Two problems:
1. I still cannot achieve a firm brake pedal even though I have bled the brakes multiple times, both with a power bleeder and the old-fashioned method of pumping the pedal.
2. My rear pads have worn down to nothing and my front pads look new.


Here's the short version of my brake problem history:

I've had a soft brake pedal since I bought the car almost four years ago. The brakes seemed to work fine though, as well as the ABS - I had to make an emergency stop coming down a hill a few years back and the brakes performed perfectly.

In the past year or two I have noticed that my rear wheels lock up (engage ABS) before the fronts. I attributed this first to the rear calipers locking, then to the ceramic pads I put on the rear being too aggressive.

I have replaced: the master cylinder (expensive); the front calipers (expensive); the rear calipers; front and rear rotors (ATE); front and rear pads (AXXIS Semi-metallic); brake hoses (Meyle); and I have bled the brakes about a dozen times, using around two gallons of DOT 4 fluid (expensive).

What else could be wrong, and how can I get a firm brake pedal?

I'm about to the point of taking the car to a shop and saying "Do what it takes to fix it." And I HATE doing that.

Just an update: I'm still having the same problems 6 years later.

My '93 sedan has been scaring me with the lack-luster braking performance lately (especially after my emergency brake shoes disintegrated) so I went so far as to buy new stainless steel hoses and have an independent Volvo shop (trusted) install them (I'm ashamed, but I simply don't have the time to do it myself these days).

No change in braking performance. I was being somewhat abusive on the way home from the shop and stood on the brake pedal as hard as I could - rears locked up but not the front. The front pads show little evidence of wear, as before.

Although the brake pedal feels just okay, and there is probably some air trapped in the system, it seems the front brakes just don't apply as hard as they should. And the car does not stop like it should. After the Volvo shop with nearly 40 years experience bled the brakes, I redid it and still no help.

I'm still operating on the theory that the ABS modulator has air trapped inside. I have not yet tried isolating the circuits to try to identify the one with the spongy pedal feel.

I read a T'bricks post suggesting that the only way to get all of the air purged from an ABS 240 is to activate the ABS several times, bleed, then do it again. I've been tearing up gravel the last couple days in an attempt. We'll see how it goes.

I did learn something interesting recently about the ABS - you can perform tests at the connector (under the friggin' passenger seat) to activate the pump and the solenoid in the ABS modulator. Might be worth trying while I bleed next time. Actually, you can activate the pump by jumpering terminals 30 and 87 of the relay on the ABS modulator. I would guess you could do the same with the solenoid . . . this might lead to me building an interrupter to cycle the solenoid and pump while bleeding.

Art, or anybody else familiar with electronics: what do the grounds inside the arrows mean inside the ABS control module (K) on the below picture? Is this a ground that is made or broken by the module? If I wanted to cycle solenoids (N, O, P) from the engine compartment would I need to jump the relay and switch the grounds as well? I don't have the Bentley in front of me, can't remember which pin it suggests grounding at the connector to activate the solenoids.

You could watch what it was doing, while braking, by adding 4 lights or LEDs inside the car, one for each solenoid and one for the pump. Splice them into the harness near the controller at the orange, green/yellow, yellow/black, and green/red wires. Refer the solenoid indicators to blue/white for common + and refer the pump motor indicator to black (ground).

The ABS light already verifies the power relay contacts for the solenoids.
--
Art Benstein near Baltimore

“How can I answer this and stay opaque? Tina Fey

That would be a neat addition to my custom switch panel in the lower cubby - twinkling lights every time I brake too hard!

Triangular pattern to represent the circuits?

A worthwhile project, I think, after the Christmas brake, er, break.

It might be a little premature, as well. If your front pads are not wearing, I doubt the controller will ever attempt to modulate them; just your rear brakes it seems. You could verify that with the geeky lights but they would serve better to validate a fix of the hydraulics afterward when you take it down the gravel road.
--
Art Benstein near Baltimore

"The realm of preconceived notions is not a friendly place to have an opinion."

