Brake seizure

The front two callipers of my GTD have just seized onto the disks. They must've been very good brakes as the front locked solid and the back wheels spun!
The radiant heat has damaged all of the rubber parts in the suspension so I need to know where these parts were sourced from. I believe my GTD is a very early one (chassis no, 4786) with no modifications from the basic build. I've searched the forums and suspect that the steering rack came from a Cortina but which one? Similarly since the discs are now toast which Granada/Scorpio did they come from?
Any ideas would be welcome

Rob, I have a complete set of front discs/callipers here for sale if you want them, Frank ( East Sussex)

Rob,

The rack was Cortina MkIV. You could refit std granada brakes, which are rather indequate for the front, but it seems an ideal opportunity to fit something much better?

Frank you've got PM.

Rob,
WHY did your front brakes both lock on suddenly.A very worrying situation for you and could have been fatal.
Please elaborate if you can as it may have significance to others with similar set-ups.

Regards,

Graham @ GTA.

Firstly thanks to Frank and Dave for the info.
I was on my way back from the monthly meeting at Bullington Cross when I noticed a slight bias to the left on braking.
I got home Ok and on the Saturday I took the car out for a test drive. At first the car was fine, braking smoothly and straight. Then after about 20 miles the bias returned so I returned home and inspected the nearside front brakes.
It took some effort to rotate the wheel so I removed it and the brake pads and tried to recess the calliper pistons. These pistons were difficult to recess but after a couple of minutes they seemed to be OK so I pumped the brakes a couple of times (without starting the engine - this is probably an important point) and the problem had gone away.
I decided to take the car around the block to see if the problem could be recreated. I'd covered about a mile when the bias returned so I turned around and headed home. On the way back the brakes started to bind but being only a mile from home I kept to a low speed (I followed a bus doing about 20MPH for most of the way) and just as I was entering my drive I applied a little braking and WHAM! full stop. Half on the drive and half on the (narrow) road. I tried to coax it onto the drive (or at least further off the road) using a little throttle but the back wheels just spun.
Investigation showed that both front callipers had seized onto the discs. The heat generated during this episode had blued the discs and damaged all the rubber parts of the suspension and steering.
I found a thin layer of fine black/brown crud in the bottom of the brake reservoir for the front brakes and when I drained the Automec silicone fluid instead of being a transparent purple colour it was a hazy orange colour.
My first thought was that either contaminants had some how gotten into the system or the master cylinder seal was breaking up and that either way it had created a blockage which had created a kind of one way valve and allowed a pressure build up.
I have since been informed that the problem is likely to be a valve in the servo unit which I have yet to investigate.
As an aside I also looked at the rear callipers and I found that these were mounted on the bottom of the disc with the bleed valve at the lowest point! How the back brakes are bleed I can only imagine after all air bubbles rise to the top of a liquid!
Any ideas anyone?

Hi Rob, I have a recurrent problem like this with the rear brakes, at first I thought it was the handbrake, but last week when I was returning home, I noted some squeaking from the left rear, this was stopped by gently dabbing the brake, and I noted that in slow traffic it was as though the handbrake was on. When I got home the left rear had started to really squeak and was quite hot. The handbrake cable was slack and I could operate the levers by hand, so handbrake seemed ok. The next day I checked the left caliper / piston which seemed ok. When I put it back, verything was free, but when I operated the brakes (engine off) the rear brakes did not release. At this point I opened the right rear bleed nipple, and fluid came out and the brakes released.
Conclusion is that there is residual hydraulic pressure in the rear brake circuit. I suppose this points to a sticking valve in the servo or maybe the master cylinder.
When I started the engine and went for a drive everything was ok, but somehow I don't think that will be the end of the problem.

This seems to have the basic ingredients of your problem.

I am thinking that after 13 years of little use, I should replace or get seal kits for the servos / master cylinders.

regards

Dave

Automec silicone fluid you say. Had that fluid always been in your system from new or did you replace old fluid with this new fluid.
The mixing of the two can produce breakdown of seals etc and i,ll warrant that that is what has caused the residue and colour change and much of your problem. Be interesting to see what condition all your seals are in.
Good fortune in getting it all sorted.

Regards,

Graham.

I bought the car as a road going concern last August (it was registered in Sept '01) and I don't actually know if it's had anything other than Automec in the system. I've now drained the back brakes and the fluid seems fine.
I've checked the seal in the front brakes' master cylinder and it seems fine.

Anyone know if Lochheed remote servos can be serviced?

Rob
Try speaking to Kimbers in Southampton. Paul is particularly helpful.
They gave me all the advice I needed and helped me sort my brakes including having the calipers rebuild with new pistons and seals. They were adamant that I should stick with 'ordinary' brake fluid, rather than using synthetic as they said any trace of a mixture can destroy seals.

To bleed your rear calipers - just unbolt them from the uprights and hold them with the nipple at the top while you bleed them.

I overhauled my Lockheed servos a few weeks ago - I got all the parts mail order here : -
http://www.powertrackbrakes.co.uk/brakes.html
You do need to try and find out which servos you have - powertrack will help you with this.

I had a similar problem on my KVA. It runs a set of Tilton pedals with a brake balance bar operating the front and rear master cylinders. The bearing inside the head of the pedal which the bar runs through had worn badly. Changed that and the problem was sorted.

