I posted a new thread here yesterday evening which seems to have disappeared...

I outlined problems experience with a rebuilt gearbox which subsequently seemed to lock up on more than 1 gear, causing 2nd and 1st to wear in a very short space of time.

I ended up on the M2 services along with the "other" Roy trying to resolve the problem but to no avail, it was tow truck time!

today, I spent time with Martin, my local electrician trying to find the horrible negative earth problem which I suspect had caused the gear control panel to burn out, causing 2nd and 1st to engage while 4th was selected.

The answer is the window wiper!! Strange as it may seem, that was causing the negative to earth. the wiper motor was found to be live to earth; disconnect it and the fault almost went. Further investigation found the tacho had been earthed to the body as well.

We ended up bypassing the auto control panel, re-adjusting the gears and found the gears now seem top work as they should. Only a test run will prove the theory correct.

Thanks again to Roy Lane for his roadside help, and Martin Strange of MS Electrics for his help today.

Hi Roy
We had a similar fault with our gears before, multiply gears selecting at once or slow changes.
Traced it too the connector loom on the gear box. Wires sleeves had broken down and were shorting on outer casing, plus previous operators bodged repairs had failed so was shorting on outer casing.

Well done for tracking down the faults, bet that was a challenge!
Barry

Yes, not much, having been out to adjust the gears 3 times in 3 days, and spent a "happy" afternoon in sub-zero temperatures with Martin the sparks trying to solve the problem.

I heard late on Friday that the bus made it to its new home north of South Mimms and still had 1st and 2nd gears working.

Meanwhile I've just had a weekend in Germany trying to get a recon RT pump working properly, and trying to find an indicator flasher unit on an RM that had been rewired in Germany, but not to any LT diagram.

Both tasks were impossible!

Unfortunately this problem has not gone away. This RML has been towed back again, having caused rush hour chaos at the Dartford Tunnel last Friday!

We removed the auto gear panel and had it tested by PSV electrical who said it was ok, by-pass wiring was put in on the "christmas tree" making it manual change only. A new 7 core cable was run from said christmas tree to the box to eliminate that source of problems and road tested. the auto box was re-instated.

The bus went from near Dover to Welwyn no problems; from there to olympia and back, and by then 1st and 2nd had started to go again. so the bus was driven back towards here, and died at Dartford toll booth!

So now it's back in my place, the EP valve block has been replaced by an overhauled unit, electrically sound. Testing time with volts on said EP unit and all gears engage, having been re-adjusted; yes, the adjusters DO work and do not wind themselves off.

I stripped the gear change lever and found no faults there. However, when it was re-connected and tested, no gears at all! There is a clicking from somewhere in the panel a the back of th cab which only sounds in 1st, 2nd, auto and reverse, indicating to me that there is continuity from the gear change to the panel. Looking at my RMC wiring diagram for guidance, (I don't have the Cummins wiring diagram) I see there's a pair of wires from the gear stick to the panel which is labelled as an auto neutral. Anyone got any ideas what this should do?

Also, Roy Lane's RM handbook says there is an auto reset on the gear stick, actuated by pulling the reverse knob out and holding the gear stick down for 10 seconds. Maybe either of these are causing the peoblem of no continuity to the gearbox. I also seem to have the negative to body earth fault again!

Has anyone got any more ideas? This box still seems to engage 1st and 2nd when it's running in 4th! It's not a physical problem in the box as the adjusters do not wind themselves off. Incidentally, the box was rebuilt by Lionel Moss who has been rebuilding these for years.

My bus number (if any): RML2532

Hi Roy

Does the bus have the original signal generator on the gearbox or a transducer on the back axle? If it is the latter, I had a problem with gears when I first got my bus and it was eventually traced to a break in the wire close to the transducer.

My bus number (if any): RM2302

Thanks Brian, it has a tranducer. I suspect if that was the problem the gears wouldn't change, but it's worth a look!Maybe there's a self-check that prevents gears engaging if the wire's broken?

My bus number (if any): RML2532

Roy

With the RML Cummins / 551 gear control unit there will not be the 2 wires from the gear selector switch to the control panel as on the RM/C RCL types. They used the auto neutral when for instance the rear wheels locked up and the original cav/scg gear control panels required resetting by holding the gear selector lever down with reverse gear catch pulled out.

