Slipping clutches in PD TDI engines are not a problem of the clutch itself!

Hi,

As the title suggests, clutch slippage is usually not a problem with the clutch itself.

Okay, let's go through it step by step. For the past 70,000 kilometers, I've been constantly dealing with a slipping clutch. In the spring of 2005, we got a new one, but then, after 20,000 km, it started slipping again last week.
So, another one yesterday. Everything seemed okay, but after 150 km, the fun was over again. What's the point of this nonsense? Since I didn't assume a triple material defect, the error must have been located elsewhere.
The error occurs consistently when temperatures are between -5°C and +5°C.
So, I took a closer look at the issue and found that the residual pressure from the clutch slave cylinder on the release lever was significant. I shimmed the cylinder by 4mm, and the slipping stopped. In addition, various starting problems have also been resolved.
So, it looks like a new clutch cylinder will probably be needed.
However, there's still one annoying issue. The inconsistent pressure point is frustrating. I also think that's still... I promise.

Bertil wrote:

I shimmed the cylinder by 4mm, and the slipping is gone. In addition, various initial setup problems have also been resolved.

Hi Bertil,

If I understand correctly, the clutch should now disengage later.
What kind of difficulties did you have getting here?

How is the automatic adjustment of the clutch actuation mechanism actually implemented?
It's not just the hydraulics that are adjusting (the fluid volume between the donor and receiver pistons), and you'll soon be having the same problem again, right...?

Quote:

However, there is still one unpleasant issue remaining. The changing pressure point is annoying.

Have you observed this issue in other TDIs as well, or just in yours?

ulf wrote:

...if I understand correctly, the clutch should now disengage later?

No, the automatic clutch play adjustment takes care of that.

Quote:

What kind of difficulties did you have getting here?

From choking to vomiting.

Quote:

How is the automatic adjustment of the clutch actuation mechanism actually implemented?

Just like with the cable coupling. "Using a compression spring to apply a specific preload to the mechanism."
If this spring is too strong, the clutch will slip because it disengages slightly (it's like keeping your foot on the clutch pedal). If it's too weak, the clutch will engage very early or may not disengage properly. This mechanism must therefore be precisely adjusted to the specific printing plate being used.

Quote:

It's not just the hydraulics that are adjusting (the fluid volume between the donor and receiver pistons), and you'll soon be having the same problem again, right...?

I only adjusted the spring pressure with this temporary "makeshift" measure to be able to make a clearer statement. I will replace the receiver cylinder.

This morning, when I was at the mechanic's, I was quite surprised. The wrong clutch slave cylinder is installed in my vehicle. It should be a 1J0 721 261 H, which has now been replaced by the 1J0 721 261 J. However, I have a 1J0 721 261 D installed. We weren't able to quickly determine which vehicle this slave cylinder belongs to. In any case, the pressure pin on the "D" type is about 2 cm longer than on the "J" type. This means that the clutch was always in a slightly disengaged state. Therefore, the pressure plate has lost some of its clamping force.
Unfortunately, I cannot currently determine whether this is a modification made by VW or whether the old receiver cylinder was incorrect.

Quote:

Have you observed this in other TDIs as well, or only in yours?

Yes, for all those who experienced clutch slippage (or later experienced it).
I'm just stating that there are likely connections between them. I'm definitely sticking my neck out with this statement.

Bertil wrote:

...I have a 1J0 721 261 D installed. Unfortunately, we were unable to quickly determine which machine this cylinder belongs to. ...

From a VW Transporter, the good piece emerges.

Bertil wrote:

From a VW Transporter, the good piece

emerges.
Ah yes, those who drive vans have the upper hand...

But seriously: Has your clutch actually disengaged earlier because of this, compared to other cars, or did the adjustment mechanism compensate for the shift?

hi,
I just replaced the clutch, including the flywheel, on my T4 (engine code: AJT, gearbox code: DUJ).
My mileage is 172,000 kilometers.
and at 110,000 km, the clutch, pressure plate, and release bearing were also replaced.
In both cases, the reason was that the clutch was slipping.
Now I've come across this thread and I think the receiver cylinder might be the cause of the problem in my case as well.
and my part number is also 1J0 721 261 H.
Should I also have the 1J0 721 261 D part installed in my car?
I'll take a look!
if so, then ...