I found out today that the connector at the ABS modulator/pump has a cover that snaps off the back, allowing easy access for tests on that end of the system. Ground pin 11 to run the pump (no more than 2 seconds, warns Bentley); pin 2 tests the solenoid relay.

Pins 1, 3, and 5 of course activate the solenoids. I heard each click, but the odd thing was that one click is all I could get. I was hoping to cycle the solenoid open and closed while bleeding brakes, but after every time I activated a solenoid, I'd have to turn the key off, then back to position II to do it again. Must be a protective feature that I'll have to study more to bypass.

In any case, good start to learning about the ABS module.

I took the car out for some minor vandalism again, drifting off the road onto the gravel shoulder, and was able to get the ABS to modulate each front brake circuit, I think. Bled another pint of brake fluid through each front caliper. Lather rinse, repeat. Finally, I also popped the master cylinder off the booster to check for fluid, and decided to extend the push rod a bit. I found it a few mm short of touching the end of the master cylinder at rest.

Conclusion is that the car seems to stop a bit better, but the pedal still feels terrible. I still think I'm looking for a compressible causing a mushy feel, i.e. air. I think I'll drive it for a while and reevaluate.

Another 6 years? Sooner, I hope.

If you can get a chance, scratch that itch about the solenoids needing a power off reset once set. That could only be a feature of the controller, so repeat the test, but monitor the pin with a test light or voltmeter as you ground it to operate it. See if the voltage remains low after lifting the ground probe, and then if it goes high again when you cycle the power.
--
Art Benstein near Baltimore

Does the name Pavlov ring a bell?

While Googling the Brickboard for more answers, I came across this photo comparing the '91 ABS junction block (top) to the pre-ABS "Octopus" (bottom):



Which I found quite surprising because the junction box in my '93 240 has more resemblance to the bottom valve (the "octopus") than the top junction box, except that it does not have the switch.

So on a hunch, I stopped reading about 240 brakes and read about 740/940 brakes. Look what the Volvo greenbook says of '92+ models:



Yep, I'm pretty sure I have a reducing valve which limits pressure to the rear brakes except under failure of the fronts, at which point it dumps braking power to the rear.

I think I might be on to something...

Sean, the description is incorrect in your findings above. The top photo is that of a '91, but it is a NON-ABS '91 junction block -- a coveted pick and pull item for replacing the item on the bottom.

An ABS '91 has the pressure reducer you see in your 93. I have one saved from a car for the eventual curiosity take-apart Saturday. It does not function anything like the octopus, which was a pressure differential switch, rebuildable only in giving it new o-rings (doubtful success) or replacing the switch (might as well just clean it).

But it sure sounds like something which could have snapped in your car when you hit the brakes hard that one day things changed for you.
--
Art Benstein near Baltimore

Despite rumors to the contrary, a mime is actually a very satisfying thing to waste.

Art, you are of course right; I misread the photo description. Maybe I did the same thing years ago, as I was sure that the ABS system was not supposed to have any proportioning valve exterior to the modulator. In fact, in my recent searching, I have seen that and similar sentiments posted many times on multiple forums. I think the general misconception is that ABS 240s have no octopus, thus, no problematic valves.

Now I learn that not only does the ABS system have a proportioning valve, but a rather complex one at that. (Now I understand what you were trying to tell me about the value of the brake components on the '91 parts car I had last year.)

I wonder if I could gut the junction block, doing away with the safety valve?

"I wonder if I could gut the junction block, doing away with the safety valve? "

Something tells me that's how it is acting now; as if it is gutted, or a spring has rusted, allowing intermingling of front and rear fluid pressure. That would explain the worn rear pads and no braking force on the fronts.

Just a guess, of course.
--
Art Benstein near Baltimore

Dijon vu: the same mustard as before.

My guess is similar: that at some point the thing got half-cocked to the front-failure mode and is now limiting the pressure there rather than the rear. I have seen some mention on the interwebs of these devices being related to a spongy pedal, but nobody has any anecdotes regarding the 240.

