Snagger Posted June 3, 2019 Share Posted June 3, 2019 The unit behaves the same way as a two-speed automatic, except that automatics usually use hydraulic pressure in both directions, holding each gear in drive, not using springs in one direction. They always have the clutch packs immersed, so I can't imagine for a moment this would be different - the linings would overheat and break up in no time if they weren't lubricated while in their slipping mode. I still think you need to test the springs' stiffness, not just their length, and check whichever clutch pack is compressed by the springs for wear, if just to rule them out and point the finger squarely at the piston o-ring leak. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2019 Share Posted June 3, 2019 Given you have a spare OD, I think you have three options Ralph 1. Use the springs from your old OD in the one you bought from Neil and see if that fixes it 2. Use the rear casing from your old OD on the unit you bought from Neil - this would rule out the pump and solenoid bore then 3. Replace the broken part in your old OD with the part from this one Point three has the best chances of success and is least faff as it really ought to work, but having tried to help Neil fix that OD you have now, I am curious if 1 or 2 would fix it as I have a slipping one on the shelf!! The springs came from D44 I think so one would expect them to be ok, but as pointed out above, no guarantee 1 Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted June 3, 2019 Share Posted June 3, 2019 Been skimming this with interest, the actuation method on these seems to be a weak point, is there any way to convert them to just be on/off using a mechanical linkage, lever, cable, or clutch-slave style actuator? Quote Link to comment Share on other sites More sharing options...
western Posted June 3, 2019 Author Share Posted June 3, 2019 FF. I have no idea if any of your suggestions would work, I can't have my 110 off the road to sort out a none hydraulic/ electrical system, it's my only vehicle. Swapping the rear case with pistons in might work but I would want to replace the seals first & swap the filter as one is now very clean, my old unit is stripped & hasn't seen any oil for a year, so wouldn't trust the seals, if it doesn't fix the problem. I would also need to use the planet gear set from this overdrive as my old one was siezed. Think I will order a set of piston seals & 4 springs & see if that works, my old unit started slipping as well but the might have been down to the broken part inside. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 3, 2019 Share Posted June 3, 2019 I presume, that the solenoid on these turns on/off the flow of fluid which moves the friction surfaces apart, thus giving you overdrive. So in simple terms, if it slips when disengaged, surely it can only be: Friction surfaces failed Springs too weak (that hold the friction surfaces together) High pressure ATF getting past the seals in the solenoid Have I missed anything there? Quote Link to comment Share on other sites More sharing options...
western Posted June 3, 2019 Author Share Posted June 3, 2019 That's about it AFAIK, I need to get the solenoid off to look at the bore but need a spanner to modify as my existing spanner is to wide to fit the gap where the solly nut is. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 3, 2019 Share Posted June 3, 2019 2 hours ago, Bowie69 said: I presume, that the solenoid on these turns on/off the flow of fluid which moves the friction surfaces apart, thus giving you overdrive. So in simple terms, if it slips when disengaged, surely it can only be: Friction surfaces failed Springs too weak (that hold the friction surfaces together) High pressure ATF getting past the seals in the solenoid Have I missed anything there? I think thats all. The clutch was new on this OD so i think Ralph can rule that out for sure. My suggestions above would deal with the other two issues. Quote Link to comment Share on other sites More sharing options...
western Posted June 4, 2019 Author Share Posted June 4, 2019 I can swap the solenoid over from my old unit as it was working, bit reluctant to use the springs from my old unit, would rather use new springs, The cone friction material is undamaged as are the 2 surfaces it works with, there isn't much else that can be changed, other than new seals in pistons & pump part. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2019 Share Posted June 4, 2019 We tried three solenoids on that OD Ralph so i wouldnt waste your time on a fourth! That solenoid on it is new. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2019 Share Posted June 4, 2019 Just to add - You can test the solenoids easily with 12v across the terminals Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 4, 2019 Share Posted June 4, 2019 Is there a pressure relief valve? Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2019 Share Posted June 4, 2019 Think so - its under one of the circular plates in the bottom of the unit. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 4, 2019 Share Posted June 4, 2019 If it was giving an over-pressure, could be forcing fluid past the seals in the solenoid/somewhere else. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2019 Share Posted June 4, 2019 So a jammed pressure releif mechanism? Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted June 4, 2019 Share Posted June 4, 2019 Essentially, yes. Sorry, head has been buried on code all day, my English is starting to read like a Linux manual Quote Link to comment Share on other sites More sharing options...
