Braking problem

[dave h 2]

I'd double check on a vehicle specific forum/discussion group, or in the workshop manual on this - cycling the ABS system like that doesn't necessarily do anything, and bleeding the ABS module on some vehicles requires the use of a scan tool.
Some systems just bleed conventionally, and some are complete nightmares for no obvious reason.

I'm not familiar with that vehicle, but if its a common problem I guarantee you wont be alone - if it isn't a common issue then you can look elsewhere - but that would be my first port of call.

There are mentions of the Scan tool being needed on Dodge ram forums

 

[BelgiqueB]

Discs or drums at the rear?

Discs on all four corners

It calls out "faulty servo" to me.

Plumbed in a T piece in the servo pump pressure line, i get 50 bar when turning the wheels, 110 bar when i hit the wheels endstop. When pressing the braken pedal the pressure also goes up to 110 bar, so seems to be working allright?

Sometimes when bleeding a system people push the pedal all the way to the floor and into the unworn part of the master cylinder, for whatever reason I've known this to damage master cylinder seals, without the engine running place pressure on and off the pedal, jiggle it if you get me and see if the pedal creeps down to the floor

I installed a new master cylinder, problem remained the same as with the old master cylinder.

Did you bleed abs unit separately as well? Sometimes you need to and then re-bleed the brakes again. Otherwise I'd go for damaged mcyl.seals

I didn't as i have not have a scantool that can operate the abs unit.

Reverse bleeding to the modulator has twice saved the day for me.

What do you mean by this, i'm assuming you are talking about the ABS modulator?

Id be bleeding it again ,,, just as a starting point

I must've bled it 15 times at this point, all i get is a perfect stream of oil.


Reading all this, it seems like i'll have to invest in a 2nd hand scan tool that has abs bleeding capability...

 

[ajlelectronics]

What do you mean by this, i'm assuming you are talking about the ABS modulator?

Get a large syringe and some bleed tubing and put them together. Fill syringe with fluid and inject into the brake calliper nipple until it overflows at the modulator.

 

[james butler]

silly question but did you bleed the brakes diagonally ie rear left then front right, rear right then front left?
if you didnt and just did the furthest away in order this can mean your chasing air bubbles round the system and never coming out

 

[Bornfree]

I would clamp the caliper pistons fully in one at a time to see if one caliper makes any difference.

 

[8ob]

Have you bled the load compensating valve? Air can and does hang up in them.

Bob

 

[BelgiqueB]

Scan tool arrived, but unfortunately it didn't fix the issue.

However not all is lost.. , when i do the brake bleed procedure the feeling in the pedal is exactly the same as when the engine is running. With the engine off the pedal is firm, with the engine running it's soft and goes to the floor. If I do the brake bleed procedure with the scan tool (key on, engine off), the pedal is firm until the ABS pump is activated and then it goes to the floor, the exact same way as when the engine is running.

The scan tool shows no codes concerning the ABS system, the scan tool also has some more extensive functions, see picture below.

• When I activate the 'pump' with the scan tool the pedal drops to the floor similar as to when i start the engine
• When I activate either the left front, right front or the rear dump valve the pedal drops about 1 inch and then holds firm.

Since the feeling in the pedal is exactly the same when doing the brake bleed procedure, I'm thinking the ABS module is faulty, any thoughts on that? Throwing parts at this problem is becoming expensive :-(

Thanks, Christof.

 

[m_c]

The pedal can sink when the ABS works.

Do you have the proper ABS bleeding procedure?
Typically you need to connect a pressure bleeder (some systems can need quite high pressure), then open/close whatever bleed nipple the process says.

If you don't have the correct procedure, connect the pressure bleeder, open a nipple, and activate the valve for that corner a few times.
Also try running the pump when you have each nipple open.

 

[jo1010]

Sheesh. Things to try then....
1. Clamp off all flexi hoses and see if you get a good pedal when engine runs. If not then air still in abs modulator. If yes, then a wheel cylinder problem. Repeat clamping to identify which one is faulty.
2. Try manually bleeding with engine running - this brings booster into play. Check the stream of fluid from each caliper. If one is slow that suggests where the problem is
3. Jack up vehicle on stands, wheels off, bleed tube into a container of brake fluid and cycle the abs pumping the pedal with one caliper nipple cracked open.
4. Check the calipers are on with nipples at top of the caliper (haha ...sometimes it's possible to put them back on the wrong way up)
5. I think abs modulator failure unlkely - no warning lights showing ? And no stored codes?

