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I'm looking for advice from fellow owners with regard my non-working overdrive (All-syncro later type gearbox with compact overdrive). Since restoring the car (which has only covered 67,000 miles) the overdrive hasn't worked at all. I've tried everything to remedy the situation (new spring which increased pressure to its correct spec, cleaned
everything possible, adjusted solenoid no end of times etc etc) but it still wouldn't work. Having finally decided to remove the overdrive (with gearbox/engine still in
situ) I am having problems seperating the overdrive from gearbox - its seperated about 3mm but that's about it. I've tried pry bars etc but it just won't budge. Having removed the six nuts and studs as per the manual it rotates about 15 degrees clockwise/anticlockwise but won't come any further back.
I finally decided (having done research) to remove the rear casing, which would come away with the annulus. Again, about 3mm of rear movement, but no more.
The car was off the road for about 20 years and I suspect the sliding member has stuck to either the annulus or the input shaft. I note that when I turn the assembly by the 15 degrees the brake ring also turns but the output shaft (which connects to propshaft) doesn't, so I don't think the sliding member is stuck to that - hence it must be stuck in the dis-engaged position. That makes sense as, when on the road, it drives fine backwards and forwards but I'm always looking for that extra 'fifth gear'.
So, my problem is - how can I seperate the overdrive from the gearbox (I've tried the big hammer on the brake ring as suggested to no avail). If anyone has any suggestions I would be really grateful ??
SUCCESS !!! Overdrive now removed, following advice from John at Overdrive Spares in Rugby ("Give the output yolk a good thrashing with a hammer" ). I had been trying to remove it by hitting the mounting pin fitted underneath the overdrive but that wouldn't apply purely longitudinal force. It took a few good bashes but then it suddenly seperated. It would seem that the clutch assembly and/or the splined sun gear was seized on the shaft. I've now stripped the overdrive down and all appears in good condition - although I'll fit new O rings to the pistons and a new gasket as a matter of course befoe fitting it all back together. As the car/overdrive has only covered 65K miles I'm hopeful that when its re-installed evrything will work as it should ! (Fingers crossed). John said that it's very common for the clutch unit to become seized after such a long period of idleness.
UPDATE: Last post should've said 'Dave' at Overdrive Spares in Rugby (UK). Having spoken with him on several occassions during the past few months I cannot recommend
him enough - he has a deep knowledge of Laycock Overdrive units and is only too willing to chat and give advice. I've also bought various parts from him and his prices are very
reasonable (unlike other so-called Jaguar specialists that wanted £13 P&P to send two paper gaskets and a couple of piston O rings !!) I have no affiliation to Overdrive Spares but I think good service should be acknowledged.
"I'VE GOT OVERDRIVE !! " At long last the overdrive is now working. Finally managed to remove the unit with a large rubber mallet - Dave at Overdrive Spares advised me to whack the output yolk, rather than the vertical mounting pin (as that could crack the aluminium casing). After half a dozen thumps it seperated. By hitting the yolk more rearwards pressure is exerted than with the pin. Anyway, I've stripped the unit down (the sliding member had well and truly stuck to the annulus through long-term inactivity. Better to be stuck'off' than 'on'.)
. I've replaced the two rubber seals on the pistons, checked all components, which were in superb condition and rebuilt with a new adaptor/front case gasket. There are no gaskets between the rear casing/brake ring/front casing but I coated the joints with 'Wellseal' before re-assembly.
Re-fitting the unit underneath the car was a bit of a hassle but, after a couple of adjustments of the splines with a long screwdriver, it slid back on easily enough. I made sure to adjust the solenoid with the unit on the bench rather than lying on my back under the car. Then followed the slow process of re-fitting all removed components (propshaft, rear engine/gearbox mount, speedo cable, radiator, electric fan, grille etc). With baited breath I started the engine (after re-filling the gearbox/overdrive with EP90 GL4 oil of course) and gradually moved through the gears to fourth (the car was sitting on ramps at the front and axle stands/trolley jack at the rear). With the speedo showing 30mph I switched on the overdrive but no click from solenoid and no change in road speed - DAMN !! It transpired that the wiring on top of gearbox had hardened with age and the copper wire strands were visible in various places, so it was likely that this was the problem. Having accumulated plenty of wiring looms over the years I managed to find all the necessary 5 & 17 amp cables (in the correct colours as well) and made a new short loom. Once fitted I jumped back into the car and repeated the process - EUREKA ! When selected the overdrive gently kicked in and the speedo showed an increase from 30mph to 38mph (Obviously, on the road it would be the rev counter that 'drops').
Took the car for a short drive and all works fine - it's so much nicer to drive - I no longer feel that the engine is over-revving in fourth above 30mph. A quick check underneath on my return showed an oil leak from the non-return valve/pump nut (it transpired that I had nicked it slightly so I carefully flattened it in the vice, put wellseal around the washer and thread and re-fitted same - leak thankfully cured. I then double checked the oil level (car must be level) and topped it up slightly so that oil just dripped from the oil filler and lowered the vehicle. Job done at long last.
