Hard brake pedal after driving a while

Jakg · 29th June 2016, 19:04

Bit of an odd one.

If I drive for say 20 miles without using the brakes, when I do come to use them the pedal requires a lot more force than usual and doesn't seem to slow the car down anywhere near as much as usual.

If I then apply the brakes again - fine.

Thinking something vacuum related.

Any ideas?

Ravinder · 29th June 2016, 19:27

Vacuum or air in the system, perhaps?

murphyv310 · 29th June 2016, 19:32

Faulty vacuum pump or pipework.
Diesels don't use the inlet manifold for vacuum as they are not throttled.

HarryM1BYT · 29th June 2016, 19:40

Quote:

Originally Posted by Jakg

Bit of an odd one.

If I drive for say 20 miles without using the brakes, when I do come to use them the pedal requires a lot more force than usual and doesn't seem to slow the car down anywhere near as much as usual.

If I then apply the brakes again - fine.

Thinking something vacuum related.

Any ideas?

Does the pedal also seem more solid when you first press it?

One test you could try, is how long the servo holds its vacuum for once parked up / engine off. Mine holds it indefinitely - I can go to the car days after I have parked up and get around three presses of the pedal, before exhausting the vacuum/ pedal going solid with engine off.

Jakg · 29th June 2016, 23:08

Quote:

Originally Posted by murphyv310

Faulty vacuum pump or pipework.

Is there a diagram anywhere of all the vac lines? I've replaced the ones going from the EGR to the battery box already just in case.

Quote:

Originally Posted by Ravinder

Vacuum or air in the system, perhaps?

I don't see how air in the brakes would be likely to cause this?

Quote:

Originally Posted by HarryM1BYT

Does the pedal also seem more solid when you first press it?

Apologies if this a silly question - with the engine off or on? Off its stiff as a rock.

HarryM1BYT · 30th June 2016, 06:49

Quote:

Originally Posted by Jakg

Apologies if this a silly question - with the engine off or on? Off its stiff as a rock.

If it instantly or very soon after goes hard after switching the engine off, then you have a vacuum leak.

With the engine off and for at least several hours, it should hold enough vacuum to press the pedal with vacuum assistance available for 1 to 3 full presses of the brake pedal. Mine manages 3 days/weeks after engine off.

If the vacuum is exhausted as above and the pedal kept pressed down, whilst the engine is started, the pedal should become soft and go down. Note I am not sure whether it uses a mechanical pump or an electric pump, so engine off, might need the ignition to be off too.

Hard = there will be very little movement when you press the pedal, which means no vacuum assistance available.

Soft = the vacuum/ servo will be assisting you to press the pedal so it will feel much softer under your foot.

If it fails that test, then likely you have a vacuum leak somewhere - The pipe work, the EGR, the vacuum pump, or the servo itself.

I am slightly puzzled by your suggestion that on the road, your brakes are initially poor, but then improve after the first press.

Jakg · 1st July 2016, 19:03

Quote:

Originally Posted by HarryM1BYT

If it instantly or very soon after goes hard after switching the engine off, then you have a vacuum leak.

With the engine off and for at least several hours, it should hold enough vacuum to press the pedal with vacuum assistance available for 1 to 3 full presses of the brake pedal. Mine manages 3 days/weeks after engine off.

If the vacuum is exhausted as above and the pedal kept pressed down, whilst the engine is started, the pedal should become soft and go down. Note I am not sure whether it uses a mechanical pump or an electric pump, so engine off, might need the ignition to be off too.

Hard = there will be very little movement when you press the pedal, which means no vacuum assistance available.

Soft = the vacuum/ servo will be assisting you to press the pedal so it will feel much softer under your foot.

If it fails that test, then likely you have a vacuum leak somewhere - The pipe work, the EGR, the vacuum pump, or the servo itself.

I am slightly puzzled by your suggestion that on the road, your brakes are initially poor, but then improve after the first press.

I gave it 10 mins after a drive and I got two assisted pedal pumps before I lost vacuum.

klarzy · 1st July 2016, 19:37

If you have an EGR bypass or have disabled the EGR solenoid, make sure the cloth covered vac line to this or the pin on the bypass is not perished or free as this will lose vacuum, especially as the engine is cold the CPU will try to open the EGR valve and this will leak

HarryM1BYT · 1st July 2016, 20:00

Quote:

Originally Posted by Jakg

I gave it 10 mins after a drive and I got two assisted pedal pumps before I lost vacuum.

Unlikely to be a vac leak, under normal conditions then..

Klarzy maybe has the answer above?

Jakg · 1st July 2016, 20:30

Quote:

Originally Posted by klarzy

If you have an EGR bypass or have disabled the EGR solenoid, make sure the cloth covered vac line to this or the pin on the bypass is not perished or free as this will lose vacuum, especially as the engine is cold the CPU will try to open the EGR valve and this will leak

Quote:

Originally Posted by Jakg

Is there a diagram anywhere of all the vac lines? I've replaced the ones going from the EGR to the battery box already just in case.

It's bypassed but as above the hose has been replaced - but the leak could be further up the chain?

29th June 2016, 19:04	#1
Jakg This is my second home N/A Join Date: Feb 2010 Location: Suffolk Posts: 6,867 Thanks: 0 Thanked 397 Times in 302 Posts	Hard brake pedal after driving a while Bit of an odd one. If I drive for say 20 miles without using the brakes, when I do come to use them the pedal requires a lot more force than usual and doesn't seem to slow the car down anywhere near as much as usual. If I then apply the brakes again - fine. Thinking something vacuum related. Any ideas?

29th June 2016, 19:27	#2
Ravinder This is my second home Rover 75 saloon x2, Rover 75 Tourer x2, Rover 220 Coupe Turbo Join Date: Aug 2010 Location: Kirkcaldy, Fife Posts: 9,036 Thanks: 2,278 Thanked 2,852 Times in 1,718 Posts	Vacuum or air in the system, perhaps? __________________ Wanted - Indian bride. Cash waiting. (All sorted - bargain) First name and forum name: Ravinder Rover 75 2.0 CDT Connoisseur SE 116 (160 remap) Royal Blue (JFM) This vehicle was the 50,481st 75 to run off the production line, out of 112,381 This vehicle was the 2,238th 75 CDT Connoisseur SE to be made out of 3,775 This vehicle was the 5,002nd 75 in Royal Blue (code: JFM) to be made out of 14,420 Royal Blue 75s

29th June 2016, 19:32	#3
murphyv310 This is my second home Hyundai i10 998cc Join Date: Mar 2012 Location: Kilmarnock Posts: 6,602 Thanks: 2,088 Thanked 2,298 Times in 1,349 Posts	Faulty vacuum pump or pipework. Diesels don't use the inlet manifold for vacuum as they are not throttled. __________________ Cheers from Trevor MM0KJJ

1st July 2016, 19:37	#8
klarzy This is my second home none but not gone Join Date: Mar 2013 Location: March, Cambs Posts: 16,437 Thanks: 894 Thanked 4,247 Times in 3,025 Posts	If you have an EGR bypass or have disabled the EGR solenoid, make sure the cloth covered vac line to this or the pin on the bypass is not perished or free as this will lose vacuum, especially as the engine is cold the CPU will try to open the EGR valve and this will leak __________________ [SIGPIC][/SIGPIC]….All praise Bananaswan….