Jump to content
  • When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Transmission Tunnel Build for Rx8 Transmission swap.


Dudeland

Recommended Posts

I just got the clutch for the rx8 transmission today. 

 

I am going to have to pull the interior to weld some tabs to the bottom side of the floor.   If I believe what Lucky from HRG says, it is better to cut the whole tunnel out and then build it back  from there.  In the FWIW category I think he is right.  I am only one person, and my ability to balance and install the transmission ten times while it dangles over my entire body,  while pounding on the tunnel, blind to what it may be hitting seems like a nightmare.  I am a big guy and and press a good amount, but what am I trying to prove by beating it with a hammer?  With the tunnel cut out  I can center and measure everything, and install the rear transmission support member without any headaches, then put the cutout back on, tag in whatever bits I need to give it some breathing room.

 

I could maybe zip it up the middle and spread it I guess. Is that a better? 

 

Butchery or the smart call?   

 

Thoughts?

 

P.S The project list is moving along nicely.  I am thinking 3-4 weeks before I can really lean into the surgery. 

 

 

 

"Goosed" 1975 BMW 2002

 

Link to comment
Share on other sites

Bear in mind the entire driveline sits in the car at an angle. If I remember correctly from the last time I measured, it crosses the centerline around the rear of the transmission. 
 

The front of the crankshaft is offset to the left of the car and the pinion of the differential is offset to the right side of the car. 
 

Take lots of measurements before you start cutting your references away. 

Link to comment
Share on other sites

5 minutes ago, Lorin said:

Bear in mind the entire driveline sits in the car at an angle. If I remember correctly from the last time I measured, it crosses the centerline around the rear of the transmission. 
 

The front of the crankshaft is offset to the left of the car and the pinion of the differential is offset to the right side of the car. 
 

Take lots of measurements before you start cutting your references away. 

To be clear I am not proposing to cut the existing cross member out or any reference point.  On the contrary,  with the top pulled off I can measure and be precise in the placement.  

 

With that said you are saying that the driveline isn't parallel with the body?.   I am wondering how that would influence the use of a one piece drive shaft.    I suspect that I may have to go to something exotic like CF...  not sure yet.   

 

Why was there a two piece driveshaft in these cars anyway? Less stress on the output shaft bearing? 

 

 

"Goosed" 1975 BMW 2002

 

Link to comment
Share on other sites

It would influence a one piece shaft because ideally you should have equal and opposed u joint angles on each end. To do that you would need to “straighten” the engine/trans but it would not be easy to get much angle at the u joint at each end without moving rear of the trans towards the driver which is not desirable in my opinion. Too small of a  u joint angle is also not enough to my understanding to get the needle bearings to roll around but neither does a stock 2002 for that matter. 2-3 degree u joint angle is minimum in my understanding. 

 

Not that I’ve ever looked into this sort of thing, haha !

 

The driveshaft speed potential is pretty high on a 2002 so a two piece shaft allows much smaller diameters in regards to the rpm requirements. At 5 speed (245) length you need a driveshaft larger than would clear the rear subframe to spin top speed. A carbon or other lightweight shaft would  improve that situation. 


The driveline in a 2002 is not not parallel to the centerline of the car. Neither is an E30 and I suspect many bmws. I didn’t believe what I was seeing the first time I measured it but once I knew I could see it at a glance. Sort of like the first time you notice V8 valve covers don’t sit directly across from each other, they are offset front to rear.  


Im not saying any of this is impossible, just some things to consider. 

Now, if you just want to gently cruise it to the local taco stand to impress the ladies and take Instagram shots with it you can ignore anything I’m talking about. 

 

Edited by Lorin
  • Like 1
Link to comment
Share on other sites

3 hours ago, Lorin said:

It would influence a one piece shaft because ideally you should have equal and opposed u joint angles on each end. To do that you would need to “straighten” the engine/trans but it would not be easy to get much angle at the u joint at each end without moving rear of the trans towards the driver which is not desirable in my opinion. Too small of a  u joint angle is also not enough to my understanding to get the needle bearings to roll around but neither does a stock 2002 for that matter. 2-3 degree u joint angle is minimum in my understanding. 

 

Not that I’ve ever looked into this sort of thing, haha !

