Transmission Alignment Problems - Gearbox and Diff dont line up  

metalhead

I think modifying the transmission tunnel is your best bet. I'd be surprised if it was illegal to do so provided it was blue plated, but I'm not familiar with the Qld system. Can you just stretch it, or will it be a cut off the top and replace it job? Either way, this will be the easist option, and even if it is illegal it will be very difficult for anyone to know that it has been done if it is done properly and tidily once it has carpet and paint over it.

Lowering the front of the engine would also be a good option, but without seeing it it is hard to say how easy it would be. I would be surprised though if you couldn't get the same clearances with a custom wet sump as with a dry sump, by moving where the bowl of the sump is. Keep in mind that depending on the amount you lower it you may have issues with clearance for other things needing adjusting, such as turbo manifolds and cooler piping. On the upside it would improve your center of gravity slightly. Does moving the engine forwards or (preferably from a weight distribution point of view) backwards improve the situation at all?

The only other thing - from what youre saying, is the gearbox touching the tunnel? This is bad, it will put vibrations through the chassis and can cause other issues.

ron180

you cant shim the diff cradle like in a 180/S13 to get a better angle or lower the diff in the cradle

bang the tunnel out with a sledge hammer to get some more clearance and replace gbox crossmember to bring gbox angle up

Duj

I got a great suggestion Mike!

*Sell the Rotary engine and box, fit a standard 1.6l piston motor&box and drive it!
Obviously its causing you mega dramas in every department
And your whinging is beyond a joke now !
(have you been embarrassed enough yet?)

Its a fairly modified car and its not going to be perfect!
also may I ask what ''parts'' were damaged due to the angle on the gbox...?

I drove/owned it for 2 years and had loads of fun!

I just dont understand why you cant jus drive it and be happy...

headsense

I dont know the full story here but add my two cents . It is quite common that both diff and gearbox are not in perfect alignment , it happens through your suspensions bump and rebound and when lowering and raising the car as well .
I assume the car was smooth to drive prior to the diff failure ? A severe misaligment would have been obvious from vibration at a particular speed or right through the speed range as well as premature universal failure before a diff failure .
If the car has uppper and lower control arms locating the diff , you have the option of fitting adjustable arms to allow pinion angle adjustment .
Another option in the case of short drive shafts and severe angles may be a double cardan joint which is a common mod in Jeep Wranglers and Suzuki Sierras .
Before you do anything accurately measure the diff pinion angle and gearbox output shaft angle so you know the actual misalignment and refer to a driveline specialist so you acutally know your exceeding the range of the fitted universals .
Avoid sledge hammering the floor pan it looks like shit and while not technically illegal could cause know end of grief with vechile inspections cause its plain shit rough .
If you only need a little room heat hte floor with and oxy and work it when soft , just dont go overboard
In the event you cut and shut the tunnel a replacement bracing is generally reuqired to regain lost strength .
Last time i had to do this the brace had to be substantially larger than the whole to ensure rigidity . Also the brace had to be fittdinside the vechile and looked shithouse under the carpet , was heavy too

lil_mike

when my mechanic gets back from greivance leave you can call him. his wife passed away on tuesday last week so he is not the best right now. but he was absolutley disgusted with the way this car has been built. i dont really care what you say or think about how i'm whingeing all the time. i've got damn good reason to.

honestly, i dont care if it was you, the previous owner, the original mechanic or whatever that has fucked something up, but dodgy work has been done and it is really starting to show through. did i mention that we have to refabricate the powerplant frame as well since its only held on with two bolts? oh, that and the fact that the mount for the powerplant frame is on the opposite side of the diff? so how did that connect up i wonder? my mechanic is fairly certain that the tranmission alignment has caused the diff to snap since it it basically split down the middle as well. i've also gone in and looked at everything he siad and confirmed it all with a second opinion from another workshop. if you still think i'm talking shit then your more than welcome to call him when he gets back.


no, it wasnt smooth to drive before the diff died. when you came off throttle it would jerk and shudder violently until you put the clutch in. it did this at anywhere over 15km/h.

we cant do a cut and shut on the tranmsission tunnel due to laws in QLD. even then though, the amount we would have to do a lot of it to make it fit from what i saw.

the main problem here is that we cant raise the gearbox up high enough to meet the diff. if we try it hits the tranmission tunnel. this is a rough sketch of the problem:


its a crappy drawing, but you get the idea. the problem comes from the engine being put in on a slight angle, with the nose pointing upwards a little. the angle is about 10 degrees i think., but that is with the gearbox touching the floor of the car.

metalhead

What a load of shit. A properly modified car will not have the kind of issues this guy has been having. I'd be pissed too if I'd had all the problems he's had.

