TR250 & TR6 Brakes
Troubleshooting Brakes

These notes describe what I did on my car for my personal use and are provided here for entertainment; they are not meant to be instructions for others to do maintenance on their vehicles. 

I divide the troubleshooting into categories depending on the severity of the problem.  It is been my experience that minor problems are sometimes masked by the major problems so it's best to get the major ones out of the way first.  

No Brakes:  This is the problem where the pedal goes all the way to the floor when pressed. This means that both the front and rear hydraulics systems are not working properly. (If the pedal goes part way to the floor and then firms up, it's likely that only half the system has failed.)  I assume here that the brakes have been working and then failed.  If the brakes have never been filled and bled properly after the system was opened, I follow the filling and bleeding process described in the "Bleeding & Adjusting Brakes" note.

If the brakes had been working and then failed with the pedal going to the floor, then there must be a leak someplace in the system.  Since both halves of the system must be malfunctioning or one has a leak and the two halves are connected through a failure of the PWDA seals or the secondary piston seal.  I attack this problem one half at a time.  

The first thing I do is check the fluid level in the reservoir.  The following are the possibilities:

If the forward reservoir is low or empty and the rear reservoir is near or at the proper level, there is a leak in  the rear brake system (recall that the smaller forward reservoir is for the rear brakes).   I take a quick look and the lines from the master cylinder to the rear wheel cylinders.  If there is a leak sufficient to empty the reservoir, the fluid should be obvious --- unless it is combined with other fluid leaks.   I'd check around the PDWA switch and along the hoses near the rear suspension arms first.  If no leaks are detected here, I'd then pull the hubs and look at the wheel cylinders.   If no leaks are detected, I'd refill the rear system with fluid and try to bleed it --- see the part on bleeding the brakes.  Once the system is pressurized, one should be able to spot the leaking fluid.

If the rear reservoir for the front brakes is empty I'd follow the same procedure as above for the front.   After checking the hoses, I'd check around the calipers.  If no leaks are spotted I'd loosen the nuts holding the master cylinder to the servo.  It's possible that the fluid is leaking past the primary piston and into the area between the master cylinder and servo.  There is a sketch of this phenomenon in the part describing the servo overhaul.  Again, if the source of the leak is not found, I'd fill and bleed the system and then try to find the leak.   (It's been my experience that master cylinder seals are the most likely to fail followed by the hoses, then the seals in the rear wheel cylinders.  I've never had the seals fail on a caliper -- but others have, so don't completely overlook them.)  

If both reservoirs are empty, then there is either one leak plus a leak between the two sides or a leak in both sides the system.  I'd use the same procedure as above to find one of the leaks and then proceed from there. 

Tip:  I've had several cases where the PDWA seals have failed.   This is easy to check by unscrewing the switch in the top of the PDWA.  If there is fluid under the switch, then the seals are leaking and the PDWA must be overhauled.   What a mess ---- the master cylinder must be drained or the fluid will come out when the pipes to the PDWA are unscrewed.  

If the system goes from working to no pedal and no problem is found and the system seems to function after refilling and bleeding, I am very suspicious.  I don't trust the system until I find the problem.

Another type of failure is where the brakes aren't working properly but there is fluid in the reservoir.  This problem can be caused by a failure of the tipping valve and/or the secondary piston supply valve.  I encountered this problem a number of years ago.  The problem was in the servo where something prevented the primary piston returning all the way.  The net effect was that the front brakes had insufficient fluid.  I don't remember the root cause of the problem or if I determined the problem; I may have just replaced the servo with another one I had laying around.  

The more common tipping valve and/or the secondary piston supply valve problem is that they leak.  When they leak, the piston merely pushes the fluid back into the reservoir when the pedal is pressed.  The one I've had the most difficulty with is secondary supply valve.  As the seals deteriorate, some of the seal material builds up around the valve area at the back of the cylinder.  This area must be cleaned thoroughly during the rebuild.  A leaking tipping valve and/or the secondary piston supply valve can be detected by observing the reservoir level when the pedal is pressed.  A slight disturbance in the fluid is usually observable when a little fluid is pushed back in the reservoir as the valve is being closed.  If the level is the reservoir increases when the pedal is pressed, then the seal is not sealing.     

