Other Disco 1 V8 Auto gearbox

Hi all, I'm posting this in the Disco section as it relates to a V8 Auto, but the engine and box are actually in my Defender 90, into which I installed a 3.9i V8 and 4HP22 transmission from a Discovery 1, a couple of years ago. Apologies in advance if this is a long post!

I drove the Discovery before I pulled everything out of it and it drove very well. During the transplant, I separated the engine and box, to fix some engine oil leaks. The torque converter was also removed from the box at this time.

I put everything back together, checking the flex plate stacking height, which was correct. When I had installed everything into the Defender, everything worked and drove, but there has always been this odd resonant vibration, almost a buzzing, under normal acceleration. It’s quite a heavy noise/vibration, but it’s more of a buzz than a rumble, if that makes sense. If you accelerate hard (foot flat down) it’s less obvious; possibly doesn’t do it at all. I’ve checked and re-checked and I can’t find anything touching the chassis anywhere, and have also asked other people to check in case I missed something, but nothing doing. I’ve also tried 3 different exhaust systems and it’s not that.

The Defender has done about 1500 miles since the conversion. Quite recently, I realised that I had not been checking the transmission fluid level correctly, i.e I had been checking it with the engine off, not with it running and cycling the gears. Entirely my mistake. It has always been at the upper level of the marks on the dipstick when static, but when I checked it running and cycling the gears, I needed to add about a litre to bring it to the middle of the dipstick marks.

This didn’t cure the vibration. (Which I’m not completely certain is the transmission anyway, but I have started to wonder about TC shudder being the cause). I used Comma MVATF Plus, fully synthetic, fluid to top it up, which states that it is DII/DIII compatible, but a few other things have also come to light since I topped it up. Firstly, when cold, I have a high-pitched whine from the transmission when engaging Drive and pulling away. This stops after a mile or two when everything is warmed up. Also, when stopping the car, the engine seems to die down to very low RPM, almost stalling, but does hold itself and then returns to tickover revs. If the engine is revved with the trans in neutral, it revs cleanly and returns to tickover with no issues, so it does appear that it is the transmission causing this. Lastly, the downshifts seem to be much more noticeable than they were previously.

I’m wondering now whether all the issues (the buzzing/vibration, the lumpy downshifts and the drain on engine power at tickover) might all relate to the torque converter? Or perhaps there is something else that I am not aware of? I’m a fairly competent home mechanic (I did the complete conversion single-handed) but I have limited experience with auto transmissions.

Would the apparent lack of 1 litre of ATF, whilst obviously not a good thing, have done any lasting damage? The total capacity is about 9 litres, so yes, it did need the extra added but it's not like it was half-empty or anything. The Defender isn’t used heavily at all, and has only ever towed a 1-tonne trailer once for about 10 miles.

Thoughts and suggestions much appreciated!

Cappo said:

Would the apparent lack of 1 litre of ATF, whilst obviously not a good thing, have done any lasting damage? The total capacity is about 9 litres, so yes, it did need the extra added but it's not like it was half-empty or anything. The Defender isn’t used heavily at all, and has only ever towed a 1-tonne trailer once for about 10 miles.

Thoughts and suggestions much appreciated!

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Give Ashcroft gearboxes a call, they appear to be happy to give owners with gearbox issues advice.

Well, its never a good idea to have low oil level any where, theres no doubt something is going to happen that isn’t good… eventually.

As for the low auto gearbox fluid level, my understanding after 35 years with owning a LR auto the gearbox won’t select or has difficulty in selecting the ratios then overheating etc etc.
As for oil brands, Comma is highly rated, dexron 3 compatible is the grade to use in D1 auto which supersede dexron 2 when the D1 was manufactured alone with the RRc.
The only reason for the auto gearbox fluid loss is a leak, much the same as the fluid in the PSU system..

Good evening fellow Kentish resident, and thanks for your reply. I did actually send Ashcroft an email which was basically a copy of my post above, but they haven't replied; perhaps it's easier to chat on the phone for them so maybe I'll try a call.

I've been puzzled by this heavy buzz/vibration ever since I got the 90 on the road, and never yet found the cause. If it turned out to be the TC then that wouldn't be such a disastrous thing to fix really.

Cappo said:

Good evening fellow Kentish resident, and thanks for your reply. I did actually send Ashcroft an email which was basically a copy of my post above, but they haven't replied; perhaps it's easier to chat on the phone for them so maybe I'll try a call.

I've been puzzled by this heavy buzz/vibration ever since I got the 90 on the road, and never yet found the cause. If it turned out to be the TC then that wouldn't be such a disastrous thing to fix really.

