Discussion
phazed 11.83 said:
debaron said:
phazed said:
He's going back to T5.
Any ideas why?
Boosted LS1 said:
I may be able to fit a Gear Vendors overdrive, assuming I have space for it. If I understand things correctly I'll have an 8 speed :-)
I looked closely at fitting an overdrive to my Chimaera a few years back, it's an old school idea but a brilliant one, I'm a huge overdrive fan, splitting gears at a flick of a switch is a joy when you're pushing along on a windy road.Only two weeks ago my mate turns up with his old orange MGB, which not wishing to be unkind is about one more welded patch away from yet another MoT failure, its also serving up what felt like about 80hp at best, but it has got an overdrive and it works a treat
.I peddled that 80hp BMC slug up to the next village as hard as I could, and even harder on the way back, flicking in and out of overdrive took me right back to an old Triumph Vittesse I had, when I made it back I was literally grinning from ear to ear
Trouble, as I discovered to my great disappointment, to put a Laycock overdrive in a TVR Chimaera is not as easy as you think. For a start the prop is already super short, and worse still the pinion flange on the BTR Diff is slightly offset, I could be wrong but to me it looked like these two elements would make fitting an overdrive to a Chimaera neigh on impossible
The angle of what would end up being a super short 10" prop would simply be way too severe for the UJs, and that is a crying shame
Years ago I owned a Holby Hunter which had a similar over drive to what you describe. It was great fun. I think the switch was on the gear stick but I can't be sure now.
The Gear Vendors unit looks pretty huge in diameter but I'd need to see it's dimensions before I'd know if it would fit a TR8 ;-)
The Gear Vendors unit looks pretty huge in diameter but I'd need to see it's dimensions before I'd know if it would fit a TR8 ;-)
Boosted LS1 said:
Years ago I owned a Holby Hunter which had a similar over drive to what you describe. It was great fun. I think the switch was on the gear stick but I can't be sure now.
The Gear Vendors unit looks pretty huge in diameter but I'd need to see it's dimensions before I'd know if it would fit a TR8 ;-)
Stags too had this format Laycock unit with the switch in the gear knob The Gear Vendors unit looks pretty huge in diameter but I'd need to see it's dimensions before I'd know if it would fit a TR8 ;-)
very James Bond Sardonicus said:
tags too had this format Laycock unit with the switch in the gear knob very James Bond
You can also get a little box of electronics so if you're in overdrive it'll automatically drop back into direct drive when you change gear. very James Bond https://www.youtube.com/watch?v=Jt87PwW5fmk
https://www.youtube.com/watch?v=zGEVUG4n5m4
It means you can row up the box enjoying the split ratios as you go, on a four speed box with overdrive on the top three ratios you only ever need to press the button in gear to re-engage the overdrive.
On a four speed box with overdrive on the top two ratios it looks like this.....
1. Direct 1st
2. Direct 2nd
3. Direct 3rd
4. Overdrive 3rd
5. Direct 4th
6. Overdrive 4th
Effectively a six speed box.
My old boss had a Triumph TR3 with overdrive that he raced in classic rallies in the Alps, to help give him the edge on the tight hairpins we allowed the overdrive unit to work in 2nd too giving the following.....
1. Direct 1st
2. Direct 2nd
3. Overdrive 2nd
4. Direct 3rd
5. Overdrive 3rd
6. Direct 4th
7. Overdrive 4th
Effectively a seven speed box.
On our T5 it would look like this.....
1. Direct 1st
2. Direct 2nd
3. Overdrive 2nd
4. Direct 3rd
5. Overdrive 3rd
6. Direct 4th
7. Overdrive 4th
8. Direct 5th
9. Overdrive 5th
Effectively a nine speed box.
Complete overkill of course, but there are two great features to consider.....