 

[BelgiqueB]

The pedal can sink when the ABS works.

Do you have the proper ABS bleeding procedure?
Typically you need to connect a pressure bleeder (some systems can need quite high pressure), then open/close whatever bleed nipple the process says.

If you don't have the correct procedure, connect the pressure bleeder, open a nipple, and activate the valve for that corner a few times.
Also try running the pump when you have each nipple open.

Sheesh. Things to try then....
1. Clamp off all flexi hoses and see if you get a good pedal when engine runs. If not then air still in abs modulator. If yes, then a wheel cylinder problem. Repeat clamping to identify which one is faulty.
2. Try manually bleeding with engine running - this brings booster into play. Check the stream of fluid from each caliper. If one is slow that suggests where the problem is
3. Jack up vehicle on stands, wheels off, bleed tube into a container of brake fluid and cycle the abs pumping the pedal with one caliper nipple cracked open.
4. Check the calipers are on with nipples at top of the caliper (haha ...sometimes it's possible to put them back on the wrong way up)
5. I think abs modulator failure unlkely - no warning lights showing ? And no stored codes?

Back with an update, still no succes i'm afraid.

Did all of the above, am using a power bleeder that puts the entire system under pressure (between 10 and 20 psi), while having the system under pressure and with the engine running I re-bled the abs module using the scan tool, re-bled 5 times per caliper but still no improvement, saw no bubbles whatsoever during the bleeding procedure.

Then clamped off the rubber hoses for the four calipers as suggested and suprise suprise a firm pedal, turns out that there is an issue with both the front calipers. Releasing the clamps on the rear caliper hoses gives no difference, however releasing the clamp on either of the front calipers gives a firm pedal.

The front calipers are four piston calipers, upon further inspection on both calipers there is one piston that retracts more than the rest, on the good pistons i'm unable to put a 0,05 mm feeler gauge inbetween when the system is depressurized looks like they stay in contact with the pad , on the 'bad' pistons i can put a 0,1mm feeler gauge inbetween. It takes a couple of cm of brake pedal depressing before i can visually see the piston engaging the pad and only then the pedal gets firmer.

Looks like i messed something up on rebuilding the calipers and will have to pull them apart to see what the issue is. Any tips welcome :-)

 

[Misterg]

View attachment 501925

Are those old pads?

 

[jo1010]

You might get clues from what was replaced in the refurb? New pistons? New seals? Are parts correct?
Before taking caliper off I'd take one pad out at a time and watch how the pistons move with one or two strokes of the pedal - they should all move at the same rate. Slow ones show where the problem is. Repeat test for each pair of pistons.
Beyond that it's stripping and inspecting pistons (measuring pistons too) bores and seals

 

[dobbslc]

It would be worth checking how far the pistons retract once the peddle is lifted.

 

[8ob]

The problem is the brake pad ( lower picture), the plate itself looks distorted. Its acting like a spring and pushing the piston back. Put new pads in it.

Bob

 

[BelgiqueB]

Touché :-), and the worst part with hindsight it's also the logical conclusion. All i did was refurbish the brake calipers, so a large possibility that the issue was there and not further up in the system. Good thing is I have a nice scan tool now for future use :-).

 

[BelgiqueB]

The problem is the brake pad ( lower picture), the plate itself looks distorted. Its acting like a spring and pushing the piston back. Put new pads in it.

Bob

Will have a look into it and see how straight they are, they are good quality EBS pads though.

What's the function of the thin sheetmetal plate on the back of the pads between the pistons and the pad itself?

 

[BelgiqueB]

Are those old pads?

Used pads but still have plenty of life in them.

 

[Haz87]

Used pads but still have plenty of life in them.

Really? Unless the angle is confusing me or the disc has a huge outer lip, they look pretty bloomin' low.

Also, I know you you said they are good quality EBS pads - I assume you mean EBC? In which case were they from a truly reputable source, EBC have to be up there as one of the most counterfeited pads going.

 

[RWD3M]

What's the function of the thin sheetmetal plate on the back of the pads between the pistons and the pad itself?

To prevent squealing. Otherwise known as an anti-squeal shim.

 

[Misterg]

Used pads but still have plenty of life in them.

They look at least 80% worn to me, and they look to be tapered (which I think is causing all the symptoms you describe).