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C@n you remember the oil colour when you ch@nged it, if it w@s more brown th@n red then the
prob is the TC.

I only topped it up Kev, not a full change, although I'm thinking of trying that next. I'll double check the oil colour tomorrow as it's been used a little bit since I posted, so that might give the game away.

R U sure it isn't worn engine mounts?

Hmm, I haven't changed those. The engine seems very solid if you try and rock it (I did that to rule out anything moving and then touching the chassis) so I had assumed that the mounts were OK, but that's a low cost option to try, thanks.

Cappo said:

but there has always been this odd resonant vibration, almost a buzzing, under normal acceleration. It’s quite a heavy noise/vibration, but it’s more of a buzz than a rumble

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I'd suggest that the flex plate might be loose or cracked.. You should be able to inspect the plate, either through the holes for bolts or by removing the inspection cover on the bottom of the bellhousing - depending on which bellhousing you have..

Cappo said:

when stopping the car, the engine seems to die down to very low RPM, almost stalling, but does hold itself and then returns to tickover revs.

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I don't know which ECU system you have, but I'd suspect the base idle sensor if fitted..

Cappo said:

Would the apparent lack of 1 litre of ATF, whilst obviously not a good thing, have done any lasting damage?

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Unlikely IME - comma have a decent reputation, so unlikely to be that IMO..As you say, probably best avoided, but over 1500 miles of light use, in a lighter vehicle - I think you'd be very unlucky to have created issues..

Cappo said:

Lastly, the downshifts seem to be much more noticeable than they were previously.

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I'd change the oil and filter in the first instance, and go from there - I'd flush the cooler too - dirty filthy job, but worth it IMHO

kevstar said:

C@n you remember the oil colour when you ch@nged it, if it w@s more brown th@n red then the prob is the TC.

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+1 - whats the lockup clutch like ? starting to slip ?

Stanleysteamer said:

R U sure it isn't worn engine mounts?

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And/or transmission mounts - they even come loose - ask me how I know !

Disco1BFG said:

I'd suggest that the flex plate might be loose or cracked.. You should be able to inspect the plate, either through the holes for bolts or by removing the inspection cover on the bottom of the bellhousing - depending on which bellhousing you have..

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I once had this happen on a Mark III Cortina!.
The flex plate was cracked and split all around the centre so it was in two pieces but very closely together like a piece in a jigsaw puzzle. It was a firm's car and it was most noticeble when being put into drive where it sort of clunked. Once the mechanic had changed it he gave it to me as my boss was trying to say that it must have been caused by my harsh driving. The mech said that wasn't the reason. My boss had a degree in Mech Eng and changed his mind once he saw it. To look at it you'd be amazed the car drove at all, well I was!
Different car from a different era!

Stanleysteamer said:

I once had this happen on a Mark III Cortina!.
The flex plate was cracked and split all around the centre so it was in two pieces but very closely together like a piece in a jigsaw puzzle. It was a firm's car and it was most noticeble when being put into drive where it sort of clunked. Once the mechanic had changed it he gave it to me as my boss was trying to say that it must have been caused by my harsh driving. The mech said that wasn't the reason. My boss had a degree in Mech Eng and changed his mind once he saw it. To look at it you'd be amazed the car drove at all, well I was!
Different car from a different era!

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Mirrors my experience - it is amazing that they will still drive given the lack of integrity.. but they do Think I still have my "two piece" flex plate somewhere

The modern materials are somewhat more tolerant of flexing, but the technology is the same - it isn't broke, and thankfully no one has fixed it

Cappo said:

Would the apparent lack of 1 litre of ATF, whilst obviously not a good thing, have done any lasting damage? T

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When the box in my D2 was leaking I'd lose that quite quickly, I just kept on topping it up until I got it fixed, I think on occasions I'd lose up to 2 litres. it appears to have done no damage at all.

I haven't worked out how to quote and reply on here so I'll reply in order!

@kevstar - I've just looked and yes, I would say it's more brown than red. I took a picture, which of course doesn't show the colours very well, but I'll try and upload that. Is it worth doing a change, or just biting the bullet with the TC?