1. Snappy solenoid switching from direct 3rd up into overdrive 3rd, then back down to direct 3rd at a flick of a switch
And
2. The double overdrive, which is effectively a sixth gear
Forget the 9 speed thing, it's pointless in a Rover V8 TVR, but the above two elements alone would make it a brilliant addition especially as it would be less than half the cost of fitting a TKO6060, sadly fitting an overdrive unit to my Chimaera looked very tricky indeed.
The frustrating thing is the space in the chassis tunnel is there, it's just the short prop length and offset diff pinion flange conspire to mean the UJs would probably be forced to operate at impossible angles, well that's what it looked like to me.
Saying that... I'd love to be corrected
Edited by ChimpOnGas on Wednesday 4th October 21:55
Boosted LS1 said:
Oh so much fun. I wonder why this isn't available anymore?
The overdrives offered by Gear Vendors are just beefed up Laycock-de-Normanville 'J' Type units, I expect they bought the blue prints for very little money. Invented by a Briton, one Edgar de Normanville, and manufactured by automotive supplier Laycock Products, the unit basically consisted of a solenoid-activated planetary gearset residing between the standard manual transmission and driveshaft, offering a reduction in gear ratio at the driver’s command.At the press of a button or flip of a switch (depending on the car) in the cockpit, the overdrive would engage and lower the engine speed relative to the driveshaft, markedly improving fuel economy.
Advantages? Transmission development has always been pricey, and as fuel economy began to become a priority for automakers, the idea of a fuel-saving external add-on to an existing 3- or 4-speed manual transmission was an appealing one. Not only that, but the nature of the Laycock Overdrive meant that it could be engaged at any time, even in the lower gears, effectively doubling the number of ratios at a driver’s disposal.
Downsides? Added complexity, mainly. The solenoid in particular could be finicky on higher mileage cars, and frequently the overdrive unit had its own fill and drain plug separate from the “main” transmission, requiring a unique maintenance interval. As all-in-one 5-speeds with integrated overdrive became de rigeur, the Laycock Overdrive faded from the scene.
The torque limitation isn't really in the overdrive unit itself as these were built crazy strong, the limit will always be how much torque the gearbox can take which is why most car makers that fitted overdrives limited the overdrive operation to the top two gears, and often just top. The Gear Vendors unit is nearly always used in drag racing on the back of an auto where they regularly see 1,000ft/lbs of torque.
They are fekin heavy though, but I love overdrives with a passion, I even fitted one to my bicycle
On a push of a button all my existing gears are reduced by a factor of 2.5, therefore, it's not just a "nice-to-have" gadget that gives some additional gears, no it's more than a doubling of the number of gears, mostly without any overlap!
I use it with a Shimano 7 speed hub to give me 14 gears over a huge range, in top I'm standing on the pedals and going down hill at 45mph, in bottom my legs are spinning like a clown and I can virtually crawl up a wall
I like odd engineering solutions that work great, and that's another reason why I run my Chimaera on gas
Edited by ChimpOnGas on Wednesday 4th October 23:41
Possibly of limited interest because of the aforementioned space limitations in chim/griff, but these people do a self contained overdrive unit that you add in-line in the transmission. Maybe enough length of prop in a cerbera to squeeze one in at an angle? A talented machine shop could make the drivetrain CV rather than UJ if angles are an issue. After all they cope with the g/box and diff torque multiplication so would be plenty robust enough on a short prop.
At one point i had the crazy idea of double overdriving my Stag, but went to a taller diff ratio instead
http://www.overdrive-repairs.co.uk/products.php?ca...
At one point i had the crazy idea of double overdriving my Stag, but went to a taller diff ratio instead
http://www.overdrive-repairs.co.uk/products.php?ca...
