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TopazMan

J-type overdrive switches on TR6

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I have a late British TR6 Pi (CR series) with J-type overdrive. I discovered that the overdrive works in all gears, incl reverse, and have reversed in ignorance many times over 19 years with the overdrive left on, but without causing damage. To get to the bottom of this, I removed the gearbox tunnel and discovered that one of the spade connectors on the top switch (3rd & 4th gear enabling) had come off. Testing then showed that neither that switch nor the reversing light switch was working, so I've replaced both and they now work fine. The mystery is that my J-type, which should only have two switches actually has three - all close to the gearstick end of the gearbox top cover, reversing light on nearside, 3rd/4th gear on top and the extra one on the offside. Testing shows that the extra switch enables overdrive in all gears, incl reverse, but not in neutral. Does anyone have a similar set-up. or know why this extra switch is there? The three switches are connected in series, so I have pulled the spades off the extra switch, wrapped them in insulating tape and intend to leave the rest of the wiring as is. This way, the reversing lights work and the overdrive only works in 3rd and 4th gears. The irony is that of the three original switches, the extra one is the only one that works! Advice please?

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Has the extra switch been retro fitted to provide overdrive in 2nd as per A Type O/D? next point when I picked up BUO I had O/D in ALL gears but found the fault not under the gear box tunnel but due to a short circuit in the O/D switch wiring in the column.

 

ATB Graham

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Curse of the PO attempting to get overdrive in 2,3 and 4 and getting it wrong.

 

Actually, thinking about it he probably thought that all was OK as he had overdrive in 2,3 and 4 but plus a few unintended others.

Edited by peejay4A

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Hi Topazman,

welcome to the forum. Have you got a name?

 

On the 'A' type there are 2 switches for the OD - 2nd is one switch and 3rd/4th another switch. These are in parallel NOT series

On the 'J' Type with only OD on 3/4 there should be one switch.

OD on 2nd gear on a TR6 may not be a good idea - TRiumph didn't fancy it.

 

The switch is normally open circuit when not selected. So only shorted (working) when that gear is selected. That way Reverse and 1st can't be selected (ho ho ho)

 

Roger

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Topaz,

 

Is it possible your gearbox is from the US?

 

From '72 on, the US cars were fitted with a 'Seat Belt Neutral Safety Switch' on the righthand side (offside in the UK) of the gear change casing. This formed an interlock for the seatbelt module.

 

Oddly enough it was deleted for the '76 model.

 

Cheers

Graeme

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Topaz,

 

Is it possible your gearbox is from the US?

 

From '72 on, the US cars were fitted with a 'Seat Belt Neutral Safety Switch' on the righthand side (offside in the UK) of the gear change casing. This formed an interlock for the seatbelt module.

 

Oddly enough it was deleted for the '76 model.

 

Cheers

Graeme

If that is used as an overdrive switch then it would give overdrive in all gears.

Stuart.

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Thanks everyone (for Roger - my name is Denis. Why "Topazman"? Because I've got a very rare Topaz TR6 and a Topaz Stag. What other name could I use?!). The consensus seems to be that the extra switch was fitted to achieve overdrive in 2nd, but succeeded in providing it in all gears. the car is definitely a UK-spec, not an ex-US example, but the extra switch is fitted on the offside near the gearstick, so it may well be in the seatbelt module hole, thus giving overdrive to all gears. I've put it all back now, with overdrive just in 3rd and 4th. My experience blows out all the doom-mongers who said reversing with overdrive would destroy the overdrive and gearbox!

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Hi Denis,

it's good that you have sorted out your switches.

Overdrive in reverse can damage the casing.

There is a unidirectional clutch type thing inside that drives roller bearing into a tapering groove.

If you give reverse an enthusiastic punch then the roller bearings will try to pass through the tapering groove and burst the case.

 

I have been lucky in the past but you can't always rely on luck.

 

Roger

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Roger, don't believe anything this bloke says. He' s only got a Topaz 6 and Stag to save on touch up paint!

 

Allan

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