reb78 Posted July 8, 2013 Share Posted July 8, 2013 As above. Today, my GKN OD has been reluctant and, at times near impossible, to get to disengage. I've done nearly 300 miles today. 150 to my destination, then after about 100 on the return journey, I went to flick it out of OD to overtake something on the motorway, and it was slow to disengage, then jumped in and out of OD even though the switch was in the off position. It was fine if I left it engaged, but if I tried to disengage, it just jumped around. Luckily, when coming off the slip road, it did what it should have done and under 30, it disengaged properly. Anyone else had this? Its done it twice recently, generally towards the end of a long, hot 150 mile motorway run. I'll go out and check/change the oil shortly. I need to do a 300 mile round trip to Taunton in it on Weds, another 150 to Warwickshire on Thurs, and then 90 on Fri with not much time to dismantle it if there is a problem!! Quote Link to comment Share on other sites More sharing options...
western Posted July 8, 2013 Share Posted July 8, 2013 change or top up the oil, mine does this when the oil is old or low. Quote Link to comment Share on other sites More sharing options...
TSD Posted July 8, 2013 Share Posted July 8, 2013 It's jumping in and out of OD because the oil pressure is still building, despite the fact that it's switched off. Mine did it for the first time on an unusually hot day, after a long motorway run too. When you drop the oil, take the square plate out and clean the filter. If that doesn't cure it, then it's probably time to strip it down, clean out all the swarf from the oil pump, and maybe replace the O ring seals. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 8, 2013 Author Share Posted July 8, 2013 Thanks fellas. Just changed the oil. It was pretty black. Its been in about 8k miles. I usually change it at a service every 6k, but I left it last time as I had renewed it in between services last time when I had the gearbox off to replace a leaky input seal. It really doesn't like the heat. The oil that came out looks really crappy. In a beige bucket: and some on some white tissue: That oil was the fancy difflock evo stuff that you can use instead of ATF/MTF. The thing I wondered when buying it was whether it would handle the heat better than ATF. I guess the answer is no as it has gone the same way. Anyway. Have re-filled with normal ATF and will drain and re-fill again when I service it in 500 miles Quote Link to comment Share on other sites More sharing options...
western Posted July 8, 2013 Share Posted July 8, 2013 I just use normal Castrol TQFATF/PAS fluid in mine, seems to work OK. Quote Link to comment Share on other sites More sharing options...
Snagger Posted July 8, 2013 Share Posted July 8, 2013 I have heard from mechanics that the GKN is prone to cooking its ATF and needs frequent replacement. I was also told that solenoid failures are not uncommon. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 8, 2013 Author Share Posted July 8, 2013 I just use normal Castrol TQFATF/PAS fluid in mine, seems to work OK. Yeah, I had until recently, but it was always coming out fairly burnt looking (even with 6k oil change intervals), so I thought I would try the difflock stuff. My conclusion is its a bit of a waste of money and ATF will do in the future. I noticed no difference to changes in the main box with it either. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 8, 2013 Author Share Posted July 8, 2013 I have heard from mechanics that the GKN is prone to cooking its ATF and needs frequent replacement. I was also told that solenoid failures are not uncommon. I'll stick religiously to 6k now. This is the first time for ages that I have let it run over that. Funny really as I think the GKN manual says 50k miles for oil changes! I've even added the roverdrive transfer box sump and replaced the handbrake with an x-brake, but it still gets pretty hot down there. I'd love to add an oil cooler for the overdrive - didn't they make one at some point that attaches where that bolt is that you would assume is the drain plug but actually isnt?? Quote Link to comment Share on other sites More sharing options...
