Swing Arm Differential Mounting: Pros and Cons

[pdoggy]

I have been looking at two different ways of mounting the differential on our '05 car. The first being the traditional differential carriers that are attached to the rear box of the chassis that hold the differental. The second way is mounting the differential directly to the engine using the swing arm mounts that come stock with the engine. A very nice picture is shown on the WWU thread started about 4 months ago by stotera.

I'd definitely like to see some more designs or pictures of cars that use this approach if anyone out the is willing to give me a look in the right direction.

But the main point of this post has more to do with swing arm mounting in general:
I have found some of the Pros to be:
1)This configuration makes packaging easier because there are no rear box constraints
2)Makes alignment easier because there are no alignment concerns due to chassis flex
3)Less sprocket wear due to misaligned chains
4)This configuration removes the largest stress on the chassis and transfers it to the engine mount and the members between the engine and the differential.

I have found some of the Cons to be:
1)This configuration is more complex and harder to design than the alternative
2)Not all engines have swing arm mounts, which limits the amount of engines that this method can be performed on

As you all can see, I don't have a an overwhelming amount of information and it is somewhat difficult to find info on this subjuect. Feel free to reply and offer any insight you have on this topic.

Brian
UNM Racing

[pdoggy]

I have been looking at two different ways of mounting the differential on our '05 car. The first being the traditional differential carriers that are attached to the rear box of the chassis that hold the differental. The second way is mounting the differential directly to the engine using the swing arm mounts that come stock with the engine. A very nice picture is shown on the WWU thread started about 4 months ago by stotera.

I'd definitely like to see some more designs or pictures of cars that use this approach if anyone out the is willing to give me a look in the right direction.

But the main point of this post has more to do with swing arm mounting in general:
I have found some of the Pros to be:
1)This configuration makes packaging easier because there are no rear box constraints
2)Makes alignment easier because there are no alignment concerns due to chassis flex
3)Less sprocket wear due to misaligned chains
4)This configuration removes the largest stress on the chassis and transfers it to the engine mount and the members between the engine and the differential.

I have found some of the Cons to be:
1)This configuration is more complex and harder to design than the alternative
2)Not all engines have swing arm mounts, which limits the amount of engines that this method can be performed on

As you all can see, I don't have a an overwhelming amount of information and it is somewhat difficult to find info on this subjuect. Feel free to reply and offer any insight you have on this topic.

Brian
UNM Racing

[Daves]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> have found some of the Pros to be:
1)This configuration makes packaging easier because there are no rear box constraints
2)Makes alignment easier because there are no alignment concerns due to chassis flex
3)Less sprocket wear due to misaligned chains
4)This configuration removes the largest stress on the chassis and transfers it to the engine mount and the members between the engine and the differential.

I have found some of the Cons to be:
1)This configuration is more complex and harder to design than the alternative
2)Not all engines have swing arm mounts, which limits the amount of engines that this method can be performed on <HR></BLOCKQUOTE>

Pro 1: Exactly - you can install and test your differential setup before the chassis is every completed, making engine/transmission-differential mounting beneficial to "concurrent" design.

Pro 2: This is a minor issue from my experience. We have mounted the diff. to the chassis for 3 years, but we have never had chain wear problems, in spite of imperfect alignment. Chains really are technical wonders.

Pro 3: Ditto, no wear problems.

Pro 4: You've hit the nail on the head. Usually the chassis engineers test the chassis' torsional rigidity based on the suspension hard points. However, a large force is transferred through the differential mounts because of acceleration and because of braking, and this can be detrimental to the chassis. I believe the braking force imposed on the differential mounts may be even greater than the force from the chain, assuming the brake caliper is mounted to one of the differential mounts.

Con 1: It may appear that mounting to the engine/transmission is more difficult, but it really depends on your design. I now think it is actually easier than mounting to the chassis because of the time saved by not having to wait for chassis completion. (Pro 1)

Con 2: You're right -- not all engines have swing arm mounts, but not all engines have transmissions attached to them, either. If you use a separate engine and tranmsission, you could look into mounting the differential to the transmission. Or when you're selecting an engine in your conceptual phase (sounds like you're in this phase now), you can make "swingarm mounts" one of your specifications or constraints.

As to your original request for images and ideas, I would recommend looking at Western Australia's diff. mounts. They are a similar idea to Western Washington's because of the eccentric adjustment. However, instead of using set screws, they incorporate cap screws in shear stress. Maybe they're even in double shear -- I'm not sure. West. Aust. had outboard brakes, too, so that removed a major stress from their diff. mounts.

Oh, and be creative. I wish I was more so.

[jack]

At WWU, we have always had the "direct to engine" diff mount design, so i really don't know how it compares to the other style of mounting that UW, Cornell, and others use. ours seemed to work ok, and it was pretty light, especially since we got rid of a whole extra bulkhead, similar to UWA. As for the adjustment done by slots, i think that was kind of a crappy way to do it. UWA had a much better idea. Also, make sure there is something keeping the two bearings holding the diff co-planar, if they get out of wack at all, the diff will walk to one side of the assembly.

oh, we had outboard brakes too.

here is a unique way to do it, that i dont think i have seen anyone do yet:

http://users.breathe.com/defiant1/djracecars/IMAGES/firetrans.jpg

[Daves]

The Firecat's system that you provided a link to appears similar to Western Australia's in that it has a rear plate that many items mount to. The Firecat's plate is aluminum, but W.A.'s is carbon fibre. The Firecat's differential also appers to be fixed. I guess it has an adjustable idler sprocket.

[jack]

yes, but UWA's diff mounts directly to the engine, not to the rear bulkhead, unlike the firecat.