Brief Encounter II - The Sequel

Tell us your ongoing tales and experiences with your French car here. Post pictures of your car here as well.

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CitroJim
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Post by CitroJim »

xantia_v6 wrote: I don't follow your reasoning there, I seem to recall that the transmission fluid was not burnt?
The oil had very recently been changed before the 'box finally died. That was Ok but of course there was no telling what the old, original oil was like.... That could well have been well toasty. In fact, it's likely it did only in the order of a few hundred miles on the new oil.
xantia_v6 wrote: To digress a little, you earlier said that it is believed that the lock-up clutch breaks up, causing the filter to block, and the pump to fail. I wonder if it happens the other way around, as the lockup clutch is (I think) hydraulically operated, so a loss of pressure due to a worn pump would cause the clutch to overheat and break up, blocking the filter...
That's very possibly how it happens :) A torque convertor needs a copious supply of oil to keep it cool so any reduction in flow, for whatever reason, will make it run hot and stress the clutch.

Hopefully, in a few days, we'll know a bit more...

admiral51
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Post by admiral51 »

Just been having a look in Clubxm down thread and found this comment made by a certain Citrijim in regards to V6 autobox..............................

"I will update the thread on Club-XM as soon as there is concrete news on the state of my gearbox. I have new concerns about the lock-up clutch in the TC breaking up :twisted: "

Now thats really spooky :lol: :lol:

Colin

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CitroJim
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Post by CitroJim »

admiral51 wrote: Now thats really spooky :lol: :lol:
:lol: :lol: :lol: How ones words can come back to haunt...

The only "concrete" news so far on the "concrete" is that it's not. A sample I left to dry as a test has gone soft and powdery so it should be no problem to flush it out :lol:

Intrigued to know what it is/was though.

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Post by CitroJim »

I now know why the gearbox died (or rather what is very dead inside it) but first thing's first...

Before I could split the 'box away from the engine, I had to firmly prop the engine on blocks so that I could release it from the crane and use the crane to lift the 'box off.

I put a stout baulk of wood on the flat area just ahead of the bellhousing

Image

And two props at the front:

Image

This arrangement allows the engine to sit very steady and steady enough to remove the 'box. before the 'box can be removed, the hose to the cooler has to be disconnected and then the TDC sensor is exposed and this must be removed. Then it's just five big bellhousing bolts, a careful lift and pull and...

Viola :D

Image

Then, after an hours-worth of careful cleaning with the 'box hanging high on the crane to ensure no contamination when opened up, it was time to strip and finally reveal the problems within.

Sure enough the oil filter is blocked. No surprise there. Interestingly, there are no magnets on the filter case :?

There was a lot of debris in the bottom of the gearcase, in the region of the filter intake.

Image

But where had it come from?

From clutch B, that's where...

Image

The friction material has COMPLETELY disappeared :shock:

Here's a close-up....

Image

You can see bits of friction material but basically, what now looks like a plain steel plate should be friction material.

Clutch B is one of the main clutches and is engaged in every gear except 2nd and 4th. You can also see from the picture that the drum of Clutch B is jammed against warped plates. This clutch has been very hot.

The rest of the 'box looks OK although the oil pump shows signs of a little wear; the peaks of the teeth are worn and all other clutches show signs of wear compared to my other spares 'box.

I reckon what happened is that the debris from the wearing clutches started to clog the filter, and with a worn pump, oil pressure fell, Clutch B started to slip and burned itself out and triggered a chain-reaction in that more and more debris circulated in the oil to block the filter further until it blocked completely and the 'box died. I think the amount the other clutches appear to have worn is normal enough for the mileage. Clutch F shows wear to the extent that the diagonal grooves that are normally seen on clutch friction plates are only just visible.

So, the spares 'box will be dismantled again and all the clutches and the oil pump internals transferred into my cases. I'll also not take a chance with the Torque Convertor as it too is likely full of debris from Clutch B although I don't think it is the root cause. Had I not found Clutch B wrecked, the TC would have been prime suspect.

Good job I have a spares donor 'box as the parts mine requires would cost an arm and a leg.

