Overdrive question

[Duncan Skye]

Since thelast repair on the valve buckets, I’m getting more use out of the car now. There is one thing that puzzles me though – I can’tfind anything on the forum and I can’t figure it out.
This conditionhas existed since I put the car on the road a year ago, and the gear knob switchis brand new, fitted during the rebuild. Wiring from the gear knob switch has been renewed through to the overdrivesolenoid. The car has a manual box with an‘A’ type overdrive unit. During therebuild, I did not look inside the gearbox or overdrive as I had been told theyworked fine, so the only thing I did was make sure the filter behind the bigbrass plug on the bottom was clean – which it was. The condition is the same, hot or cold andhas been consistent since the rebuild.
Let’s assumewe’re driving along on the open road and I wish to switch the overdrive out. It happens instantly. Switching it back in again takes a fewseconds before anything happens, and it often goes in so softly only a glanceat the tacho tells me it’s gone back in.
Now, if Ileave it switched in and drop down into second (where overdrive isautomatically switched out), all is well, though when I change up into third,the overdrive comes in instantly, good and strong.
How is itthat I get an immediate 'in' selection when going from 2^nd to third, butif I manually switch it out, it takes longer to come back in?
Any clues? Duncan, Skye

[4x4]

Gremilns

[mjb67]

Maybe it comes in quicker because of the use of the clutch?

[Duncan Skye]

Gremilns

Oh, I agree with you there - I'm just trying to find out which gremlin it is, though - an electrical one, a mechanical or one of the mysterious ones.. They're the worst, I hear. Duncan, Skye.

[Duncan Skye]

Maybe it comes in quicker because of the use of the clutch?

Hi, Matthew, Possibly - I must admit I hadn't thought of that, so I'll give it some thought. Overdrives are not my strong point, but possibly it prefers to come in when there's no 'weight' on the transmission. Next time I'm out, I'll try engaging it on a feather-light throttle to see if that makes any difference. If that's so, then it clearly was one of the gremlins that 4X4 refers to. Idiosyncratic to the car. Many thanks Matthew, Duncan, Skye.

[flying farmer]

Sounds like it might be low oil pressure, or a partly blocked oil passage. The A type overdrive usually comes in with a bang as it has a hydraulic accumulator. The J type has to build pressure from when the switch is engaged so is softer engaging. Alternatively the clutch linings could be worn, not that I have ever seen this unless the overdrive is prone to slipping

The fact it engages easily when going up the gears is because the overdrive is not under load when the clutch is depressed, this gives it chance to engage before the load comes onto the overdrive clutch rather than it having to drag down the the rotating mass of the engine.

Another possibility is that a previous owner has tipped a friction reducing additive into the gear oil, not a good idea on an overdrive unit relying on the friction of the overdrive clutches to work.

Try lifting the throttle as you engage overdrive as this will give the overdrive an easier time.

Neil

[Bandit1200]

There is a company called o/d spares based in Rugby. They bought all the parts and tooling when the OE company went belly up.
I had a problem with a leaky J Type and called them on 01788 540666. They couldn't have been more helpful and are prepared to give technical advice for free.
I visited them and it was like visiting overdrive world. They have shelves stacked to the roof with all manner of o/d parts and clearly lived for the product.
I have no connection with this company other than as a very satisfied customer. Give them a call and I bet you'll be surprised by their depth of knowledge.

Steve

[Firept]

Duncan.
Try this:-
With the ignition on and the engine stopped select 3rd or 4th and then flick the switch on the o/d , with the door open you should hear an immediate klunk as the solenoid engages try it 2 or 3 times if its a loud klunk and sounds really positive then its an oil pressure problem in the box probably the 2 "0" rings on the control valves.
If however its sound light ,slow or a bit feeble then it well be the Solenoid as it has a pair of contacts on the top that should be made when off and broken when the solenoid is "in" its so that you get a good pull in and then a hold current you could also try using a good real moving coil meter (not digital as they are not fast enough) and measure the current a good old AVO 8 or similar will do the job remove the o/d fuse and watch the current with the above set up and you should see a high current to start with followed by about 8 to 10 amps from memory hold current (dont quote me on that) as its a long time since I've measured it.
I must admit as the "A" type goes in with thump when using it I always dip the clutch as I switch it in and out saves the sudden load change on the transmission.

Paul.

PS I use the SX75-90 GL4 as it seems to suit the box better.