Soft Brakes: I've found that a soft or spongy brake pedal usually indicates that there is still a little air in the system and bleeding (again) is in order.  I suggest one use the helper approach described under bleeding the system.  If the system has been working and then a soft pedal develops, the problem is likely something else as it is difficult for air to get into the system once it has been working.  The reservoir should be checked first.  If one of the parts is way down or empty, then there is likely a leak someplace and I use the approach described above.  If the reservoir is full or near full, then it is possible that the tipping valve and/or the secondary piston supply valve are leaking.  This can be detected by observing the fluid level in the reservoir when the pedal is pressed as described above.      

Brakes don't release:  The problem isn't as serious as the brakes failing to stop the car.  However, if the car is continued to be driven with the brakes dragging, it's likely the fluid in the associated wheel cylinders or calipers will boil leading to vapor lock and system failure.  

Now is a good time for a war story from the Triumph email list

Last October my TR6 brakes locked up, fortunately just a block away from home. I had no idea why this happened, so after determining that it was only the FRONT brakes that were locking up I enlisted the collective wisdom of the list and followed all suggestions. Thanks, folks. 

Since then, I worked my way through the system, putting in all these parts:
  1. front brake hoses
  2. rear brake hoses
  3. master cylinder rebuild kit
  4. what the heck -- might as well do the rest of the brakes.......
  5. front caliper kits
  6. rear cylinder kits
  7. front pads
  8. rear shoes
  9. turn drums
  10. reface rotors
  11. Well, while I have the rears apart, might as well pull the half shafts and lube the splines...........Oh oh - grease on the brake shoes, need to rebuild the hubs...
    had a machine shop press them apart and found two broken hubs (broken a long time, still haven't figured out why) two used hubs bearings and seals for rear hubs
Test drive. Brakes locked up!!!  I then determined that the seal for the secondary piston in the master cylinder was loose in the bore -- probably been rebored in the past -- which called for a new master cylinder

Got it all together today and took it for a test drive........guess what.........the front brakes locked up!!!!

Without disturbing the hydraulic system, I unbolted my (new) master cylinder from the servo unit and -- presto -- the front brakes released!  So I replaced the
servo unit

Guess what all this cost? Would you believe close to $1000?

Besides, I'm not really sure it's fixed, but I've sure got a nice braking system on my economical-to-maintain LBC......................glad it gets good gas mileage

I describe this approach as ready-fire-aim.  However, I can't be too critical as I'm guilty of the same thing.  The TR6 is about 30 years old and much of the system was probably ready for a rebuild.  The technique was to replace one part of the system at a time until the defective part was found.   The big mistake was that he started on the wrong end.   

Troubleshooting does however present the risk of introducing a second problem in the process of trying to solve the first problem.   I think this is common when troubleshooting electrical problems, possibly because the electrical system is less well understood by many. 

To troubleshoot a  "brakes won't release" problem I'd first determine whether it is one or more wheel.   

  • If it is a single wheel, then the problem is most likely in that individual caliper or wheel cylinder, the pipes and hoses to that part of the system or a single handbrake cable.  
  • If it is both front wheels or both rear wheels the problem is most likely in that part of the system common to both wheels such as the common pipes, the PDWA, the master cylinder, servo or handbrake (rear brakes only).  

The symptoms described above where front brakes won't release indicated that the problem is in the part of the system common to both front brakes -- between the tee in the front brake lines and the pedal.  In this case, I'd partially open the line at the PDWA.  There would have been pressure there and after the pressure was released, the front wheels would have been free.  (A plugged line or hose will frequently pass fluid under the high pressure from the pedal and servo but not let all the fluid return when the pedal is released.  This leaves the cylinders or calipers with some pressure and the brakes to drag.)  The next step would be to apply the brakes and find that they lock up again.  Then --- crack the line to the front brakes at the master cylinder. There would have been pressure there too (ruling out the PDWA and the line from the master cylinder to the PDWA).  It is at this point with fluid all over the place that you thank goodness you installed DOT5 fluid --- or start looking up the telephone numbers of the painter.   So --- the problem must be in the master cylinder, right?  Not so fast, we have the servo and pedal too.  I'd operate the pedal again, verify that the brakes are on after the pedal is released, and then loosen the  master cylinder without opening the hydraulic system.  In this case we would have found the brakes released as he described above.    

