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[D]

Was driving up north today. Somewhere along the journey the brake pedal started feeling a bit wooden. Lost the soft, progressive feel it had. Still had braking, just a different feel. Intermittently it switched back to a normal feel and then went wooden agin. A higher biting point as well, or perhaps less travel before I started getting a load of resistance.

Havent had a chance to look at the brake reservoir, but will do so tomorrow. But short of being low on brake fluid , what else could this be?

Also do the rear pads have wear sensors in them?

[ffcgary1]

Yes pads have ware sensors to one wheel only on some 3.2's.

[dbug]

No wear sensors on rear brakes - fronts both sides on pfl and mfl, nearside front only on fls

[chrisgixer]

Vacuum issue? Would you describe the problem is a difference in the level of servo assistance?

Pas side front brake calliper is the only wear sensor on the 3.2.

[05omegav6]

Vacuum issue? Would you describe the problem is a difference in the level of servo assistance?

Pas side front brake calliper is the only wear sensor on the 3.2.

Worth checking for chafing where the main vacuum hose crosses the air con pipes... does the car still idle normally

[chrisgixer]

As Al said. Plus, when starting the car with foot in the brake, you can feel the pedal resistance and the bight point change position, as the vacuum and servo assistance chimes in with engine revs.

Does that feeling at the pedal remind you of the symptoms you describe?

[D]

Yes, it does seem like the servo assistance is variable. Odd thing is that it seems to come and go.

Al, why did you ask about idle?

Any pictures of what this vacuum pipe looks like?

[firemoth]

Definitely servo assistance issue, probably down to vacuum. The comforting thing is your brakes won't fail. But be prepared to have to press your brakes hard if servo goes all together. I drove an astra like this for 3 months when the vacuum pump went altogether. What I would do if you intend to keep using the car, keep engine off and pump your brakes until the pedal is very firm. That is what you've potentially got to deal with. Try pointing car downhill and let it roll down (engine off ignition on) then you'll get a feel for what braking feels like with no servo assistance. When you start your engine the pedal will regain its normal feel (as long as your servo doesn't pack up altogether)

It's not recommended to drive like this, but it's doable if needed. I did a test emergency stop in mine to make sure I still had full breaking capacity if needed

[chrisgixer]

Yes, it does seem like the servo assistance is variable. Odd thing is that it seems to come and go.

Al, why did you ask about idle?

Any pictures of what this vacuum pipe looks like?

The brake servo is assisted by vacuum. The vacuum is taken from the plenum which runs at negative pressure when the throttle is closed, although throttle will vary on Dbw cars to allow tick over.

But, if there is a leak in the vacuum pipe for instance, (or anywhere else in the plenum connections such as the breather system for that matter) then that means more air is getting in to the plenum, and hence the engine inlet, than the maf has metered and more than the throttle has allowed. So the tick over will affected.

Throttle let's sir in. Air in means more revs. Let more air in anywhere else also means more revs. Therefor a vac leak means more revs, and as Al suggested, an uneven tick over.

Uneven, because is air gets in and the revs go up, the ecu will see this and close the throttle tickover setting to try to maintain 550rpm at all times. So the idle/tickover speed will go up and down and sometimes almost stall as the ecu tries to juggle the numbers and keep the engine idle speed constant. If it didn't, the tickover would sit at say, 1000rpm depending on how bad the leak is.

[TheBoy]

I too would suggest thoroughly checking vac system.

[TheBoy]

Uneven, because is air gets in and the revs go up, the ecu will see this and close the throttle tickover setting to try to maintain 550rpm at all times. So the idle/tickover speed will go up and down and sometimes almost stall as the ecu tries to juggle the numbers and keep the engine idle speed constant. If it didn't, the tickover would sit at say, 1000rpm depending on how bad the leak is.

Not quite - even if you held the throttle (or ICV) in a set position, you'd usually still get a hunt, same as you do on carburetted cars .

With injected cars, there is the further complication of the ECU trying to keep stuff in balance, but the hunt will already exist behind this, and the ECU is fighting the hunt.

[05omegav6]

The big black pipe from the passenger side of the plenum is the vacuum pipe as it crosses over the aircon pipe towards the bulkhead it chafes. A hole might only be present under certain conditions, hence the intermittence of your issue.

To test, engine idling, pop the bonnet and identify the vacuum pipe where it exits the plenum. Follow it along until it reaches the aircon pipe. They will likely be touching. Separate them and you will hear it hissing and the idle will stumble.

Ideally it will need a replacement pipe, but you can wrap it with tape as a temporary fix

[tigers_gonads]

Take the multirams vacuum system out of the equation by remove the 2 plastic vacuum pipes off the nipples on the brake servo pipe. Make sure they are well taped up and leak proof and go for a drive to see if it makes any difference.
Note fuel economy / performance will suffer a little 

[D]

As an update to this thread, the vaccum pipe was indeed leaking as Al thought. A bit of tape has temporarily patched it up.

Looking at a proper fix, what is the part no: for that tube running off the left edge of the plenum and how big a job is it to replace. Need to get the car in for a full service, cam belt etc. So may as well get everything sorted at the same time.

Also who seems to be fixing Omegas on OOF nowadays. Currently in W Yorkshire for 2 weeks if location is of any use.

[Andy H]

DLK is offering his services in the London area at the end of the month On my to London if anyone needs any work doing