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The Reason Why CV Boot Clamp Failure is Common

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thetwistedsock   
Thu May 15 2014, 03:58pm
Member No: #35500
Joined: May 12 2014
Location: Staffordshire
I own a 1.6 HDi Loeb but this information will apply to all models sharing the same driveshafts and if other variants also use the same clamping method then the information is also relevant to those.

First of all I would like to say that I have professional experience from working with driveshafts, I have an additional specialism with CV boot testing. I have recently had to replace both large clamps on my outboard boots.

The type of clamp used is known as a multicrimp band. This type of clamp is used for sealing systems because it offers a more even clamping force distribution around the circumference of the boot/joint interface. The typical clamps are manufactured with surfaces that overlap and are drawn together using one of a few methods which draws the two overlapping ends of the circle together to reduce the internal diameter - hopefully that makes sense.

The multicrimp band is closed using a collet (I can explain this separately if needed) which slightly deforms the band in about 24 positions around the circumference. It also weighs less and is more suitable for an automated assembly process (so costs less and costs less, respectively).

The type of multicrimp band I found in use on my car is a strip of aluminium formed into a circle and then fixed together using a resistance weld (spot, or projection - I can't quite tell although if it's projection welding then the projections don't conform to BS EN standard sizes).

The expansion and contraction of the CV joint and hence the multicrimp band over the years has led to fatigue failure through the weld. Please see the attached photos. The type of band I'm used to seeing is either of solid construction or each end is joined using what we call a puzzle lock (sorry, no photos of that - but imagine two mating shapes and you'll get the idea).

I replaced these original clamps last week with some Oetiker stepless ear clamps. This type of clamp is robust and manufactured from stainless steel, however there is a closure mechanism which protrudes about 6mm from the surface of the clamp and could potentially have been unsuitable due to the enhanced "swing" which is the design space allowed for such a closure.

The internal diameter of the original clamps was 89mm. The replacement ones I used were 90mm and this dimension is before closure. If I had a greater selection available to me I would have chosen 92mm or 93mm, I should also say that the clamps are 10mm width (same as the original) and 1.0mm thick.

The outside diameter of the large end of the boots exceeds the internal diameter of the clamp which makes reassembly difficult, or I'd say challenging. It is only possible to reassemble by fixing the clamp to the boot and then fitting the boot/clamp assembly over the end of the CV joint.

This is all doable with the driveshaft still assembled to the car. A suitable amount of grease was inserted into the CV boot prior to reassembly, the grease used was Olistamoly 2LN. There is a tool to use to close stepless ear clamps, I have access to a variety of these but it's possible to improvise and use some blunt pincers if necessary.

I can upload some photos of a replaced clamp if it would be useful?

I hope this is good information, if so I can put some more up another time.

The last thing I'd like to say is if possible please think twice if you're tempted to change the CV boot for a non-original design (outboard in particular). CV boots are validated to each application and variant. Third party ones might work well - if anyone has changed theirs I'd be interested to know how they have performed.











5 User said Thank You to thetwistedsock for this Post :
 Web Admin Only (16 May 2014 : 01:40) , Honest (16 May 2014 : 14:09) , Ant1979 (17 May 2014 : 01:27) , Grumpy GrandPa (07 Jun 2014 : 08:01) , mortartube (25 Feb 2016 : 07:40)
Grumpy GrandPa   
Sat Jun 07 2014, 08:01am
Member No: #10746
Joined: Aug 28 2009
Location: Hull: UK City of Culture 2017
Mine was dead.
Now replaced, many thanks
 

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