Overdrive clutch type
Moderators: scimjim, Lukeyboy46, erikscimitardemon, Roger Pennington, philhoward
- Old and Slow
- RSSOC Member
- Posts: 1137
- Joined: Tue Jan 20, 2015 5:37 pm
- Location: East Berks
- Has thanked: 2 times
- Been thanked: 55 times
Overdrive clutch type
AFAIK overdrives are built with "sun and planet gears" and are switched in by a solenoid operating a brake band. If there's no brake band the drive passes straight through. however if there's some debris in the O/D then this might put your trip to France at risk. I wonder if flushing out with a couple of oil changes might be a quick solution, not to get the O/D working, but to minimise the likelihood of something else going wrong.
Greater experts than me might have a view on this.
Greater experts than me might have a view on this.
Philip Needham
Ashley-bodied TR3; '54 Ford Consul; '55 AC 2-Litre Saloon;'65 850 Mini; '70 Ford Zodiac MkIV; XR3i
'81 911SC Targa, '64 Sabre Six
Ashley-bodied TR3; '54 Ford Consul; '55 AC 2-Litre Saloon;'65 850 Mini; '70 Ford Zodiac MkIV; XR3i
'81 911SC Targa, '64 Sabre Six
-
- RSSOC Member
- Posts: 1655
- Joined: Sat Aug 10, 2013 1:09 pm
- Location: Haute-Saône,France
- Has thanked: 64 times
- Been thanked: 93 times
Overdrive clutch type
My understanding is that the overdrive has a double cone clutch. One face at a time is engaged, while the other face is free to spin. If either face is worn out, you can experience slip , whether in direct drive or in O/D. Mine is beginning to slip slightly in direct, but not in O/D. So if you lose one side of the lining entirely, I would imagine you would lose drive completely. Could you piece of debris be a segment of a cone-shaped band of clutch friction material?
"When I grow up, I want to be me"
-Kermit Weeks
Current: SE6A; 998 Mini.Previous: Morris Minor,Ford8, Cortinas Mk1 &2,MG Midget 1932,Morgan 3W 1934,Lagonda Rapier,Honda S800, Austin Maxi,Citroen GSA, Riley ElfMk2,Peugeot 505,Rover 420 SDI
-Kermit Weeks
Current: SE6A; 998 Mini.Previous: Morris Minor,Ford8, Cortinas Mk1 &2,MG Midget 1932,Morgan 3W 1934,Lagonda Rapier,Honda S800, Austin Maxi,Citroen GSA, Riley ElfMk2,Peugeot 505,Rover 420 SDI
-
- RSSOC Member
- Posts: 2161
- Joined: Fri Apr 24, 2009 10:11 am
- Location: Steeton, Yorkshire Dales
- Has thanked: 26 times
- Been thanked: 150 times
Overdrive clutch type
Sorry Phil but you can`t "Flush" an OD unit, not in the way you can Flush an engine by replacing the oil after running the car.
The OD picks up the oil from the GB and then pressurises it through an eccentric pump driven by the gearbox outpout shaft, the oil does not get splashed around, as it does in the engine by the crankshaft.
The oil then drains back through the casting of the OD back into the GB.
Mark
The OD picks up the oil from the GB and then pressurises it through an eccentric pump driven by the gearbox outpout shaft, the oil does not get splashed around, as it does in the engine by the crankshaft.
The oil then drains back through the casting of the OD back into the GB.
Mark
Last edited by gtcse8 on Fri Jun 21, 2019 7:45 am, edited 1 time in total.
Mark Wilson. See the Beast on youtube under" RELIANT SCIMITAR CONVERSION LOL.,Three Se5a, Se6a, Two Se6b`s,1 & 1/2 GTC`s & not a lot of sense
EX SST 1800Ti
EX SST 1800Ti
-
- RSSOC Member
- Posts: 2161
- Joined: Fri Apr 24, 2009 10:11 am
- Location: Steeton, Yorkshire Dales
- Has thanked: 26 times
- Been thanked: 150 times
Overdrive clutch type
EDIT
I had engine on my mind with reference to "Flushing after running.
The point I was trying get over was that the engine oil has a far harder life than the GB oil.
The engine oil is sent to the top of the heads and then flows back into the sump, hitting the camshaft and crankshaft and being violently thrown against the inside of the block, thereby washing any contaminates into the sump.
The GB oil has a far easier route, and is only "Stirred up by the gears in the GB section.
The bit that is collected by the eccentric pump is then pushed through the hydraulic clutch at the rear of the box, then it simply drains back into the bottom of the box.

I had engine on my mind with reference to "Flushing after running.
The point I was trying get over was that the engine oil has a far harder life than the GB oil.
The engine oil is sent to the top of the heads and then flows back into the sump, hitting the camshaft and crankshaft and being violently thrown against the inside of the block, thereby washing any contaminates into the sump.
The GB oil has a far easier route, and is only "Stirred up by the gears in the GB section.
The bit that is collected by the eccentric pump is then pushed through the hydraulic clutch at the rear of the box, then it simply drains back into the bottom of the box.

