My 1998 3.2 sport has always had a low brake pedal but it has got progressively worse. It nevertheless passes it's MOT each year, although when stationary the pedal can be pressed right down to the floor. Sometimes the transmission interlock won't disengage. The garage have suggested that the abs pump may require changing but I don't want to embark on this cost if it is something else. Needless to say the system has had fluid change, bleeding etc and flexible hoses checked/renewed. Any thoughts on this??

 

I've feel this same issue on many other this era or later cars. You can press the pedal almost straight to the floor if pressed with somewhat more force. But there is some resistance and it would not slam right to the floor mat. And still brakes do work as normal and have great braking force. If all mechanical brake stuff is okay, then it is propably master cylinder. But this is just guess. Abs hydraulic unit has electromechanical valves and fluid passages. It can not make this issue unless there is somewhere air in the system. But air in the system should be easily spotted in MOT. I have had few times where there is air in the abs unit and it is very stubborn air. Only way to get it out from there is to do hard braking at gravel road or slippery asphalt so that all of the wheels tries to lockup. So press it with all of your force for few seconds. Then bleed it again.

 

Thanks Vauxi, that is very helpful. I was more inclined to suspect the master cylinder myself. It's going into the garage next week, I'll ask them to focus on the master cylinder and re-bleeding.

 

The master cylinder would exhibit the faults cited. Unfortunately, in these cars, there are other things that mimic that failure as well.

 

Thanks RandyS!

 

At the age of these, it is quite likely that many of the rubber hydraulic parts are drying out. Rebuilding or replacing the calipers is easy, so is a rebuild of the master cylinder. But be especially careful with the bleeding process.

 

Probably master, but perhaps not.

 

Brake systems usually give a few symptoms before failure, but it is important not to ignore them.

 

spongy pedal with no feel is a feature

interlock issue is probably pedal switch going out

 

Spongy with no feel is definetly thing in modern european cars. X308 is towards that but faaaar from it. If al 4693 is slamming pedal with strong force it will go deep down. But if it slams to the floor mat like there is no resistance then there is a problem.

Al 4690 with engine off drain the vacuum off the booster by pressing brake pedal several times until it gets firm. Then wait for minute or two and press it again with force. It should not go to the floor mat ever. If it does, then there is issue with the brakes.

 

Almost every car I have ever owned had brakes with a spongy feel. The sole exception to that was
an International Scout which had a pedal that was rock hard. It stopped well but no sponge. Then
there was the opposite situation, a Chevy Silverado that always seemed to have a high pedal but
did not stiffen up or brake till you were halfway to the floor.

 

I've had a very frustrating day with the ATE calipers on these cars, and went through a fair bit of fluid trying to get a pedal. Once you do it is a night v day difference.

I tried the pressing the pedal the wedging it, and leaving overnight, on the floor after a good few pumps.
purged all lines at the pump - not recommended.
Finally found air trapped in the upper most part of the front calipers, I removed them rotated so the bleed nipples where upper most and the 'air', a few bubbles was all it needed.

Give it a go if you can.

 

Thanks for the tip! My XJR has a horrible pedal and I have new pads and fluid ready to go. Will definitely be doing this when bleeding using my Motive Pressure Bleeder.

 

Remember to bleed the lines closest to the master cylinder first. The real
trick is to unbolt each front caliper and rotate it until the bleed nipple faces up.
Bleed as usual, pedal pump until all the bubbles are gone, then close the nipple,
and bolt the caliper back up. Repeat on the other side. The problem is that the
bleeder nipple is not at the top of the brake cylinder and air gets trapped there.
This, of course, is bleeding the conventional way.

 

thanks

 

I'll be using a pressure bleeder so not sure if this applies, but if bleeding conventionally won't havin the caliper unbolted cause the caliper piston to extend too far when the pedal is depressed? Not sure if that's an issue, but I definitely plan to have the caliper off and nipple facing up to get all air out so I'm curious.

 

+1 to the pressure bleeder, an amazing tool that pays for itself in only one full car bleed. Make sure to do the trick of adding a pneumatic quick disconnect at the master cylinder adapter cap to make the use much easier.
Also on older systems, the MC can develop uneven wear (bore wears at most used initial portion, but not at bottom half) and using the pedal bleed method can accelerate wear on seals due to this.

Regarding the piston pushing out while moving the caliper around, you can use a "piston retractor" or "brake pad spreader" tool against the caliper piston to hold it in place while the caliper is out.

 

Regarding the piston pushing out while moving the caliper around, you can use a "piston retractor" or "brake pad spreader" tool against the caliper piston to hold it in place while the caliper is out.[/QUOTE]

Yes of course! Ha, can't believe I didnt think of that. Thanks.

 

You should always bleed the furthest away from the master cyl, working toward the closest.

 

Yes...that was supposed to say furthest,,,,not closest.
Thanks for the catch Probesport.