Both our Routemasters are misbehaving!!

RML with Cummins engine, starts OK flag goes up lights off.
Soon as a gear is selected the warning light comes on. EP valve is a newly reconditioned one.
Put lever back in neutral and after a few seconds the light goes out.

RM AEC engine
Brake warning light stays on, and the flag down. Brake pump is new, accumulators charged, brakes on the bus work fine but flag still stays down.
Where does the flag pick up that there is a fault from? Is it possible the Westinghouse unit is at fault?

Any ideas suggestions, thoughts as usual very welcome...

Thanks in advance.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

AEC: check wiring behind o/s/f wing which goes to the microswitches. Check the correct operation of the microswitches.


Cummins: red light or white light? Drain the air tank water and or oil will not be appreciated by the pneumatic components.

white light: short probably somewhere in region of the flag unit.

red light: there is an air or an air leak when in gear, or there is a problem with the low pressure switch, or there is a problem with the actual pressure available either to the reservoir or the gearbox or both. Check that the operation and settings of the unloader valve, reducer valve and low pressure switch are consistently within spec. Check the wiring for the low pressure switch.

Thanks Roy
We suspect there may be an air leak around the gearbox on the RML,,,
Will pass on other suggestions to Philippe
Many thanks gain

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

It seems there's a lot of naughty Routemasters out there at the moment. Both roy and myself have clients who have air problems with their RMs. It's a good job we talk to each other about such things.

No doubt roy will impart information about his latest exploits. My latest is with a client "somewhere in the north" who ahs 2 RMs, both died at roughly the same time within the space of a week

One has an Iveco which I done some work on a couple of years ago. That had a tacho fitted and lost gears after that. It turned out that the tacho installer used the speedo sender on the back axle to get the pulse for the tacho, not realising the same sender wheel was also used to change gear. He cut a number of teeth off i to get the tacho right, but by doing that meant the gears wouldn't change. that cost a lot for a sender wheel a an expensive train journey up north.

That one lost gears the other day. It had already been re-wired to work manually as a temporary measure. Having spoken to roy about it, the client was advised to do a thorough check on the air system to make sure a) the compressor was giving the required pressure b) the unloader valve was cuiting in and out and c) the reducer valve was giving the correct pressure. Also check for air leaks on the bus. I'm waiting to hear back about that one.

The other I believe has an AEC engine. That too lost gears with a burning smell and a lot of rattling. That turned out to be the compressor breaking up; low air pressure caused gears to slip, hence the burning smell and loss of movement. He fitted a 24v compressor to get the bus moving again and fitted smaller belts to run the Plessy pump to maintian the brake pressure until he gets the compressor rebuilt.

During these conversations Queensbridge Engineering who seem to rebuild most RM gearboxes these day suggested upping the pressure on refurbished buses to 85psi to take into account the higher torque of modern engines. they've had a couple of units back under warranty and low pressure was reckoned to be the cause.

As for Brian and Philippe's problems, check wiring and WD40 in the Westinghouse flag unti, they tend to gum up. Also check the feed from the starter switch panel to the flag unit.

My bus number (if any): RML2532

For Brian and Philippe, have you tried the flag test switchlocated in the back of the regulator box ner the bottom, it has 3 or 4 positions. That will test for operation. I can't remember what they all do, no doubt someone else will remember. Maybe some has moved the switch to the wrong position while doing other work in that area?

My bus number (if any): RML2532

Hello Brian

The switch mentioned works as follows

SWITCH POSITION
N = NORMAL USE- Flag up/Light off if both systems are charged
2 = FLAG DROPS LIGHT OFF- Charged or not
1 = CHARGED: Flag up/Light off
DISCHARGED: Flag down/light on

I have never found it very useful and modified mine so that positions 1 and 2 isolate the two pressure switches and tests them individually. Simple mod and it is great except for one flaw. If i leave in position one or two by mistake it allows operation on only one switch and you will not know if the other fails which is cleary unsafe. I will rethink this as I want it right but do not believe the original method was good enough to show which switch is at fault.

With the Roof website now gone the code needed to upload a picture is no longer available. It was some text that you placed before and after the url of the drawing. If someone can email that to me I can put a drawing on here for the circuit. I will email you the drawing later.

