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front diff mount strengthen set - to bolt on


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Hi,

 

during christmas holiday I realised this diff mount strengthen set - to bolt on.

It's for my not broken front diff mounts. Any assessment is welcome? Is it an improvement?

 

Ciao Marco

 

 

 

 

 

Edited by Z320
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Looks very nicely engineered. Would be interesting to see how it transfered the loads from the diff

Cheers

Tim

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Of course your part will strengthen the area of the front mount. And that is very good.

 

Keep in mind, though, that it is not the mount, itself, that breaks.

 

What happens is that the right-front pin (stud) moves- from the twisting torque of the differential.

This results in the base- around the pin- cracking.

That base crack needs to be welded shut, and reinforced with a base plate over top of the weld, and around the pin.

 

Once this is accomplished, your reinforcement block will reduce future stress on the pin.

Edited by Sapphire72
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Hi Marco,

You have been busy:)

The clamps will limit flexing of the plate as a result of the bending moment that the pin exerts on the plate to some degree, which is good.

The advantage of you nice design is also that no welding is required, which is a big plus.

 

It does not adress poor weld geometry/finish, especially around the pin, which promotes fatigue cracking.

It also does not bridge the plate to the cross member, and this is what the welded plates do: they make a strong box section of an otherwise very flexible design.

The resultant limited movement (from loads) results in lower localized stresses thus reducing the risk of fatigue.

This is why I feel the welded box is a better solution.

 

Regards,

Waldi

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Re the nylock nut in the third photo. I believe it is not considered good practice for the bolt to be flush with the top of the nut - there should be a minumum of one full thread showing according to the ISO design guide and industry guidance is for a minumum of two full threads.

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Re the nylock nut in the third photo. I believe it is not considered good practice for the bolt to be flush with the top of the nut - there should be a minumum of one full thread showing according to the ISO design guide and industry guidance is for a minumum of two full threads.

In aerospace I believe it is 1 1/2 threads exposed... Any more adds weight any less and it is considered unsafe.

 

Roger

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Rogger I have never heard of this before, they don't say these things for no reason, but why should it make a difference, if the nylon area has fully covered the thread?

 

always learning here!!!!!!!!!!!!

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Nicely machined brackets but as stated wont make a ha`porth of difference to the actual problem where the front right hand pin gets punched upwards and the rear left hand pin gets pulled downwards due to torque action though it may stop the rear left bracket splitting at the base when the pin gets pulled down.

Stuart.

post-3753-0-25940300-1515332329_thumb.jpg

post-3753-0-78468800-1515332329_thumb.jpg

Edited by stuart
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Hi together,

 

without any doubt welding is the best to do,

but these mounts on my TR4A IRS are not broken and there is no need to repair them.

 

And it seems to me, confirmed by your ansers (thanks),

that welding them with the body on the frame is only half the improvement.

 

Special thank to Shapphire for the advice to strength the welding around the pin

AND to add a base plate over the weld. I would do that on top of the "bridge". Not easy but I have got an idea.

 

As long as these mount are OK I use my clamps and hope for some advantage from that

and do not open a new project, following my loving wife's advice: repair nothing that is not broken.

 

Dear RobH, thanks for your interest and adcive. I it is obvious you own no IRS and never worked on one.

This lovely construction and the too short threads are a faulty construction of the engineers of this car.

 

Ciao Marco

Edited by Z320
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Nicely machined brackets but as stated wont make a ha`porth of difference to the actual problem where the front right hand pin gets punched upwards and the rear left hand pin gets pulled downwards due to torque action though it may stop the rear left bracket splitting at the base when the pin gets pulled down.

Stuart.

attachicon.gifMarks TR5 071 (600 x 450).jpg

attachicon.gifCopy of Marks TR5 090.jpg

It seems like the torque reaction would pull the right pin down, not push it up.

Berry

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Hi Berry,

looking rearwards at the input to the diff. the input pinion is rotating clockwise.

If you apply sudden power or lock the wheels with power on then the offside of the diff will want to rise and so push the pin upwards.

 

 

Roger

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Hi Berry,

I can see where you are coming from as most reaction is against the mover.

 

However I think this is not the case. The CW rotation of the propshaft wants to lift the stud but the freedom of movement removes the forces.

If at some stage it is not free to rotate - the inertia of hard power on etc - then the force will go upwards.

 

Roger

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Rogger I have never heard of this before, they don't say these things for no reason, but why should it make a difference, if the nylon area has fully covered the thread?

 

always learning here!!!!!!!!!!!!

OK thats Logical, thank you.

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Roger is correct on the torque reaction question. It can be difficult to picture, but it actually depends on whether the unit under consideration is a source or a "consumer" of the torque.

 

At the pinion, a diff is a consumer of torque. At the output half shafts, it is a source.

 

Ed

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Roger-Maybe I am overthinking this situation. If you are drilling a hole(chuck turning CC) with a handheld drill motor and the bit becomes bound in the hole, the torque reaction will cause the drill motor to rotate CCW. In this example, the chuck is the driveshaft/pinion and the drill motor is the diff case.

Berry-Not convinced that the light in the refrigerator goes out when the door is closed.

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Hi Berry,

In your drill scenario that is correct. The drill goes CW, The drill bit jams and the work piece does not move so the drill/motor must go the other way (CCW).

 

If you had the work piece attached to a long pin and the pin is attached/welded through a plate (like the diff bridge pin) and you start drilling there would be a load trying to push the pin out.

This pushing force is equal (ish) to the cutting forces with the bit/metal.

 

If the bit suddenly jams you would have all the force of the drill motor instantaneously hitting the pin.

OK the drill motor body would eventually try to go the other way but only after the damage is done.

 

Repeat this a 1000 times and the pin will come out.

 

Roger

 

And yes, the light stays on.

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Dingle--

 

In your drill analogy, it would be better to consider the drill motor as the car engine, the drill bit as the drive shaft, and the workpiece as the diff. With torque, there will be an opposite rotation of the drill motor (engine block), but the workpiece (the diff) will try to rotate the same direction as the drill bit (drive shaft).

 

Ed

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Ed&Roger-I guess what got me to thinking about this scenario is that I have repaired 2 right front diff pins. The area around the welds on the frame was cracked (undoubtedly by flexing) but the pins did not appear to be pushed upward. I had always assumed that the pins were being pushed downward on acceleration by the torque reaction of the diff pumpkin and mounting plate..

Too much thinking, resulting in a headache. I shall have to nap until the pain goes away.

Berry

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