft brake hoses but when I opened them I had 2 lefts, not one left and one right (mis packaged). So I put the new left soft line on and left the right clamped, still quite firm. Released the right clamp and the peddal semi-soft again. So I had 2 different problems: after I did the rear drums and did my road testing, I had to re-re-adjust them, and the front soft hoses were flexing even though I couldnt' feel them flex. I'll have the new right hose on tomorow AM and it should be a done deal Link to comment Share on other sites More sharing options...
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