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Lost top gear

On my way to an event near Cambridge, I suddenly lost top gear from the gearbox whilst travelling along the A1 so had to continue 25 miles in 2nd or 3rd. gear (all the lower gears work OK). I had no warning that trouble was brewing, it suddenly failed. Any ideas why the gearbox refuses to work in top gear?

My bus number (if any): RML2672

Re: Lost top gear

Three potential causes: electrical, pneumatic and mechanical, unfortunately none of which are going to be easy to check if not in a workshop unless you have a shorting plug or the control panel has been by-passed anyway. A visual check of the air pipe to the top gear piston is about the limit in the middle of a field.

Re: Lost top gear

Thank you Roy, I'll have a look today - might be a slow ride home with Hazards going!

My bus number (if any): RML2672

Re: Lost top gear

This week seems to be all about gearboxes with the problems of RML 2502 in Western France,

As Roy says many possibilities, but one thing I learnt with trying to drive RM 48 back home, 4th gear is not self adjusting so best to get someone who knows about RM gear boxes to look at 4th speed in the box. It may need adjusting...

You can also check by listening if air is getting through when 4th is selected, also check gearbox and EP valve pipes have not been hit by something thrown up under the bus.

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

Re: Lost top gear

I don't think 4th is adjustable, it consists of clutch plates which can become worn. As roy says, difficult to diagnose on the internet.

Along with others I've spent a lot of time in the last couple of weeks trying to help resolve problems with gearboxes in France, Scotland and elsewhere and not received a penny for my time. It's always nice to be able to help someone out who is in trouble but with gearboxes they are very time-consuming to explain to someone on the net or by phone.

I got stung badly by someone on an internet forum a couple of years ago who got a lot of free advice then never sent something back for 6 months that he had little intention of buying in the first place. As my transport manager reminded me today, never give advice; if it's the wrong advice the chances are I'd get sued for it.


My bus number (if any): RML2532

Re: Lost top gear

From your description of the operating fault Mr Pell it seems the problem occurred all of a sudden with no advance warning of any impending fault.In my opinion I believe the fault is a electrical one. The cause could be that the EP unit is not receiving a electrical signal to energise the 4th speed solenoid.


Possible causes are for a Wilson GB32 gearbox:-

a) Broken wire connection at the EP terminal block cover therefore the solenoid is not being energised

b) Dirty connection between 4th gear terminal post and the spring loaded solenoid plunger at the EP unit cover plate

c) 4th speed solenoid valve jammed or seized in the closed position mechanically

d) Internal wiring fault at the 30pin plug control panel or the loom wiring to the EP unit

c) Sudden air loss when 4th speed is selected, but red warning light would show

If top speed adjustment was pending you would have experienced a slipping speed

My bus number (if any): Ex LTE Bus Engineering

Re: Lost top gear

Check where the 7 core cable comes out of the conduit near the gearbox. Our bus lost all gears a few years back. that cable had worn thrugh due to exposure to oil from the compressor and heat. Otherwise maybe a dry joint somewhere in the control board.

My bus number (if any): RML2532

Re: Lost top gear

The difficulty in diagnosis arises because the only gears that can be selected from stationary are 1st, 2nd and reverse. The other two gears are inhibited until the panel receives a speed signal from the transducer on the rear axle. This and the wiring to it have been the subject of a fair number of posts calling for gear loss help on various Fora over the years, however none of these have been recent.

It is possible to adjust all the gears but without the necessary go no-go gauges,a source of compressed air at the constant correct pressure and knowledge of the proper procedure it is possible to either create problems or cause damage. The garage electricians had dedicated test gear to carry out fault finding, without this things become a lot more difficult and time consuming.

Re: Lost top gear

Excellent check list for future reference thank you Michael.

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

Re: Lost top gear

Some people are asking about the by=pass plug used for getting round gear problems and test boxes. From what I understand the original LT plugs and test boxes are only suitable for the AEC or Leyland engine version, they are not suitable for the refurbs with later gear control panels. the feed arrangements and polarities differ.

My bus number (if any): RML2532

Re: Lost top gear

Thank you to everyone for their useful advise and help. I now have the problem of the lost top gear sorted.
On closer inspection of the gearbox area, I noted a disconnected pipe on the nearside of the gearbox. Just a 5 minute job to reconnect the pipe and tighten the nut. Everything working correctly now!

My bus number (if any): RML2672

Re: Lost top gear

Makes a change to have a simple fix! Are they metal or plastic pipes from the EP block to the gearbox?

My bus number (if any): RML2532

Re: Lost top gear

Metal pipes

My bus number (if any): RML2672