Laycock de Normanville OverDrive

Does anyone have any knowledge and/or experiencie with this accessory? I know it was avialable as optional equipment in 1975-1976 Hornets, Gremlins and Pacers as a fuel economy measure. It was used only with column-mounted three speed manual transmissions.

How effective/reliable it is in terms of fue economy or even performance applications?

I have a 1981 VAM Rally GT (Spirit GT) with a 282 cubic inches inline six cylinder. It is coupled to a TREMEC 176-F four-speed manual transmission with Hurst linkage and a Spicer axle with 3.31:1 rear gear ratio.

In highway driving, I try to keep my vacuumeter between 10 and 15 and my tachometer at 2000-2200 RPMs.

This is done with the point of keeping the highest efficiency in my engine, keeping stable not just the temperature but also the fuel consumption. Also, if I can make it to my destination in less time that would be great.

However, the problem I have is that at this point the speed I obtain is 90 kilometers an hour (56 miles por hour) in straight ground. Going uphill the speed drops to 80 kilometers an hour and going downhill it rises up to 100 kilometers an hour.

The legal speed limit in Mexico for straight highways is 100-110 kilometers and hour (62.5 and 68 miles per hour).

Can a Laycock de Normanville OverDrive unit be adapted/used in the 176-F transmission?

I know it was used in the 150-T model three-speed manual in the US.

I am really looking forward to both better highway fuel economy and higher speed with my car.

I thought about swapping the original 3.31:1 rear gear ratio in favor of a 3.07:1 used in other VAM cars, but I would lose towing capacity and standstill acceleration.

I considered swapping the 176-F transmission in favor a Jeep unit used behind the 4.0 engine (models: T5, AX-5 or AX-15). But, this would require several adaptations such as pushing back the transmission crossmember, shortening out the driveshaft and then rebalancing it, cutting-off a new shifter lever hollow on the transmission tunnel due to different position of it (and no Hurst linkage here).

All this seems to be also relatively expensive to achieve aside from the whole ordeal of adapting it. Also, we know that the Spirit already has a very short drvieshaft, I don't know if making it even shorted would affect anything or if there is some kind of limit into shortening it.

I need to know how much of an alternative using the LN Overdrive would be and if it can be used in my transmission. At first sight it seems to be less demanding in terms of adaptations.

I would also need to cut short the driveshaft for this, make the unit be fixed to the rear shaft of the transmission and have no idea of how to install the control of the overdrive in the inside of my car. I don't know if the fact that my car is a floor shift has anything to do.

If I can keep both my original transmission and original differential, this is the way I would choose to go.

Thanks in advance.


Edited by Rambler Mexicano - Jun/04/2016 at 2:29pm

The problem would be this:
Quote

Can a Laycock de Normanville OverDrive unit be adapted/used in the 176-F transmission?

Unquote
And I think the answer would be no. That overdrive unit would have been some form of integral part as an option in VAM produced vehicles. It would not have been an option on U.S. vehicles at all. I believe the only overdrive ever offered would have been a Borg Warner unit and then it would have last been offered some where in the 1960's. And at that they were an integral part of the transmission.
It would not be practical to try to adapt it to something other than what it was offered on or with.

A gear vendors overdrive would work for your situation, but they are a bit expensive.

The overdrive will only fit the 150T. To make it fit your transmission requires a special adapter between the trans and OD unit and a special output shaft. Your best bet is to change the transmission to a five speed, either a Jeep five speed or Ford V-8 T-5. There are many articles on putting a T-5 behind and AMC V-8. The six has the same needs -- the AMC six bell is used to put a Ford T-5 behind an AMC V-8.

Your cheapest and easiest option is to change the rear axle ratio. You will lose some take-off and towing capacity, but you can't have everything!

"optimum" cruise is a combination of many things, but the big chunks: engine and cam, the two two gears in your transmission (or top gear plus OD), axle, tires. spark timing and carburetion too. carbs interact in this mess in an annoying way...