Another mention of the reducing valve in the Volvo greenbook:



I notice parts sites sell them for 740, 940s, even FWD models, but not for 240s!

Wonder if there's a rebuild kit like for the non-ABS octopus?

I see something similar to this my 93 240, it is mounted down on the frame where the octopus was located on earlier cars. Not under the MC as depicted.
Dan

Dan,
Mine is in the same place you describe, on my '93 240. Surprising that there is so little information about a potentially critical part of the ABS 240 brakes. Even most parts sites don't have it listed for 240s, but 740s through S90s all have it listed.

The arrow indicates the pin is an output on the module. The ground symbol inside gives you a clue what to expect when active. These look like open collector outputs, meaning they supply a "ground" to the external solenoid or relay they are activating. In all these cases I would feel safe substituting a physical ground (jumper to ground) to create the same effect, or if you wanted to see if they were active, a test light referenced to battery + would be lighted when active.

Instead of jumping the relay 30 to 87, you would just supply the ground to the relay coil to have the same effect, which at the same time verifies the relay works.
--
Art Benstein near Baltimore

"Shun those who say we have eyes in order to see, and instead say we see because we happen to have eyes."

I bled them one more time this morning, this time with my father's aid, the old-fashioned way. The brakes are not firm, but they feel safe now. That's the best I've ever achieved. Maybe I'll drive it for a while and try bleeding again, but I guess I have to accept that these brakes may never be whiplash hard.

I'm hoping the new calipers fix the front/rear imbalance problem.

all 4 calipers WILL bleed with abs not electrically energised

little or no front pad wear indicating zero or near front brake line pressure while system energized

to confirm no line pressure at the front calipers you would need to get a gauge test kit to measure line pressure with the brake applied with the engine idling. but i suspect you have little or no front line pressure.

worn out rear pads

new calipers, new MC.

imo the front serving solenoids in your abs modulator are not opening when energized to allow fluid pressure into the front calipers and or the electrical circuits (ABS ECU) which send signals to the modulator are not sending a signal.

i do not think at this point trapped air within the abs modulator ... alone is causing your problem.

I've thought maybe something was wrong with the ABS system, but that doesn't make sense either. To my knowledge (not extensive, concerning ABS) the brakes function like a normal hydraulic system with no electronic fiddling until a wheel locks up. So electrical ABS problems shouldn't be causing a spongy pedal, right? Also, my ABS light has never been lit (yes, the bulb works).

What if a fuse were burnt out or a connector loose/severed/corroded? Wouldn't I get an ABS warning light? Even then, would it affect brake pressure?

A friend (one of our board members) has driven my car and noticed the spongy pedal. She also has an ABS system, but her pedal is rock hard. Now here's the kicker - I'm pretty sure she said she disconnected the ABS system. That should be proof right there that ABS or no, the brake system will function fine.

Hmm. If I ever figure this one out, I'll make sure you all know the answer. I'm out to bleed my brakes a few more times.

Yup, my ABS does not work. Not sure why, never bothered to track it down. The light is burnt out/gone. I'm guessing the PO couldn't/didn't want to fix and so pulled the bulb. Anyway, I had the same soft pedal as you until I put new front calipers on the car. So you can get working brakes without working ABS, but it could still be an ABS issue.

I described your problem to Ben, his thought was that it could be a proportioning valve, if the volvo has one. That could explain why the front brakes aren't doing enough work, hence unworn pads, and the soft brakes come from having to push harder to make the rear brakes do all the work. Granted, I don't actually know if volvos have a proportioning valve--it may be part of the junction box?

I also came upon this post about ABS stuff (http://forums.swedespeed.com/zerothread?id=122441). Not sure if it's relevant, but thought I'd share. If you want to try replacing any ABS parts, you're welcome to whatever there is on my parts car--that one did have working ABS.

