Scooby
|
| posted on 18/11/03 at 05:28 PM |
|
|
IRS Diff. Mounting
Hi guys,
I need help with a stupid question, sorry!.
Does the Sierra diff unit have to be flexibly mounted in the chassis, as in the Sierra, or can it be bolted straight to the chassis? Is it vital to
have flexibility? (ooh-err!) If so why?
This must have cropped up on here before, but I can't find it!
Cheers
|
|
|
|
|
Alan B
|
| posted on 18/11/03 at 05:37 PM |
|
|
Guessing here.....
I'm sure they are solid mounted in locost applications.
In the Sierra it would be flexibly mounted to reduce noise transmission...can't think of any other reason..
|
|
|
GO
|
| posted on 18/11/03 at 05:45 PM |
|
|
Confirming Alans guess... defo solid mounted.
|
|
|
stephen_gusterson
|
| posted on 18/11/03 at 06:28 PM |
|
|
i solid mounted mine. the donor car is also solid mounted to the suspension frame - then thats mounted on pretty hard rubber to the car.
atb
steve
ps - make sure you mount it well as all the drive torque bears into the chassis via the diff.
|
|
|
Simon
|
| posted on 18/11/03 at 10:23 PM |
|
|
Scooby,
Mine's solidly mounted - see pic - it's not
shown, but I have yet to fit the rear diff to body mount.
Tiger mount theirs solidly, and I don't doubt a few of the other manufacturers do
HTH
ATB
Simon
 
Rescued attachment 2003_1116Image0032.JPG
|
|
|
JoelP
|
| posted on 18/11/03 at 10:38 PM |
|
|
interesting pic, did you weld the rear mount directly onto the chassis? i messed about putting a mounting plate on so it is bolted. is that part even
needed when the diff is bolted to the chassis? on mine it helps hold the subframe on...
|
|
|
Simon
|
| posted on 19/11/03 at 12:28 AM |
|
|
Joel,
Rear mounting part of chassis. The rubber part will be bolted to diff and upper mounting when I can find it!!
ATB
Simon
|
|
|
Simon
|
| posted on 19/11/03 at 09:35 AM |
|
|
Syd,
Inclined to agree, but the rubber is incredibly stiff.
I figured it wouldn't do any harm, plus the "3rd" bolt set isn't being used (smallest at the bottom front of diff), just the
two that can be seen in the pic.
ATB
Simon
|
|
|
ned
|
| posted on 19/11/03 at 09:53 AM |
|
|
MK mount their dif solidly and don't use the rear rubber mount, its not much use once the dif is solidly mounted at the front.
Ned.
beware, I've got yellow skin
|
|
|
jcduroc
|
| posted on 19/11/03 at 03:43 PM |
|
|
quote:
Originally posted by ned
MK mount their dif solidly and don't use the rear rubber mount, its not much use once the dif is solidly mounted at the front.
Ned.
Most Locost kit-car builders mount the Sierra diff on 2 points (see attached pic).
I would always use 3-points:
a) either these 2 and the front ones or
b) these 2 plus the rear one.
Alternative b) is my favorite as it allows to use the rear bulkhead for attachement.
 
Rescued attachment Diff_left.gif
JCM
|
|
|
stephen_gusterson
|
| posted on 19/11/03 at 10:22 PM |
|
|
i used all of them
that settles it then 
atb
steve
|
|
|
MikeR
|
| posted on 20/11/03 at 12:52 PM |
|
|
I think the general wisdom from the Cateringvan people is that more mountings are better. Some of the high powered cars (200bhp) have been breaking
the front mounting points on the car due to the repeated stresses put through that section.
|
|
|
JoelP
|
| posted on 20/11/03 at 02:09 PM |
|
|
the rubber one may stop the diff falling off but it isnt going to relieve any stress from the front mountings cos its totally flexible.
|
|
|
ned
|
| posted on 20/11/03 at 02:15 PM |
|
|
for strength/high power issues webbing could be added to the mounting points running out sideways to try and relieve any torque being transmitted
through the chassis....
I'm not aware of an MK Indy's having any these problems and some of them run pokey engines.
Ned.
[Edited on 20/11/03 by ned]
beware, I've got yellow skin
|
|
|
Mix
|
| posted on 20/11/03 at 06:06 PM |
|
|
I intend to use the three 'hard ' mounts as I feel this will give the most positive location.
As far as the torque reaction goes, isn't the greatest force the one that is exerted in the axis of the drive shafts, (tending to lift the
front of the car)?
If I am correct in my assumption then this would make using the front mount a far more efficient option than the rear.
Mick
Pondering the best way to allow a front diff mounting to be removable after the trans tunnell is skinned.
|
|
|
stephen_gusterson
|
| posted on 20/11/03 at 08:14 PM |
|
|
i didnt use the rubber mount. if you chuck that away you gain two extra tapped holes at the rear to act as a mount.
The way I see it is that when the engine applies torque, two things could happen.
a. the diff wants to rotate.
b. it cant, so tha shaft and wheels do instead.
So, the torque that drives the car forwards is all acting on the diff mounts. If you only mount the diff at the front hou have quite a small point of
leverage trying to hold the diff to the car. If you also use the back mount, you are adding a further secure point several inches back that will
create a better anchor point and lower the stresses on the front mounts.
It doesnt need to be rubber mounted at rear.......
crappy pic follows
 
