TE21 Brake fade

I have experienced anew and unusual situation with my TE brakes where after a period of round town driving the pedal started to fade though it never went to the floor and the brakes still pulled you up. Pumping the pedal had no effect. After sitting in the garage for a few hours the pedal movement returned to normal.  I have a weeping O/S outer cylinder which I will deal with over the winter but I have never experienced the brake fade before on the TE or in my driving past. Possibilities seem to be 1) excessive water in the system, boiling at the caliper and acting like air. this re-set once the brakes cooled. 2) Air in the system though how did everything return to normal after standing. 3) The weeping seal lets air get drawn into the system on de-application of the brakes but over time the air rises out of the caliper to the servo and dissipates. (what genius put the servo as the high point in the system I don't know but flogging would be too good for them!) 4) A servo problem. (On modern cars if you push the pedal before you start the car you can feel the pedal move down as the vacuum takes hold but on this Alvis the movement is virtually imperceptible. I know the servo is a very low boost but seems there should be some noticeable movement?) Anyone got a good method for testing the servo? I would appreciate any comments or views, has anyone experienced anything similar? I am going to re-build all the calipers over the winter and re-build the servo (I got a kit). Anyone with advice on doing those jobs.  Steve Haycock Posted by haysx0 06/10/2015 12:21:32

Brake fade as you decscribe it is possibly a servo problem, or sticking caliper pistons if they are not used much.  It is unlikely to be a seal or fluid problem if you maintain a hard pedal, and braking can be effected albeit with greater effort. If the fluid boils or master cylinder is ineffective, you would probably have pedal to the floor and trousers at the cleaners.  You may check caliper / cylinder piston function with a rolling road brake test to see if braking effort is equal and correct at each pair of wheels. best done before and during the `fade´ situation has been achieved. If the same braking efficiency % is achieved, albeit with different pedal effort, then it's probably a servo-related problem.  As a process of elimination, check for any vacuum leaks between the manifold, the vac. resevoir and the servo itself. There are multiple possibilities for vacuum leaks which may cause variable braking efficiency.  Start at one end (manifold or Servo) and locate / inspect all vacuum hose and it's connections at each point. The Vac. hose hardens with age, softens with fluids spilt on it, and connections can loosen. Check if there is a working non-return connection in the Vac. resevoir. Check the vac. resevoir for corrosion / pinholing.  As a test, just bypass all existing vac. hoses etc. with a temporary vac. hose and non-return between manifold stub and servo connection. Make sure that any hose used is really for vacuum and can not collapse. If braking efficiency is maintained then it is a vacuum problem and not a servo problem.  If you are confident that all the Vac. equipment is in good condition then the servo itself is in question.  The 3 litre has a powerful servo. If the servo is not effective the master-cylinder will be acting directly on the calipers / cylinders with good braking function but requiring much more effort.  To compare servo function / non-function you can by-pass the servo by installing a temporary brake-pipe from master-cylinder direct out to the brake-pipes (e.g. at cross piece). Then try the brakes again (after bleeding), and see if it replicates the `faded´ situation. If so, then the `fade´ issue is probably servo related.  I think the TE may have a Lockheed servo with moving main piston, which is not the easiest to rebuild. In case it is found to be at fault, it may prove much easier and more cost effective (i.e. adviseable) to install a new servo with the same ratio (e.g. from Chris Prince). And at the same time replace all vacuum hoses / non-returns as required, and re-paint the vac. resevoir after checking it for corrosion + pinholing.  A weeping rear cylinder is often possible to re-seal with careful cleaning, internal polishing and a new set of seals. Use correct rubber-grease when installing the seals as it helps to prevent sticking pistons during periods of non-use.  After any work on the 3 litre brakes the bleeding is very, very important and not always easy. Even when it appears that bleeding is complete, it is possible for a small amount of air to remain trapped under the servo reaction piston, which may cause the front brakes to bind after the system warms up. On cooling, they then free-off as the servo relaxes. This problem is lessened if the servo is installed with reaction piston underneath, so trapped air rises during bleeding, but pipework routing does not always allow this. So have plenty of fluid on hand, at least one extra pair of hands, and bleed multiple times, vigorously, with engine not running, and then again with engine running, repeated until you are 100% happy with the result.  Giles Lacey Posted by lacey giles 09/10/2015 08:54:09

Tony Sounds like the partial failure and then temporary recovery of one of the internal seals in the master cylinder,the one that isolates the reservoir supply is suspect , the giveaway is fluid sitting on top of the reservoir container.I have had this happen on 2 TE's. If you operate the pedal rapidly you may encourage the seal to start working again......until the next time Solution strip, clean reassemble with new seals and lots of rubber grease, change the fluid whist you are at it The internal condition of the master cylinder will horrify you,& the recovery spring may have rusted through,the m/c is the lowest point of the system and everything ends up there, also take the chance to remove 50 years of build up from the brake light switch, it works better with the fluid directly in touch.  Some cars have cast iron cylinders,others aluminium, the seals are different and the former get very rusty inside. The wheel cylinders are easy once you have done one though removing one of the rear caliper bolts can be entertaining Good Luck Peter Posted by Peter Martin 13/10/2015 15:23:58

Thanks Guys, I have decided to do a complete re-build of all calipers and the servo, which is indeed a Lockheed one. I have all the re-build kits so here is hoping. The master cylinder is only 9 months old (Chris Prince one) so I don't intend to mess with it unless I have to but I have seen fluid on the top of the reservoir in the past so maybe the new master is a problem as well. I believe you have to adjust the rod in a specific manner to ensure the piston travel allows fluid to enter from the reservoir. Any advice on that please. Servo's are a fairly expensive item though I have found replacements from brake specialists much cheaper than Chris. I will try a re-build first.  Thanks again Steve H Posted by haysx0 18/10/2015 14:24:59

The master-cylinder / pedal-rod adjustment is required to ensure sufficient free-play. Insufficient free-play can cause brakes to bind. Details of free-play dimension are in the manual I think. I installed a Chris Prince Master-cyl. a couple of years ago and it has been trouble-free, but as usual bleeding was very time-consuming until completed.  The Lockheed servo (2.3:1) is not as easy to rebuild as later diaphragm types, full seal kits are very hard to come by and can be expensive too. You may have to make some seals yourself. Look for corrosion in the main (pressed-steel) cylinder, and on the chromed actuator-rod. The servo actuator-rod connected onto the main pistonrequires precise adjustment but it should be OK to take the existing dimensions before dismantling. I have a copy of the original parts drawing / break-down with Lockheed part numbers which has proved very helpful. There were a few versions of the servo, all appearing identical from the outside (Jaguar + Aston used them too) but each with slightly different internals.  Giles Lacey Posted by lacey giles 18/10/2015 23:12:44

Steve  Apologies for wrong name   With the brakes off the push rod must not touch the brake piston,the handbook says .015"-.020 " free axial movement.  .If the rod is in contact the brakes will not release properly, I once managed to get the front discs of TE bright orange by ignoring this in an attempt to reduce pedal travel,not good.  Good luck with the servo  Peter Posted by Peter Martin 19/10/2015 08:43:02

Giles, tried to find your email address but could not. A scan of those drawings you have would be very useful if you could send them to <!-- e --><a href="mailto:stevehaycock4@gmail.com">stevehaycock4@gmail.com</a><!-- e --> it would be much appreciated. Steve Posted by haysx0 05/11/2015 18:10:53