Practically Classics Forum

I dislike manual gearboxes. I like autos.

My Shadow has a TH400 GM box 3 speed with convertor.
Because of the convertor I think of it as 3 variable ratios.

If I want to waft and float around then I use D. This gives 26mph per 1000 rpm.

If I want to go fast simply select 2 and the car flys. The engine starts to grunt and pulls hard.

I can use kick down but selecting 2 stops the box changing up.

So to get the best from an autobox use the selector , theres no rule that Drive only should be used.

Note 1st gear is a bit mental plus engine braking. I find no advantage except on very steep hills.

My Jeep is 4 speed with locking convertor. I use 3 and 2 to get the Jeep to accelerate fast. 3rd above 40 mph is particularly good. 180bhp makes itself felt.

Bentley turbo.
These cars in 2nd go like a bat out of hell. I was passenger in one on a slip road , the driver selected 2nd saw a gap and floored it at 40 mph the front came up a bit and the car launched itself, the driver selected Drive at 80mph. No drama but very fast. That particular car is regularly driven on autobans at 120mph plus for miles.

Regards
Bob

26mph per 1000rpm? I'm amazed that a massive engine - with so much torque that the brochure writer couldn't quantify it, so had to put "undisclosed" - is as low geared as that. As an example of how I'm thinking it's awfully low for such a large engine, the Chevy Caprice SW - currently laid in my steading awaiting a fresh set of door glass to come over from Ireland as I was persuaded to accommodate it for now - is only doing 1400rpm when cruising at the legal UK motorway speed limit, so almost twice as high geared as a Rolls Royce. That can't be right can it? Last time I travelled in a Shadow it seemed very relaxed but checking how quickly the engine was turning during that journey wouldn't have been the done thing..

The 26mph per 1000 rpm is correct the max speed is 120 ish at 4500 rpm.

The engine is quiet even at 100 mph.

Remember this is a 1965 design.
A Minor is about 20mph at 1000 rpm.

The newer cars like spirits had higher gearing. The turbo r max rpm is still 4500 rpm but the max speed is north of 150mph. So gearing is much higher than a Shad.

I no longer drive fast because I am old and frail. I dont like night time.
To be honest my driving abilities were only ever average. I passed the IAM advance test and the police one. But it wasnt differcult. The police one ( I worked for them) was very easy don't speed don't hit anything. The copper was more interested in football and the Cherries. The IAM one was a bit more involved but not hard. Again don't speed and use good road positioning mirrors etc and you pass.

Shadow is 220 bhp and 250ftlbs. The turbo R is 400 bhp and 400ftlbs. Turbos are about midrange grunt. That 400 ftlbs of torture is why the turbos are so quick. The lastest version from Bentley using this engine the L410. Is 550 bhp and 500 ftlbs. Which why shadows are thrash able they don't produce enough power to hurt themselves.

Regards
Bob and good night time for bed.

One thing that I will never understand is the reason RR chose the TH400. I know that they did modify it somewhat for their own use, and accept it.

Quite why they chose the worst of the american made boxes from the time is quite beyond my comprehension.

Discuss!

The General Motors 400 box is a good gearbox. The 400 as fitted to my Shadow is the same as Jag and others.

I have no complaints. Has someone had a 400 go badly wrong
Regards
Bob

The 400 as fitted to my Shadow is the same as Jag and others.

OK, now try taking one from a Jaguar and bolting it to the Shadow's engine..

The jag version has a different convertor housing and gear change mechanism but the gearbox is essentially the same.
Kind regards
Bob

History wrote:The General Motors 400 box is a good gearbox. The 400 as fitted to my Shadow is the same as Jag and others.

I have no complaints. Has someone had a 400 go badly wrong
Regards
Bob

The answer to your question is that I have had a fair bit of experience with all of the US built autos of the period. Not only the TH400 , but also Chryslers A727 and Fords C6. Plus of course the variants. I can say, hand on heart, that I have seen plenty go badly wrong...

The big problem that the GM boxes have is gear changing problems. These can be caused by any one of several different small faults which sometimes appear singly, but most often in groups. Generally, when the first one is noticed, the best option is a rebuild - the others will soon follow!

In terms of reliability, they are a long way behind Fords C6, which in turn is a long, long way behind the Chrysler A727. The earlier versions of which have a relatively unique quality - the car can be push started if the battery goes flat!

Flatlander wrote:...Chrysler A727. The earlier versions of which have a relatively unique quality - the car can be push started if the battery goes flat!

Yes, that would be a most welcome facility even these days. Didn't some older Borg Warner devices also have the pump at the output end?

And while we're on autos; why did the Aisin-Warner 71 have a tendency toward incontinence in Volvo 240s but not so much in the Toyotas that used the same box?

JPB wrote:Didn't some older Borg Warner devices also have the pump at the output end?

Early BW35s did.

I think the DG boxes had a rear pump as well.

They are in addition to a front pump, not instead of.