Thursday, 2 December 2010

COLD AIR & VACUUM

If you think you're cold, spare a thought for our six-wheeled friends who are currently braving a relentless run of sub-zero temperatures. Tonight in the South Hams, 270 KTA and friends will be huddling together for warmth in surroundings of -8 degrees C!

And if that hasn't melted your heart, spare a thought for those of us who have been working on them in the arctic...

Here I am wearing three jumpers, two vests, six socks and Compo's hat (from "Last of the Summer Wine") last weekend.

After a couple of weekends storing up heat, I've begun work on my list of jobs-to-be-done-before-we-go-anywhere (to appear here in full shortly). The aim is that, once I've worked through the list, I should not only have cured all the outstanding issues which have so far hampered attempts at an MOT, but I'll also have performed a good deal of preventative maintenance which seems to have been lacking since... well...

First and foremost, I've been tackling a problem which seems to be at the heart of the braking issue. Comparing the vacuum gauge to that on her sisters during the Kingsbridge weekend, 270 KTA is having great trouble building up vacuum.

For the uninitiated, whilst the brakes on an SU are hydraulic, they are assisted by a servo which is operated by vacuum. Without the servo, or the vacuum, the brakes will still operate but with limited force, and are pretty useless on the road. Sounds familiar, doesn't it...

After weeks of isolating sections of the system in search of a leak, I concluded that the exhauster itself (which creates the vacuum) must be at fault. Mercifully, Colin Billington was able to provide some spares, and last weekend I became the world's leading expert in changing Bristol SU exhasuters... in the cold.

With a replacement exhauster fitted, the gauge reached levels of vacuum never before achieved, and with full vacuum the brakes worked really well. However, a trip up the drive revealed that vacuum was still too slow to build...


It's possible that, whilst the replacement exhauster is more effective than the original, it's still not quite up to the job, and with that in mind I'm going to try a third exhauster before drawing too many conclusions.

Though I might wait a few days for slightly warmer weather...

Sympathies also to SMA 5, Trevor Leach's former West Yorkshire SUL bus, who is currently snowed in "in a cold, wet building on a farm in North Yorkshire". Your South West cousins are thinking of you and rubbing their tyres together...

1 comment:

  1. Unfortunately prevention is better than cure ! Sister 1202 is saddened by this poor weather. The roads are clear but white with salt, so as a preventative precaution she will not have her extended test run yet. (She has had the fuel pump rebuilt to cure the "don't want to stop syndrome") She is also saddened that she will not be joining the "Carols down the line" as her owner is in Brighton sampling the sea airs.

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