A possible P6 project. OVERDRIVE ???

Pilkie

Pilkie

Active Member
Hi all.

In the next few weeks,I may be getting a new project P6 to play with/restore this year.
I dont want to say too much at present! :wink:
I have to go and check over the car first and then decide yes or no!
I have been looking at a triumph overdrive gearbox I have,and was wondering ?
Has anyone ever fitted an overdrive gearbox to a 2000 ???
I am sure I have heard that some prototypes were made with this in mind back in the 60's ?
If so what box did they/you use,was it difficult?
Any comments,pointers,idea's gratefully accepted!!

Dave
 
I had overdrive on an MGC and on a MGB V8. There's a certain novelty value, but I'd rather drive either a decent auto (for the lack of effort aspect of overdrive) or a five or six speed manual. From an engineering perspective, I found them rather fragile and temperamental, and it's an awful lot of weight to add in comparison to changing the gerabox for something more modern. And I'm not sure an SC would cope with the weight! I think overdrives were in their element when there was no alternative in the era of low final drive ratios and three speed boxes. As soon as overdive ratio five speed boxes became available and reliable then they very quickly became toast. If you wanted relaxed cruising in an SC I'd simply fit a V8 diff!

Chris
 
2000TC's with overdrive were almost a production reality in 1968 - some repair manuals from that age actually carry a section on it. There were several cars with it fitted, none has ever come to light to my knowledge.

A 2000TC with overdrive would have been a startling good performing machine. Which is why they probably weren't built - would have eaten into sales of Triumph 2000's, which already came with overdrive.

Saying that - as regards gear ratios - particularily my early 2000 has almost perfect ratios and you cannot imagine that a high end overdrive on 4th would have made it much better.

Clive Annable has talked in the past about the idea of putting an MGB engine and gearbox in a 4 cylinder P6. Certainly a 'modern' 2.0 litre 'B' series engine would give you all the power you need, with the overdrive flexibility.
 
Seems that us "Brits" persisted with overdrive when the Italians were fitting 5 speed boxes to Alfas and Fiats in the late 60's / early 70's . However I've just remembered the Austin Maxi , the first UK car with 5 speeds in 1968/9- it was an awful gearbox to use though
 
Good lord! The MGB variant of the B series is one of BMC's all time Duds! Almost impossible to stop it pinking, appalling fuel distribution, and it came with a notchy geriatric gearbox! Largely due to very poor casting quality control giving unequal compression across the cylinders. If I was looking for a petrol replacement for a P6 4 pot I'd use a 2ltr O series with the fuel injection from a MG Montego / Maestro. Comes with a 5 spd LT77 too. But even then, not a huge step forward over the Rover original. Really need twin cams - perhaps a Ford 2.3 out of a Sharan (of course I mean Galaxy!)? That's fairly close to the DOHC 2.2 Rover P10 engine that was based on the P6 motor.

Chris
 
I never quite understood why the overdrive units have been developed instead of gearboxes with more ratios.
Having taken apart a few gearboxes i have seen that it should be dead easy for a manufacturer to create say a five speed box out of a four speed one. For a start it does not need any new technology. Just design a slightly longer case, with longer shafts and add a pair of cogs. Oh, yes and probably another selector fork. That's it! You 're done! Consider the overdrive unit in comparison. A complete new gearbox in essence, new case, new internals, new selector mechanisms, solenoids, wiring, switches bla, bla, bla...
 
I'm definately in the 5 speed crowd here, seems pointless to go the the trouble and expense of fitting an overdrive to a gearbox as Demetris says above. I've read that the lt77 was originally a 4 speed Jaguar box, and was developed by Leyland Transmissions into the 5 speed, and some early 2 litre SD1's had only 4 gears. I think the Ford type 9 'box was also a development of an earlier 4 speed box.

Doesn't mean you shouldn't pursue the overdrive route, if thats what you want to do.
 
Fitting an alternative gearbox LT77,Toyota Supra,5sp whatever, is fine if you are into varying degrees of modernising.
I am thinking more in line with what was originaly used,in the mid 60's on a very few cars as Nick says.
It would of been a bit too much competition for Triumph in the mid 60's,so it never went into full production.
I would like to find out exactly what gearbox was used?
I was it a modified BMC or jag unit?
I probably wont do anything anyway,just curious about the history!

I haven't got it yet,might not!
And yes TP, well deduced! :wink: It is the Bournemouth one!!
Its an F reg,1967/8 2000sc manual! Possibly Burnt Grey? Red interior.
Failed mot 15 odd years ago,was repaired but never put back together and MOT'd.
 
I'm not clear what you mean by a BMC or Jag overdrive? As far as I'm aware there was only one overdrive used in the UK across all manufacturers (Ford was keen at one time too) and that was the Laycock one. I don't recall more than one model of Laycock either - no doubt there were updates over the years - but if you asked for an overdrive you got what Laycock gave you! So the variations between vehicles are about the gearbox tailshaft housing onto which the overdrive bolts, and whether the engine is powerfull enough to shred it in the lower gears, in which case the inhibitor system changed to suit.

