Okay so i finally put new pads on my car since getting it. The fronts have been squeaking but had half the pad still left.

Honestly even after rebuilding my rear calipers my brakes have never felt like what i thought they should but I really expected this to make a difference!!

Are the brakes just mediocre on XJSs or is something wrong??


My gf has a kia suv and it will slam your face on the dash. I can't even make the wheels lock up and skid. it still stops..but no better than my roomates Ford taurus....

 

The brakes on my '88 XJS would stop on a dime and give ya two cents change :-). Some is wrong. The brakes should absolutely develop enough ooomph to intentionally lock the wheels.

What kind of pads did you use? Different compositions have different characteristics. Some require a bit of warm up before they get grippy.

Did you "bed them in" according to manufacturer instructions?

On the fronts I wonder if perhaps the pads have glazed?

Do you have a soft pedal?

Lastly, do you have any sense that you're not getting full power assist?

Cheers
DD

 

Yeah i was thinking the old ones glazed. got some cheap semi metallics because i figured thatd be better for now until i can get nicer ones.

I did bed them in.

The pedal is a bit soft.

I feel like im pushing a teeny bit harder than a should.

Also when i brake it sometimes makes a bit of an airy fart sound.



My rear brakes once leaked so i rebuilt them and replaced the pads and bled all the brakes, this helped at the time...also the master has been rebuilt. They have always required a bit more pressure than normal and never stopped very well.

I have kind of assumed that the fronts need rebuilding but they haven't leaked ever so i've left them so far.

 

i dont actually know anything about brake boosters so i've never suspected it since i can't troubleshoot that. Does this sound like its leaking and now assisting enough?

Rebuild kit appears to be 35 dollars.

 

Yeah, I'm leaning towards a failing brake booster.


Cheers
DD

 

thanks alot. Again i never considered this and i guess i always figured boosters either work or don't. Hadn't thought about them having a leak and partially working.


But when i think about it there isn't anything left in the braking system to go wrong!

will update this thread once i rebuild it.


can it be removed without breaking the system open?

 

Sometimes the master cylinder can be unbolted from the booster and shifted out of the way without breaking open the hydraulics....depends on how much slack (so to speak) you have in the lines

Cheers
DD

 

My brakes also started making that fart sound and I am pretty sure it is the brake booster. Also, I just installed rebuilt rear brake calipers and I am not satisfies with the feel of the brake pedal, either... it's a little soft.

However, I don't think the two are related. If the brake booster is failing, it's going to be assisting the brakes less, which I suspect will make it harder to push the pedal down. If there is a problem in the hydraulic system (bad master cylinder, leak, air in system, etc) then it will be easier to push the pedal down farther.

So what I'm saying is:
1) If you have a brake booster problem, it will be harder for you to push the pedal down and you will have less stopping power.
2) If you have a hydraulic problem, it will be easier for you to push the pedal down and you will have less stopping power.
3) If you have both problems... well, I don't know about the pedal, but you'll definitely have less stopping power!

I am trying to figure this out, too. I am not happy with my brake pedal. I suspect I have a hydraulic problem because I can feel the power assist working when I start the car. I am thinking I either have 1) air in the system, 2) a bad master cylinder, or 3) exhaust pipes too close to brake lines or too close to the rear calipers, causing the fluid to overhead and boil. (My exhaust system is temporarily pieced together with beer cans and hose clamps.)

 

On a non-abs XJS, a soft pedal either means the system needs bleeding again, or that a flexible is going home, or that a caliper is not 100%, or that the master cylinder is not 100%. If the flexibles have not been changed, then they really should be. The safe life of a master cylinder is not more than 7 years, if that.

Assuming all the bits are in top shape, to bleed start with the rear caliper furthest from the feed, then the other one, then the front furthest from the feed, then the nearest to the master cylinder. A great deal of fluid has to be pumped through the rears to really purge them of all air. And a tiny quantity of air makes a huge difference. I always bleed my brakes again about a month after they are bled the first time, and it does make a difference, amazingly.

I have tried all sorts of gadgets too, but nothing works as well as me underneth the car and my wife pushing the pedal as instructed! But I do intend to treat myself to a set of Rob Beere's remote bleed pipes, which allow the rear to be bled via a long flexible extension pipe, fixed in place, much more easily!

 

Doug, On my 1985 the m/c can be unbolted and removed (without the hard lines attached in my case). BUT having done so, the booster could NOT be removed by unbolting it from the pedal box, as the studs on the booster were too long to allow the booster to slide forward enough to be free, as the dent in the wing that houses the booster was about 3/4 of an inch too short to allow it to slide forward enough! Another top Jaguar design!

In my case, I had to undo the pedal box nuts hiolding the assembly to the bodywork, from the top, and lift up the entire pedal and booster assembly before I could get the booster free. Not forgetting to undo the brake light switch first, of course.

 

Yes, removing the booster is tricky. I've done it only once on a Jag ....a Ser III XJ6 which has a very similar (perhaps identical) mounting configuration.....and did exactly as you described for the same reason.