western Posted June 4, 2019 Author Share Posted June 4, 2019 Relief valve is clean & free, might be woth swapping the little spring from my old unit, the bore & valve itself look in good condition, as to the solenoid I was thinking it may be sticking not fully releasing the pressure. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2019 Share Posted June 4, 2019 We thought that, but tried three solenoids and it slipped with all of them. The springs really seemed to solve it. 1 Quote Link to comment Share on other sites More sharing options...
V8 Freak Posted June 4, 2019 Share Posted June 4, 2019 The fact it slipped at the first move of the day would suggest it's not hydraulic.... Sometimes just dipping the clutch and going again solved it for days. Hence focus on the springs eventually... (As well as the extensive overhaul...) I was wondering if there was a way to pack the springs and add a little extra force to them for testing? Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 4, 2019 Share Posted June 4, 2019 Is there a way of testing spring compression forces easily? Quote Link to comment Share on other sites More sharing options...
western Posted June 5, 2019 Author Share Posted June 5, 2019 I don't know, there is no spring info in the booklets that come with the overdrive, Devon 4x4 might have the specs. I won't be doing anymore to the unit until 14/15 June as I away on detachment with work for all of next week. Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 5, 2019 Share Posted June 5, 2019 (edited) I was trying to get my head around Neils idea of spacing the springs last night. If their resting length is the same as the originals, wouldn't spacing them have the effect of making the clutch more difficult to engage in one direction? I cant quite work out which! GKN would have had the specs once, but goodness knows if they would be able to find them now if you asked and could find anyone helpful there. Edited June 5, 2019 by reb78 Quote Link to comment Share on other sites More sharing options...
V8 Freak Posted June 5, 2019 Share Posted June 5, 2019 My assumptions were basic Rich.... If there is no hydraulic pressure, the OD won't engage. Therefore the normal / default drive mode must be reliant on the springs holding the brake/clutch cone firmly in one position (locking the sun gear and annulus) and that state being changed when the hydraulic pressure forces the brake/clutch cone into position on the opposite surface (Sun gear locked stationary - forcing drive through the planetary gears / changed gearing) The hydraulic pressure is quoted to be over 400 psi, so should overcome the springs quite easily, even if the spring rate is increased..... Quote Link to comment Share on other sites More sharing options...
western Posted June 8, 2019 Author Share Posted June 8, 2019 bought a 1 inch AF OE spanner, a few minutes meeting with Mr angle grinder it got slimmed down on one side of the open end face & now fits between the OD body & solenoid, which was removed & inspected, looked very clean, but gave it a blast or 2 with brake cleaner, no nasty gunk in the port it occupies either. so this bit is looking fine. solenoid works everytime it was switched on/off too. Quote Link to comment Share on other sites More sharing options...
western Posted June 8, 2019 Author Share Posted June 8, 2019 Does any of you know where this seal is located on the overdrive, because I haven't seen one in either of my 2 units https://www.devon4x4.com/overdrive-seal.html Quote Link to comment Share on other sites More sharing options...
reb78 Posted June 9, 2019 Share Posted June 9, 2019 (edited) Pretty sure they go under the long allen bolt heads in the casing. Eta - £4.79?!?! D44 need to get a grip on their prices!! If you can get bits from Overdrive Repair Services they are always a lot more reasonable! Edited June 9, 2019 by reb78 Quote Link to comment Share on other sites More sharing options...
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