Essentially there are three ways to fit an overdrive:
1. Add it to the back of the gearbox, this was the method adopted by car makers in the 1960's when overdrives were very popular, this type of installation required the casting of a revised gearbox tail-housing, the OD would also often share the gearbox lubricant. As no such tail-housing exists for the BW T5 and an OD wouldn't last too well on ATF we are forced to look at other options
2. Mate the overdrive directly to the differential pinion flange, this carries some weight distribution advantages, in a way you're creating a transaxle
3. The overdrive is sandwiched between two short props, ie gearbox output flange to prop to overdrive input flange, then overdrive output flange to prop to diff pinion flange. You see this option adopted on vintage car OD retro fits where a self contained overdrive unit running it's own lubricant is used, it works well on a vintage Bentley but this vehicle is closer to a truck than a car, so with a super long wheelbase there's space a-plenty
To be honest the idea really demands a better assessment than my fag packet calculations and assumptive dismissal.
1. Add it to the back of the gearbox, this was the method adopted by car makers in the 1960's when overdrives were very popular, this type of installation required the casting of a revised gearbox tail-housing, the OD would also often share the gearbox lubricant. As no such tail-housing exists for the BW T5 and an OD wouldn't last too well on ATF we are forced to look at other options
2. Mate the overdrive directly to the differential pinion flange, this carries some weight distribution advantages, in a way you're creating a transaxle
3. The overdrive is sandwiched between two short props, ie gearbox output flange to prop to overdrive input flange, then overdrive output flange to prop to diff pinion flange. You see this option adopted on vintage car OD retro fits where a self contained overdrive unit running it's own lubricant is used, it works well on a vintage Bentley but this vehicle is closer to a truck than a car, so with a super long wheelbase there's space a-plenty
- Option one in it's traditional sense on a Chimaera is out for reasons already stated, although the use of a rigid connection and a self contained overdrive unit running it's own lubricant would work, but it does leave you with an impossibly short prop running from the OD output flange to the slightly offset BTR diff pinion flange
- Option two is essentially a reversal of option one, it would work but again leaves you with am impossibly short prop running from the OD output flange to the slightly offset BTR diff pinion flange
- Option three is completely out because of the limited distance we have between the gearbox output flange and the diff pinion flange
To be honest the idea really demands a better assessment than my fag packet calculations and assumptive dismissal.
Sardonicus said:
They work on a similar principal to a lorry wheel hub reduction gear set just far more complex e.g sun & planetary gears annulus etc, I reckon just too complex fragile and extra weight for what they are achieving 
These overdrive units were really a short lived solution to the fact most manufacturers only had four and often three speed boxes at their disposal, when motorway networks started to open around the world in the 1950's car makers needed a quick way to match the cruising speeds these new roads provided using their existing transmissions. As car makers and transmission specialists supplying these manufactures started to develop five speed gearboxes the traditional overdrive unit became a heavy, costly and largely redundant solution to a problem that was starting to be solved is a better way. e.g sun & planetary gears annulus etc, I reckon just too complex fragile and extra weight for what they are achieving The above relegated overdrives to the history books in a stroke but this means people these days tend to overlook their additional advantages, advantages a five speed box just can't give you. A five speed box just gives you overdrive, the epecyclic gear set within the traditional overdrive unit splits each forward ratio effectively doubling the number of available gears. Better still these split ratios are available at a flick of switch, no clutch operation is required giving the partial effect of a modern flappy paddle gearbox.
When you drive a car with a traditional overdrive unit properly this feature becomes a joy, typically 3rd becomes the gear of choice on a winding road, flicking up to overdrive 3rd on the straights and instantly down to direct 3rd to power out of each bend is highly addictive, and serves to deliver extremely rapid progress.
Using this method on my old boss' Triumph TR3 with OD in both 2nd and 3rd we saw off much more powerful opersition from XK120s and the like up in the Dolomites and Cortinas in the Norther Italian Alps. With the right diff ratio that mod we did to give OD in 2nd was the secret, a nice low direct 2nd was used as we entered the hairpin and powered out off it's steepest point right in the apex, this was followed by a snappy clutchless flick into OD 2nd for the very short straights that continued the climb into the clouds.
