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soft spongy brakes after simple pad change

Help, Advice, Owners' Discussion and DIY Tutorials devoted to the second generation C70, S40 and V50 Volvos -- awkwardly model year 2004 ½ onwards -- plus where to go for advice and discussion on Volvo's sporty C30 Coupe powered by Volvo's ubiquitous inline 5-cylinder power plant.
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dieudonneMC
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soft spongy brakes after simple pad change

Post by dieudonneMC » Wed Sep 12, 2018 2:47 pm

I changed my front pads and now have spongy brakes. No, I did not leave the cap on when pushing the caliper pistons back in for either side. Simple pad change is something I have done on many cars over the last 30 years and have done this at least 4 times on this 2006 T5 V50.

I bought a brand new master cylinder, bench bled it then we bled all of the wheels in order of Rear passenger, rear drivers, then Front passenger and finally front driver's. It seemed nice and firm but went soft as soon as the car was started. I noticed I failed to
put the MC o-ring gasket on, so had to remove the new MC and reinstall with the O-ring on it this time. We re-bled the system as before and now Same result, soft pedal when car is running. This has never happened to me before.

I noticed the vacuum pump for the booster was not working so replaced it ( used one ), rebled system this time but this time with ignition on and in the run position, still soft brakes but better. I could now drive vehicle around the block but pedal goes to the floor, pumping helps. Before I had zero stopping power! I ordered a new pump, since the used one I bought runs hot and is very loud. I believe its going to die soon.

This still does not address the original problem of a soft spongy pedal with after simple pad change. I never touched anything that involved letting air in the system. Is there anyone who can tell me why this is happening? I am almost ready to rool this car in front of a MACK truck or train or down a cliff side.

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RickHaleParker
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Re: soft spongy brakes after simple pad change

Post by RickHaleParker » Fri Sep 14, 2018 9:40 pm

My best guesstimate is: One or both of the front brake calipers where on the fritz before you changed the brake pads. When you pushed the caliper cylinder back, the caliper went over the fritz.
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Re: soft spongy brakes after simple pad change

Post by jimmy57 » Fri Sep 14, 2018 9:46 pm

Have you driven the car or just feel like it is a soft pedal and have not tried the brakes? If you sit and push the pedal with higher effort with engine running the pedal can have a lot of travel and seem soft. You need to drive it to see if they work OK. Often the effort you apply with foot is significantly more than would be needed to panic stop the car with it fully loaded. If you drive it you may see that the brakes work fine and you will then see the brake pedal sensation is normal. Brake pads are softer until they get heated and the resins that bond the pile of fiber and metal bits that make the friction material gets cured. The friction material also must be embedded into the pores of the rotor surface is new rotors are used or the existing rotors are machined.

The anti rattle spring installation not being correct is also a known cause of the pedal being reported as soft or having excess travel. Especially the excess pedal travel part.

dieudonneMC
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Re: soft spongy brakes after simple pad change

Post by dieudonneMC » Sat Sep 15, 2018 7:33 am

The car can drive but if you need to stop you will not be able to. The pedal goes down to the floor and the stopping distance is considerably longer. As far as caliper being bad.... meh, I don't know. There are no leaks around it. With the anti rattle spring I would expect noise if it were missing. It is in no way connected with the hydraulics so why on earth would it be a cause of air in the line? You make the claim but where is the connection ? Explain how that spring can impact a sealed fluid system. I am going to take the wheel off and take everything down and try again. My new vacuum pump is here so that goes on. Remember, the brakes are hard until the engine starts and then they turn to ice cream.