Cheers
DD

 

If you suspect your booster is leaking vacuum there is an easy test. Shut the car off let it sat a while 10-15 mins. Now while the car is press the brake pedal a couple of times. Do you hear it hiss and then the pedal gets real hard? if so the booster is not leaking vacuum. The other test is run the car then shut off and let sit for 10-15 mins. Remove the check valve from the booster. If you hear a hiss then there is no leak and the check valve is good. If it fails either of those tests you need to make sure the check valve is good before condemning the booster.

Things that will cause spongy pedal:
Air in the system
Air in the master
Low quality pads
finish too rough on brake rotors
glazed pads/rotors
a frozen caliper or binding caliper
pads stuck to caliper
pad pins badly rusted and pads can't move
loose wheel bearings
brake hoses

A bad brake booster will give you a rock hard pedal. A pedal that feels normal when pressing but does not stop the car well is something from my list above.

 

Question concerning brakes as well.
I've followed this post but it's gone in a different direction than my question so I'll ask mine now.
I'm not the mechanic in the family, my bro is, but we work together on these projects so I can get better acquainted with doing my own repairs.
I recently took my 88 XJS in to my local tire/brake guys. THey said my pads were about half worn an in good shape even though I heard a faint squeek from time to time. Once I picked up my car, it was SCREAMING everytime i stepped on the brakes. It seems to be more from the front brakes. I don't have a clue what they may have done!
My question is:
Would it be ok to change the front rotors and pads and hold on the rear since it's such a pain to do. I can't stand the squeeking and I have already ordered new rotors and pads for the front. Also, any suggestion on the pads themselves. What is the best choice? My brother tends to want to buy the most expensive, no problem, but do they really work better??

 

While researching options for brakes this summer, I came across this thread and it was very helpful. "1996 XJS brake replacement options". Here is the link, https://www.jaguarforums.com/forum/x...options-60488/
I ended up choosing the EBC Redstuff as well, and doing all four corners. The rears were still OK, but not knowing what was on there I didn't want to mix pads.

Bill

 

People (including me) do that all that time.....change just the fronts or just the rears. In practice there is seldom or ever a report of problems.

BUT.....

In theory there very easily *could* be a problem with the different friction characteristics of different pads causing an undesirable imbalance of braking force. This is most likely to occur, IMHO, in hard driving or an emergency/panic stop situation.....which is the very last place you'd want to discover that your brakes are sub-par or misbehaving in some way.

The safest bet, then, is to use matching friction materials front and rear.






As with oils, gas, spark plugs, and tires there are many opinions out there.

On my Jags I've used Ferodo, Mintex, and several others that I can't remember at the moment. Some were unacceptable to me and tossed in the bin after very little use. My hands-down favorite is Akebono ceramics but I'm not sure if they're available for XJSs.

After that I was most impressed with Raybestos PDG09M (rear) and PDG135M (front) on my XJS and Ser III XJ6. No noise, minimal dust, grippy but easy to modulate, did not require "warm up" to work, etc.

Cheers
DD

 

okay so i just received two very conflicting posts.

One says this definitely sounds like the brake booster, the other says it definitely isn't.

My master cylinder is rebuilt, so are my rear calipers. Only issue would be front calipers which i would like to rebuild. Visual inspection of rubber lines leaves nothing but i am aware the pressure in the system could amount to more than i can see.

So this shouldn't be a brake booster then?? I can hear air coming out and pressure does build if i pump the brakes without the engine running. but pressing the brakes become uncomfortable at lights and i find myself switching feet or temporarily placing both feet on the brake pedal when waiting.

the cost to rebuild the brake booster OR the front calipers is very similar but i don't want to waste anything on fixing the unbroken like the booster or lines if they are okay.

 

Is your idle too high?

 

no its 750 why?

 

It's the booster. You shouldn't be hearing any farting, vacuum noises. I had the same symptoms. New booster from Rockauto fixed it.

Easiest way I found is to pull the pedal box. Start by pulling the MC away from the booster by removing the bolts holding MC and the reservoir. Remove the bolt holding the distribution block on the fender so you can move the lines. Pull the reservoir out of the way. You'll be able to move the MC without cracking any lines loose. Remove the vacuum hose. Then remove the 4 bolts holding the pedal box. Carefully lift the pedal box free of the car. There may be some sealant holding it in.

When you pull and re-install the box, be careful not to snag the brake light switch.

Make or buy a tool to set the booster pushrod depth. Too loose and the pedal will feel spongy; too tight and it will not fully release. The booster pushrod should just make contact with the MC piston cup. If you google it, you will find lots of illustrations. Ford and GM work the same way as the Jag.

BTW, I can't confirm the Delco part number, but I believe the booster to be the same as a mid-70's corvette but with different pedal clevis. They won't interchange directly, but are the same design.

 

Usually a failing/failed booster makes it harder to push the pedal.

Did you try the vacuum test described above?