A bit of help needed for a Scania RM: I've changed the accumulators(not holding charge), foot valve (leaking), 2 wheel cylinders (leaking), freed the brake shoe rollers and pivots, the lot.

Bled the brakes, started the engine, pressure built up ok. Put the test gauges on the front boat, pressure was about 600psi on full service, but very little above that for emergency. Tried the gauges on the accu test points, 1200/1200, but the cut out did not seem to clunk. Back to the brake test points, lower pressure, eventually fading to nothing.

so I changed the bottom accu in case that had failed as fluid was leaking from the bleed hole on the side; again no brake line pressure; changed the top accu, again no brake line pressure.

So, that leaves the engine mounted pump as failed, or is there a non-return valve or similar somewhere in the cicuit that may be sticking?

It may be the pump has failed because it now has to overcome full accu pressure instead of a little bit?

Any ideas?

My bus number (if any): RML2532 Keeping Europe's Routemasters on the road.

Roy

You mention that the cut out does not seem to operate ( clunk ) which means it has not closed, surely this is the cause of the pressure drop. The non return valve in the hydraulic circuit is on no1 accumulator, which after the cut out valve has operated, stops no1 further pressurising no2. If the cut out does not operate on no1 this accumulator will quickly lose pressure.

My bus number (if any): RCL2250

I found the problem eventually. On the Scania RM, there is a silver block between the pump and the accus just near the accus on the chassis member with 1 pipe in and 2 pipes out. One outlet has a non-return valve to the accu feed, the top pipe goes to the tank, but via an adjustable valve.

This had been adjusted by "someone" in the past, so the pump would only deliver 600psi, not enough to pressurise the accus! so with a bit of trial and error with the test gauges attached, this was screwed in to increase the pressure from the pump.

The cut-out on the accu now works, but the accu leaks from the hole in the cut out valve, so am now waiting a replacement from my supplier!

RM1398, open top conversion, owned by a language school tot travel round Europe.

My bus number (if any): RML2532 Keeping Europe's Routemasters on the road.

OK, the third accumulator turned up this lunchtime, was fitted and doesn't leak.

Brakes now work ok, but slightly concerned that the flag drops after 6 applications, but test gauges show the pressure doesn't drop until 18 applications. Possibly best to err on the side of safety as it seems the pressure switch is set at the wrong pressure.

Now getting 70% footbrake and well over 25% on the handbrake on the Tapley meter, better than the 48%/12% before I stripped everything down!

My bus number (if any): RML2532 Keeping Europe's Routemasters on the road.

You working down in Nice then Roy? Have you seen the E mail I sent you about the RT rear axle spanner?

My bus number (if any): RTL 960 RMC 1458 RM 1585 and several RTs

Agreed, it looks like you're going to have to reset the two low pressure switches. They can be a mite tetchy to get set correctly and try your patience just a tad. Once you've got them set right, they will probably be really co-operative and start to leak.

Brian, no, I'm working in my depot, the bus came to me from Switzerland where the brakes "failed" somewhere up a mountain! A.N.Other went there to pump the accumulators with a nitrogen bottle, then they drove the bus back to the UK!!

And no, I haven't seen your email re the RT spanner, you haven't broken it have you??

Roy, thanks for your input. I've decided to leave well alone on the switches for that very reason. If the flag drops at 6, but there's reserve pressure for 18, that's erring on the side of safety in my books.

My bus number (if any): RML2532 Keeping Europe's Routemasters on the road.

Oh THAT one! I thought it was the one that the language school at Nice has got in exchange for their Leyland PD3 which you might remember also had brake problems!! Nothing wrong with the spanner, remember the arrangement we had for final payment???

My bus number (if any): RTL 960 RMC 1458 RM 1585 and several RTs

Great to read about this repair and thanks a lot for your work Roy, I don't know you but I am the driver of this Routemaster and have been travelling Europe since 2008 with our wonderful machine. Probably the bus meets with the disapproval of some because of its colour and "open top" but if they knew where this machine has taken me I think they would love it as I do:)
The person who was stuck up a mountain was kindly replacing me for ten days while I saw my ex-wife and children, last minute thing. He baulked at bringing it down the mountain, I have done loads of them, but it was getting a bit beyond it! He left the bus in Munich and flew home to Sweden, I drove it to Czech Republic and after that brought it to GB, you know the rest. What you may not know is that today I came down from a mountain in Italy, 2035 meters in altitude with a 12 Km drop on a hairpin type pass!! This was from Sestriere, and I was a bit worried I must admit, but it performed faultlessly! Many thanks again, by the way I am an old bloke who has spent his life on the roads around Europe so am used to these old buses, I am ex Southdown from the good days:)

My bus number (if any): RM 1398 :)

It's good to have faith in Lockheed!

My bus number (if any): RML2532 Keeping Europe's Routemasters on the road.