I'll try to dismantle Clutch B further but it's so well jammed together, it may not be willing.

At last we now know how a 4HP20 dies at high mileages. Seems 150K is the top whack for it :( At 100K I reckon a new set of clutches and oil pump/filter would be prudent as a preventative measure.

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Post by addo »

:shock: Good work with the forensics, again.

I wonder if (lockup) clutch disc friction material is identifiably different to the transfer clutch friction material? If it were, and there was a way to sample sludge with the gearbox in-situ, diagnosis would be simplified.

What better way to kick off a Sunday morning than some intelligently poised gearbox pr0n? :twisted: I reckon it's a great thread.

Cheers, Adam.

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Post by Deanxm »

Good, well bad news actually, but im sure you know what i mean.
All has become clear, regular hot oil changes would help keep this build up of clutch sludge in the filter to a minimum, thus retaining hydraulic presure to the clutches which stops slipage and hence reduces the rate of clutch wear which in turn slows the oil contamination and so on and so on................
Also starting to make sense why citroen will throw an entire box away if the oil is black and burnt, black burnt oil= overheated and now dead clutches with the whole box contaminated as a result.
The next question will be then how much is a refurb kit and what does it contain? i would guess all clutches, gaskets and oil seals and in the case of the HP18 a brake band too.................your right, sounds expensive :( although i may be surprised yet :lol:

Good work sir

D

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Post by red_dwarfers »

What a breakthrough! Fantastic work Jim :D

Regarding refurbishing a 'box, how many arms and legs would we be talking :?:

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CitroJim
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Post by CitroJim »

red_dwarfers wrote: Regarding refurbishing a 'box, how many arms and legs would we be talking :?:
I hate to think Kev :twisted: I had to sit down with a stiff cup of tea in front of me when I enquired the cost of a replacement oil filter and gasket set. From that I've just about recovered..

Maybe when I'm feeling strong I'll give them a call but will ensure medical assistance is on hand at the time...

Thinking on, I'm now wondering if the whining noise so often reported just before these gearboxes expire is in fact the clutch complaining rather than the oil pump?

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Post by xantia_v6 »

So, is the total lack of drive in a failed box due to lack of oil pressure, or lack of any transmission through clutch B?

And how is clutch B actuated?

I am not convinced that oil changing is much of a preventative it the filter is not changed at the same time.

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Post by Deanxm »

You may be right about the oil, but having the box running in crystal clear fluid rather than brown fluid full of clutch dust cant be a bad thing.
I would say its a lack of hydraulic pressure that would cause the clutch to burn out like that, you can see large chunks of lining in the bottom of the box around the filter from where the clutch has failed suddenly, maybe due to massive heat, i dont know if im right but has the backing from the clutch plate blued and cracked? it looks like it.
I would also think that pump failure is highly unlikely, they are built like brick out houses and will take a great deal of punishment.
I wonder also if you can get the clutches relined???.....................

D

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Post by xantia_v6 »

A thought... The whining sound would probably be caused by the pump cavitating due to pulling against a vacuum cause by the restriction of the blocked filter. It is not clear why the noise should stop when the transmission dies, maybe some seal fails, allowing air into the inlet of the pump? or maybe a dry pump won't draw enough of a vacuum to lift enough oil to seal the gears?

And another question.... It appears that your clutch B is jammed, is that just a side effect of dismantling, or was it already jammed?

And a request... It looks like I will be changing the transmisison filter in at least one of my cars. Can you provide an edited edition of this blog (or just a set of bullets), with just the essential steps?

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CitroJim
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Post by CitroJim »

That's most likely for the whining sound. It stops because with an increasing blocked filter it and the torque convertor runs dry.

Clutch B was jammed as a result of it failing and not because of my dismantling. It's not hard to see how it happened either.

Clutch B transmits drive from the torque convertor to the 1st epicyclic sun gear in first, third and reverse gears. It is engaged (hydraulically) also when in neutral and park in anticipation of either first or reverse being selected.

