Mark Allanson
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| posted on 11/9/04 at 09:49 PM |
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It was obviously used on something, or it wouldn't be there, Ford cost accountants would have stripped it off unless it was needed.
As it is there and free why not use it to refine your design?
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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stephen_gusterson
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| posted on 11/9/04 at 10:37 PM |
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quote:
Originally posted by JoelP
could be an idea!
also, though i hate to disagree, the acceleration is from the wheel, the wheel pushes the swinging arm, which pushes the subframe, which pushes the
car! if you removed the swing arm the wheel would roll forward without the car.
[Edited on 11/9/04 by JoelP]
think of where the forces are being transmitted. The wheel is being propelled by the drive shaft. the force comes thro the drive shaft to the wheel
from the diff. therefore the diff is as likely to rotate as the wheel. it doesnt as its bolted to the chassis, so the wheel goes around instead. in
normal forward movement the swing arms are lightly loaded.
thing about it - why did ford use so many bolts on the diff? And why mount the diff on such a whacking great bit of tube? Only the swing arms need
tube that big in your scenario.
Its tempting to think that the load goes thro the swing arm, but how can it? the drive shaft goes thro a wheel bearing thats not actually physically
connected solidly to the arm - cos a bearing is meant to rotate. so no direct forces go into the arm, cos the bearing rotates and transfers the force
to the wheel not the swing arm.
Imagine this situation - your hand and arm are the swing arm. grease your hand, and hold on to the drive shaft during acelleration (your hand
simulates a bearing). No torque forces would go through your hand or arm, the grease/bearing wont allow it.
jag diffs are rubber mounted. if power goes above about 400hp on the old xj-s during tuning, these mounts tend to fail, cos they cant take the
leverage forces.
atb
steve
[Edited on 11/9/04 by stephen_gusterson]
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JoelP
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| posted on 11/9/04 at 11:24 PM |
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quote:
Originally posted by stephen_gusterson
Imagine this situation - your hand and arm are the swing arm. grease your hand, and hold on to the drive shaft during acelleration (your hand
simulates a bearing). No torque forces would go through your hand or arm, the grease/bearing wont allow it.
quite right, there will be no torque reaction at my hand cos my hand isnt making the driveshaft turn. However, the wheel wants to go forward and all
that prevents it going forward is the swing arm. Remember the cv joint would let it roll forward by itself. whilst the diff feels the torque reaction,
the swing arm feels the effect of the wheel pushing on the road.
if not, why have you used 50mm swing arms?! 
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stephen_gusterson
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| posted on 12/9/04 at 12:17 AM |
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I agree that there will be a tendancy for the wheel to want to move in an arc, and so the swing arm keeps it in place. However I think thats more of a
load keeping the wheel in position - the main 'equal and opposite' forces will go back into the diff.
My swing arms are actually 40mm (not 50 as i may have said) cos thats what i could get free at the time AND cos I felt that there would be a tendency
for the weight of the car to try and twist the hub inwards, (negative camber).
I also flet at that time that loads did go into the arms - but im not convinced thats a primary load path now.
atb
steve
quote:
Originally posted by JoelP
quote:
Originally posted by stephen_gusterson
Imagine this situation - your hand and arm are the swing arm. grease your hand, and hold on to the drive shaft during acelleration (your hand
simulates a bearing). No torque forces would go through your hand or arm, the grease/bearing wont allow it.
quite right, there will be no torque reaction at my hand cos my hand isnt making the driveshaft turn. However, the wheel wants to go forward and all
that prevents it going forward is the swing arm. Remember the cv joint would let it roll forward by itself. whilst the diff feels the torque reaction,
the swing arm feels the effect of the wheel pushing on the road.
if not, why have you used 50mm swing arms?!
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blueshift
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| posted on 12/9/04 at 02:02 AM |
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quote:
Originally posted by stephen_gusterson
I agree that there will be a tendancy for the wheel to want to move in an arc, and so the swing arm keeps it in place. However I think thats more of a
load keeping the wheel in position - the main 'equal and opposite' forces will go back into the diff.
Assuming I understand you.. the swing arm takes all the directional forces, the diff only handles torque through the driveshafts. If you think about
it, the driveshafts can't transmit any other forces because of the CV joints (they'd just hinge) and the way lobro shafts plug into the
diff (any lateral force and they'd just pull out).
If the driveshafts were solid with no cv or universal joints anywhere, it'd be a different matter.
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stephen_gusterson
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| posted on 12/9/04 at 10:56 AM |
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people keep using this word torque.
its torque that does the work isnt it? where the actual 'push' originates.
If it wasnt for the swing arm, the wheel would like to travel in a circle. SO I can see Joels argument that some forces are transmitted thro the swing
arm to the car. But the actual power originates from the diff, and surely the same twisting forces on the wheel apply at the diff.
The reallt tricky bit to answer, which I doubt can be on here, is what proportion of the engine power is transmitted as a load into the diff, or a
load into the swing arm?
atb
steve
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MikeRJ
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| posted on 12/9/04 at 11:07 AM |
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quote:
Originally posted by stephen_gusterson
people keep using this word torque.
its torque that does the work isnt it? where the actual 'push' originates.
If it wasnt for the swing arm, the wheel would like to travel in a circle. SO I can see Joels argument that some forces are transmitted thro the swing
arm to the car. But the actual power originates from the diff, and surely the same twisting forces on the wheel apply at the diff.
The reallt tricky bit to answer, which I doubt can be on here, is what proportion of the engine power is transmitted as a load into the diff, or a
load into the swing arm?
No power whatsoever is transmitted into the diferential mountings, only the torque reaction from the propshaft and driveshafts is.
