My car has been in an independent Jag shop for two weeks now due to a low brake pedal!

I wanted them to replace all four calipers with OEM units as well as rotors, pads and brake lines. All of this work has been completed along with total fluid replacement and bleeding multiple times using the correct sequence (starting at right rear). The brake pedal seemed fine right after bleeding; but a couple hours later the pedal sinks about 2 -3 inches prior to any breaking pressure on the foot.

The shop cannot find any leaks and thought that the master cylinder must had rolled an o-ring due to all the bleeding and possibly inadvertently emptying the reservoir; introducing air. They installed a new OEM master cylinder after bench bleeding then went all around again and bled the entire system for air.

We still have the same exact problem…Low brake pedal after it sits an hour or two. No visible leaks anywhere.

Hopefully someone here can provide some information/suggestions. Sure would like to get her back on the road!

2014 XK 5.0 Dynamic R

 

Did they perform a vacuum test? It's behaving like a vacuum leak. What's the fluid level before and then once this occurs?

 

Hi Sean, are you referring to the test where you hold you foot on the brake pedal while the engine is off; then while maintaining your foot on the pedal; start the engine. The vacuum booster is working correctly if the pedal sinks further to the floor. (At least that’s my understanding of the test). And yes; I have personally done that test and it works as it should.

I have to say though that even when I “get into” firm pedal during hard breaking; it seems to me that a larger amount of foot force is required than you would expect on any other car?

 

No. I mean test your engine's intake vacuum.
Here is the procedure from the manual:1. Disconnect the vacuum hose from the brake booster. 2. Connect a vacuum/pressure tester to the vacuum hose. 3. Run the engine at normal operating temperature. 4. Record the vacuum reading.

• Is the reading 40.5 kPa (12 in-Hg) or greater? -> Yes

GO to Pinpoint Test G545069t26.

-> No

LOCATE and REPAIR the source of low vacuum. TEST the system for normal operation.

G545069t26 : INSPECT SYSTEM

1. Switch the engine off. 2. Reconnect the vacuum hose. 3. Inspect the brake booster, rubber grommet, and all vacuum plumbing for cracks, holes, damaged connections, or missing clamps. 4. Pump the brake pedal several times to exhaust the vacuum. Push down on the brake pedal and hold.

• Does the brake pedal move down when the engine is started? -> Yes

Vacuum system is OK.

Here's the component test from the service manual.1 . Check all hoses and connections. All unused vacuum connectors should be capped. Hoses and their connections should be correctly secured and in good condition with no holes and no collapsed areas. Inspect the valve on the brake booster for damage.

2 . Check the hydraulic brake system for leaks or low fluid.

3 . With the automatic transmission in PARK, stop the engine and apply the parking brake. Pump the brake pedal several times to exhaust all vacuum in the system. With the engine switched off and all vacuum in the system exhausted, apply the brake pedal and hold it down. Start the engine. If the vacuum system is operating, the brake pedal will tend to move downward under constant foot pressure. If no motion is felt, the vacuum booster system is not functioning.

4 . Remove the vacuum hose from the brake booster. Manifold vacuum should be available at the brake booster end of the hose with the engine at idle speed and the automatic transmission in PARK. Make sure that all unused vacuum outlets are correctly capped, hose connectors are correctly secured and vacuum hoses are in good condition. When it is established that manifold vacuum is available to the brake booster, connect the vacuum hose to the brake booster and repeat Step 3. If no downward movement of the brake pedal is felt, install a new brake booster.

5 . Operate the engine for a minimum of 10 seconds at a fast idle. Stop the engine and allow the vehicle to stand for 10 minutes. Then, apply the brake pedal with approximately 89 N (20lb) of force. The pedal feel (brake application) should be the same as that noted with the engine running. If the brake pedal feels hard (no power assist), install a new valve and then repeat the test. If the brake pedal still feels hard, install a new brake booster. If the brake pedal movement feels spongy, bleed the brake system.

 

mine's been about this soft since i got it -- indie mechanic said they're just naturally soft. you say you got the hardware replaced with OEM, meaning... it wasn't already? suppose that was the reason; someone had some aftermarket/performance parts on there for additional braking power, or stiffer feel? are you the original owner?

as mine is, there is some very light braking applied in the first inch or two of pedal travel, although it's difficult to detect. so when you say a full 2-3" and no result, i can't be sure that's actually the same as mine.

same mechanic did also point out to me that the ABS system has to be opened while bleeding the lines to do a proper job, which requires the use of SDD i guess. my DIY job at home did not change pedal feel.

lastly, i've learned to live with it. trailbraking is much much easier than on my other car with its more aggressive pad, disc booster, and shorter throw.

 

Sean, thank you very much for the detailed explanation and steps to perform this test and inspection. I will be printing this for my shop tomorrow morning when they open. I will let you know what they find.

 

I replaced the old OEM (original) with freshened OEM calipers that were painted and restored by Brake Caliper Specialists (BCS). The new calipers match the original equipment.

My pedal feels almost totally useless until depressed 2-3 inches. And when “hard” braking, the pedal gets too close to the floor for my comfort.

Regarding the ABS bleeding using SDD; my understanding is that there is no ABS bleeding procedure with 2014 XK. A Jag dealership told me that function is no longer available (said it stopped around 2008 or something like that). Do you know for sure that a 2014 XK supports ABS bleeding function with SDD or another device tool?

Another thing worth mentioning is that when I test drove the car after new calipers were installed, it sounded like someone had put a playing card in my bicycle spokes (Left front). I thought originally that this was due to the underpan not being properly installed and flapping. Could this have been the ABS unit making the noise?

 

Have them confirm the one way check valve on the booster is working also. I don't know why it's not noted in step 4 from the manual. It's a simple test and a must do when checking vacuum. Just pull it from the booster. Blow into it. It should only allow air to pass one way.

Can you list the booster part number the shop installed?

Good luck!

 

Th only way you will get a hard pedal is to install an electric brake booster to raise the vacuum to about 25 in HG

 

I know u not suppose to do this for newer cars,but try pumping them to see if they build pressure.I know I sort of have to do this when I put new brake pads on my XKR

 

Unfortunately, @Raptorcize didn't close this thread out but assume it was fixed as it's 4 months old now. Would be nice to know the resolution.

 

I had a similar problem, brake pedal on floor after sitting. Check the brake booster, slave cylinder and vacum hose. The brake booster can fill with brake fluid, usually internal leak or the master cylinder can be leaking into it. The vacum hose going to the booster and also be leaking.

 

and to add to this, quit often the brake lines have swollen 'shut'. Not really shut but the opening ID is smaller that when new which of course lessened flow based on pressure, so you push hard and less happens.
I had several older MBs that required new lines. The outer area is reinforced so when the material swells there is only one way to go. If teflon inner forget what I just said.
wj