Without the OD in second you were entering and powering out of hairpin in second just fine, but screaming the nuts off the the old Standard 3 bearing wet liner lump up the straights well outside of peak torque, shift up to the too tall 3rd and she'd bog real bad so something in between was needed. That instantly available OD split ratio between direct 2nd and direct 3rd was our secret to success, and boy did it help us surprise a few people.
Outrageous fun, and highly effective too
Overdrives rock, and that's a fact!
Edited by ChimpOnGas on Thursday 5th October 11:49
ChimpOnGas said:
Sardonicus said:
They work on a similar principal to a lorry wheel hub reduction gear set just far more complex e.g sun & planetary gears annulus etc, I reckon just too complex fragile and extra weight for what they are achieving
These overdrive units were really a short lived solution to the fact most manufacturers only had four and often three speed boxes at their disposal, when motorway networks started to open around the world in the 1950's car makers needed a quick way to match the cruising speeds these new roads provided using their existing transmissions. As car makers and transmission specialists supplying these manufactures started to develop five speed gearboxes the traditional overdrive unit became a heavy, costly and largely redundant solution to a problem that was starting to be solved is a better way. e.g sun & planetary gears annulus etc, I reckon just too complex fragile and extra weight for what they are achieving The above relegated overdrives to the history books in a stroke but this means people these days tend to overlook their additional advantages, advantages a five speed box just can't give you. A five speed box just gives you overdrive, the epecyclic gear set within the traditional overdrive unit splits each forward ratio effectively doubling the number of available gears. Better still these split ratios are available at a flick of switch, no clutch operation is required giving the partial effect of a modern flappy paddle gearbox.
When you drive a car with a traditional overdrive unit properly this feature becomes a joy, typically 3rd becomes the gear of choice on a winding road, flicking up to overdrive 3rd on the straights and instantly down to direct 3rd to power out of each bend is highly addictive, and serves to deliver extremely rapid progress.
Using this method on my old boss' Triumph TR3 with OD in both 2nd and 3rd we saw off much more powerful opersition from XK120s and the like up in the Dolomites and Cortinas in the Norther Italian Alps. With the right diff ratio that mod we did to give OD in 2nd was the secret, a nice low direct 2nd was used as we entered the hairpin and powered out off it's steepest point right in the apex, this was followed by a snappy clutchless flick into OD 2nd for the very short straights that continued the climb into the clouds.
Without the OD in second you were entering and powering out of hairpin in second just fine, but screaming the nuts off the the old Standard 3 bearing wet liner lump up the straights well outside of peak torque, shift up to the too tall 3rd and she'd bog real bad so something in between was needed. That instantly available OD split ratio between direct 2nd and OD 2nd was our secret to success, and boy did it help us surprise a few people.
Outrageous fun, and highly effective too
Overdrives rock, and that's a fact!
(young dumb and full of *** back then I guess) it's reverse gear you really need to inhibit OD from as this damages the OD unit permanently if you left the switch in by mistake that one you never inhibitor bypass 
Sardonicus said:
ep I had a stag when I was 20 and modded the inhibitor wiring to have OD work in 2nd too long side the usual 3rd & 4th good fun and often used it full power shifting which contributed to regular servo piston seal failure (o'rings) but got good at changing these more than a couple of times in situ (young dumb and full of *** back then I guess) it's reverse gear you really need to inhibit OD from as this damages the OD unit permanently if you left the switch in by mistake that one you never inhibitor bypass
Glad you're an OD fan too Simon (young dumb and full of *** back then I guess) it's reverse gear you really need to inhibit OD from as this damages the OD unit permanently if you left the switch in by mistake that one you never inhibitor bypass In my opinion a Stag remains another much underrated classic ideal for the family man looking to tour the continent, it sounds like you operated a different plan for yours
Nice
Nah, just still taking an interest in the old girls (missing mine) and trying to help in any way whilst waiting for my new girls problems to be resolved 
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