Tow starting

So rads was, like

No. Tried it on my 3.9, up to about 40mph, in and out of Drive, nothing. I could not get the engine to turn at all. I stopped before I knackered anything.

No.

The gearbox is operated by oil pressure generated when the engine is running, if the engine is not running, there is no oil pressure, so none of the clutches will engage, so no drive.

On or around Wed, 27 Apr 2005 23:25:57 +0000 (UTC), "SimonJ" enlightened us thusly:

The only boxes I know this works on is the borg-warner 35 - which had 2 pumps, one on the output shaft and one on the input shaft - and the AP/lockheed 4-speed as fitted to the mini which had a special valve you could operate to allow it to tow-start.

The 'box will indeed drive the engine, once the engine's already turning; it'll do so in any gear and give more engine braking in lower gears, although it'll never have as much engine braking as a manual, since the torque converter also works backwards and allows some slip.

the way it disengages is something to know about as well - if you're using the engine braking (most commonly off-road) and something happens that kills the engine, it'll continue to slow down until the point at which the 'box drops out of gear, whereupon it'll roll freely. If you don't realise it's going to do that, it can catch you out.

If you do what you just described, (on a quiet road) and once you have it rolling in neutral, turn the engine off, you'll find that it won't restart. Be careful 'cos you also lose the power steering...

In message , Austin Shackles writes

I had a 1968 Austin 1100 auto (4 speed box) which could be tow started.

That's 'cos it was the same AP Lockheed box as the mini. Badger.

In message , Badger writes

But what was technically different about it compared to todays boxes which appear not to want to be tow started?

The design of older boxes wasn't as clever hydraulically as the modern ones, hence the need for 2 pumps instead of one, the "rear" pump having an output proportional to roadspeed, I think, giving an equivalent pressure signal to the modern governor valve unit. A by-product was that when sufficient pressure was built up by the car rolling, you could drive the engine, unlike the modern ones that need the engine turning to give any pressure at all. That's how I understand it, anyway, but if someone else has a better explanation then I'm all ears. Badger.

That's basically it! No rear pump, no tow start - and most boxes do not, and never had have rear pumps. The rear pump was never fitted to allow tow starting (tow starting is not a design criterion) but to improve efficiency or drive-ability. JD

Well, the box on the 1100 was superb - and 4 speed in those days was revolutionary on an auto, all the others were 3 speed.

Yes, not a bad little box in its day, but I always felt it changed up a tad too quickly. More reliable than the Borg-Warner 35T/A fitted to the princess though, that's for sure! Badger.

My memory is a little hazy, but wasn't the AP gearbox design different from most automatics? JD

On or around Mon, 2 May 2005 12:06:09 +0100, hugh enlightened us thusly:

me dad was working for AP at the time that was designed. Not sure how much hand he had in designing it mind.