 

The driveshaft speed potential is pretty high on a 2002 so a two piece shaft allows much smaller diameters in regards to the rpm requirements. At 5 speed (245) length you need a driveshaft larger than would clear the rear subframe to spin top speed. A carbon or other lightweight shaft would  improve that situation. 


The driveline in a 2002 is not not parallel to the centerline of the car. Neither is an E30 and I suspect many bmws. I didn’t believe what I was seeing the first time I measured it but once I knew I could see it at a glance. Sort of like the first time you notice V8 valve covers don’t sit directly across from each other, they are offset front to rear.  


Im not saying any of this is impossible, just some things to consider. 

Now, if you just want to gently cruise it to the local taco stand to impress the ladies and take Instagram shots with it you can ignore anything I’m talking about. 

 

All of this just blew my mind 

  • Like 2

some cars

some motorcycles

some airplanes

some surfboards

Link to comment
Share on other sites

1 hour ago, danco_ said:

All of this just blew my mind 

That gives a hint that going to one piece shaft isn't trivial. I tried but had to go back. By basic calculations there was a chance it would work but the vibration was earth-shattering. Shaft was professionally done and balanced.

Racing is Life - everything before and after is just waiting!

Link to comment
Share on other sites

I am so glad I asked. Dang,  So two piece it is I guess.  This is going to be such a pain in the ass.  Why can't someone just make layshaft bearings for a getrag 245.  I am sure that I will feel different when I spin it up. 

 

 

"Goosed" 1975 BMW 2002

 

Link to comment
Share on other sites

The 2 piece shaft design bmw used is extremely accommodating. The main complaint when stock driveshaft isn’t lined up properly is a guibo that wears out quicker. Compare that to the two one piece descriptions above. 
 

Tommy and tzei, do you remember the U joint angles you were able to achieve and in which plane did you choose to create the angles ? 
 

When I was considering this it seemed like small angles in the horizontal plane would be the most convenient but obviously not much angle. 
 

Running CV joints at the ends of the driveshaft seems like it could be potentially superior to U joints in regards to vibration and they are happy to run at those angles.

 

 

Edited by Lorin
Link to comment
Share on other sites

7 hours ago, Tommy said:

By basic calculations there was a chance it would work but the vibration was earth-shattering. Shaft was professionally done and balanced.

Did you do a critical frequency calculation?  There is engineering in these things.

  • Like 1

A radiator shop is a good place to take a leak.

 

I have no idea what I'm doing but I know I'm really good at it.

Link to comment
Share on other sites

Thank you Tommy and tzei. 

 

It sounds like both of you guys had a straight driveline back to the diff just as the original 2002 design is. Since the pinion is offset to the right side of the car that leaves you with a U joint angle only at the differential which should not work optimally.

 

As designed, the 2002 driveline is straight from the crank pulley to the differential and hits the diff at (this is testing my memory) a couple degree angle. I believe the 2 piece driveshaft is the component that allows this setup to work.

 

To use a 1 piece driveshaft with angle on one end only, a CV joint would need to be used. This would be in my mind the greatest possible chance of success without major component relocation: A lightweight 1 piece shaft with a slip spline section and a CV at the diff.  I'm not convinced this would work perfectly at high speed, though.

 

I think a better solution might be to straighten the engine/trans in relation to the chassis putting the crank roughly in the center of the car then incline/decline the diff and engine to create equal and opposed u joint angles IN ONE PLANE ONLY.  This with a lightweight slip spline shaft and probably CV joints on each end in my mind at least seems like the most likely solution to work. When  I mocked this up, and my trans was pretty for back in the chassis, the u joint angles were around 1 degree.

 

A longneck diff would help things considerably by shortening the shaft length (allowing more driveshaft angle and smaller diameter) and getting it clear of the subframe.

 

It all makes the stock 2 piece shaft seem pretty easy !

 

Can someone else hurry do this so I can stop thinking about it ?!

 

 

 

..

