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Re: Gears

I will try and look tomorrow & take it for a drive to find out what it's up to. (I haven't driven it for 2 years). Last time I looked under the bonnet I remember thinking there was no plate or badge on the engine that made it easily identified.

The reports are 3rd disappears & other gears sometimes play up.

Last time I drove her I was told that auto didn't work but when driving it, I must have been to slow for 4th so it took 4th then dropped back down to 3rd but cant remember how else it behaved other than it wouldn't behave as auto in 4th. Cant even remember if it would try taking off in 4th.

I will get my facts and report back more informed.....

My bus number (if any): RM2151

Re: Gears


If this is RM2151 in Norfolk, then it is a London Central Scania conversion and retains the standard GB32 gearbox.

Andrew

My bus number (if any): RM1368

Re: Gears

Spot on Andrew it's a scania lump and standard box.

Today I only took it for a short ride but it took every gear. So I'm guessing the issue is heat/prolonged use. Will ask the regular drivers for more info.

She will engage and would pull away in any gear. So I'm wondering if the sender unit for the speed sensor has stripped its teeth? (Seems like the common fault). So I'm guessing the selector unit has been bypassed. (Lots of if's butts and maybes I know)

At present my main concern is the gears that vanish. Not been able to get under her to check electrical plug yet. Not looked for a dip stick or oil in the box yet. I'm guessing there is oil as the box is wet in places. I wonder if the contract maintenance bods have put some new fangled oil in the box and as it warms up its causing issues??? But how would that on cause issues with 1st & 3rd?

Thank you in advance.

My bus number (if any): RM2151

Re: Gears

With the bus stationary with the engine running,If you select 1st you should get 1st and the bus will move. If you select 2nd it will engage 2nd and move. Select 3rd and nothing will happen. Select 4th and it will engage 2nd as that is the auto position. when you move away, it should change from 2nd to 3rd to 4th.

The common faults are: air leaks on the pipes from the EP block to the gearbox; low air pressure, should be 65psi; worn brake bands; worn automatic slack adjusters; worn piston seals. To check for worn seals engage the errant gear and listen for bubbling in the gearbox.

it's unlikely to be worn teeth on the speedo sender as this should be on the back prop shaft on the Scania conversion.

It's difficult to diagnose gearbox faults without seeing the bus. I think Rob Duker would be your nearest RM specialist, he's near Huntingdon and may do call-outs but there will be a charge for that service.

My bus number (if any): RML2532

Re: Gears

Thank you Roy I will do the simple stuff as soon as I get time.

There is a sender unit on the back of the gear box. I didn't look further down the prop as I thought I spotted what I needed to? She is fitted with a cassette type paper tacho if that makes any odds? Is the speedo sender the same unit as the gear selector? And would this explain why the "auto" is discounted? As I say every gear will engage when selected.

My bus number (if any): RM2151

Re: Gears

If a bypass plug has been fitted to the CAV 551 gear control box above and behind the driver’s seat effectively hard wiring each gear to the selector this would allow you to select all gears ?

My bus number (if any): RML2747

Re: Gears

the only way to find put is to remove the cover panel above and behind the cab seat, have a look at whether or not there is a control panel fitted. If yes, are there any plugs in it? There should be a huge round NATO plug with acbales that go to the 12 way terminal block on the right side of the control panel. Maybe someone has hard wired it using bypass wires on the 12 way terminal block?

If there is no control panel, then obviously it's been hard wired somewhere. there may be a bypass plug fitted to the NATO connector.

There may be 2 senders on the gearbox, the speedo/tacho sender is on the right side, the SSG is on the left side. the SSG does the speed control for the gearbox. Very often these are still there but have been made redundant by a pulse sender on the diff which reads fro the propshaft.

My bus number (if any): RML2532

Re: Gears

Just for info, Rob Duker has retired and only plays with his own buses
Time catches up with all of us.
Cheers

Rob

My bus number (if any): RM7

Re: Gears

Very informative Roy the bus. Thank you
Roy Duker enjoy playing with your own buses & happy retirement.

I'm told it only looses 1st and or 3rd intermittently. So wish me luck,,,,,

My bus number (if any): RM2151

Re: Gears

Blackmore Commercials in Nottingham 0115 958 6696 have many years of Routemaster maintenance experience including Gearbox fault diagnosis. They will be able to handle the investigation and repair. Sadly in a senior moment I can't recall the name of my contact there but we speak a couple of times a year, normally on this very subject.

If it is an intermittent fault then it will be a challenge. You will be lucky if you can fix this without repeated road tests. You will be even more lucky if you can reliably prove that the fault appears without the bus needing to be in motion. The following assumes that the CAV551 panel is in cicuit. There are three stroke four systems to check: air supply/leak, gearbox mechanical fault, electrical wiring/system operation fault, speed signal fault. Start with the easiest things first but don't automatically assume that a check has categorically eliminated or proved a fault. Consider as always what work has been carried out on the vehicle and whether the fault has developed since that date. These buses are old and were run into the ground during their last days in London service, they will have been subject to repeated 'temporary' repairs to get them out on the road again the same day. If there was a cheap way of fixing the thing then the more expensive option would have been discarded. There are quite likely several underlying issues which may not on their own cause the fault but tip the scales because other things are marginal.

