Overdrive fault

Hello everybody,

I’ve got my overdrive repaired by odspares in 2007, or 30.000km ago. During that time it worked reliably, but it kicked in rather hard, i.e. a pretty loud “klonk” or similar sound, you get the idea :wink: I never switched it on while accelerating, I just kept the 4th gear in, lifted my foot from the gas pedal and flicked the switch…KLONK

Ok, per recommendation of odspares, I was using 20w50 mineral oil.

Now, after 30.000 km the overdrive gave up the ghost.
Fault diagnosis revealed:

  1. Oil pressure is around 100 psi (at approx… 25 km/h) which is below spec (490 psi).
  2. Oil level is ok (20w50 mineral oil)
  3. Solenoid and lever adjustment are ok
  4. Filter was/is super clean
  5. No heavy deposits in gear box oil (so clutch is ok I guess)
  6. Spring in accumulator piston assembly is ok
  7. Actuator valve was/is clean, ball seat looks ok
  8. The ball/seat of oil pump no-return-valve looks ok

I’ve reseated the ball valves in the actuator and no-return-valve.

Revisiting the oil pressure revealed:
The pressure is constant at 100 lb/sq.in. @30 km/h, 300 @80 km/h, regardless if engaged or not engaged (the first measurement of a series, though, showed 0 lb/sq.in. I guess the accumulator was empty at this moment).

Finally, I extracted the accumulator piston, which was sticking really really hard in the bore! I had to use a brake caliper extraction kit like this: https://www.klsupply.com/general-equipment/brake-caliper-pist-puller-set-35-6885.asp

The piston and the rings have marks and scores but they are not broken. I noticed that the rings were covered in swarf, and didn’t expand at all after the piston was extracted:

I’ve ordered a set of new rings and would give it a try.

What are you guys saying?


That is a pretty rough looking piston, if it were me, I would buy a new one. You might be able to clean it up with some sheet abrasive, starting with maybe 600git and then 800, 1000, 1200-1500. You wouldn’t want to take any measurable material off the piston, just the galling and then make it smooth.
More importantly, what does the bore look like? The same of worse I would guess. I’m assuming the bore is cast into the transmission and not replaceable separately, so the same would apply. gentle and even smoothing of the surface. Then try to figure out why this happened and prevent from happening again.


Hi Dave, did you ever extract a piston? Did it require a lot of force to get it out?

Dan you state XJ overdrive fault, the factory spec oil for a all/syncro box
is 90 ep.

Hi Peter, so you say that I am using the wrong oil?

Definitely not standard but if OD Spares told you to use it then maybe OK. There’s no logic IMO using a multigrade in a gearbox or OD. Presumably they don’t warranty your gears and shafts that would suffer with only light non-EP oil?

If there’s no 'trauma or foreign body involved then lubrication breakdown would give that kind of damage. Did they actually tell you up front to use 20W-50 or possibly mishear your question whether 20W-50 would work?

Definitely new piston and rings IMO. That thing works hard.

Hello Peter, that is interesting: you are saying that it is rather damage than simple wear.
What sound do you hear when you switch in your OD?

Normal wear just reduces part measurements until eventually they are out of spec and don’t work so well anymore. Normal wear doesn’t generate macroscopic debris like that. That’s damage, not wear. The question is how come and lubrication would be high on my suspicions if the mechanism was correctly built.

The whole point of ODs for me is the way they almost magically drop the revs in top without any noise or jerking. One minute you’re driving at 3,000 rpm, say, and you touch a little switch and the tach drops 700 revs. No mechanical sound, no lift-off the accelerator, just lower engine/exhaust hum.

Hi Peter, my OD never gently slipped into higher gear. It always produced that scary klonk-sound. I guess I’ve got a problem since it was rebuilt…

If I see what I think I’m seeing in those photos, this thing has four “rings” installed side-by-side in one wide groove in the piston? I’m not sure what the thinking was there. Looks like a recipe for – well, for exactly what you got.

New parts are definitely in order, methinks. But if you can’t find them or they are expensive, I’d be tempted to hire a machine shop to fab me a new piston. And instead of that single wide groove, I’d redesign it with two or three individual grooves, each wide enough for one of those rings. Probably wouldn’t need all four.

I might be looking for a teflon coating for the skirt, too, but that might be too much modernization for an old car.

I’ve never had a clonk on engagement on an overdrive car in normal driving. More like the kind of slurred soft change like you get when a torque converter locks up in an automatic. If you hadn’t shown your stripped parts I would have said you had a drive shaft or differential problem.

From memory I always kept the throttle depressed when changing into O/D

I am rebuilding an 1985 S3 now, but it didn’t have an engine/transmission when I bought it so I have never even ridden in one let alone driven one. I was making my comment based on many other types of piston/cylinder applications in the auto world. To me, it looks like there was very, very little lubrication or the piston got over-heated at some point and began to seize in the bore. Today’s transfer cases in a lot of SUV all wheel drives and 4 wheel drives call for ATF which is very thin, they are built for its use. An older car like ours should run with 80 or 90wt as others who have chimed in have said. However, I have no experience with Jaguar transmissions. I had some trouble getting the corroded pistons removed from the brake calipers on mine, used Liquid Wrench and made a block-off plate.


The specification says ‘hypoid 90EP’ for S1 and S2 - and 75W later.

I find it extremely strange that ordinary motor oil (20/50) is being used in a Jaguar gearbox - and the overdrive supposedly shares the same oil. What Jaguar do you actually have…?

xj6 85 Sov Europe (UK/NZ)

Hello Frank,

it’s a XJ6 S1. Dave from odspares explicitely told me, that multigrade mineral oil is ok, too.

I will flush my gearbox anyways, and give ep90 a try this time…

Strange to use 20/50 engine oil in a allsyncro box Frank, but not in a Moss box where a straight 30w oil is specified, this explains how misinformation /confusion can occur !

There are gearboxes that call for motor oil, gear oil, or ATF. I remember being astonished that RedLine MTL replaced all of them. IIRC, there is some problem with using motor oil in a gearbox with brass synchros, as additives in the oil might corrode the brass or something like that.

I initially thought ATF was a silly choice. ATF is for automatic transmissions, what’s the idea behind using it in a manual tranny? I even hypothesized that some engineer had concocted this scheme so mechs wouldn’t get confused and accidentally use manual lube in an automatic or verse visa. But upon further investigation, the use of ATF makes the most sense to me. It’s designed for gears – there are gears in an automatic – and it’s also designed to work with friction elements such as the bands in an automatic or the synchros in a manual. Any really slippery motor oil or gear oil is likely to impair the function of the synchros.

Our Mazda 626 had a very stiff gear change and I read about using ATF, did the change and it was very much improved.


On the MKV (and I believe every Jaguar using the non-synchro 1st gearbox until 1964) I have the exact opposite experience. IIRC factory recommended SAE30 engine oil for those gearboxes. In my car a workshop had put ATF both in the steering housing and the gearbox. The steering box has felt seals so ATF would run to the ground even with the car standing still. (I put in Penrite Steering Box Lube which looks like Jell-o) And the gearbox was terrible, seemed like the synchros were missing, hard to change! I changed to Castrol Classic 30W in the gearbox and the synchros on gears 2, 3 and 4 magically started working, and IMO they work well.


The Moss box had ‘square’ cut teeth, Peter - the Mini also springs to mind, with the engine and gearbox as a single unit. With hypoid cut teeth; engine oil is not suitable; the interaction between hypoid gears involve sort of ‘rubbing’ like in the differential…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

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