 

 

Edited by Lorin
Numerous grammatical corrections so Ray won’t bite me.
Link to comment
Share on other sites

17 hours ago, Dudeland said:

I am going to have to pull the interior to weld some tabs to the bottom side of the floor.   If I believe what Lucky from HRG says, it is better to cut the whole tunnel out and then build it back  from there.  In the FWIW category I think he is right.  I am only one person, and my ability to balance and install the transmission ten times while it dangles over my entire body,  while pounding on the tunnel, blind to what it may be hitting seems like a nightmare.  I am a big guy and and press a good amount, but what am I trying to prove by beating it with a hammer?  With the tunnel cut out  I can center and measure everything, and install the rear transmission support member without any headaches, then put the cutout back on, tag in whatever bits I need to give it some breathing room.

 

I could maybe zip it up the middle and spread it I guess. Is that a better? 

I went with the zip it in the middle and spread it out.  In the attached photo you can see my transmission tunnel with the rx8 tranny mounted to my engine.  I pushed the engine back farther than most, so the bell housing needed a bit extra room right at the firewall.  But this is easy: cut the slots to create some freedom of movement, then install the engine/transmission from below, with the front of the car raised with an engine hoist, engine on a rolling dolley.  

 

As you lower the car onto the engine/transmission the panels will flex, giving way to show you where you need to form or add a bit of sheet metal.  I found it easier than making an entire trans tunnel.

IMG_7645.jpg

Edited by Ian
  • Like 1

Ian
'76 M2

'02 325iT

Link to comment
Share on other sites

18 hours ago, Ian said:

I went with the zip it in the middle and spread it out.  In the attached photo you can see my transmission tunnel with the rx8 tranny mounted to my engine.  I pushed the engine back farther than most, so the bell housing needed a bit extra room right at the firewall.  But this is easy: cut the slots to create some freedom of movement, then install the engine/transmission from below, with the front of the car raised with an engine hoist, engine on a rolling dolley.  

 

As you lower the car onto the engine/transmission the panels will flex, giving way to show you where you need to form or add a bit of sheet metal.  I found it easier than making an entire trans tunnel.

IMG_7645.jpg

Thanks for the pictures.  It is extremely helpful.  Judging from the slit in the top it appears that it is a smidge higher than stock. 

 

I was hoping to install it and also be able to accomodate my Behr A/C. It will be really close, but I think I may be able to shoehorn it in, although it will be very tight.  I have kinda resigned myself to the fact that I will likely be putting the whole system on the classifieds.... no sense in having a cold car if it can't move.  And it won't work with my future turbo.... but that is another story. 

 

I agree that the installation method would be ideal, but for "reasons" I can't do it that way.  I think I will cut it out and modify it and put it back in.  It will be way easier.  If I was pulling the engine it would be a completely different story. 

"Goosed" 1975 BMW 2002

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • BMW Neue Klasse - a birth of a Sports Sedan

    BMW Neue Klasse - a birth of a Sports Sedan

    Unveiling of the Neue Klasse Unveiled in 1961, BMW 1500 sedan was a revolutionary concept at the outset of the '60s. No tail fins or chrome fountains. Instead, what you got was understated and elegant, in a modern sense, exciting to drive as nearly any sports car, and yet still comfortable for four.   The elegant little sedan was an instant sensation. In the 1500, BMW not only found the long-term solution to its dire business straits but, more importantly, created an entirely new
    History of the BMW 2002 and the 02 Series

    History of the BMW 2002 and the 02 Series

    In 1966, BMW was practically unknown in the US unless you were a touring motorcycle enthusiast or had seen an Isetta given away on a quiz show.  BMW’s sales in the US that year were just 1253 cars.  Then BMW 1600-2 came to America’s shores, tripling US sales to 4564 the following year, boosted by favorable articles in the Buff Books. Car and Driver called it “the best $2500 sedan anywhere.”  Road & Track’s road test was equally enthusiastic.  Then, BMW took a cue from American manufacturers,
    The BMW 2002 Production Run

    The BMW 2002 Production Run

    BMW 02 series are like the original Volkswagen Beetles in one way (besides both being German classic cars)—throughout their long production, they all essentially look alike—at least to the uninitiated:  small, boxy, rear-wheel drive, two-door sedan.  Aficionados know better.   Not only were there three other body styles—none, unfortunately, exported to the US—but there were some significant visual and mechanical changes over their eleven-year production run.   I’ve extracted t

  • Upcoming Events

  • Supporting Vendors

×
×
  • Create New...