Lack of power assistance

[Sheepy]

Well someone had to be the first to post in here

OK, so you all missed a monumentous event on Saturday: My kitty moved under her own power for the first time since Feb. Whilst the engine seems to run fine and she steers OK (I turned her round in the car-park outside my flat), the brakes leave something to be desired.

I had removed the pads some months ago when I realised that they were starting to rust onto the disks. I'm now thinking I'll need new disks, because they are pretty rough and rusty. We're talking deeply corroded here, not just a surface coating. Driver's side is the worst because of the water that was coming in through the top of the wing and dripping onto the disk. I get the feeling that this job will be a bit of a bitch. Anyone care to share some tips?

The other thing I realised is that I had absolutely no power assistance on the brake pedal. When I pressed the pedal repeatedly, the pressure built up, but if I stopped pumping, pedal just sank to the point where I was getting no help. I'll change the fluid, but I'm wondering if this might be a bit more serious. Can anyone offer any suggestions on this problem? I've "traditionally" avoided doing anything other than pad changes on brakes, but may need to learn quickly here!!

Thanks in advance,

Sheepy

[Martin]

Sheepy - if it were me I would get expert help. Brakes and tyres are one area that I'm prepared to pay out for peace of mind.

[Mark_B]

Sheepy

Power assistance is the force that's like a 21 stone assistant with a hobnail boot sitting next to you pressing down the pedal with you You can test braking assistance by first pressing down the brake pedal firmly, then starting the engine, the 'assistant' then presses down the pedal considerably further than you are able to without. (Start with an empty vacuum reservior by pumping the brake half a dozen times). These jags have great brake boost servos, reassuring for car this weight, as it can do really big damage crashing into anything as a friend with a TWR XJ-S found out!

I agree with Martin if you not sure what you are doing seek expert help, or at least ask an experienced in brakes freind to help you. An MOT test failure report is good value for a complete checkout if you can drive it safely and carefully there and back.

[Sheepy]

Thanks guys,

My parts suppliers have been making a few suggestions to check as well (vaccuum supply from engine, sticking caliper pistons, change fluid).

In their opinion, if there is still no assistance, then a rebuild by a specialist is the best approach. I'm inclined to agree!

Sheepy

[SimonR]

Hi Sheepy,

First of all, congratulations on getting your Jagwire going, it must have been a momentus occasion!

The reluctance to stop will certainly in part or completely be explained by the poor condition of the discs. It's all about surface area and if the discs are badly pitted and damaged there won't be as much pad in contact with the disc.

Also check the servo assistance as Mark describes, I'd be deeply suspicious of the servo or its connections if the rest of the system seems to be in good order but braking is still a lot of effort.

Finally, I used to agree with Martin about leaving brakes to a specialist but while I was a student it got to a point where I needed my car but couldn't afford to pay someone to replace a faulty GP valve. So I decided to do it myself and quickly found there's not much to brakes really. Get a decent set of open spanners so you don't round off the nuts at the unions and check for leaks when you've finished.

Since doing the GP Valve on the Maestro, I have also renewed the master cylinder, servo, flexible hoses, calipers and rear drums and it all turned out to be very easy indeed. The only bit that gave me jip was bleeding. I tried using a one-person bleed kit and found that it kept sucking air back into the calipers. In the end I got an assistant, opened the bleed screw, got them to push the pedal, and then closed the screw before they released the pedal. It worked a treat but I found that the system settled after a couple of days and another bleed was necessary.

Good luck.

[Mark_B]

I just re-read the original posting :

but if I stopped pumping, pedal just sank to the point where I was getting no help.

Pedal sinking Erk! It's a leak! Probably caliper seal(s). Power assistance make pedal travel even further towards the floor. The dual-circuit is the backs and the fronts, I'd say the last part of the pedal travel is the other circuit still working, the 'pumping up' is the leaky circuit building up pressure & leaking away, then the reservior empties!. (look for pools of fluid)

How rusty are the disks? Cos rust burns off and doesn't matter if you have some rust pits left over, it's the disk thickness that's important. Drilled hole disks still work, I've got pair on my motorbike

I replaced my front disks couple months ago, paid £32 each very good non-jaguar pattern parts. You have to remove caliper undo the wheel bearing etc. If front calipers leaking a good time to change the rubbers (I did that few year ago). Shims drop out from the drop-arm & have to go back where you found them. The bolts could be well siezed on with rust. If you've never done brakes before I'd seek practical assistance as I know the first time I did brakes maanny yeeeaars ago I cocked it up!