@Disco1BFG

• flexplate I can check. That said, it's done this ever since I finished the conversion. It's possibly getting worse tho so that's one to check. But if it has cracked near the centre/mounting bolts I guess I won't be able to see.
• It's the standard 14CUX system. What puzzles me though is that if you rev it and let it return to tickover with the box in Park or Neutral, the engine is fine - it's only when in gear?
• re the oil and filter, as per Kev above, I can change that if it's worth a try
• Lockup clutch - I don't think that is slipping, it will sit at 60mph on the motorway (or more, but that's what I usually sit at) with no slipping obvious
• Engine/Gearbox mounts - will have a look when I get a chance in the daylight

Just to clarify, I don't think it lost 1 litre suddenly, there are no obvious leaks, I think it was my own fault for measuring it wrongly from the start. It's done ~1500 miles with a litre or so short.

Thanks chaps, your knowledge and suggestions are much appreciated.

Cappo said:

But if it has cracked near the centre/mounting bolts I guess I won't be able to see.

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Possibly not, but endoscopes which use a smart phone display are quite cheap on the bay - though the cheapest will probably have insufficient resolution for seeing "up there"

Cappo said:

It's the standard 14CUX system. What puzzles me though is that if you rev it and let it return to tickover with the box in Park or Neutral, the engine is fine - it's only when in gear?

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I can't remember if the 14 has the sensor - it has been over 25 years since I spent any time on LR V8 petrol injuns.. but;

https://colinbourassa.github.io/car_stuff/14cux/

mentions a fault bit for the idle valve stepper motor ... ( under fault bits someway down the page )

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Does the oil smell ? specifically, does it smell burnt ? Colour doesn't sound too bad.. How many miles had the donor disco done ?

As already mentioned, the 3.9 has a idle control valve and should take care of the engines idle speed when a load is placed on it, such as selecting ‘drive’ with an auto or switching on AC if fitted.
It’ is misbehaving (sticking) I believe it can happen and removing the valve and cleaning can restore its operation, but then resetting the ‘base idle’ maybe required, info on that is in the workshop manual.

Tick over shouldn’t drop that far when a load is placed on it , with my engine maybe 50 rpm, so not as low that the engine could stall, anyway the revs are restored instantly back to normality which is around 740 rpm warm, or 1500rpm first starting on a cold engine as always.

Also idle speed is non adjustable as its controlled by the EFI ECU. And base idle is set in the factory so set and stays that way, unless there was some interference with the engine.

Thanks again @Disco1BFG and @discool . The engine/tickover thing is odd, it's only when you have been driving and come to a halt, the downshifts from the 'box have become more clunky, and it somehow seems to drag the engine revs down as you come to a halt. I don't know whether the transmission is dragging the engine down. In every other respect the engine runs well. When it starts from cold, the high revs die back to tickover quite quickly which I think is the correct behaviour.

I'll have a whiff of the oil tomorrow. Re the poor old Disco's mileage, I can't remember but I think it might have been high, 160k rings a bell. When I first looked at it, I thought it was too good to be a donor, but when I looked more closely, there was a massive split in the chassis (well over a foot long) and the bulkhead was rotten as well. And it had a fairly recent MOT!

The 14CUX MUST have a vehicle speed signal. Make sure that's functional and wired to the ECU first. If it's not, if may be your only problem. While the vehicle is coming to a stop, the revs should be held higher (because of the road speed reading to the ECU - from memory, about 1000?) then drop smoothly to idle as you pull up. This is actually done to help smooth out the bump as the auto drops into 1st as you stop, if the revs are too low, it thunks in and lurches a bit.

Rovergauge is a REALLY useful tool to get for 14CUX cars.

There are a bunch of things to set right, before fiddling too much. Setting it up right makes it much easier to tweak the little things. So many of these things have been dicked with by people who are just bodging it up, it's a good idea to sort it out once and for all.

Before I did all these, I would have very unstable idle, sometimes stalling, sometimes high idle and plenty of stalling when engaging D or R.

In park or neutral, Idle should be 700 RPM and in D or R 600 (all when warm and not moving) - The ECU requests these speeds. As mentioned above, you can't adjust it... though people do wind out the idle bypass to crank it up, as a bodge to overcome other issues. Sometimes the fiddle the idle CO pot on the MAF too, to make up for vacuum leaks.

Idle is dramatically affected by even minor vacuum leaks. clean out the breather hoses and "flame trap", including the restrictor in the TEE between the plenum and the big hoses (behind the dizzy), but also make sure the dipstick seal is in place and working and the dipstick tube is into the block tight. Make sure the breather pipes are correctly routed (air is drawn in the LHS rear rocker cover through the tiny bleed to the vacuum hose to the airbox (or through a tiny filter or early cars) then from the RHS front rocker ("flame trap") across to the Tee into the Plenum and over to the Throttle Body. At idle, air is sucked into the plenum through this system, via the restrictor in the tee. The breather system provides a base airflow, which the base idle screw and the stepper motor add onto. The whole breather and idle system can get clogged over time, because the blow-by gasses have exhaust in them and can leave carbon anyway, especially in the cooler areas and the small orifices. A leaking dipstick adds a lot of excess air and if the system isn't working well, the base idle screw and stepper can't function as intended.