Tanuki Posted July 8, 2013 Share Posted July 8, 2013 I'm rather familiar with the overdrive-in-question (it being fitted to thousands of cars in the 1960s/1970s when sold by Laycock: think Triumphs/Ford-Transit-rapid-intervention-vehicless/Volvos/TVRs/Reliant-Scimitars/Leyland-DAF riot-buses/Bentleys/Bristols/Humbers/MGs/Austin-Healeys/Rovers). Failure to release is a sign of the thing not depressurising when the solenoid/control-linkage tells it 'overdrive off'. Drop the bottom plate and change the filters. Don't just clean them - replace them. These guys: http://www.overdrive-repairs.co.uk/ are worth a call. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 8, 2013 Author Share Posted July 8, 2013 I'm rather familiar with the overdrive-in-question (it being fitted to thousands of cars in the 1960s/1970s when sold by Laycock: think Triumphs/Ford-Transit-rapid-intervention-vehicless/Volvos/TVRs/Reliant-Scimitars/Leyland-DAF riot-buses/Bentleys/Bristols/Humbers/MGs/Austin-Healeys/Rovers). Failure to release is a sign of the thing not depressurising when the solenoid/control-linkage tells it 'overdrive off'. Drop the bottom plate and change the filters. Don't just clean them - replace them. These guys: http://www.overdrive-repairs.co.uk/ are worth a call. oooooooo. Good link. Much better spares prices than D44! There is only one filter that is easily accessible on this under the bottom plate. Its a mesh type one that sits in the oil sump (if you can really call that tiny reservoir a sump!!) Where would I find any other filters? I've had it apart in the past and cant recall an internal one, but it was a long time ago. Quote Link to comment Share on other sites More sharing options...
Tanuki Posted July 8, 2013 Share Posted July 8, 2013 There is only one filter that is easily accessible on this under the bottom plate. Its a mesh type one that sits in the oil sump (if you can really call that tiny reservoir a sump!!)Where would I find any other filters? I've had it apart in the past and cant recall an internal one, but it was a long time ago. The ones I'm familiar with have a small cylindrical barrel-shaped filter - like an old-style paper oil-filter but fitted in a metallic mesh casing. To get to it you dropped the bottom-plate from the overdrive and then used a spanner with 2 pins that engaged with 2 holes in the screwed plug that retains this filter. Have a look at: http://www.scimitarweb.co.uk/~donkennedy/ODFilterClean/ODFilterClean.htm in particular http://www.scimitarweb.co.uk/~donkennedy/ODFilterClean/Filter.jpg [i've spent rather too much time doing this] Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 8, 2013 Author Share Posted July 8, 2013 That's really handy. Thanks. Are those plugs screwed in tight? Just wondering what sort of tool I will need to knock up to remove it. I might give that OD company a call to get the right filter for this. I presume that one is the high pressure filter? Quote Link to comment Share on other sites More sharing options...
Tanuki Posted July 8, 2013 Share Posted July 8, 2013 That's really handy. Thanks.Are those plugs screwed in tight? Just wondering what sort of tool I will need to knock up to remove it. I might give that OD company a call to get the right filter for this. I presume that one is the high pressure filter? The plugs are screwed in fairly tight, yes. Back in the days I regularly played with these things I made up my own service-tool - a six-inch long length of stainless-steel flat bar with two holes and a couple of suitably-sized high tensile steel pins staked through with a quick flash of TIG on the back to keep the pins in place. Yes, the thing in question is the HP filter. Quote Link to comment Share on other sites More sharing options...
western Posted July 8, 2013 Share Posted July 8, 2013 I'm rather familiar with the overdrive-in-question (it being fitted to thousands of cars in the 1960s/1970s when sold by Laycock: think Triumphs/Ford-Transit-rapid-intervention-vehicless/Volvos/TVRs/Reliant-Scimitars/Leyland-DAF riot-buses/Bentleys/Bristols/Humbers/MGs/Austin-Healeys/Rovers).Failure to release is a sign of the thing not depressurising when the solenoid/control-linkage tells it 'overdrive off'. Drop the bottom plate and change the filters. Don't just clean them - replace them. These guys: http://www.overdrive-repairs.co.uk/ are worth a call. limk above no worky, but this one does. http://www.overdrive-repairs.co.uk/ Quote Link to comment Share on other sites More sharing options...