Anything that causes the servo to hang up such that the push rod keeps the master cylinder primary piston from returning far enough to operate the tipping valve will cause a problem.  In the case of the example, I'd pull the master cylinder and see where the end of pushrod is relative to the front of the servo.  This measurement is discussed near the end of the servo note.  I believe the correct adjustment is with the end of the the push rod about 0.035" short of the front of the servo.                    

If the problem was with the rear wheels, I'd first check that the handbrake was released and there was slack in the cable.   These cables corrode and can hang up. This is more of a problem if the cables have been exposed to road salt.   

If the problem is limited to a single wheel,  I'd first try to determine if the problem is mechanical or hydraulic.  If a rear wheel, I'd check that handbrake cable first.  Next, I'd open the bleed nipple of the associated caliper or wheel cylinder.  If there is hydraulic pressure that is released, then the line is restricted someplace between the bleed nipple and the first tee in tee line --- the hoses are the most likely culprits.  Other possibilities are the lines, the tee and the cylinder or caliper.    If there is no hydraulic pressure when the bleed nipple is opened I unscrew the bleed nipple completely to make sure the nipple isn't plugged.   If still no pressure, the likely problem is that the piston is stuck in the wheel cylinder or one or both the pistons are stuck in the caliper.  

Insufficient Pedal:  If the brake pedal is firm but there is very little pedal, I would guess that either the rear brakes need adjustment (see note on bleeding and adjusting) or half the system has failed in which case I'd used the approached describe under "no brakes" above.   

Servo Problems: The most common servo problem is that the brake pedal requires much more force to stop the car because the servo had quit working.  The section on servos contains a test setup one can use to diagnose the health of a servo. 

I have another war story here about an intermittent  servo.  Last spring on a Buckeye Triumphs Saturday driving event I noticed that the brakes on my TR250 were acting strange; sometimes they were fine and sometimes they were really hard to press.   This drive had many starts and stops so I was able to discern a pattern; if the brakes hadn't been applied for a couple minutes, they were fine.  If I used them several times within a few tens of seconds, they got successively harder to operate.    Then I remembered observing that the hose from the manifold to the servo was pinched at the manifold end and thinking "it's a miracle that thing works".  When I got home I slipped a short piece of copper tubing inside the hose where it was pinched and took a test drive --- fixed it.   That hose on the TR250 and early TR6's makes a 180 degree bend at the manifold, a poor design for a vacuum hose that is prone to squeezing in on itself anyway.  The design was improved later, in '70 I think, to reduce the bend to about 90 degrees.  The hose is still working with the copper tubing ---- I want to keep the old hose because I can't find a replacement with the yellow stripe.

Brake Warning Lamp: It has been my experience that most problems with the brake lamp are unrelated to the brakes.   This is probably because the POs have been more adept at cutting, sawing, scarping, and destroying electrical components than brake components.  Maybe their side cutters were so dull that they couldn't make it through the hydraulic lines,  just the wires.  I'm not going to go into the wiring here since Dan Masters has published an excellent book called TRIUMPH TR250-TR6 ELECTRICAL MAINTENANCE HANDBOOK.  It's a steal at $30 postpaid in the US (  For those of you that don't want to get a new copy from Dan, you can pick up used ones on ebay once in a while for $40 or $50.   I will however go over the things to check to make sure the brake warning light is functioning property.  Brake warning lamp operation is essentially the same for the TR250 through '75TR6.  The '76 is slightly different. 

