name: Waheed Khan

question: Hi, I have a technical Question that is causing a lot of debate and discomfort amongst many enthusiasts and would appreciate it if you could give me a definitive and technical answer to help me propagate the information.

I hope you will appreciate that the Haldex units are being used by many enthusiasts like myself ( www.wak-tt.com ).

Some of us get our cars power tested on rolling roads and myself I will only run on a 4wd drive rolling road, others pull the haldex fuse and run power runs up to 130mph with the rear wheels stationary.

The Question is I believe that this could be harmful to the haldex others say there is no harm.

Can you confirm or deny what you believe, I'd appreciate a technical explanation if possible. If you think it should be ok or its bad I'd just like to be able to confirm to the other owners.

your help in clearing this up would be most appreciated. regards Waheed

car: Audi TT

submit: Send

Hi Waheed,

Yes, we definately appreciate all the enthusiasts out there with the Haldex coupling :)

You are also right regarding your question. To pull the Haldex fuse to remove the AWD function is fine when it comes to lower speeds but the speeds that you are talking about is definately not good for the system since the driveshaft will not stop spinning just because they are removing the fuse. Removing the fuse makes it easier on the Haldex coupling but at high speed it is still getting some beating.

Best Regards,
Mats Johansson

HI Mats,

 thanks for the quick response, can you offer any more details.

 Most appreciate its a wet clutch system with 2 sets of plates that are pushed together the problem is the debate around this is if the fuse is pulled, the plates are seperated, the actuators are disabled ,  so what is the concern about damage?

 Is it not the case that there is simply a drive shaft spinning with not torque being transferred to the rear within the box?

 The other question related to this is your website FAQ states that 2 wheel towing is allowed but see your manufacturer for recommendations.

Is there a maximum speed or duration of towing that Haldex recommend for safety?

 many thanks for your time, sorry if I am asking for more technical details but these enthusiasts are highly technical.

 Plus I am also interested in the engineering side of it. :o)

 best regards

Waheed

Johansson, Mats - Detroit USA" <Mats.Johansson@Haldex.com> wrote:

Well, the concern is that unless they remove the drive shaft there will still be rotation sent in to the coupling.

The discs (7 of them, not 2) is separated but with the high rotation of the driveshaft the pistons inside the coupling will start pumping the oil around in an open loop in the coupling and in high speeds there will be a slight pressure (drag torque) that will cause the discs to press together. If you are only using one set of rollers that means that the coupling tries to transfer torque to the rear wheels that are strapped down and not moving and the coupling, driveshaft and ptu get more loads then they are ment for. (got a bit confusing there, just get back to me if you do not understand what i mean.)

 

When it comes to two wheel towing i can unfortunately not answer you regarding the limits. We (haldex) manage very high speed for a very long distance but there is more parts then Haldex on the powertrain so we have to follow the vehicle manufacturers recommendations.

 

_________________________________________
Mats Johansson
Engineering & Quality manager

There is this text on one of the mechanical specification pages ..

 "To ensure the function and minimum activation time, the annular pistons are constantly in contact with the rollers via a low pressure, maintained by a small electric pump in the coupling. The pump works only when the vehicle's engine is running. The coupling is deactivated when the engine is off, making it possible to tow the vehicle with one axle lifted. "

 Doesnt this mean that the pump wont be running when the fuse is pulled?
regards

Waheed

The ELECTRICAL pump will not work when the fuse is out but the mechanical diff pump will still be working.This is not a problem when the vehicle is being towed but on a testbench with only one set of rollers in high speed it can create a problem.

 Best Regards,

Mats

Many thanks Mats,

 As I understand it, when driven on rollers the input shaft is turning and the mechanical pump activated because of the difference in rotation between input and output. This input shaft rotation is where the problem occurs in the hi speeds achieved against a stationary output shaft.

 When Towing, front wheels are off the ground,  the input shaft is stationary and the output would be turning because the rear wheels are being turned. But the pump is driven by the input shaft so is not running and this is ok for the short duration and low speed during towing.

 Does that sound about right?

:o)

 best regards

Waheed

I think he got it! ;)

_________________________________________
Mats Johansson
Engineering & Quality manager

HALDEX TRACTION AB
44708 Helm Street
Plymouth, MI 48170
U.S.A.

PHONE +1 734 737 0435
DIRECT +1 734 737 0433
FAX +1 734 737 0436
CELL +1 248 910 9489
E-MAIL mats.johansson@haldex.com

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