Auto vs manual

[Will]

Is the standard auto lower geared than manual overdrive if so what's rev's at cruising speed
Thanks

[edd]

My stag sits very happy at about 2500 going at about 70 mph when excelerating I rarley have to go above 3000 revs seeing as I'm still running in I still have all the power I need it seems. Mines a manual overdrive and I love being in control whilst driving.

[Seaking]

mine is a zf conversion 30mph per 1000 rpm very happy with it
Cheers Glenn

[mole42]

ZF auto on 60 section tyres, 25MPH per 1000. Want to change the diff soon....

[wilf]

BW35 - rpm is speed x 50

i.e. 70mph pretty much = 3500rpm.

Quite frantic in other words, especially compared to overgeared moderns (mine does 2000rpm at 100mph!) but bang in the meat of the torque curve.

[KOY 23]

Top gear in a BW35 is just under 20mph/1000, MOD and ZF are around 25mph/1000rpm. 3rd gear in a ZF is very close to top in BW35, which gives a great indication of what lifeusedto be like.

[Nigel W]

I think you will find that the automatic is geared the same as 4th on the manual box without overdrive.

[V Mad]

I think you will find that the automatic is geared the same as 4th on the manual box without overdrive.

It is, except that, as there is slip in the torque converter, then effectively its geared even lower.

[KOY 23]

How many non overdrive models were made?

[cosmicwheels]

How many non overdrive models were made?

Is there a echo in here

[mole42]

It is, except that, as there is slip in the torque converter, then effectively its geared even lower.

There shouldn't be any slip in the torque converter when cruising if your fluid levels are correct. However, the diff ratio was usually different which accounts for the poorer fuel consumption.

The BW35 and 65 auto boxes both had a 1:1 top gear - the advantage of the ZF modification is that the ZF has 1:1 as 3rd gear so that the ZF top gear becomes effectively the same as a MOD in top+overdrive.

[Will]

Thanks looking for manual then

[Staggard]

There shouldn't be any slip in the torque converter when cruising if your fluid levels are correct. However, the diff ratio was usually different which accounts for the poorer fuel consumption. The BW35 and 65 auto boxes both had a 1:1 top gear - the advantage of the ZF modification is that the ZF has 1:1 as 3rd gear so that the ZF top gear becomes effectively the same as a MOD in top+overdrive.

Why have they introduced lock up coverters then ? When I was in my BW classes I was told that when fluid is involved the would always be a loss of power transmission.

[wilf]

Mine still slips at higher engine speeds, it has no torque converter lock up at all. I like the slippy old thing, very era-correct.

[mole42]

In many mechanical/fluid systems there is no loss at all - you wouldn't want any slippage in your brake system would you?

The engineers designing the torque converter will ensure that as much power is transmitted through as possible. There will be some inefficiency - that's why the fluid gets hot but there should not be any appreciable 'slip' in the torque converter. Most early writing about the torque converter would suggest that, as the load requirements become matched to the power delivery, the torque converter effectively fluid locks and transmits all the power straight through.