GM180 auto box problem maybe Dave Plowman has an idea?

Sorry that I can't help with the rest of your posting but I'm very intrigued by the statement above. I'm not mechanically inclined at all, so as a layman with no knowledge of such things, what is torque converter lockup and, if I was driving a car with auto transmission that had some sort of fault that prevented lockup, just exactly what symptoms would I notice?

TIA,

John

So there is a vacuum pump with a variable bleed controlled by a pot on the throttle and some relays / electronics of some sort?

It shouldnt be too difficult to rig up a proper throttle body on the intake manifold with a vacuum take off and a throttle plate linked to the injector pump would it, off something like a Tranny ??

On my SD1 it will change up very early on a light throttle. But I've not heard of a GM 180 with a TC lockup.

I'd say the vacuum from the brake pump should be modified by the electrics in the control unit - as it would be originally designed to be more or less constant for the brakes? In other words it's simply an add on box rather than a true rework of the box for a diesel app which tries to mimic the vacuum from a petrol engine.

Well, high vacuum on the petrol setup causes it to change early. Lower vacuum causes it to hang on to the gears - or change down if very low and within the speed range as set by the internal hydraulic valves.

Is there some sort of potentiometer on the actual throttle? That would mimic to some extent the vacuum - but not for part throttle change downs. You'd also need a speed input for that.

I'm willing to bet it's down to an electrical fault. If that's sort of beyond you I'd be happy to have a look at the box if it can run without it.

The vacuum variation is done entirely mechanically, no electrics there at all. The torque converter definitely is a lock up type (to the other poster this is a feature to reduce drag and improve efficiency, almost like another gear when it kicks in, on Japanese boxes is almost unnoticeable) The electrics which are just a few ordinary looking relays are only connected to the gearbox and to power, there is a vacuum sensor there too t'eed off the feed to the gearbox. There doesn't appear to be any electronics control as such unless they are built into one of the relays as far as I know there is no electronic speed sensor unless it is internal (unlikely) .

Mrcheerful

Have you tried connecting a vacuum gauge, to see if the vacuum is doing what you at least think it should?

How? Have you put a gauge across it to see how it reacts to throttle position?

Never knew there was a version with this.

Relays can be used to provide a logic circuit - possibly the earliest way of doing so. But of course would have to be self contained in the way they act on the vacuum - since there's no electrical control on a 180. Unless this version differs in that too.

not yet, I'll dig out a gauge and a tee piece.

definitely something in the box is electrically controlled or sends as there is a thing on the side. guess I'll have to put a meter on that, or undo and see. I must admit I was hoping someone would say something like : oh yes, that is caused by the epicyclic dimodulator unit or something along those lines.

Mrcheerful

Not the speedo drive?

It's a pretty rare box I'd say.

I did a quick Google and learnt as you said that some versions of the TH180 had a TC lockup. You live and learn. Couldn't find anything about diesel apps, though. I know some convert it to pure cable operation for dragster use. But I doubt they're worried about anything other than full throttle operation there.

Have you tried Bedford for a workshop manual? They used to produce decent ones.

I know that many diesel autos use a cable - like the BW-35. I can't see how a combination of vacuum pump and electrics can give proper control without reference to the 'throttle' position. Are you sure it ever worked properly or could there be some bits missing? Like the injector pump was changed?

It has a speedo cable. I am not sure it has ever worked correctly, no! Bedford as such have now gone, any parts are just what can be found. I am pretty sure everything is there and original. My thoughts are that the vacuum modulator on the pump is the problem, as Moray said I will have to rig up a gauge and see what actually occurs, and try to establish what the electrical bit does.

Mrcheerful

My main point is that to alter the speeds it changes up at you need to know in some way how much 'throttle' you're applying. On a petrol engine this can be achieved by straight vacuum, but not on a diesel. Other way is some form of connection to the throttle mechanism. A cable or some form of electrical output from a pot. etc. If yours has no such input from the 'throttle' you have the answer - it never will work as it should. Are there any unused connectors on the electrical box or a wiring loom going nowhere? Or a mechanical link missing?

As I said the only way I can think it should work is by modifying a near constant vacuum from the brake pump to something approximating that of a petrol engine. Which *must* involve an input from the accelerator mechanism.

the strange assembly on the pump would equate to a throttle variation, but only of vacuum, no electrics there, there is no evidence of anything missing, the van came straight from the gas board, and I don't think they would have messed about. I reckon it must be this vacuum variation device, maybe it doesn't vary it at all, a gauge on the line may give the answer.

Mrcheerful

Can I ask how? Any connection to the 'throttle' mechanism?

Replacement injector pump of the wrong type because that's all they had at the time? Then vehicle got sold off?

Should do. I'm intrigued by the problem.

As the 'throttle' is opened this strange vacuum line 'adjuster' moves. I'll try and get a picture of it. Quite how it would work is supposition, all I can think is that it bleeds some vacuum away to 'raise' the modulator pressure, looks like it doesn't work so the modulator gets full vacuum no matter what. As to the vacuum to the relay and the electrical thing on the box, I haven't a clue, I cold just disconnect the electric side and take it for a run, I don't see it will harm anything? I could also bypass the vacuum variator, if it is exactly the same then I have isolated the faulty bit.

Mrcheerful