Hi Leo,

ulf wrote:

But seriously: Has your clutch actually disengaged earlier because of this, compared to other cars, or did the adjustment mechanism compensate for the shift?

The clutch disengaged when I just put my foot on the pedal. Now I have to press the clutch pedal down extremely far before it disengages.

@leo_b

You can have 261D from me. Is Tip Top okay?

I compared both cylinders in terms of their function and dimensions. The "D" cylinder is 5-10mm longer. After I installed the J, the difference was no longer as significant as it was before the installation.
Now the clutch engages much earlier, and the engagement point no longer shifts. The feel of the pressure is completely different; it's very soft and not as stiff as before.

Good night!

Bertil wrote:

The clutch disengaged when I just put my foot on the pedal. Now I have to press the clutch pedal down extremely far before it disengages. Bitte gib den Text an, den du übersetzt haben möchtest. Now the clutch engages much earlier, and the engagement point no longer shifts. The feel of the pressure is completely different; it's very soft and not as stiff as before.

Okay, then the early engagement when pressing the pedal should actually be a good indicator to distinguish between correctly and incorrectly assembled vehicles.

And the other clutch candidates you've driven must also have had a clutch that disengages very early...?
If so, that would be worth a significant entry in the error database .

Could it be that the well-known slipping problems with the 74 kW motors are all (or mostly) caused by faulty clutch actuator cylinders? That would be something.

ulf wrote:

Okay, then the early engagement when pressing the pedal should actually be a good indicator to distinguish between correctly and incorrectly assembled vehicles. And the other clutch candidates you've driven must also have had a clutch that disengages very early...? If so, that would be worth a significant entry in the error database . Could it be that the well-known slipping problems with the 74 kW motors are all (or mostly) caused by faulty clutch actuator cylinders? That would be something.

I have the same suspicion about my AJT engine with 65 kW.
What supports my suspicion is also the fact that some other drivers of this type of vehicle are experiencing the same issue in the T4 forum.

Hi Leo,

Since I'm not familiar with hydraulic systems, my question is:

Is the actuator cylinder located on the outside of the transmission, and if so, can the part number be identified without disassembly?
Sure, here's the translation:

'I drive an AXR too...'
But so far, no clutch slippage, despite the increased power and 90,000 km of driving school use.

Hati wrote:

Since I am not familiar with hydraulic actuation, my question is: Is the actuator cylinder located on the outside of the transmission?

Yes!

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...and if so, is it possible to identify the equipment number without disassembling it?

Yes!
The only thing in the way is the air conditioning unit.

Quote:

Sure, here's the translation: "I drive an AXR too..." But so far, no clutch slippage, despite the performance increase and 90,000 km of driving school use.

Then, keep your hands off. Never touch a running system.

Ulf wrote:

Could the well-known slipping problems with the 74 kW motors be caused entirely (or mostly) by faulty clutch cylinders? That would be something

.

No, not just that.
By the way, this doesn't only apply to the 74kW engines. I know enough drivers of 96 + 110kW cars who have the same problem.

Yesterday, I went to the Miotorshow in Essen, and I visited ZF SACHS Race Engineering to inquire about a reinforced pressure plate and clutch disc for my AXR. Supposedly, according to various parts dealers, they don't exist. But that was wrong. They are available for almost every car, including my AXR. The smallest combination (300Nm) normally costs just under 700 Euros (currently, they are offering a 20% discount).

But let's get back to the main topic. Why do so many 74kW clutches slip? Very simple:
The EUH gearbox (used in the AXR, among others) is designed for 250 Nm, and the Sachs clutch is also rated for that. In theory, this shouldn't be a problem, as the AXR (and also the ATD) are "detuned" to 240 Nm in the Polo/Golf (the ATD has 250 Nm in the Passat). However, there are still some production variations where the actual power output significantly exceeds this. (Mine, for example, measured 119.5 hp on a dyno and approximately 115 hp according to KPower). When it's cold and oxygen-rich, the engine can sometimes produce a few extra horsepower and Nm, which can ultimately overload the clutch. It is therefore quite possible that a motor that is "running rich" can immediately overload the clutch.
So, it's not a clutch problem, but an engine problem!