Set the timing correctly too, making sure the vacuum advance works (and isn't leaking vacuum) and the air gap for the pickup in the dizzy is correct. I run my timing at 10 degrees BTDC on 95 RON fuel. Check the fuel pressure regulator vacuum hose for splits.

The throttle plate should be within 0.5mm of vertical, measured from the plenum inlet (so top and bottom of the plate to where the hose clamps on). It should be totally closed, but shoudn't stick in the bore. The spindle shaft can leak too, not good. It should NEVER be adjusted to increase idle speed - the adjuster screw is UNDER the plenum and a pain to get too, but usually doesn't need adjusting. The Throttle position sensor needs to work smoothly too (this can be seen in rovergauge, or you can measure it with a meter - the voltages are online somewhere - the 14CUX "learns" this value, to a tiny extent - as long as it's within a plausible range)

Remove the base idle screw entirely and clean the whole path, a few doses of foaming intake cleaner is good (I use Nulon brand, but I think it's an Aus and NZ brand, so seafoam? or Subaru Upper cylinder cleaner) and a long cable tie can get poked down into the plenum orifice. replace the screw afterwards.

AND THEN...remove the air bypass hose and the stepper motor, and clean them out too. lightly lube the stepper - WD40 or similar very light oil is OK. replace the stepper, leave the hose off and block both ends at the stepper housing and throttle body. Alternatively, if you have Rovergauge, press the button to close the the idle stepper a few times and quickly remove the plug while it's closed and the hose can stay on.

While running and warmed up entirely (well into the 80's on Rovergauge), adjust the base idle screw to give you an idle of 500 to 550 rpm with no loads - best done with Rovergauge, because the dash rev counter is inaccurate, but it will sound very low. Really, the lower the better, as long as it's stable. Once that's done, replace the idle bypass hose and plug the stepper back in - and start it up again. It shouldn't take long for the idle to bump back to 700 in P. Sometimes this requires a restart of the engine - turn it off for 20 seconds or so first.

When you turn the engine off, wait a few seconds and you should be able to hear/feel the stepper setting it's base position. When you turn on the ignition, it should open up to a point determined by ECU sensor inputs.

Once that is done your idle should be at the speeds above.... In theory Different software version behave very slightly differently, but I've not seen warm idle speeds different to those on an automatic Land Rover (only TVRs etc and I thnk manual Land rovers are 800RPM?).

After I did all that, my idle was great, except for hot restarts (after sitting for 5 or 10 minutes) would result in stalling when selecting drive. I had a leaking injector - I tested it by installing a switch in the fuel pump feed and turning it off, to stall from fuel starvation each time and it was much better. After repalcing the injectors with new Bosch units, that's fine too. I get rock stable idle, zero stalling and totally smooth transition from moving to stopped and vice-versa.

It sounds like a lot of work, but it's really just a saturday morning Plus they don't ALL need doing on the same day - much of it can be done as you can be bothered.

hi @AllanWorms , thank you for this. I'm reasonably OK on the 14CUX but you're clearly a long way ahead of me! I do have the speed sensor connected up, and I have Rovergauge, so I'll check that that is still working OK. At some point in the past I did run through the base idea setting procedure as well. I'll have a crack at your list when I get a chance.

Dunno about that. I consolidated all the info on the net and in the manual, then filtered out the bullcrap and when through everything in what appeared to be methodical order. I really like the smooth idle and it sounds great - I used to live in fear of it stalling at stops all the time, Or while trying to do a 5 point turn... because 3 isn't easy in a Disco

Do you have oxygen sensors? running a cat tune?

I've since written a new EEPROM for the ECU, after reading the Pistonheads thread. I tweaked the idle speeds, rev limit and the fuelling a touch... I'm a nerd. What can I say

Oxygen sensors yes, and it's running whatever it came with in the Disco which I assume was the original, although we all know what assumption is!!

Small update from me: been in contact with Dave Ashcroft via email, he suggested a few things including dropping the front prop and running it with the centre diff locked. Tried that, and there was a much heavier vibration, like the worst out of balance wheel in the world. I don't know what that indicates yet. Put the prop back on and the vibration went straight away, so obv related to the CDL, but as to how and why, I'm in the dark!