Clutch B relies on good oil pressure to operate properly and given it has the job of transmitting the most torque (take-offs in first and third gear kickdowns) it works hard and it only needs a bit of wear on both its plates and the oil pump to start to slip udner heavy load. It is also telling that Brake F (second epicyclic sun gear brake) is also badly worn as this clutch (for it is a clutch despite acting as a brake) is engaged in first and second gears.

Clutch E (which transmits drive from the TC to the 1st epicyclic planetary carrier) is barely worn but then again, it has a comparatively easy life just being engaged in 2nd, 3rd and 4th gears.

I've not had a chance to look at the other brakes (C and D) just yet but would expect to find them OK as D is the reverse brake and C 1st epiclyclic sun gear brake, only operative in 4th gear.

So what happened? Clutch B works hard. It wears, clutch dust builds up in the oil and the filter begins to clog, this and wear in the pump reduces oil pressure which in turn, reduces the operating pressure for Blutch B. It slips more, wears more and and a vicious circle starts. Finally, it slips so much and gets so hot that all the friction material is shed and the plates weld together.

Changing from third (where Clutches B and E are both engaged) to fourth should release Clucth B and apply Brake C. If Clutch B is welded together, the application of Brake C (which works on B's drum) will cause the plates in B to warp and distort and ride the drum as I found.

As your 'box is occasionally slipping Xantia V6, I reckon yours is showing very early signs of being on the way out and likely it is Clutch B that is slipping. Because of how Clutch B operates and it's role, a rough change from 1st to 2nd gear may be a sign it is wearing and slipping.

The good news is that apart from Clutch B, the rest of my 'box is undamaged and in good condition. I shall therefore only replace the clutch plates and naturally give the casings a good clean to get rid of the debris. Luckily, the filter has done a good job as there is no sign of debris past the filter whatsoever.

So, I would advise that any 4HP20 approaching 100K or beyond but still working is likely to just need new B and F clutch plates, a new filter, a gasket and a good clean-out.

I'll try to get a price for new clutch plates in a while.

I'm in the process of writing up how to strip and overhaul a 4HP20 on my website but there are no short-cuts. It's and engine out and a full gearbox strip to get at the filter and the clutches. The website will explain the gearbox but not the engine removal. I'd be happy to write up the procedure. It's long and tedious. I reckon to do this maintenance on a gearbox it would take a good week and that's with no "value addeds" being done whilst the engine is out, such as cambelt, water pump and so on.

It's not hard to see why a gearbox failure on a V6 is so costly in labour.

EDIT: Error on the function of Clutch E corrected in the text above.

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Post by addo »

Great work; I'm loving every minute of this. It would be excellent to see a similar thread on the AL4.

Sure they're complicated - but think of the savings overall!

Regards, Adam.

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CitroJim
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Post by CitroJim »

The AL4 is very similar Adam, both use the same Simpson (or Ravigneaux) epicyclic gearsets and have clutches and brakes that do the same jobs.

For Clutches B and E in the 4HP20 read E1 and E2 in the AL4 and for Clutch C read Brake F1

The two other brakes in the AL4 are bands and are F3 and F4

So basically, what goes for the 4HP20 also applies to the AL4. I would also surmise the AL4 is at the same risk of failing at high mileages in much the same manner as the 4HP20.

Do you have a copy of the AL4 Training Manual Adam? If not, I can email you a copy but it's big at 1.2Mb.

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Post by CitroJim »

Not a lot done this evening but I did striop down the remaining clutches and found (as expected) Brake C and Brake D to be fine.

In dismantling Brake D (reverse gear brake) I find I need to make up a special tool to evenly compress its diaphragm spring to pop it's retainer clip back in.

Here's a shot of the burned Clutch B plates. Two still have some friction material intact and it looks as ift is was not havily worn, which supports my thoughs on failing oil pressure as the root cause. Two plates are still firmly welded together!

Image

Sorry it's not the best of pictures as it's hard to capture it fully but on the plate in the foreground you can see some grooved friction material, just!

I found the Clutch B drum is damaged beyond reuse due to the B plates riding over it. In the picture below, the damage in the form of grooves is clearly visble as well as signs of heating.

Image

I hope to have the 'box rebuilt over the Easter break. The casings are now empty, just about, and ready for some intensive cleaning.