With the 6-speed transmission, the torque limit is 350 Nm. I don't have access to the ARL data right now, but I believe the standard torque value is 320 Nm.

Okay:
"The PD TDI engine could definitely handle significantly more power if the power transmission (clutch/gearbox) were designed to accommodate it." However, this would represent a significant additional financial burden and would make the cars even more expensive.
2. The components used are designed and manufactured with extremely tight tolerances. The potential variation in the series production already pushes these parts beyond the acceptable limit.
3. It is not impossible that there is a manufacturing defect (as in the case of mine).

Those who are looking for a reinforced clutch for their car can visit the WebCat from ZF Sachs. However, the reinforced clutches are only available through a workaround. The manufacturer of these parts is called SRE (Sachs Race Engineering), and the feature is disabled by default.
Okay, put a checkmark next to "SRE" (see the image)!
The parts can then be ordered from every ZF Sachs dealer.


Here's something else about the receiver cylinder.
According to the Sachs technician, the release cylinder is designed to match the pressure exerted on the pressure plate, and failures can definitely occur due to faulty release cylinders. However, he is not aware of any such case!
Based on the specifications, both components I mentioned should have the same mechanical dimensions, except for the pressure springs used to compensate for clutch play, which are different.

Bertil wrote:

By the way, this doesn't only apply to the 74kW engines. I know enough drivers with 96 + 110kw engines who have the same problem

.
But they still have some additional reserves beyond the nominal maximum of the input torque, which is 350 Nm:
96 kW = 310 Nm
110 kW = 320 Nm
117 kW (Ibiza Cupra) = 330 Nm, which on paper still provides double the reserve (20 Nm) compared to the AXR (10 Nm).

By the way, according to the documentation, the 6-speed transmissions use a hydraulic release bearing instead of an external clutch release cylinder and release lever.

But, in the 96 + 110 kW drivers you know, does the clutch also slip noticeably early on, perhaps? Assembly error?

Quote:

117 kW (Ibiza Cupra) = 330 Nm, which on paper still provides double the reserve (20 Nm) compared to the AXR (10 Nm).

Really??

330 Nm + 6% = 350 Nm
240 Nm + 4% = 250 Nm

Quote:

But, in the 96 + 110 kW drivers you know, does the clutch also slip so noticeably early -> possibly a mounting error?

No, not all of them, just a noticeable shift in the pressure point.

Bertil wrote:

330Nm + 6% = 350Nm 240Nm + 4% = 250Nm

Yes, yes, the old story about comparing differences or ratios...

Quote:

But, in the 96 + 110kW drivers you know, does the clutch also slip so noticeably early -> possibly a mounting error? No, not all of them, just a noticeable shift in the pressure point.

Hm, what exactly do you mean by that?
The fact that it disengages at different times, sometimes earlier and sometimes later (but never extremely early), means you can never really get used to the clutch.
or that the pedal travel between full disengagement and full engagement is too long?

ulf wrote:

Yes, yes, the old story about comparing differences or ratios...

Unfortunately, that's the case...

Quote:

... The fact that it disengages at different times, sometimes earlier and sometimes later (but never extremely early), means you can never really get used to the clutch. ...

Exactly that... However, in some cases, these couplings also separate very early on.

I've gathered even more information about the receiver cylinder.
The part number 1J0 721 261 D was actually installed in the ATD/AXR models with the EUH (old AKTE version from 01).
Later, the receiver cylinder was replaced with a "... H". This should reduce clutch slippage.
The ... H was then exchanged for the ... J. The D engine was then only used in the Volkswagen Transporter.

So, no mistakes!
Nevertheless, I should have replaced the clutch slave cylinder with the new one.

Bertil wrote:

The fact that it disengages at different times, sometimes earlier and sometimes later (but never extremely early), meaning you can never really get used to the clutch, ... Exactly that... Sometimes, these clutches also disengage extremely early.

Ah, then at least I can feel relatively safe (for now) . . .

Do you have any ideas or suggestions as to where the "variations" in the clutch engagement point might originate in 6-speed transmissions (with the slave cylinder located on the release bearing)?
Air in the hydraulic system should, in my opinion, rather lead to delayed engagement and a large slip range.