Rescued attachment diffmount.jpg
|
|
|
JoelP
|
| posted on 20/11/03 at 09:38 PM |
|
|
good picture actually, makes sense. Might have a go at doing that to mine tommorow. thanks ste!
|
|
|
JohnN
|
| posted on 20/11/03 at 09:46 PM |
|
|
Stephen - Did you tip your car on its side to take the "crappy", actually good picture? Just looking at the brickwork in the background
|
|
|
MikeR
|
| posted on 20/11/03 at 11:00 PM |
|
|
Naah, he's got a brick roof 
|
|
|
stephen_gusterson
|
| posted on 20/11/03 at 11:25 PM |
|
|
It could be that I was just passing the 'yard of bricks' at indianapolis
actually, I drove to see the track 2 weeks ago on my USA trip. 500 miles to get there and back (appropriate!) and 7 1/2 hrs driving, but it was worth
it just to have been there.
BTW - there was a piccy put on here a few months ago about a jet powered indy car....remember that? Well...I saw it - its actually in the museum
there. Took some nice pics of it. a 4wd side mounted jet car....now no ones done that here!
follows is, as guessed, a pic of the car on its side. Way too heavy to do that to it now!
I havnt said this for a while but 'my cars not standard, its a morgan lookalike'. So it has swinging arm IRS of my own design. prob no
better than a live axle, but at least I was different.
My diff carrier is two 2.5mm plates. The front edge is welded to the back of the tranny tunnel, and the top of the plates are welded to two 2 inch rhs
beams that run from bulkhead to a further 2 inch cross member at the back of the car. The rear diff mount then goes to the same two members. Even tho
a locost isnt anything like this, im sure you will have a point in the area of the diff cage to use the back mounts. The diff itself has a very robust
rear end, on the donor the diff actually supports the subframe at this point. As a mounting point, it seems to have considerable 'balls'.
atb
steve
 
Rescued attachment diff2.jpg
|
|
|
Mix
|
| posted on 21/11/03 at 08:54 AM |
|
|
Good point Steve to use the rear mount as a solid mount in addition to the front ones, I think I'll incorporate it in my build as it will
increase rigidity in that area. I will still use the forward mount as this has the longest moment arm from the driveshafts making it the most
efficient in resisting the torque reaction.
Mick
|
|
|
craig1410
|
| posted on 21/11/03 at 01:02 PM |
|
|
I'm using the front 3 mountings myself as these provide more than enough strength and all my mountings are solid, not rubber. This arrangement
gives me more room at the back for my de-dion axle, especially if I milled the rear mounting off the diff. It might also be handy if you wanted a
bigger fuel tank.
I can see the logic behind using the rear mount but I just think that it is way overkill as the diff internals or driveshafts will break long before
the diff mounts if you use the front three. They are M12 bolts and set screws after all and there are six of them. I only have 4 M10 and 2 M8
fasteners holding my engine and gearbox in place and it's a Rover V8 lump... (Before you say it, I am using the same mounts which came out of
the SD1 donor so they are perfectly fit for purpose)
Cheers,
Craig.
|
|
|
ned
|
 posted on 21/11/03 at 01:27 PM |
|
|
Craig,
DO NOT mill the rear mounting off the dif casing, I tried to take it off with a grinder but the casting goes up into the mount and I ended up with a
hole in the backplate of the dif.
Be Warned!
Ned.
beware, I've got yellow skin
|
|
|
craig1410
|
| posted on 21/11/03 at 01:33 PM |
|
|
Thanks Ned I would only have taken off as much material as the depth of the screw holes would allow but I appreciate the warning all the same. I
don't intend to remove it anyway as I don't need to.
Cheers,
Craig.
|
|
|
jcduroc
|
| posted on 21/11/03 at 10:16 PM |
|
|
quote:
Originally posted by stephen_gusterson
... BTW - there was a piccy put on here a few months ago about a jet powered indy car....remember that? Well...I saw it - its actually in the museum
there. Took some nice pics of it. a 4wd side mounted jet car....now no ones done that here!
Wasn't that a Lotus?
quote:
Originally posted by stephen_gusterson
... My diff carrier is two 2.5mm plates. The front edge is welded to the back of the tranny tunnel, and the top of the plates are welded to two 2 inch
rhs beams that run from bulkhead to a further 2 inch cross member at the back of the car. The rear diff mount then goes to the same two members. Even
tho a locost isnt anything like this, im sure you will have a point in the area of the diff cage to use the back mounts. The diff itself has a very
robust rear end, on the donor the diff actually supports the subframe at this point. As a mounting point, it seems to have considerable
'balls'.
atb
steve
Originally the Sierra diff attaches to a subframe at 3 (double-bolt) points: front, top and bottom middle.
The subframe itself attaches to the coque in 3 points: 2 lower front attachements and a rear one, which happens to be the rear 2-bolt
attachement in the diff (as Stephen pointed out).
We have combinations of 4/3, ie, 4!/3! = 4; which one is (or is supposed to be) the best combination?
Open discussion, I guess!
Cheers
Joćo
JCM
|
|
|
