Automatic / Manual Chassis Differences

OK, reviewing pics that I have, been sent to me, etc. and info that is on here, I have established a few things.

1. MK1 chassis: the manual trans chassis mounts (the parts welded to the car) are not only in different locations vs automatic trans mounts, they are arranged differently, IE one side is higher up in the chassis than the other.

MK1 automatic crossmember (shown here modified to work with an S13 manual transmission)


MK1 manual crossmember (shown here modified to work with an S13 manual transmission)


^notice how the MK1 manual crossmember is on one plane only- one side isn't offset like the MK1 automatic crossmember.

2. MK2 chassis: Nissan got smarter, and used the same basic layout for both manual and automatic transmissions. The actual crossmember itself is almost the same between the manual and auto cars, as shown here:

^notice the outer portion is the same, but the center section varies depending on the actual rubber mount that bolts to the transmission.

BUT the location is still different- the automatic trans mounting is further towards the rear, basically directly underneath the shifter, and the manual trans mounting is further forward, about 6inches from the shifter hole.
....... I am trying to figure out what that difference is, exactly.

THIS IS MK2
manual

(metal thing is fork of forklift, this is jyard car, pic courtesy of sinestro)

automatic

^notice how the actual mounting locations themselves are set further back in the chassis. Instead of being forward of the shift hole, they are basically dead center under the hole.

The greatest challenge here is..

I want to make a FRESH design, working with Waylon, and others,

To have a 100% BOLT ON    

Automatic trans-> manual trans conversion mount,
FOR
stock engines (CA and VG),
and the S13/14 engines. (KA/CA-DET/SR)

I was studying some of Colin's pics with the RB swap,
and I think something similar could be done,
and as long as it was designed right,
It could be used in several different applications.

A design would be finalized (may take one or two shots, but we'll do it), CAD drawings would be done, and posted up. Then anyone could have it made/make it themselves.

So we're clear, I'm speaking of this part MAINLY, which is the MK1 AUTOMATIC crossmember.  MK2 Automatic->Manual Crossmember conversions are going to be much simpler, more or less just a spacer.  Read on further in this thread for more details.  

Only w/o the modifications and WITH the original rubber parts and stuff... (photo courtesy of Waylon)

Colin's



It no doubt works but its a lil flimsy IMO as is.  A spine welded transversly onto it's underside would add a lot to this design.  In fact it would be quite good then.  Simple and effective.  It would need to be modified (two bends) to work with the uneven auto chassis mounting points (one is higher than the other) but that is minor considering the design.  My only concern then is the mounted height of the trans.  Don't know how close the shifter is to the tunnel.  I designed mine to be very close cause thats what I wanted at the time.  Not sure if an inch or so height difference really matters though.  If too low then extra boxing at the trans mount point could be made and if too high then extra boxing at the lower body mount point.

Here is my modification to the existing auto trans crossmember.




More labor intensive to make and rather overkill.  Also relies on having an auto crossmember to modify so that excludes it from being a shippable bolt-on solution.  But hey its strong as shit, lol.  At least its a great solution for a DIYer with a welder in-hand.

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Waylon, thanks for putting that together right there!

I'm aware of the challanges that the auto chassis has, and can account for them, and very much agree with you regarding the design of Colin's unit (at first I was like  but hey it works I guess). I've got a plan for the trans-height issue, as thats already something I've encountered working on Henry's and Jason's car, so that should work out.

The thing would definitely be sturdy, and would not require the use of the original part IE replaces everything. Yours works Waylon because you have the skills, and more importantly the tools, to make that, which isn't always the case for everybody. Having a bolt-up solution would be great.

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Here is more photographic evidence of the similarites in MK2 crossmembers.  Note the outer frame is identical, the inner portion varies slightly on how it actually attaches to the rubber mount that bolts to the trans.  I hybrid these two mounts- taking the unrusted one's outer portion and inserting my inner rusted manual portion, attached the actual rubber trans mount, and bolted my CA20 manual setup back into my car.

My 87 CA20 Manual crossmember is the rusted one, the other is a 87 V6 Automatic crossmember.






NOTE on mine, the rusty one closer, still has part of the actual rubber mount on it (the torn off section is chilln to the side) that the V6 auto one does not even have holes for the rubber mount to bolt up to.

Some SE V6 pictures, 1988 AUTOMATIC car.

Oh, and guess what I see there, I see some rubber shit on it, so it obviously mounts onto it somehow.

What I was studying is this design of the manual trans



Normally the bolt is in the location further to the right, but there seems to be similar tabs farther rearward, probably,... about where the trans xmember location is on the automatic cars.

heres another pic


obviously not quite as beefy, but that could be addressed

some dimensions of those mounting points

The distance between the two, from the centers of the bolt holes/slots

5 5/8"

Width of rearward location


Width of normal mount location (forward of other one)



This is interesting, some concepts I need to play with some more.

I think the rear tabs could be used as locations to bolt the Manual-styled motor mount and Crossmember to, and then install directly into the automatic mk2 chassis.

heres my crossmember for my auto Mk1.5 chassis, with 5spd KA. it bolts to the rearward mount that isnt commonly used, so thats definitely a go on that. as you can see theres notches on it so it sits flat and doesnt conflict with that spline. the "weights" on mine have since been cut off because of exhaust conflicts with no ill effects. i also filled the stock mount with windo weld urethane junk and its pretty stiff. everything has held up great so far, with a few drift events and alot of spirited driving

AWESOME man!   Was it pretty much a bolt-up thing or did you have to slot anything?  Does it lean slightly forward or rearward?

The mount that rage came up with is similar to mine, cept maybe a little cleaner lookin  did yours work just like that in that position on the trans, where the exhaust hanger was... mine still had to go back slightly, maybe due to my design.  I used some road sign post and a plate of sheet metal. The road sign post, the square kind with the holes was basically predrilled to fit right where i wanted it, and allmost the right thickness to keep the trans level, the plate of stainless steel was used to get back where i needed, i'll have to get a picture of that sometime...

Its pretty much bolt up ordeal, the actual 4 chassis mount holes were a little off so i had to oval them or round them out more. also don't tell anyone but i only have 2 out of the 4 bolts holding everything in. seems fine? but its probably dangerous. as far as leaning, its pretty much dead center, but i can take pics. i also didnt have to cut anything for the transmission tunnel. win/win?

AUTOMATIC MK2 Notch reference pics.....





[mod edit: Andrew's sick ass coupe soon to destroy the street of southern ca!]

So whats my best bet for using a C trans on my MKI CA20 auto car?
Full custom crossmember? lol

alex, it would not be much different than running a S13 'C' trans in your car, so you'll need something like what Waylon made.  either I can do this for you or you could try something like what rage did, either require custom work, it might just be easier to run with Waylon's design in your mk1 chassis.

So my shifter would sit farther back even though its just a MKII C trans? Or the mounting would be the same as S13 and I'd just need to get a boot and be done?

Were can i find mk2 crossmember bushings? Mine are non existant.

Rock Auto or any number of parts suppliers may have them.

More importantly, you should start a WTB thread for these items rather than resurrecting a thread that hasn't been active in 7 years.