Looks like the 240 ABS has no proportioning valve. The regular 240 brake system has pressure regulators which keep too much force from being applied to rear brakes, but I see nothing of the sort (in Bentley) on the ABS system. Of course, it could be built into the ABS modulator box. Good thought, though. Thank Ben for me.

I appreciate the offer, Laine, I might think about taking you up on it next time my brakes piss me off/scare me. There's really only one thing I haven't replaced in the ABS system, and that's the ABS modulator.

Hi Laine!

Yeah, I remember you saying that new front calipers fixed your problem. I've finally got all the calipers replaced, new pads, and I've bled a lot of expensive fluid through the system. Still not great - feels about the same.

I'm going to check into the proportioning valve thing. I don't know what could possibly go wrong with one to make it behave this way, but it's worth a shot.

Thanks!

Hi Sean,

No, I haven't run into this.

Could be a red herring, but a friend got air in his modulator, an Alfred Teves (ATe) device called an HCU in Fordspeak as used in his 93 Exploder. The official literature all calls for a special electrical tool to cycle the solenoids and work the air out, fixing the mushy pedal. Some info in the forums alluded to the air eventually migrating through merely by using the ABS on loose surfaces.

I'd never heard of air pockets in Volvo ABS bleeding, and the friend with the Exploder rigged a windshield washer pump as a pressure bleeder in reverse - forcing his DOT-3 up from the wheel cylinders - to watch the air bubble out in the rez.

Front pads not getting applied sure does localize the problem. Is it possible to deadhead the fronts past the modulator?
--
Art Benstein near Baltimore

TLH FCK OCT BCR

"Deadhead the fronts past the modulator?" Sorry, Art, I don't understand. Translate please.

Good idea about the modulator though. I have a spare windshield washer pump, I could always try the same thing.

These brakes are now soft to the point of dangerous. Last time I had to bleed several times just to get enough pedal to feel somewhat comfortable driving. $30 in fluid. I'm going to start recapturing my expelled fluid in a clean jar, filter it, then run it back through.

Wonder if I can fools the ABS system into modulating the brakes while I bleed . . .

"Deadhead the fronts past the modulator?" Sorry, Art, I don't understand. Translate please.


I suppose you are trying to figure out what dancing bears have to do with ABS.

What I mean is, a methodical approach to finding the compressible in a system made up of non-compressibles would have you divide and conquer. If it appears your rear brakes are working, but fronts not, the sponginess is likely in the front circuits, so "deadheading" amounts to plugging the line to isolate the part where something is giving the springy feel of air.

This is, like I said, probably a snipe hunt, if there's no way to block the lines to include the modulator but exclude the front calipers. In the non-ABS, the circuits are triangular, so putting a soldered-shut brake line on either primary or secondary master port can help find where the air is hiding. I'm pretty sure I learned about the mismatched-half non-ABS front caliper rebuilds that way.

I was hoping someone experienced with ABS in the 240 would have chimed in. I am not.
--
Art Benstein near Baltimore


"Any intelligent fool can make things bigger and more complex. It takes a touch of genius - and a lot of courage - to move in the opposite direction."
-Albert Einstein

Art, I think I could do it, yes. Next time I feel like cracking the lines and buying another gallon of fluid, I'll give it a try. I see no reason I couldn't block off the front calipers - block the rear, block both, and so on - to see where the spongy pedal is coming from. Dollars to donuts the problem is the ABS modulator. Whether air or dirt is trapped, or something is out of adjustment or broken, I suspect the modulator box of allowing too much pressure to the rear brakes and giving me a soft pedal.

Thanks for the thoughts. Once again, I'm a little poorer and exhausted, so I'm calling it quits for a while. The brakes are back to their lackluster, though moderately effective, performance.

have you ever messed with the brake balance valve (or whatever technical term it's called)? sounds like your rear brake is getting more pressure than they should. how do the rear hoses look like?

Haven't messed with anything beyond what I've listed. I haven't checked the rear hose either, I guess I should, but I would think a weak hose would cause the opposite problem (weak rear brakes).