I was thinking about why overdrives existed in the first place. In the fifties syncromesh was in its infancy and wasn't generally up to coping with first gear. So first tended to be a crawl up the side of a house gear and 2nd was lower than is customary now to avoid having to change into first on the move. Third and top then had a lot of range to span and there was a tendency to use a lower final drive to help them both out. In this envronment overdrive made sense. Many manufacturers were not very good at gearboxes in general (Ford was and remains a glorious exception) and Rover demonstrated this with bells on with the 3500S box. At least an epicyclic (which is what an overdrive is) tends to be robust in terms of shafts bearings and casings! In the US in the fifties a complete transmission could well comprise a wide range torque convertor and a two speed epicyclic...errmm that's an overdrive isn't it?

As to how the overdrive came not to be used in production James Taylor is a bit sketchy. He doesn't specify the date of the car test fitted, but reading between the lines I'd reckon late '64. He says the actual overdrive box came out of a Triumph 2000 that was lying around in the experimental department. He also thinks it went with the low ratio 4.1:1diff from the rally cars. That would make some sense with the comments above. Chances are that the overall gearing was therefore around the same as a standard car, just with sharper take off and easier overtaking. Today it would have been used to give an overgeared motorway cruise top! Note then that the failure to adopt overdrive predates both the Leyland takeover and the merger into BL.

Would I fit one to an SC today? No way!

Chris
 
The overdrive unit was very popular on Standard Vanguards which originally only had 3 gears, hence overdrive was effectively a fourth gear. The overdrive unit was then married to the 4 speed Standard Vanguard gearbox which was an option on 4 cylinder engined cars and more or less standard equipment on the 6 cylinder cars. When the Standard Motor Company bought the Triumph company, the overdrive unit was carried forward to the next generation Standard car, the 'Standard 2000' which was the Vanguard replacement
That car once in production was renamed the Triumph 2000, therefore the overdrive unit used on the Triumph came from the early 50's. As we have two Standard Vanguards here Chris, I will take a picture of the overdrive unit when the weather warms up abit.
I have the Standard Vanguard workshop manuals here Pilkie, so if you want, I'll scan the appropriate pages for you and email them over.
 
I once retrofitted a Laycock overdrive unit to my 1959 MKII Zodiac, I dont know if it was worth the effort, I am sure my back is still suffereing from the experience......as someone has already said the weight of these in comparison to a simple 5 speed box....
How ever on the plus side it was a real easy (except for the weight) experience so long as your input shaft can match to the existing gearbox rear would be a fun thing to do but in the current technology climate I would definatly be labeling it a retrograde step. Actual interfacing into the wiring should be easy as the overdrivew pretty much is a stand alone unit, of course finding a good overdrive unit would be difficult, when I did mine in the early 80's it took a lot of hunting to find bits to get one up to orig spec. I am quite sure very few will survive accept for maybe the triumph variant as after all when was the last time you saw a Vangaurd 6 or ford fitted with one.

PS in regard to Marks comment re the extra gear, if my memory serves me correctly you could have overdrive on 2nd and 3rd gears in my Zodiac as the overdrive was enabled by a governor which cut in at 30 MPH (or where ever you preset it to) but also had an enabling cable tio the unit, making the 3 speed a 5 speeder

Graeme
 
When I say overdrive I mean was a Jag or BMC o/d gearbox of the period used as a unit,or was a rover 2000 box adapted to fit.
 
I'd say it would be simpler to adapt the rear end of the P6 box than to adapt the front end of a Triumph box. Also if there was any ambition to use it in production they'd have wanted to explore how easy it was to mod the Rover box. So most likely that it would be the Rover box.

Chris
 
As far as i know overdrive was an option in series Land Rovers.
So maybe they started something from there...
 
Laycock was an option on the P4 and most cars came with it, if you have ever been in a standard P4 without o/d ( except 95 ) then you are limited to about 60mph with a lot of engine noise. With o/d cruising at 70mph is comfortable and more speed than that easily available.

The P4 95's had a different axle ratio to give the same overall engine/road speed as the cars with o/d.

Landrovers had Fairey overdrives and I'm sure there was another make available, but at the moment can't remember the name.

I'm not aware that Rover used o/d on the earlier cars.
 
The overdrive fitted to Series Land Rovers is a completely different animal as it needs the clutch to select or deselect.
Car overdrives have their own clutch built in to them so can be selected instantly by a flick of the switch. This is why I absolutely love them and would fit one to my 2000TC like a shot if it was possible. I have one on my Triumph Vitesse and it's an absolute joy to use.

I have a couple of spare units off a Stag or Dolomite Sprint (same gearboxes), but fitting one to a non overdrive gearbox would need a longer mainshaft, with matching splines. No doubt one could be made up specially, but it would cost a bit, and fitting it would require a complete strip-down of the gearbox.

Volvo or MGB overdrive gearboxes also use Laycock units and are pretty cheap and plentiful.
 
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