The TR250 through '75TR6 all have the brake warning lamp wired in series with the oil pressure warning lamp and low oil pressure switch and are powered from the white ignition circuit (same as the coil).  When the ignition switch is turned on with engine not running, power is applied to the two lights in series, which are also in series with the low oil pressure switch to ground. Since the engine is not running, the low oil pressure switch should be on and both lamps should light dimly (dim because they are in series and each get only half voltage).  This verifies that the lamps are in working order, the oil pressure switch is functioning, and no one has disconnected or cut the wires.   When the engine is started, the oil pressure should build, the low oil pressure switch should operate and both the oil pressure and brake warning lights should go out.   If both lights don't go out, the oil pressure is low, the switch is not working or someone has hosed the wiring.   If the brake warning switch in the PDWA is operated, the brake warning lamp will be on bright and the oil pressure warning will not work. (Note: if the brake warning lamp is on bright, then the oil pressure warning lamp doesn't work!)  Apparently the designers thought the brake warning was more important than the oil pressuring warning.  The brake warning lamp signals that the PDWA piston has moved off center due to a pressure differential between the front and rear halves of the system.  This can happen during the bleeding process.  The first thing I do is disconnect the switch at the PDWA and verify that the lamp goes out.  (If not, I troubleshoot the electrical circuit.)  Next I unscrew the switch, connect the wiring back to the switch and touch the end of the switch to the PDWA.  If the light goes back on here, the switch is defective.  If not, the PDWA piston is off center.  If the piston is off center, I shine a flashlight into the hole in the PDWA where the switch goes and use a sharp instrument such as a scribe to push the piston back to the center.  I then reassemble everything, make sure the brake lamp is not on bright, start the car, and push the brake pedal.  It the light comes on bright again then the PDWA has sensed a pressure differential.  One side of the system still has some air or a leak --- the side that the piston moves to is the side with the low pressure.  If the system had just been filled, then more bleeding is probably required.     

The '76TR6 has the brake warning circuit separated from the oil pressure warning system.   A switch was also installed on the handbrake lever to turn on the brake warning lamp when the handbrake is on.   When the ignition switch is turned on, the warning lamp will usually be on because the handbrake is on.  If the lamp fails to go out when the handbrake is released, then something is wrong.  I block the wheels here,  release the handbrake and then disconnect the the PDWA switch and see if the lamp goes out.  If it stays on, there is a problem in the wiring, most likely the wiring around the handbrake switch.  If the lamp goes out, I touch the switch plunger to the PDWA.  If the lamp comes back on, then the switch is defective.  If the lamp stays off, then the PDWA piston is off center.  If the piston is off center, I shine a flashlight  into the hole in the PDWA where the switch goes and use a sharp instrument such as a scribe to push the piston back to the center.  I then reassemble everything, make sure the brake lamp is not on bright, start the car, and push the brake pedal.  It the light comes on bright again then the PDWA has sensed a pressure differential.  One side of the system still has some air or a leak --- the side that the piston moves to is the side with the low pressure.  If the system had just been filled, then more bleeding is probably required.   The '76 has a neat warning lamp test feature.  If the brake lamp is out before the car is started (handbrake released), the warning lamp should light when the starter is engaged.  This is a bulb test feature.  If it doesn't light, then the bulb is bad or there is some other electrical problem

More experience  (war stories):  I'll add things here that I learn from my own experience or learn from others.  The first I noticed on the Triumph email list as I was working on the initial draft.   

From Triumph email list 3/31/02  & 4/1/02. 

Question:  My wife and I were working on her TR250's brakes.  The pedal felt mushy and was going down to far. So I bought a rebuilt kit and rebuilt the master cylinder. We bled the brakes and the pedal start felt firm and was engaging earlier. So we took it for a test drive. Well, after driving about ten miles the brake pedal started going down too far again (although it feels firmer still). I looked at all the bleed valves and the master cylinder connections and can't see any evidence of leaks.

There seems to be some fluid coming up into the front section of the reservoir when she steps on the brake. Does this indicate a bad seal in the master cylinder?  Any other ideas?  

My Response: The fluid coming back into the front reservoir sounds like the supply valve for the secondary piston (rear brakes) is leaking. However, I'd make sure the rear brakes are adjusted properly before taking the master cylinder apart (again). 

Interesting Response From Another Lister:  I recently went through a similar saga on my TR6.  It took a long time to find out that the master cylinder had been bored out and the new rebuild kit seals did not fit the bore.