[Sheepy]

Hi Mark,

I must admit that I didn't check the fluid level in the system (or look for a leak anywhere). I'll add that to the list for Saturday

As for the disks, I was under the impression that the deeper rusting was likely to be frowned upon when it came to MOT testers?

Fortunately I've decided to investigate further before buying parts (I've made that mistake before!!).

Sheepy

[Martin]

If the rusting on the discs is that deep then get them changed regardless of what the MOT man might say. You only get one life.

[Telsmoneypit]

"You have to remove caliper undo the wheel bearing etc. If front calipers leaking a good time to change the rubbers (I did that few year ago). "

No you don't The disc bolts and discs can be removed without disturbing the caliper.

[Martin]

The hub can be removed with the caliper still in place. There is a hole in the brake backplate through which you can undo the hub bolts one at a time. Can you then slide the disc out as well?

[Mark_B]

> "You have to remove caliper undo the wheel bearing etc.

No you don't The disc bolts and discs can be removed without disturbing the caliper.

I did start doing that but wasn't absolutely sure at the time it would do it or not, but alas some bolts weren't having any of it, they'd never been undone since the car was built. Had to remove hub completely from the stubaxle and put the the whole thing stud side downwards onto an old jag wheel to hold it steady enough for me to stand over it so get the siezed bolts off and the remove the disc. I ended up ordering new stubaxles both sides, very good pattern ones about £30 each, so in my case anyway I still would have had removed the caliper out the way. Mine <might> had come undone with caliper in situ with an air-wrench, I wish I had one. If you end up having to disassemble bearing like I had to, a good tip is to wrap lots of clingfilm everywhere you can while the bearing is open. Don't forget to do the bearing preload adjustment, the best way I've seen so far was in the JEC magazine.

[Sheepy]

Not had much time on the brakes today (been sorting electrics instead).

Can now say that with engine off, pedal is rock hard after a couple of presses. Pedal sinks further when engine started. So now I guess the problem isn't so much "lack of assistance", but rather just poor performance of brakes.

I'm going to check each piston in turn (tomorrow if dry) to make sure they are moving, and I'll also change the fluid to see how that affects things.

Sheepy

[ptjs1]

Sorry - last post was from me! Hadn't logged in properly!

[Sheepy]

Morning All,

Well spent yesterday afternoon working on the brakes (And all I felt like doing last night was nursing a glass or two in front of the telly rather than posting about it on the web!!)

I started by checking the calipers. With the wheels off, I removed each pad in turn (replaced with a pad ground down to the backing-plate) and pumped the brakes until the pistons moved. Results were not encouraging: Nearside caliper, three pistons moved, but two refused to retract. Offside caliper, only two pistons moved. So basically, I had three working pistons (out of eight!). The two which stuck out wouldn't retract even when I used a 4ft pry-bar!

At that point, I decided that since I was now faced with removing the calipers, I might as well strip the disks off too.

Calipers were simple : just undo the two bolts holding them on (plus the brake line of course). I did need an extension bar to give a bit more torque.

Disks were a bit harder, but a lot easier than I imagined. I put the wheelnuts back on, and by jamming my 4ft bar between two nuts, I was able to prevent the hub turning whilst I slacked off the bolts (one at a time through the gap in the shield).

Once off, I found that the back of the disks was much worse than the front of them. Whilst they might outwardly look almost OK, the back was very corroded. Something worth looking out for!

So now I'm off to part with a few quid for disks and calipers. I did strip and re-assemble the rear calipers myself a few years ago, but would rather not do the fronts as they are in a worse state, and I know how long I'd take to do them!

Cheers,

Sheepy

[Mark_B]

While S/H spares are currently cheap and plentiful, I'd buy off eBay a pair of used calipers anyway, plus a new seal kit. You might find the replacement calipers are good enough to fit after a little bit of fettling perhaps using a seal or dustcover or 2 from the kit. Left over you'll have some spares you might need in the future when S/H parts are getting scarcer.