Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Overdrives..Phil H
@philhoward
Club Retro Rides Member 133
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The strongest overdrive box fitted to any triumph was the A type overdrive fitted to the 6 cylinder fuel injected triumph engines ie Tr5 Tr6, Mk1 and Mk2 2.5Pi saloons, the Jtype is a weaker overdrive unit not used in the triumph scene for raceing or uprated engines, ive added overdrive to second gear in my triumph saloon by wireing in an extra relay no problems, but it is 160ftb torque at 4000rpm in top gear, i don't no what Lh overdrive means all ive heard of is Atype Jtype or Dtype fitted to triumph. also correct me if I'm wrong but the scimitar gear box is a very heavy cast iron unit where as most others were alloy Yep - it’s a heavy lump of a gearbox but an Essex V6 almost creates its own gravity so it’s all relative. Where does the D type come in the strength league tables, if the LH is stronger than those? J at the bottom, one assumes..
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Overdrives..Phil H
@philhoward
Club Retro Rides Member 133
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The big problem is I would need a new tail shaft and housing as the gear shift is on the tail shaft and there is not enough room for the side selector box and I would be wanting to do the box change without cutting the floor. I would only want the overdrive in 3rd and 4th as any of the lower gears would put too much load on the over drive which is why over drive only engage in 3rd & 4th gears. Scimitar gearbox in question (less bellhousing, but it’s an Essex fit): I think it’s the same basic gearbox as yours, except for the remote?
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Last Edit: Aug 6, 2019 21:03:37 GMT by Phil H
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scimjim
Club Retro Rides Member
Posts: 1,503
Club RR Member Number: 8
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Overdrives..scimjim
@scimjim
Club Retro Rides Member 8
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The big problem is I would need a new tail shaft and housing as the gear shift is on the tail shaft and there is not enough room for the side selector box and I would be wanting to do the box change without cutting the floor. I would only want the overdrive in 3rd and 4th as any of the lower gears would put too much load on the over drive which is why over drive only engage in 3rd & 4th gears. Is it particularly tight in the transmission tunnel? That’s the same type 5 gearbox that Reliant used (with and without overdrive) the overdrive box just has the remote removed and two rods run outside around the overdrive unit. The side rail box is a type F.
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Overdrives..peteh1969
@peteh1969
Club Retro Rides Member 107
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Yes it is a very tight tunnel it would be a future thing to do any way.
I have to re build her first and get her back on the road first.
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Sorry, question unrelated to most of this thread, but the J type is fitted to bedford CF's. If this is a weaker one, how come its fine in these? Is the strength of the overdrive unit purely a consideration of engine output? 2.3 bedford engine is something like 80bhp and 100lbft so not loads of power. Does the weight and aerodynamics of the vehicle not play a part in the stress on the overdrive?
Just curious.
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Overdrives..Phil H
@philhoward
Club Retro Rides Member 133
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The J type was used on the 73-85 Scimitar without any issue so can’t be all that weak, but it’s all relative.
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scimjim
Club Retro Rides Member
Posts: 1,503
Club RR Member Number: 8
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Overdrives..scimjim
@scimjim
Club Retro Rides Member 8
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I’ve never seen any actual hard evidence to support the assertion that X is stronger than Y. There are some old stories of poorly manufactured parts (much like the Essex dizzy/oil pump pencil drive) and some obvious differences in operation and hydraulic pressures, but nothing concrete.
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Aug 11, 2019 22:45:32 GMT
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Given that the overdrives used in transits had to be capable of being used fully (over) laden with a trailer behind and mainly di or V6 power I don't think you will break one.
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Phil H
Posted a lot
Posts: 1,448
Club RR Member Number: 133
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Overdrives..Phil H
@philhoward
Club Retro Rides Member 133
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Mission accepted
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Aug 13, 2019 11:12:36 GMT
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if there's not enough room for the side entry box is there enough for the overdrive or is it the selector housing on top of the gear case which is the issue?
The rods themselves could be replaced with cables or bent to drop lower down easily enough if they are the issue.
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