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Mar 12, 2016 17:45:14 GMT
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I need some schooling.
I know they drop the final ratio.
ive bought a van with overdrive. I don't think the switches are working, not tried yet as ive not picked it up.
How do they operate? Solenoid? Not supposed to use in 1st 2nd or reverse? Anything that automaticaly stops you doing that?
Switch in and out while driving? Clutch in?
I know nothing about them!
(Bedford cf by the way)
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steveg
Posted a lot
Posts: 1,565
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Mar 12, 2016 18:23:04 GMT
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I know a bit about overdrives on Triumphs but would imagine the one on the Bedford is similar if not the same. There is a solenoid to operate them and usually switches that allow it to operate in third and top gear. On the Triumph they are fitted to the gear selector housing. Normally it's fine to just engage overdrive whilst driving but switching out normally needs use of the clutch otherwise it's a bit jerky.
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Mar 12, 2016 18:32:20 GMT
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Think of it as a second gearbox bolting on the back of the usual one. It has two states - straight through and step-up (overdrive, either 22, 25 or 28% depending on the OD unit fitted). They are hydraulically operated and activated by a switch (usually on the gear knob or column).
Normally only to be operated in 3 and 4th gears with inhibitor switches on the gear box to make this happen.
You switch them in/out by operating the switch when in 3rd or 4th gear. No need to use the clutch.
If not working it tends to be electrical and just a matter of sorting to through the circuit checking connections and switches. There may be a relay involved though from what I can find the overdrive that ends up on CFs is the Laycock J-type which doesn't have to have a relay.
Seems like a rare and useful thing to be fitted to a CF......
Nick
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1967 Triumph Vitesse convertible (old friend) 1996 Audi A6 2.5 TDI Avant (still durability testing) 1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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Mar 12, 2016 18:33:10 GMT
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The bedfords normaly have a gearstick switch too but this one has dodgy aftermarket toggles. Not sure how its wired so no idea why it has 2. One red, one green. Whats to stop you forgetting and leaving it in overdrive permenantly? It looked a bit like the wire on the solenoid is broken.
Once I have the van ill get a proper look, just trying to get an idea for how its supposes to be.
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Mar 12, 2016 18:35:45 GMT
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Inhibitor switches...
in gearbox or on gearbox?
It is very rare in a cf. Presumably fitted later hence the wrong switch.
I dunno.
REALLY hope it can be made to work!
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Mar 12, 2016 18:39:31 GMT
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HI, I would assume that's going to be a Laycock overdrive. Yes the switch for it will operate a solenoid which is a cylindrical looking affair on the side of the unit, this controls internal oil pressure to change the ratio. Which it why it only works in third and fourth because the internal pump is driven by the gearbox mainshaft and needs the revs to produce enough pressure. There will be a switch on the main gearbox so it only operates in third and fourth. Changing into O/D can be done without using the clutch but it's preferable to at least ease up on the throttle, changing back out will need an increase in revs so is best done using the clutch. You will after a while be able to do it seamlessly. Usual reason for it not working is dirty connection on the solenoid because of its environment under the vehicle. A rare thing nowadays and an expensive option in their day but are a joy to use.
Colin
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Mar 12, 2016 18:44:06 GMT
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Hi, There's nothing stopping you leaving it in overdrive but it will only work when you change into third, but this tends to give a big step in gearing from second and you will know straight away. The 3/4 switch can be either into the box or on the linkage.
Colin
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Last Edit: Mar 12, 2016 18:46:21 GMT by colnerov
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Mar 12, 2016 18:46:59 GMT
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Ok, so all in needs is a switch to feed/cut power to the solenoid.
So its not even going to be possible to accidently select overdrive in the wrong gear then.
If the solenoid is energised at any other time, start up, or in first etc, what happens when I change into third? It just then automatically engages overdrive too?
Why has it got 2 switches? There next to each other but I guess one may be for something different.
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Mar 12, 2016 18:47:53 GMT
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I replied at the same time
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Mar 12, 2016 20:41:31 GMT
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If it's on switches they may have bypassed the inhibits. You can (on transits) with bodgery make them work in 1st and 2nd as a splitter for heavy work (obviously this isn't ideal and will shorten their life)
Using them in reverse is usually game over.
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Mar 13, 2016 18:08:15 GMT
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If not working it tends to be electrical ... ^ This! The OD on my Hunter was dead when I got the car and I got told faults are electrical at least 90% of the time. Mine turned out to be a loose wire on the gearbox solenoid. 2 months to trace the fault, 2 minutes to fix it I like it a lot but the ratios are odd : 1st - 2nd - 3rd - 3rd with OD - 4th - 4th with OD. You should be able to test with the ignition on but without starting the engine. Put a multimeter or testlight onto the gearbox solenoid - put van in gear 3 or 4 and play with the unidentified switched until you get power My control is on a spring loaded indicator-type stalk that always returns to center. Up to engage OD - middle does nothing - down to disengage. Fix it
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Mar 13, 2016 18:14:14 GMT
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I will definately be fixing it. it was a large part of the reason why I bought a van with rotten chassis leg and rust holes in the gutters
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