The complete system needs 24 volts and sufficient constant air pressure to work so check both and think about it being possibly an intermittent fault. What can you see and what can you Hear? Are the battery terminals tight/corroded? What does the various wiring look like to the rear axle speed transducer and to the EP valve? In a QUIET environment can you hear the EP valve solenoids engage when someone selects each gear; 3 and 4 won't work if the CAV 551 panel is in circuit, you will hear 2 when 4 is selected.


Re: Gears

Rob Duker
Just for info, Rob Duker has retired and only plays with his own buses
Time catches up with all of us.
Cheers

Rob
Likewise with roythebus, I'm tending to only play with our own buses these days, it's getting too much hassle doing stuff for others! Hence the sale of parts mentioned elsewhere on here. Age and ill health catching up.

My bus number (if any): RML2532

Re: Gears

Little update. The "brain" has been bypassed for the gears. I'm told it was done many moons ago as it was the easiest solution to what ever the problem at the time was. (I may plug it in and see what happens)

I'm still trying to ask all those that have had gear issues when driving her what the symtoms are.

Obviously it wont play up if I go on a test drive.

Anyone got wiring diagrams for a Scania conversation or original, to help speed me up?

Cheers Tyson

My bus number (if any): RM2151

Re: Gears

Either you want the Scania conversion or the original; they are wired differently.

I have th RMC wiring and Cummins wiring diagrams.

My bus number (if any): RML2532

Re: Gears

Then I need the scania one!
I foolishly thought they used the old wiring harnesses..

My bus number (if any): RM2151

Re: Gears

Many of the Scania powered buses were originally converted from AEC/Leyland engines to Iveco and then repowered again to Scania. A few were converted directly to Scania from the original engine. Others will know but 2151 seems to have been a New Cross bus which I think was one of the last bastions of original power in any quantity.

Having had a look at the Cummins and Iveco wiring diagrams I can't see any difference between them which relates to the gearbox. The differences which do exist are all within the CAV 551 panel and its optional features. I am not aware of there being a specific Scania wiring diagram available. The electrical termination number locations and wire colouring are the same between the two diagrams.

You need to establish if the is a pole wheel and transducer attached to the input shaft of the rear axle to determine whether the bus has the later CAV 551 panel system, or the earlier SCG/ CAV system which also requires an accelerator switch on the o/s/f of the A frame and a speed sensitive generator attached to the gearbox. The presence of these latter alone is not a means of identification.

Re: Gears

I thought, I may be wrong that the London General Scania's had a different brain than the others, I thought it was built by J S Components. If I could figure out how to post a picture I you can see the one fitted to RM1797 which was a New Cross Scania.

Try this https://www.flickr.com/photos/30266527@N02/48828024506/in/dateposted-public/

Cheers

Rob

My bus number (if any): RM7

Re: Gears

As I've posted on here and on FB groups before, the difference is in the gear control panel. On the original set-up, the gear selector switches positive via the control panel and positive from there to the EP block on the gearbox.

On the refurb buses, the selector switches postive to the control box, that then switches negative to the EP block. Hence the importance of ensuring there's NO negative to body. A lot of people fit cigarette lighters/satnav/radio to the bus and ground everything as they would with a car. then strap the negative battery to the body. That's all well and good until the wiring for the gearbox chafes through, usually near the gearbox. As there's now one positive wire there and five negatives, whichever negative touches the body will engage a gear. the driver will also select a gear. you then get 2 gears selected at a time. Your gearbox will eventually fail. If by chance the positive return from th gearbox touches the body, you get a short circuit. When this happens the easy answer is to disconnect the control panel and bypass it.

Then you find the tacho or speedo doesn't work because that relies on the control panel for its feed.

For some reason unknown to me it's always 3rd gear that gives problems. I must have changed about a dozen gearboxes over the last 7 years with the same problems.

The wiring on the gear side is the same for the original and refurb buses; it's how it is switched in the control box that is different. The 2 different panel are interchangeable but they cannot be swapped and be expected to work. Also the by-pass plugs that are available or the originals won't work properly with refurbs. The wiring on the refurb variants IS different for things like engine run solenoid, charging systems, warning devices and the like, not to mention Centrecomm radio and CCTV!

My bus number (if any): RML2532

Re: Gears

Rob Duker
I thought, I may be wrong that the London General Scania's had a different brain than the others, I thought it was built by J S Components. If I could figure out how to post a picture I you can see the one fitted to RM1797 which was a New Cross Scania.

Try this https://www.flickr.com/photos/30266527@N02/48828024506/in/dateposted-public/

Cheers

Rob
Copy the address and open it in your browser. that control box certainly is different, not seen one of those before. J&S went broke many years ago, the only bloke who may know the wiring on that is Mick Brown who used to work there.

The refurb buses use the same control panel as the DMS as the panel was found to be more reliable than the original type; the only defects usually found on them is the soldered joints are going dry after so many years. The earlier panels had relays, later ones are solid-state from what I've been told.

My bus number (if any): RML2532