Good news! and an inspiration for others in the same boat! As I mentioned in your other thread on this issue my OD was rebuilt over 20 years ago & I saw it operating on the bench. It now refuses to engage & all is well up to & including the solenoid. Before I pull it out I'm going to try a few more adjustments as I'm warned that the pin through lever in the casing hole method is not accurate but I suspect the unit is stuck disengaged through no use.
Last edited by Glyn M Ruck; 06-18-2019 at 11:00 AM.
Good luck Glyn. The first thing that Dave (Overdrive Spares) asked me when I sought advice was "Has it been off the road for a long time ?". When I said it had been for around 15-20 years he said that the most likely casue was the sliding joint had probably become seized/stuck onto the Annulus - there's a fair amount of force exerted on the sliding joint by the six springs when overdrive is 'off' . You would think that being surrounded by oil it wouldn't get stuck, but I presume the oil gradually sinks to the bottom leaving the aforementioned parts 'dry' ??
Anyone got any advice on repairing/welding the threaded female Laycock DeNormanville OD rear transmission mount post? I have an aluminum spool gun and I also have a lump of clean aluminum i could carve up, not sure the best way to tackle this....
This approach looked promising but it's a much bigger bolt size and my sheared off area is quite a bit larger...
Good luck Glyn. The first thing that Dave (Overdrive Spares) asked me when I sought advice was "Has it been off the road for a long time ?". When I said it had been for around 15-20 years he said that the most likely casue was the sliding joint had probably become seized/stuck onto the Annulus - there's a fair amount of force exerted on the sliding joint by the six springs when overdrive is 'off' . You would think that being surrounded by oil it wouldn't get stuck, but I presume the oil gradually sinks to the bottom leaving the aforementioned parts 'dry' ??
BFH with rubber cover worked. Dave Twigger at Overdrive Spares in Rugby knows more about Laycock DN Overdrives than most on the planet. He is a most helpful gent & more than happy to help even if he sells you nothing.
Anyone got any advice on repairing/welding the threaded female Laycock DeNormanville OD rear transmission mount post? I have an aluminum spool gun and I also have a lump of clean aluminum i could carve up, not sure the best way to tackle this....
This approach looked promising but it's a much bigger bolt size and my sheared off area is quite a bit larger...
I have a suspicion that the aluminium overdrive casing may suffer from fatigue if the prop shaft is out of balance or a rear wheel of a live axle car is out of balance or out of round. It's worth checking for and eliminating any source of drive train vibration as well as repairing/replacing the overdrive.
I've been talking to Dave for a year or so on this. He's sending me £300 of rebuild parts shortly. He can also send me a repaired rear casing sub assembly, apparently the rear mount shearing off is a common issue and it is a commonly requested exchange part.
I have a 4 speed overdrive gearbox from an 64- 68 S type that I am going to be rebuilding and inserting into my series 1 xj6, which also has a mkX 3 SU manifold setup from previous owner. Pretty ratty car but that's why I bought it.
I will have to do some fab for the rear gearbox support so may be doing some tweaks on the welded up rear casing. Twigger told me after seeing this photo it was an easy one. I can either find someone locally to weld it up, send it to OD spares for a replacement when I have all this lot apart shortly or have a crack at it myself which is usually my preferred option. your point about prop shaft misalignment is noted Glyn, very good observation. I was going to fab up a rear gearbox mount with some sort of rubber donut to cradle the protruding damaged area once it's ready to be installed.It will need a custom driveshaft.
I've been watching various videos of aluminum welding repairs and also of rebuilding LdN overdrives in prep for this new project in the coming weeks.
Oliver, For swapping between Mk2, S type, and XJ, you should be aware of differences in the lengths of the tailpiece on the o/d. Mk2 and (I think) S type have long tails like your broken one while XJ cars have a short tail.
Oliver, For swapping between Mk2, S type, and XJ, you should be aware of differences in the lengths of the tailpiece on the o/d. Mk2 and (I think) S type have long tails like your broken one while XJ cars have a short tail.
Thanks for this. Yes, will need some fab and shortened driveshaft, but Twigger said this is the compact type, we shall see. Main thing is to get ti ll operational first...
Last edited by olivermarks; 12-24-2023 at 01:16 PM.
On the Mk2, the overall length of the 4 synch plus compact overdrive and Moss plus original non-compact are about the same. The consequence is that not all compacts are the same length; that on the Mk2 is longer (due to the extended tail) than the one from the XJ. To install an overdrive in an XJ, it's probably easier to start with one from an XJ. In fact, there may be more of them available.
On the Mk2, the overall length of the 4 synch plus compact overdrive and Moss plus original non-compact are about the same. The consequence is that not all compacts are the same length; that on the Mk2 is longer (due to the extended tail) than the one from the XJ. To install an overdrive in an XJ, it's probably easier to start with one from an XJ. In fact, there may be more of them available.
Hi Peter, according to Dave Twigger 'The 28 60572 is a unit from 1964-1968 3.8l S type jag and is exactly the same as an XJ6 series 1 4.2l we can supply everything for that unit'. I'm in the US so manual boxes/ODs for Xj6 on> are very rare. I'm pretty sure i'm going to be fabbing up brackets etc anyway as I'm replacing the anemic Bore WornOut slush box...
05-26-2019, 08:52 AM
Mk2 overdrive woes - advice sought
