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Modu lied lock-up scores

28th October 1977
Page 30
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Page 30, 28th October 1977 — Modu lied lock-up scores
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WHEN CM tested the Vol* F86 eight-wheeler and F* tractive unit, both fitted with Allison automatic transmission, we found that unless the vehicles were travelling at at least 30mpli there was virtually no engine braking.

This is because, below that speed, the automatic torque converter lock-up clutch disengages and allows the torque converter to take over.

We were told by Volvo that a modulated lock-up deviqe, which allows engine brakiii* in all other gears, would I* available.

CM has not been able to t a vehicle fitted with this at open day organised by Detr4lt Diesel Allison Internation4 Europe at its Willingborou4 factory.

The vehicle we tested was a Bedford TM 6x2 24-ton rigid fitted with a Detroit 6V 71 engine and Allison MT654 transmission.

I found that the modulated lock-up on this vehicle worked extremely well, writes Steve Gray.

Driving at around 40mph — when lock-up was engaged automatically — it was possible to bring the selector lever down through the gears and slow the lorry down as one would do with a manual box.

Inhibitors

Inhibitors prevent the gearbox from being abused by down changes at too high a speed.

The MT65 is a five-speed gearbox — with a manually selected first gear — but the MT644 is a four-speed version.

Both transmissions are now converted by Detroit Diesel Allison's new warranty.

This covers free parts and labour, plus removal and replacement of the transmission, for 24 months and unlimited mileage.

Restrictions to this apply only to misuse, incorrect maintenance procedure or when the repair work is undertaken by other than an authorised DDA dealer.

Detroit's open day also provided the opportunity to try other applications of the Allison transmission. An SD refuse vehicle — ideal for automatic transmission — was shown fitted with a Leyland 401 diesel and MT640 transmission. The vehicle is in use with North Bedfordshire Borough Council.

Two other Bedfords, a TM 6x42 ton drawbar unit and a TK330 were also there. The first was fitted with a CLT 750 transmission; the second had the AT 540 gearbox.

The 7.50 tonne (7.38 ton) TK was also a good choice for an automatic gearbox.

Its 5.4 litre (230cuin) Bedford diesel gave it a lively performance and it would make an ideal combination for an urban delivery vehicle.

Although Detroit Diesel Allison imports the transmissions complete from the US it does assemble two of the Detroit Diesels it offers.

The 8V71 and 6V71 are, assembled at Wellingborough using 70 per cent American and 30 per cent US sourced parts.

It hopes to increase this by sourcing more parts, such as pistons and liners, from the UK and Europe.

Before any parts are accepted, however, they must come under the parent company's scrutiny to ensure they meet its standard.

As far as automatics for lorries and buses are concerned Allison believes it is pioneering the concept. Competition which would help to develop the market would be welcome, it says.

Tags

People: Steve Gray
Locations: Detroit

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