Good day all,

I'm the proud new owner of a 2002 Discovery 2 that seems to have been kept in great shape by the PO, I have a question and haven't been able to find a definitive answer in the forums so forgive yet another brakes question.

I have a situation on starting the rig where the first couple of presses of the pedal are rock solid, as if there is no booster assistance, after that though there appears to be assistance and maybe a little longer throw on the pedal than I would maybe expect before a bite with a small hissing sound in the top 25% of the pedal and then it starts to grip. The hissing might be anecdotal and something else moving around like the pedal itself but there's a faint noise.

The question I guess is, is this normal to need to run for a moment and pump the brakes to get the booster assistance feeling?

The previous owner has recently replaced the master cylinder (at a reputable workshop), the proportioning valve is only a couple of years old maybe 20k on it, the rear pads and discs are brand new.
The brake pedal feels to hold pressure when holding foot on it for 10-15 seconds before it starts to very very slowly move a little more, I do mean marginally. When pumping the brakes with the motor running the bite point does get higher.

Trying to work out what might be the issue, I am thinking to try to actuate the ABS and Traction control somehow and re-bleed and also have some suspicion that these symptoms might be related to the brake booster/servo? Is there a definitive bleeding procedure for someone without a scanner that does an ABS bleed? I see a lot of different information on here... not trying to start an argument!

Appreciate any thoughts from those more knowledgeable than I.

 

Try checking the the booster using these tests https://www.yourmechanic.com/article...0not%20leaking.
The hiss could be a vacuum leak.

 

Thanks for the link and input, I plan to do some more testing of the booster but glad to hear another voice push me in that direction.

 

what are you referring to when you say the "proportioning valve"?

do you mean the ABS Modulator?

as far as rebleeding, depending on where you are located, there may be another forum member with a scanner that could help bleed the ABS Modulator.

 

You can bleed the brakes pretty easy with an On/Off toggle switch, 20 foot piece of speaker wire, piece of 1/4 inch clear aquarium hose, and a plastic bottle to catch the fluid. Here is a link I saved from another thread I found while searching on here. No need for an expensive scanner for this operation.
https://www.aulro.com/afvb/discovery...akes-solo.html

 

Yeah apologies forgot the correct name for it.

I see in the forum tech stickies there’s a bleeding procedure that has no mention of the modulator and says to bleed in an order that would be quite alien to me. I’m out in Woodville TX which is pretty far from anywhere. I’d be surprised to come across a member unless I drove down to Houston.

 

thank you for the link, a lot of good information here! I’ll go through it with detail tonight at work, looked on the surface like there’s still some disagreement about method and using the hdc etc, confusing stuff at a glance

thanks again

 

Ok so per the linked tests -

method 1 - start with foot on brake and pedal should dip with vacuum - passed

method 2 - turn engine off after a few minutes, pump pedal and should get stiffer - questionable, gets marginally stiffer but doesn’t continue to stiffen

method 3 - ordered vacuum tester and will inspect lines and check valve when I have a few minutes

 

Still waiting on vacuum tester to arrive but got a replacement brake booster off a junker just in case.

One thing I’ve noticed is if I start the car, run for a minute, then mash the brake pedal before setting off I have better immediate brake feel.

 

Thanks to those that helped!!!

Swapped in a brake booster from a junk yard and problem is solved.

Not sure if the problem was the rod on the old one, when I pulled the booster the rod was flopping about inside and when I turned it upside down it fell out. My theory is it wasn’t seating correctly on the master cylinder until there was manipulation of the pedal, but I may be (probably am) completely wrong.

Didn’t pull the master off just gently bent out of the way so didn’t bleed yet either, so this way I can be pretty confident the booster was the problem.

Now I’m just pulling to the left a little under heavy initial braking but that’s a problem for another day.