DSM & 3SI

This post is to document some of my 3000gt/stealth and dsm differences and similarities findings. Mostly with Suspension/Drive terrain.

With what started off as a rear diff seal replacement and looking at what is needed to mount my 4piston 3si FRONT brakes. Then hearing about the fast guys running a 3si rear end.
I ended up with a 3si front suspension and rear subframe setup laying in my garage.

Since I found barely ANY information on this on the interweb,This will be a fairly lengthily and ongoing documentation. I may need some help from the mods to organize this as we go


I will look at the following:

-Subframe Measurements Similarities
-Rear Upper/lower Control arms
-Rear Axle Cups
-Rear Hubs
-Rear Trailing arm
-Rear Brakes
-Rear Swaybar
-Front Knuckle
-Front Brakes

Rear Subframe Measurements & Similarities

Differences:
-Over all the track width is about 4 inches wider
-rear wheel power steering rack and linkage
-rear diff mounts differently
-subframe mounts to car are different distances.

Similarities(sadly my 3si rear subframe did not come with axles or a diff):
-The trailing arm looks to have an almost identical shape
-The axle cups also mount at the trailing arm and are also 4 bolt
-Upper and lower trailing arms look similar

(Sorry about the inter web photos)
DSM Rear Subframe

3000gt Rear Subframe



So I began to look closer at things. Trailing arms have some slight differences, internal ebrake, wider, shock mount is lower and thicker. Other that they are very similar.

Axle cups are both 4 bolt and look to be the same distance from the trailing arm, but the bolt spacing is noticeably larger and it is mounted with a larger nut.

Upper and lower control arms look to be almost identical, with same lengths, however larger mounting hardware on both ends.

I will elaborate on all of these later.
--

Next looking at the track width, many people on the internet suggest that these are 2 completely different cars and always note the track width difference of about 4".

So me being a curious cat, I set out to see where the width came from.

After measuring the upper and lower control arm mounting points, they came out the same as the DSM! Looks like mitsu engineers kept the same suspension geometry between the two cars.

Next I measured between the mounting points on the subframe(where the diff sits.) I could only measure the lower mounts, but the distance between them came out 2" wider than the DSMs.

So we found where 2" came from, now to find the remaining 2" I went to the trailing arms.
The arms look different, but after closer inspection, the mounting points were all very close.
The width of the trailing arm where the hub goes in, looked to be almost 1" 1/8 wider than the DSM.
So on each arm it looks like we gain about 1" track width per side.

Rear Axle Cups and Hubs

Cups

Differences:
-one is noticeably larger than the other,
-the bolt spacing is different,
-and a larger nut is used to secure the cup to the hub shaft.

Similarities:
-The "height" of the cups are the same
-The spline count and shaft are identical.
-This meaning, the cups are interchangeable with the correct mounting hardware.






Onto the Hub/shaft:

Differences:
-3SI one is longer(to make up the extra hub width)
-The threaded end is larger on the 3si (hence the larger nut)

Similarities:
-Everything else.

Thanks for the write up, I heard Jason D is making his own rear tubular rear SF which is stronger than OEM. Personally, with all the stress i get from daily life, i don't think i have any time left to play around with different parts that may fit DSM. I give you credit for doing it. Currently my setup i pure bolt on with OEM/EVO stuff. I enjoy keeping it simple and straightforward, my 2 cents.

This would only be applicable to the 1Gs and it would give us a drum-style rear brake setup which would allow us to easily upgrade our rear breaks without losing e-brake functionality. Additionally it would give us a wider track (desired) and possibly the ability to use the 3si rear end (desired). And it will also be a lot cheaper than a tubular subframe.

Sorry guys. I was getting to that but photo bucket seems to be failing me.
I have alot more to post still but salomon gives the coles notes(we've been chatting about this for awhile)
Wider track, internal ebrakes, ability to run 3si, or evo 8,9 maybe 10? brembos on the rear.
So far the modifications seem quite minimal.
STAY TUNED!

This is very interesting! Would you run the same wheels in the rear? Would you then have to have up the rear fenders to get your wheels to fit and function?

Realistically you'd need fender flares and want a high offset wheel to fit any kind of wide wheel under the fender flares. 1" extra track width on either side is HUGE. That's 25.4mm ie to keep the outside face of a set of wheels with +30 offset at the same position relative to the centre of the car you'd need to switch to a +55 offset.

The front 3si hubs would allow us to run bolt on bearings instead of press-in, and would also make the VR4 4-pot brakes and rotors be a bolt-on affair. Track width in the front would also increase (though not as much as the rear).

That would be great, I assume it's easier to find those bearings?

Sorry for my suspension geometry ignorance but what's the advantage of increasing track width if your tires will have the same contact spot relative to the car?

I'm no expert but, I believe there would be less lateral roll. However added understeer could be a side effect which these cars are already bad for. But I wont know until I try!

Suspension geometry would remain mostly the same as all the width is gained in the trailing arm/hub.

Rear Trailing arm

Here is the meat and potatoes to this whole adventure.
I plan on using the 3si rear trailing arm so I can:
-Retain an ebrake
-Run Larger vented rotors
-Bolt up 3si, or evo 8 calipers WITHOUT brackets.

(I don't believe there is any rear brake upgrade for our cars that will allow you to retain the e-brake)

Differences:
-Shock mount distance from centre is longer. This will actually lower the car.
-Shock mount is thicker. BUT in my one picture you can see that mitsu just welded a piece of metal dowel overtop of another dowel. I am hoping to cut the dowel off and the mount underneath will be the same size as the dsm one! TBD
-Width, you can clearly see an inch, if not more difference in width.
-Internal e-brake obviously. E-brake cable capability TBD.
-Balljoints. Now there are a couple ways to make this work. It seems ALL the fastening hardware is larger on the 3si stuff. subframe mounting bolts, and balljoints. I could have either:
-used the 3si control arms, and had a sleeve pressed into the subframe mounting side for the smaller DSM bolt.
-Used the 3si control arms, drill out the dsm subframe for a larger bolt that the 3si uses.
-Press out the 3si balljoint, and press it into the DSM lower arm.

I chose the last option. ***But NOTE*** through my searching there is no oem balljoint available for the 3si. You need to purchase the arm. ($300) OR use a joint from an 80's dodge D50 and use ring shims to make up the larger gap for the snap ring groove. (not a huge deal)

Luckily with my adjustable camber arms the upper balljoint shank flares out enough to work with the upper trailing arm mounting point.

Lower Control Arms

Differences:
-Subframe mounting side, the bushing and sleeve is larger
-Trailing arm mounting side, balljoint shank is slightly larger.

Similarities:
-Length appears to be identical
-Balljoint diameter is the same
-Swaybar end links appear to be the same

As stated previously, the 3si balljoint will need to be pressed into the DSM lower arm to use the 3si trailing arm.

Test fit.
Wasn't expecting it to be this wide. But ohwell.

Looks pretty sweet if you can get a wider flare.

Is this the full subframe or just the trailing arm?

This project is rad! Are the 3si parts significantly heavier? That spindle looks pretty beefy.

This is just using the arms. The subframe of a 3si mounts wider on the car and is totally different from a dsm.


Thanks man!
The arm alone is a bit heavier. I could try and get a weight difference between the two. It may be about 5lbs...

It may not seem like much but I will also have the added weight from the internal ebrakes, slightly longer hub/shaft and the larger vented rotors.