Mark Wilson. See the Beast on youtube under" RELIANT SCIMITAR CONVERSION LOL.,Three Se5a, Se6a, Two Se6b`s,1 & 1/2 GTC`s & not a lot of sense
EX SST 1800Ti
EX SST 1800Ti
- Old and Slow
- RSSOC Member
- Posts: 1137
- Joined: Tue Jan 20, 2015 5:37 pm
- Location: East Berks
- Has thanked: 2 times
- Been thanked: 55 times
Overdrive clutch type
Thanks to all above for clarifying my initial (inexpert) comment. I don't think I'd risk the trip to France then. 

Philip Needham
Ashley-bodied TR3; '54 Ford Consul; '55 AC 2-Litre Saloon;'65 850 Mini; '70 Ford Zodiac MkIV; XR3i
'81 911SC Targa, '64 Sabre Six
Ashley-bodied TR3; '54 Ford Consul; '55 AC 2-Litre Saloon;'65 850 Mini; '70 Ford Zodiac MkIV; XR3i
'81 911SC Targa, '64 Sabre Six
-
- RSSOC Member
- Posts: 634
- Joined: Sat Nov 14, 2015 11:54 am
- Location: Swindon
- Has thanked: 9 times
- Been thanked: 30 times
Overdrive clutch type
I am the eternal optimist. I will be cruising on the lesser roads at lower speeds.
Mark is going to supply me as used overdrive, which will keep thing simple when it is time to change. More ducks to line up.
Steve.
Mark is going to supply me as used overdrive, which will keep thing simple when it is time to change. More ducks to line up.
Steve.
SE5a 'Fancier'
- David Tew
- RSSOC Member
- Posts: 557
- Joined: Sun Aug 06, 2006 11:09 am
- Location: Cotswolds
- Has thanked: 13 times
- Been thanked: 48 times
Overdrive clutch type
When you change the OD make sure you fit (or make) the correct gasket with an oil-return hole at the bottom. I've seen them assembled with a plain gasket which causes oil to collect in the OD rather than doing it's job in the gearbox. 

- My wife says I don't listen to her ...... or something like that! -
SE4B Coupe - rebuilt on brand-new chassis.
Bought in 1978 and an RSSOC member since. 😲
SE4B Coupe - rebuilt on brand-new chassis.
Bought in 1978 and an RSSOC member since. 😲
- Dennis Nicholas
- RSSOC Member
- Posts: 688
- Joined: Wed Jun 20, 2007 1:22 pm
- Location: Devon
- Has thanked: 58 times
- Been thanked: 33 times
Overdrive clutch type
Rev Light
Have a look at http://www.buckeyetriumphs.org/technica ... 1/JOD1.HTM
All will be revealed.
Bear in mind that Scimitar GTE Overdrive introduced from Chassis No. 932478 incorporated gearbox and overdrive units of a new design.
Also google J type Laycock overdrive units. Popular motoring did a good strip/overhaul article (Nov 1977).
Also Moss Europe have a good exploded diagram for J spares for Triumph Spitfire.
That will keep you busy for a while
Dennis
Have a look at http://www.buckeyetriumphs.org/technica ... 1/JOD1.HTM
All will be revealed.
Bear in mind that Scimitar GTE Overdrive introduced from Chassis No. 932478 incorporated gearbox and overdrive units of a new design.
Also google J type Laycock overdrive units. Popular motoring did a good strip/overhaul article (Nov 1977).
Also Moss Europe have a good exploded diagram for J spares for Triumph Spitfire.
That will keep you busy for a while

Dennis
Dennis Nicholas(RSSOC)
1980 GTC Trafalgar Blue, 2010 basic Skoda Yeti (petrol), Austin 7s, Rileys.
1980 GTC Trafalgar Blue, 2010 basic Skoda Yeti (petrol), Austin 7s, Rileys.
- Dennis Nicholas
- RSSOC Member
- Posts: 688
- Joined: Wed Jun 20, 2007 1:22 pm
- Location: Devon
- Has thanked: 58 times
- Been thanked: 33 times
Overdrive clutch type
Looks like buckeyetriumphs have changed their webpage set up. Try https://static1.squarespace.com/static/ ... Part+I.pdf
There are subsequent parts 11 and 111. Just search on their site "J type overdrive".
There are subsequent parts 11 and 111. Just search on their site "J type overdrive".
Dennis Nicholas(RSSOC)
1980 GTC Trafalgar Blue, 2010 basic Skoda Yeti (petrol), Austin 7s, Rileys.
1980 GTC Trafalgar Blue, 2010 basic Skoda Yeti (petrol), Austin 7s, Rileys.