Ridgeback Posted February 10, 2012 Share Posted February 10, 2012 I have 2 gkn overdrives for my td5 90. One came with it when I first got the 90 "they said you might want this for parts" and the other was fitted and working. One day It lost all drive so I took it off. Does anyone know how easy they are to fix. I know lots of people don't rate them because at £1200 each they are not worth the money but I have 2 already and it was good when it worked . I was told that Deven4x4 sell the parts now. Quote Link to comment Share on other sites More sharing options...
western Posted February 10, 2012 Share Posted February 10, 2012 Yes Devon4x4 took all the parts from GKN, when GKN ceased production/support, had mine for years & it's been fine, had to change the speed sensor & fluid but that's all. I love it on long trips. Quote Link to comment Share on other sites More sharing options...
101sean Posted February 10, 2012 Share Posted February 10, 2012 Gave up on mine but they aren't too hard to take apart, you need a press to remove the bearings though. They are very similar to the Type J OD fitted to Volvos and Triumphs in the 60s http://www.buckeyetr...d/JOD1/JOD1.htm Mine in bits - Quote Link to comment Share on other sites More sharing options...
reb78 Posted February 10, 2012 Share Posted February 10, 2012 Sean said what i was thinking and also put up the useful link that i was thinking of! They really are simple to take apart. I dismantled mine to renew all of the gaskets. p.s. If you want to get rid of them as spares, i might be interested in one for spare parts for mine (depending on the price). Quote Link to comment Share on other sites More sharing options...
Ridgeback Posted February 10, 2012 Author Share Posted February 10, 2012 Thanks for the photos, they don't look that bad to have ago at . Why did you give up on yours ? Quote Link to comment Share on other sites More sharing options...
mmgemini Posted February 11, 2012 Share Posted February 11, 2012 Devon charged me over 700quid to repair my GKIN. 12.000 miles later it's back to where is was before Devon repaired it. I find that without the O/D I can get 25MPG so it's coming off. What are they worth ? Quote Link to comment Share on other sites More sharing options...
simonr Posted February 11, 2012 Share Posted February 11, 2012 What actually breaks when they loose drive? Might it be possible to get a new part made in 300M or something that will more likely survive? Si Quote Link to comment Share on other sites More sharing options...
Ridgeback Posted February 11, 2012 Author Share Posted February 11, 2012 I am not 100% sure what goes wrong with them. After reading up on stuff I found on the web, I think it's something to do with oil pressure. If I am correct, when the oil pressure drops, the drive clutch stops allowing you any drive. If it just stopped working in overdrive it would not be such a problem but when mine stopped working I could not get any drive and needed the AA to get me home. Quote Link to comment Share on other sites More sharing options...
mmgemini Posted February 11, 2012 Share Posted February 11, 2012 Hmm Mine won't select....Stopped working but I still have drive. There's three problems that I see. The oil seal between the transfer box and the O/ D fails. Allowing EP90 into the ATF..... The second, which we discussed at the club on Monday, is that you's supposed to engage O/ O when using full throttle without the clutsh. It doesn't half bang when you do that. So I dip the clutch...Aparently that's wrong Third one is I drive to low down the rev range using the torque from the engine instead of revs. Quote Link to comment Share on other sites More sharing options...
simonr Posted February 11, 2012 Share Posted February 11, 2012 If it's like the laycock ones, there is an oil pump which only develops enough pressure to engage the OD when you are travelling above a certain speed. You select OD then it engages when the pressure is high enough. It's intended to only allow it to be used when the engine is outputting lower torque and protect the OD. Low oil or the EP90 getting mixed with ATF would drop the pressure and prevent it engaging. I would assume that the normal drive is returned via a spring, but it is possible this is hydraulic as well so it could get stuck in the mid way position between drive & OD I.e. Neutral. I think it would be worth stripping, replacing all the seals you can find, filter, pressure relief valve if it has one and oil and see if that fixes it. If not, it ought to be possible to use an external pump to operate the clutch? Si Quote Link to comment Share on other sites More sharing options...
western Posted February 11, 2012 Share Posted February 11, 2012 GKN unit is effectivly a Laycock Type R as in the old Triumph 2.5PI 6 cylinder cars & some Jaguars, GKN's instruction state engage/disengage with power [throttle] on, do not use clutch, mine works fine this way I never touch the clutch to put OD in/out, they are a bit slow to operate if the oil level is low or needs changing. Quote Link to comment Share on other sites More sharing options...
reb78 Posted February 11, 2012 Share Posted February 11, 2012 GKN's instruction state engage/disengage with power [throttle] on, do not use clutch, mine works fine this way I never touch the clutch to put OD in/out, they are a bit slow to operate if the oil level is low or needs changing. Mine engages fine with the power on, but it bangs 8/10 times if i disengage like that. So i engage under throttle and disengage by dipping the clutch quickly (doesnt need to be completely disengaged, just a slight pressure on the pedal). The oil seals on the adaptor plate are a common problem - D44 sell uprated seals for this - note that there are two seals and they go face to face - TXB ][ OD (the seals are the ][). The other is the sealed bearing - the big orange one on the adaptor plate. Failure of any of these leads to transfer of oils between the TXB and OD. EP90 in the OD is bad news as the pump cant cope and it will jump in and out of gear and eventually fail to engage at all. Checking the breathers are clear is also a good idea as pressure build up int he TXB due to a blocked breather may force the oil into the OD. The other reason for failure to engage may be a faulty solenoid i suppose. Can take these apart and test them with a battery though - you should see the plunger pop in and out as you apply and take off the charge from the battery. Getting further into the OD, there are two plungers in the back that oil pressure forces out and they pull the mechanism backwards and engage it via the cone clutch (i think this is right), but a failed o ring around those plungers may also mean the thing wont engage. IIRC Mike, you have bypassed the speed sensor and control unit on yours but for others a faulty speed sensor may be a reason for failure to engage - there is a post somewhere noting the RS equivilent to the GKN speed sensor (and it is a damn site cheaper than the spare part from D44!! - i like their products, and the fact that they still support these units for spares, but the prices are sky high!) Quote Link to comment Share on other sites More sharing options...
mmgemini Posted February 11, 2012 Share Posted February 11, 2012 Yes reb. I thought it was the solenoid but I gave up on it.....As soon as it's warm the O/ D id coming off. Quote Link to comment Share on other sites More sharing options...
simonr Posted February 11, 2012 Share Posted February 11, 2012 If the problems with them are hydraulic or control related, they should be straightforward to fix. Maybe I'll keep an eye on eBay! Si Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted February 11, 2012 Share Posted February 11, 2012 ditto Quote Link to comment Share on other sites More sharing options...
101sean Posted February 11, 2012 Share Posted February 11, 2012 My problems started when it worked loose on the back of the Tbox. I rebuilt it inc the big orange bearing (it's not a standard size, only available new from NTN, mine came from D4x4 but wasn't new). I had continual oil exchange problems, gave up on it in the end. It was great while it worked and was best changing up under full load, I used to change down when dropping through the gears at roundabouts etc. Quote Link to comment Share on other sites More sharing options...
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