My bus number (if any): M1001, RML2276, T806

I don't think the original method was designed to troubleshoot faulty microswitches per se. Rather its purpose was to be part of the 12 week routine safety-related maintenance procedure when hydraulic pressure gauges were connected to carry out a full system check. Just turning the test switch to 1 or 2 and slowly depleting pressure merely indicates that the switch is in working order, either because the flag falls and the white light comes on (1) or the white light illuminates (2).The actual pressure available when the warning operates could be close to zero. In other words it works but not as intended. This is why the MOT test, when carried out correctly, checked to see whether there is some braking effort at each wheel when the warning is operating.

Any operator using these buses commercially should ensure that either they, or their service provider, has the ability and means to check the correct operation of the hydraulic braking and warning systems. To fail to do so leaves the persons legally responsible in a potentially difficult position.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

The test switch wasn’t used, as far as I’m aware in conjunction with any pressure test. It was purely a circuit test and not very good at that. Mine rewired allows me to choose 1 switch at a time and test by charging and discharging and have the flag and light operate. It points me to which switch is operating first and may point to which switch or accumulator etc has the problem. I just need a method of not allowing to remain in a test position. I may fit a buzzer to sound when in the test position.

Re the RML Cummins engine
We have now fitted a new EP valve, we get pressure (no red light) in neutral.
Engage 1st, 2nd 3rd... all OK :)
but immediately we put it into top ...the red light comes on Same with reverse! :(
Is it worth using pneumatic grease on the gear pistons as we do on the RTs.... Gearbox pistons need changing? Any other ideas very welcome.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

Typical of these pox ridden buses, they are a blank blank pain, as soon as you have fixed one issue another one arises, you have never finished. They are long overdue being converted into coke cans. Whatever one may think of TfL or the operating companies they were no fools, just about everything on these buses is worn out. Unless parts are replaced with NEW then nothing can be ruled out.

As so often with gas and liquid leaks we can frequently only find the minor weeps once we have fixed the major leaks.

So Cummins RML: should have a CAV551 panel which means that if it is not bypassed then 3rd and 4th gear cannot be selected when stationary. That means that if the bus is parked then you are not selecting 3rd gear so it may or may not have an air leak. Ditto 4th gear.

In the circumstances described then we can say that there is an air leak in reverse and an air leak when the lever is in 4th but the gearbox has actually selected 2nd.......unless we have by passed the panel.

We either have to by pass the panel, fool the panel into thinking it is in a different gear or test with the bus moving at an appropriate speed. Since we can't go looking for air leaks under the bus while in motion, the easiest thing to do is to connect an air gauge to the ISO test point on the air tank and view the recorded pressure in the cab when driving and using manual gear selection. You may have to drive some distance since the fault could be intermittent, it may require vibration or full operating temperature to trigger. You can also tee into the pipework for any gear with a second air gauge to register pressure.

Once you have ruled out a random red light fault(which is all you really know presently) then to check while indoors you can either by pass the panel which will check from the gear selector to the pistons including the replacement EPV; or to check the pistons only, connect the relevant piston union(s) to the workshop air line; or swap over air pipes - extending as needed - so that selecting 1st or 2nd operates the suspect gear.

It is of course possible if road resting indicates a somewhat random nature of FOURTH gear apparently having an air leak, then the actual problem may be the unloader valve's non return valve leaking and the valve either occasionally failing to cut in, or to cut in only below red light pressure. This could be due to oil/water/carbon contamination.

Sorry Roy, you should have added that it was converted to semi-automatic and the gear changes are done with the rear jacked up so not stationary as such.

The unloader valve could be very relevant to the problem as Philippe said whilst driving it back when we bought it back, it appeared to have stopped "unloading", so maybe a leak caused that?

However the light doesn't come on now except when selecting 4th and reverse. i have told Philippe to try and get under the gearbox and get someone to select different gears, so he can see and hear what is going on.

Thanks for all the suggestions I will pass them on.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs

I would suggest either leaking pipes from the ep block to the gears or leaking seals in the box. You can do a stationary test by getting pressue up, stop engine, set ignition on and select the appropriate gear. You will either hear the air leak if it's a leaking pipe or bubbles in the gearbox. Lift the floor trap up to hear properly what's happening or get someone to lie underneath.

Plastic pipes ahave a tendency to gto brittle after about 10 ears, metal pipes vibrate and leak round the olives.

My bus number (if any): RML2532

Thanks Roy, much appreciated.

My bus number (if any): RTL 960, RM 1585, RML 2667 and several RTs