As Brian has mentioned if there is a problem with the wiring to the transducer or the transducer itself, this will cause the type of faults you have, that is why it is crucial to have a bypass plug with you at all times.
I would disconnect the 551 unit and run the bus in semi auto while checking the transducer wiring. It might be worth rechecking the gear selector switch to make sure all the contacts and wires are sound, and the wiring at the ep valves again.

Having had a truck in lately with a similar problem in that it would be disabled at any time.
Engineers spent hours with it, changed a lot of components and still problems occurred.

In the end the unit was completely rewired. Took 3 days with a new loom.

It has since run 80.000 miles with no failures and now has the best performance reliability of the type in our fleet!

I would suggest the wiring is too elderly and unreliable now on an RM to make operating one a bit of a liability.

And post refurbs and RMLs will probably need bespoke looms.

Easier for original AEC and Leyland specs

Thanks for the tips chaps. We've already run a new 7 core to the EP block and tried it as manual only, still have the same problem. I've removed the gear switch to check it, and now there's no gears at all.

I managed to get a Cummins wiring diagram and a Lucas book that describes and lists the wiring mods for the type 551 box today, and Lucas test lamp box, so that's on the agenda for tomorrow.

I don't see how the gearbox can be at fault as that will rely either on air or electricity to get multi gear selection.

Roy Lane suggested the reset facility on the gear selector. This is getting volts in the selector but should have been totally disconnected as it's not required for the 551 panel; this may be the cause of the problem!

Having spent all day on this bus, the previous evening I'd lost the feed to the gear selector. Surprised to find it had come back this morning...for about 10 minutes!

More delving and the removal of about 30m of redundant wiring from the cab. Why oh why do people leave old wires in place? Most were live and could have been causing intermittant faults.

I ended up running a temporary feed to the gear selector and all gears worked. So, out on a road test, and after 4 miles 1st and 2nd had gone again1 Pah.

Back to base on 3rd and 4th...lid off the box. what i reckon it is is the self-adjusters unadjust when the box is hot. I adjusted them again and tried the gears about 50 times in each gear and all seems ok, but have removed the self-adjusters for further investigation.

I reckon this has been a combination of problems of duff wiring and slack adjusters.

A long shot but is the correct oil in the gearbox.?
The wrong oil can overheat and cause a pressure build up.

Problem solved at last!! there was a combination of factors, negative earth faults, bad wiring on the 7 core to the gearbox, loads of spurious wiring in the cab panels; I removed over 30m of redundant wiring! There was also a fault with the feed from the air warning lamp via the handbrake switch to the gear select feed! I used the spare 24v feed still in the gearchange selector from the redundant reset circuit for this!

Then in the box, it had old type self-adjusters. These were adjusting off when the box was hot, typically after a 3 mile test drive! So the springs were replaced and the problem solved.

Thanks to Roy Lane for his help, Austin of GoCoach for lending his test box and wiring diagram and advice and Lionel Moss.

the bus is RML2498, now with Buspitality of Welham Green, Herts.

Glad to hear the good news, these kind of faults are so frustrating. It sounds as if the major problem was in the gearbox, combined with a neutral wire failure. Lucky you had the reset wiring still in place, was this copper or al out of curiosity.
I would still carry a bypass plug though, just as a get you home device should a problem occur with the transducer / 551 unit. All this talk of the 551unit being bomb proof is not to be believed, if all the buses with them were in real service work the majority would have probably failed by now and component wise they are likely to cause problems at any time due to age.

The slack adjuster springs were not the problem. The gearbox was overheating due to 2nd gear dragging due to the wiring faults. This caused the running gear to overheat, which could have caused the adjuster to slacken off. I fitted the same springs back in and the bus is still working fine.

The gear selector is copper, standard 7-core trailer wire!

As for carrying the get-you-home plug, if you have one, fine, but in my years of running RMs for private hire I've hever had a panel fail so badly that the bus couldn't be driven home. According to Lucas and LT stats, in 5 years of operating DMS buses with 551 panels, only 6 out of 1800 failed in that period due to manufacturing problems, hence their use on the RM fleet.

(that maybe because the DMS fleet was so unreliable they were off the road most of the time anyway...)

My bus number (if any): RML2532