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Re: soft spongy brakes after simple pad change

Post by crlande » Sat Sep 15, 2018 7:47 am

Air in the ABS control module? I have read it is a bear to get air out of all the channels without activating the valves and pistons inside the module.

dieudonneMC
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Re: soft spongy brakes after simple pad change

Post by dieudonneMC » Sat Sep 15, 2018 9:11 am

I have heard of air in ABS, yes! It happens on bmw, benz, etc so why not volvo. The question is how is it removed? Can we bleed with the motor running? The bigger question is this: How does air get intoduced into a closed system in the first place? I have been doing this same procedure for decades with many different automobiles and this has never happened to me or anyone I know. I am headed outside to pull apart the wheel and have another inspection. And we will see. Mind you, there was nothing at all wrong with these devilish brakes ahead of just changing the darn pads!

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Re: soft spongy brakes after simple pad change

Post by matthew1 » Sat Sep 15, 2018 9:12 pm

From a post by Neil Baird on the MVS Facebook page:
I have had this problem before 4 times on 4 different makes of car, on a SAAB 900 it was an air-lock caused by one of the rear calipers having the bleed nipple in a position that ment when even when it was bled installed on the car , it was not at the highest point so air could not be forced out of it , this was a caliper that was replaced at some stage with an aftermarket " re-conditioned" exchange one .

Also on a mazda 5 mpv this problem was air that entered by low fluid levels, this was fixed by using a positive pressure bleed in reverse , it was time consuming as each caliper had to have its own reservoir and the feed pipe cable tied on to keep it from jumping off and spraying fluid everywhere, each pressurised feed was fed by the removed wheels air pressure supply in the tyres once let down to 15psi , and took 4 people to initiate all at once, and I was at the master cyl emptying the frothy fluid as it burbled up to the top.

On a XC90 we isolated a bulging flexi by clamping 3 corners with a pincher just as the metal brake pipe meets the rubber flexi hose, made with 2 large washers on a bolt/nut. nsf was the culprit , the fluid actually made 3 inches of the rubber pipe slowly swell like a sausage when you applied constant heavy brake pedal, and it disappeared when pressure was off. ( main dealer had charged for new servo here and owner was furious) ,

Peugeot 406 had air in the abs block , bled with slackening and tightening the pipes with the positive pressure kit feeding the master . The usual golf gti (1984 on ) problem that the seals in the master turn inside out or whatever when you force the fluid back in volume when spreading the caliper pistons .

Interestingly a Volvo 940 clutch slave/master was never successfully fixed and suffered a flappy clutch pedal at random , the master and slave wee replaced, the master and slave wee replaced again all to various degrees of its fixed, ohh no its not , highs and lows . Eventually I found out the previous elderly owner had died of a heart attack whilst loading the boot , and laid in there overnight at his allotment ( vegetable patch for you in the USA) which was the reason for the odd stain on the boot (trunk) floor from his body fluids. I sold the car the next day as it was probably haunted...….
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1997 850 T5, MSD ignition coil, Hallman manual boost controller, injectors, R bumper, OMP strut brace [gone]
2004 V70 R [gone]

dieudonneMC
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Year and Model: 2006 v50
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Re: soft spongy brakes after simple pad change

Post by dieudonneMC » Sun Sep 16, 2018 2:29 pm

Wow, those are interesting scenarios especially the last one. I would have sold it as well. They all seem to be different to my case but I was going to try rebleeding the master cylinder. The bench bleed lines were not clear so I could not observe the bubbles. I found clear tubing. We did try bleeding to all 4 wheel with the motor running with a very small improvement in pedal softness. The new vac pump helped too. We are still in the same situation however so I will redo the MC install and see what happens.

dieudonneMC
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Year and Model: 2006 v50
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Re: soft spongy brakes after simple pad change

Post by dieudonneMC » Tue Oct 02, 2018 2:34 pm

I skipped fooling with the master cylinder again. In stead I rebled the lines using a vacuum pump. Someone suggested doing a gravity bleeding, would have taken a lot of time. So I have the best result yet now but brake pedal now goes lower than before for the brake action to begin.

The car will stop but now I have to pump the pedal. I
Am now driving carefully and strategically. This will be temporary bc that dog won't hunt! I cannot stop on a dime right now. Im not so sure MC is bad, but it could be. What is the next step?

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