Snagger Posted July 9, 2013 Share Posted July 9, 2013 A thread for the archive, me thinks! GKN overdrives don't enjoy a good reputation for reliability, perhaps because they were designed for smaller, lighter vehicles which don't work as hard, and they need more frequent servicing than their unaltered schedules state. It seems some of the guys here have them cracked and are getting good reliability as a result, with a little more care than the manuals dictate. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 9, 2013 Author Share Posted July 9, 2013 A thread for the archive, me thinks! GKN overdrives don't enjoy a good reputation for reliability, perhaps because they were designed for smaller, lighter vehicles which don't work as hard, and they need more frequent servicing than their unaltered schedules state. It seems some of the guys here have them cracked and are getting good reliability as a result, with a little more care than the manuals dictate. I agree. Mine was bought secondhand for £500 about five years ago. Its done about 50k miles with me. I had to replace the two face to face seals and the orange bearing after a few months, but it has run well since then. Having that other filter pointed out is really useful, along with a link to where to buy one. The solenoid on the link above is about £40 cheaper than the one D44 sells! I always thought it was a shame Ashcrofts didnt take these on since they probably would have redesigned all of the faliure parts and made a much better unit! There are a couple of other threads that would be worth tagging to this one to make it a technical resource. I'll find them when i have time. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 9, 2013 Share Posted July 9, 2013 Is it really the same basic device that was fitted to, for example, Dolomites and the like in the 1970s? Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted July 9, 2013 Share Posted July 9, 2013 I wonder if these chaps do a replacement clutch for the overdrive ? Slipping when cold caused loss of drive which was quite hairy if you were puling onto a roundabout. It is a great device if only it would work reliably. I miss having it fitted Mo Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 9, 2013 Author Share Posted July 9, 2013 I wonder if these chaps do a replacement clutch for the overdrive ? Slipping when cold caused loss of drive which was quite hairy if you were puling onto a roundabout.It is a great device if only it would work reliably. I miss having it fitted Mo I think they might Mo. I looked last night with you and Neil in mind. Its £120 which is also a lot less than i heard D44 was selling them for! It looks like they can re-con them as they have a surcharge for return of the old unit, so i guess this means they re-use them. 7th item down on the J type spares here: http://www.overdrive-repairs.co.uk/buy_spares.php We'd have to check it is the same as the one fitted to the LR overdrives, but they have confirmed already that the HP filter is the same. Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 9, 2013 Author Share Posted July 9, 2013 Is it really the same basic device that was fitted to, for example, Dolomites and the like in the 1970s? I think it is similar, but my understanding is that our version for 4x4s sends drive out of the front to the transfer box instead of letting it out the back to the propshaft. Tanuki might be better placed to answer the question. I guess this might mean there is a potential difference in the cone clutch?? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 9, 2013 Share Posted July 9, 2013 Found this link in another Lr4x4 post, very informative, and very similar to an old Dolomite gearbox I pulled apart when I was about ~20! http://www.buckeyetriumphs.org/technical/jod/JOD1/JOD1.htm Quote Link to comment Share on other sites More sharing options...
Tanuki Posted July 9, 2013 Share Posted July 9, 2013 I think it is similar, but my understanding is that our version for 4x4s sends drive out of the front to the transfer box instead of letting it out the back to the propshaft. Tanuki might be better placed to answer the question. I guess this might mean there is a potential difference in the cone clutch?? Yes the basic design of the GKN overdrive is indeed the same as used on 50s/60s/.70s cars: basically it's an epicyclic geartrain with hydraulically operated cone-clutch, and a direct-drive mechanism in the centre (for transmitting the torque when the O/D is not engaged)..There's a built-in oil pump to provide the hydraulic pressure, and a solenoid to control feed ot pressure to the pistons that operate the cone-clutch. Only difference between the 'traditional' RWD-car-style setup and the LR implementation is that the LR version is a 'coaxial' drive version [input and output members run inside each other, with one essentially being a tube] whereas the traditional RWD version is in-line with both input and output being solid shafts. Apart from that,the underlying technology is identical! Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 9, 2013 Share Posted July 9, 2013 Seem to remember them not being that reliable with an 1850 dolomite engine in front of them, it's no wonder that they struggle to survive on 6K oil changes in a LR. Quote Link to comment Share on other sites More sharing options...
western Posted July 9, 2013 Share Posted July 9, 2013 mine doesn't get any special treatment, I only ever engage or disengage while it's under load & never use the clutch, Quote Link to comment Share on other sites More sharing options...
reb78 Posted July 9, 2013 Author Share Posted July 9, 2013 mine doesn't get any special treatment, I only ever engage or disengage while it's under load & never use the clutch, Blimey. Mine bangs right out of gear if I come out without the clutch. It engages smoothly as it should under power though. Quote Link to comment Share on other sites More sharing options...
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