The swingarm takes all the lateral and longitudinal forces required to brake, accelerate and go around corners.
In a live axle design the trailing arms have the dual function of tranmitting braking/acceleration forces into the chassis and also resisting the
torque reaction of the diff. With an IRS design the diff mounts take the torque reactions and whatever suspension type is used deals with the rest.
The differential has no net longitudinal or lateral forces exerted on it or by it.
By the way, power does work, torque can only apply a static force.
[Edited on 12/9/04 by MikeRJ]
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blueshift
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| posted on 12/9/04 at 12:08 PM |
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the "twist" originates at the diff. the "push" originates at the contact patch between the tyre and the road, resisting the
"twist". that creates forward force on the wheel, which is resisted by the swing arm (accelerating the car)
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stephen_gusterson
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| posted on 12/9/04 at 06:33 PM |
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so, mike, as I understand you, you are saying that under constant speed in a straight line, the diff is under no loads at all?
we have been talking just in terms of torque - the power is also going down the shaft into the diff. Do you really think that there are no loads on
the diff at all?
ford went well over the top with 8 bolts and that thick diff casing.
atb
steve
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matt_claydon
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| posted on 12/9/04 at 06:59 PM |
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Rotational forces and linear forces must always be considered separately. As we all know, every force must be balanced by an equal an opposite one -
the torque at the wheel is balanced by the torque in the diff, hence the need for strong diff casing/mountings. The linear force exerted on the tyre
by the road must be balanced by an equal and opposite linear force somewhere else - in this case from the swing arm via the hub carrier and
bearing.
Cheers
Matt.
Diagram:
 
Rescued attachment untitled.GIF
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JoelP
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| posted on 12/9/04 at 07:20 PM |
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matt has it in a nutshell.
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MikeRJ
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| posted on 12/9/04 at 09:07 PM |
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quote:
Originally posted by stephen_gusterson
so, mike, as I understand you, you are saying that under constant speed in a straight line, the diff is under no loads at all?
Not at all, as I said the differential mounting have to cope with the torque reaction i.e. twisting force. What I am saying is that the diff
mountings play no part in actually pushing the car along the road, other than to stop the diff spining around, which is what I mean by exterting no
net longitudinal force.
[Edited on 12/9/04 by MikeRJ]
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Mark Allanson
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| posted on 12/9/04 at 09:42 PM |
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All this science is going over my head a bit, just put a sierra on a rolling road and look at the diff on full accelleration and full braking. its
like a wild animal trying to escape, just beef up the brackets a bit.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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paulbeyer
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| posted on 12/9/04 at 10:32 PM |
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quote:
Originally posted by James
In what field did you consult? Thought you did Telelcomms?
Cheers,
James
Sorry to take it off topic again, but James did ask.
You're right I was in telecomms until my recent redundancy. Prior to that I was a Land Surveyor then a sales rep selling surveying equipment. It
was during this time that I was selling equipment to the police accident investigation units (also the RAF accident investigation team based at RAF
St Athatn near cardiff). The police soon realised that the same equipment could be used to survey scenes of crimes and it was during this early stage
that Fred Wests expolits came to light. As it was such a high profile case they asked me to act as a consultant to survey the murder scenes as they
were still in a learning process and worried that they might screw things up if left to their own devices. 25 Cromwell St. was a really wierd place.
Fred had built an extension on the back of the house and used the external wall of the church next door as one of the walls in his kitchen. He simply
hung the wall units straight on to the brick work that was originall the outside wall of the church, no render or plaster, nothing. I've read
quite a few reports on t'internet but none have mentioned the donkey.
I was also roped into the investigation of the chinook crash in the Mull of Kintyre but I've mentioned that on this forum before.
Sorry back OT now.
7 out of 10 people suffer with hemorrhoids. Does that mean the other 3 enjoy them?
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stephen_gusterson
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| posted on 12/9/04 at 10:34 PM |
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I also agree with matt.
cept no one knows what proportion of the load is exerted at the diff, or the swing arms.
However, both of mine are pretty beefy.
atb
steve
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stephen_gusterson
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| posted on 12/9/04 at 10:37 PM |
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so, not only was fred a murderer, but a cowboy builder too!!!
atb
steve
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blueshift
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| posted on 13/9/04 at 01:52 AM |
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I know!
the diff feels all the torque, and the swing arms feel all the longitudinal (correct word? non-rotational, anyway) forces
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stephen_gusterson
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| posted on 13/9/04 at 08:56 AM |
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and, expressed in a
'im trying to rip this bit off the car' force, how does that translate?
Sure sounds like the diff wants to do the same thing as the tyres.
atb
steve
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MikeRJ
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| posted on 13/9/04 at 01:14 PM |
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quote:
Originally posted by Syd Bridge Also, if you look at how the chassis weight is put to the road, you'll see that the diff has a
part to play.
Syd, could you explain this a little further?
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Alan B
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| posted on 13/9/04 at 03:55 PM |
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quote:
Originally posted by pbura
2. Freezing them and giving the wood chipper a workout.............
Ah Fargo....great movie....
Anyway..back to topic....
which was???
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JoelP
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| posted on 13/9/04 at 05:32 PM |
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someone had great fun doing a donut at the end of his road last night... allegedly!
my cap pissed of down the road big time. but all in all, lots of fun and nothing broke or bent. if i had a trailer, i would give it some abuse on a
field.
anyway, im getting a 2 litre cos the 1.6 isnt enough, and i may as well change it before registering it...
cheers for the input folk. so far the mods on the cards are sorting the back diff mount, and the top shocker mount. might change the fuel tank too so
that extra bracing will fit. i suspect the boat tank would be difficult to get thru the test, due to removability and the fact that the vent leaks
when upside down.
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