Rob,
I was coming back from Stoneleigh after having just got my GTD back on the road after it had only done 1450 miles in 8 years (significant). Running down the M40 from Leamington Spa to High Wycombe, the car felt as if it was running on a corrugated surface. On pulling off the slip road, the front brakes were smoking and stinking to high heaven and the discs were an interesting shade of blue! The whole lot went back to normal after only a few minutes' stop. Further investigation once the excitement died down revealed that the brakes were slow to release - sometimes taking up to 5 seconds before the car stopped slowing down.
So, off to Wealden Engineering, where Frank Catt had modified the pedals and fitted twin Tilton master cylinders some month before. He went straight for the front servo, where there is a little shuttle valve that releases brake pressure when the air pressure across a diaphragm is equalised (the valve is down the hole in the centre of the pic). The shuttle bore had rust in it; a pencil with very fine emery wrapped round it polished out the bore so the shuttle valve slipped in and out smoothly - you will need to lubricate the shuttle seals with brake fluid and have a pair of fine-nosed internal pliers to grip the inside of the valve to get it out. Don't force it in, you won't get it out again! Also when reassembling the diaphragm, make sure to seat the diaphragm lugs in the recesses in the cover properly, as an air leak will cause the same symptoms.
With the engine running and an assistant turning the front wheels, stamp on the brake pedal and check that the brakes come off IMMEDIATELY on release. If they don't, listen for the air leak with a piece of hose.
If this doesn't help you sort it, contact Wealden Engineering. They love bleeding brakes 3 times in a morning and can whip a servo to bits in seconds!

Thanks Tony, that was a good tip for me, the shuttle valve has fluid on the inside, and air on the outside, so the valve bore can rust. I did both servos, sure enough the servo for the rear brakes had patches of rust and had collected some between the seals. I used a 7.5mm drill shank with 1200 grade emery wrapped around it.
Missed your comment "make sure to seat the diaphragm lugs in the recesses in the cover properly" and had a whistling noise due to the leak. Seems ok now, time will tell.
Ken thanks for your tip, my balance bar bearing was ok.
Thanks to Paul for the link, I'll get overhaul kits.
Rob comiserations to you for finding out the hard way but many thanks for keeping me from the same fate.
The forum delivers yet again! /ubbthreads/images/graemlins/cool.gif
regards
Dave

Just in case it isn't anywhere else on the forum I thought the following I found on the web might be of interest:

"Silicone: Lockheed says it does not make it or market it.
I was told to use DOT 3 type in a servo braked car. Reason given was possible sticking brake pedal/non release of the servo due to the non-return of the valve in the servo.
They have had several returned servos from people with older cars that had the above problems all traced to silicone brake fluid use."

Rob, et al,

I tried silicone and it turned from pretty purple to sludgy brown within a month and just sitting in the garage with the system capped. I have been told that Ford Dot 3 high performance brake fluid is the best and what all the racers over here use. I'll never even think about silicone again, let alone try it.

Lynn

Having refurbished the servos, I am still not happy with them, the front brakes do tend to stick when used gently, and the pedal tends to have a little too much movement for my liking. The result is that I tend to pump the pedal once just before I actually need to brake. Ocaisionally, I hear a servo whistle or moan, but there are no continuous air leaks. Ive checked everything, and checked the air valves and bled the brakes repeatedly, and although they stop the car fine, I'm losing confidence in them and want to make a change.
I note that some of you are not using servos, so my first test will be to get some bundy made up to bypass the servos, and see what the brakes are like without them.
Other than that, I may need to change the servos. The reason I say that is the Lockheed spares supplier made the comment that these were not the 'normal' GT40 replica choice, which means that they may not be 100% suitable.
The servos have the tag number 4257 818 7, ser nos L46F and L48F. Can anyone say whether these are inappropriate for the GT40 with standard brakes in any way?
Any comments or suggestions appreciated.

regards
Dave

I recently removed my servos expecting to have a better felling on the pedal. I got it, but of course i have to give a stronger effort to have the equivalent braking power.
I red this post with a great attention as i have also big troubles with my braking system, i noticed returning back from Le Mans last time that the front is shaking more and more, i had a look to my front right disc and discovered a wear on the external circle of the rotor, very strange. The only thing i did before was to change my pads, which should have no impact on the perimeter. I wonder if my caliper is not untightened or something like this. Anyway, the braking on the GTD seems to be always the very bad point. /ubbthreads/images/graemlins/frown.gif

Hi Fred,
I remember the 'GTD Spindle / upright impact on braking performance' thread, and I know you have been looking at your brakes carefully.
Another idea if you cannot find anything wrong with the brakes.
When the front shakes, the cause can also be play or wear in the steering. This is a very common cause of judder under braking. If you have judder, then it could affect the wear pattern on the disc, so ot is possible that it is a steering problem.
Two examples;
1 I had an XK150 which had developed a severe judder, the steering rack was mounted on rubber mounts. One of the mounts had delaminated.
2 My Dax40 tended to judder under braking. I found that one of the mounting U brackets was too big and there was 2 or 3mm slack in the mount. I shortened the bracket and the braking is now very smooth.

So judder can also be play in the steering so check everything carefully.

regards
Dave

hmm using silicone brake fluid is asking for trouble IMHO..
just a comment in general and might/might not be relevant to the brake seizure. I think silicone is an 80's throwback and by hindsight never was a good idea. So what if normal fluids are more hydrscopic, as I am assuming that us owners of high-perf cars change oil/fluids/filters/pads etc at shorter intervals than the trillion mile interval suggetsed by todays manufacturers