[Duncan Skye]

Sounds like it might be low oil pressure, or a partly blocked oil passage. The A type overdrive usually comes in with a bang as it has a hydraulic accumulator. The J type has to build pressure from when the switch is engaged so is softer engaging. Alternatively the clutch linings could be worn, not that I have ever seen this unless the overdrive is prone to slipping

The fact it engages easily when going up the gears is because the overdrive is not under load when the clutch is depressed, this gives it chance to engage before the load comes onto the overdrive clutch rather than it having to drag down the the rotating mass of the engine.

Another possibility is that a previous owner has tipped a friction reducing additive into the gear oil, not a good idea on an overdrive unit relying on the friction of the overdrive clutches to work.

Try lifting the throttle as you engage overdrive as this will give the overdrive an easier time.

Neil

Thanks Neil, and sorry I couldn't reply sooner - the internet had slowed to an impractical crawl yesterday. No, the overdrive doesn't slip, so I'm hoping that its clutch linings are OK. I'll try dipping the clutch when flicking it in to see if that helps. Weather here has been dull, very misty and damp for the last week - a complete reversal of what the rest of the country are getting so once it dries up a bit, I'll take her out and see what works. Many thanks for the tips. Duncan, Skye.

[Duncan Skye]

There is a company called o/d spares based in Rugby. They bought all the parts and tooling when the OE company went belly up.
I had a problem with a leaky J Type and called them on 01788 540666. They couldn't have been more helpful and are prepared to give technical advice for free.
I visited them and it was like visiting overdrive world. They have shelves stacked to the roof with all manner of o/d parts and clearly lived for the product.
I have no connection with this company other than as a very satisfied customer. Give them a call and I bet you'll be surprised by their depth of knowledge.

Steve

Thanks, Steve, I'll try out Neil and Paul's suggestions before giving them a call. The more I can tell them about the condition, the better. The last thing I want is to be caught with is the overdrive stuck out, with 200 miles to go before I get home. With many thanks, Duncan, Skye.

[Duncan Skye]

Duncan.
Try this:-
With the ignition on and the engine stopped select 3rd or 4th and then flick the switch on the o/d , with the door open you should hear an immediate klunk as the solenoid engages try it 2 or 3 times if its a loud klunk and sounds really positive then its an oil pressure problem in the box probably the 2 "0" rings on the control valves.
If however its sound light ,slow or a bit feeble then it well be the Solenoid as it has a pair of contacts on the top that should be made when off and broken when the solenoid is "in" its so that you get a good pull in and then a hold current you could also try using a good real moving coil meter (not digital as they are not fast enough) and measure the current a good old AVO 8 or similar will do the job remove the o/d fuse and watch the current with the above set up and you should see a high current to start with followed by about 8 to 10 amps from memory hold current (dont quote me on that) as its a long time since I've measured it.
I must admit as the "A" type goes in with thump when using it I always dip the clutch as I switch it in and out saves the sudden load change on the transmission.

Paul.

PS I use the SX75-90 GL4 as it seems to suit the box better.

Dear Paul, Many thanks for those thoughts. With the door open, I can hear a very positive sharp click when selecting 'In' but am not sure I'm hearing anything on selecting 'Out'. I'm beginning to think I'll have to get the catalogue out to see what 'O' rings I need, and to work out whether I can replace them myself. Failing that, I might just give O/D Spares in Rugby a call, as Steve suggests. However, as you suggest, I'll try dipping the clutch as I select 'In' to see if that helps. I hope it does, because deep down, I really, really don't want to take that bit of it all apart again. Par for the course, I know, but.. Thanks for your thoughts and help, Duncan, Skye.

[KOY 23]

Hi Duncan.

Great that you're back.

[Duncan Skye]

Hi Duncan.

Great that you're back.

Back, yes, but not fully in circulation. My workload has eased and I'm able to get my head up and look around a bit again. Pity I had to come back with a problem but as always, the forum has helped with some knowledge and tips for me to be getting on with. Take care, Duncan, Skye.

[jleyton]

[QUOTE=Duncan Skye;236616] The last thing I want is to be caught with is the overdrive stuck out, with 200 miles to go before I get home. With many thanks, Duncan,

Duncan, Skye.OTE]

Hi
hi bDuncan,

[Mike Stevens]

I Guess what Julian was trying to say was - if the overdrive gets stuck ON, be very careful in the lower gears, not giving it too much wellie, and do not, repeat not, select reverse. If you do you will find that the car won't go backwards and the application of any power will break the uni-directional clutch in the back of the overdrive. Yes it will. I've done it!

Cheers,
Mike.