Mike, if you don't want to modify the transmission tunnel you're looking at a lot more work. It's hard to say without seeing the car, but I would think that your only other option is to move forward and/or lower the engine, which you said will require a custom sump. It would also be worth looking into the 'double cardan joint' that headsense is talking about. I have no knowledge of these but would assume a driveshaft place would know what it is and whether it is an option for your situation. Certainly a different driveshaft would be by far the easiest option.

headsense

A conventional universal joint will cause the driveshaft to speed up or slow through each revolution and cause a corresponding change in the velocity of the driven shaft. This change in speed causes natural vibrations to occur through the driveline necessitating a third type of universal joint -- the double cardan joint. A rolling ball moves in a curved groove, located between two yoke-and-cross universal joints, connected to each other by a coupling yoke. The result is uniform motion as the driveshaft rotates, avoiding the fluctuations in driveshaft speeds.


Figure 6 Exploded view of a typical double cardan U-joint assembly.

headsense

I'm an electrician and back yard mechanic not a driveline guys so maybe Cardan joints are not the fix , but the long and the short of it is to measure the opposing angles off diff and geabox . Seek advice , if to severe move motor foward and or down into the bay or go 4wd style and fit body lifting blocks ...............kidding

lil_mike

its not that i dont want to modify the transmission tunnel, its that we cant. by law we arent allowed to modify them in queensland on this type of chassis. after looking at the engine bay myself, it looks like there could be a few other obstacles in the way if we tried to lower the nose. mainly exhaust manifold and turbo along with a few other issues.


ok, i understand what your saying there headsense. that seems like it could work actually and might save us some trouble. would such a joint go at the gearbox end or diff end, or would it go, say in the middle of a drive shaft?

thanks headsense.

headsense

Typically gearbox end of tailshaft as this is where the transition of angles is highest and so compensation required hence Cardan joint .

a mid shaft arrangement like a commodore for example , I would have thought not be suitable as it would have to hang quite low under the car and you ultimately end up with both front and rear shaft running on angles , and this type of joint would have angular limitations . I believe ( havent own commodore for 10 years now ) that the front half of the shaft is in the near level plane and the rear half running in a downward angle to the diff . Plenty of guys use 1 piece shafts but the single downward angle will forrce the tailshaft into the handbrake assembly and hit the tunnel on severly lowered cars

If your in Brisbane measure the angles and talk to Driveline Services Australia ( Rocklea / Brendale ) or someone like that

Its hard to tell you much more without physically seeing and taking the measurements / considering the options ................and my first hand dirveline experience is all Ford / 4WD and diesel stationary engines and gearboxes

lil_mike

ok thanks headsense. the car is with driveline services at brendale and they have been looking after the whole thing. they've been pretty good about it (considering this has taken us almost 5 months to fix).

would there be any legality issues with a Cardan joint or engineering required? i'm assuming it would be legal if they use them on 4wd's?

EDIT: nope, cardan joint wont work. its too bulky to fit in there. we could do it, but the moment the suspension started moving we would have problems with it smashing into the trans tunnel and other things again dammit.

headsense

Thats to bad , sounds like its time to cut and shut the engine mounts , the floor pan , the front crossmember or maybe even reverse the sump.

Short of fixing it myself i cant offer much else ...........heres hoping you get it sorted

lil_mike

if we cant fix it without going completely overboard i'll rip it out and rethink the whole thing. we've got someone coming in to have a look who's doing a similar conversion but with a renesis engine. so hopefully he can sort something out.

MR2Mark

I dont presume to know much about unusual engine and driveline swaps into mx-5's so just pretend I am thinking out loud and correct me if I am totally wrong.

Would it be possible to do a little of each of your original solutions?

If there are any prominant ridges or bumps on the transmission that prevent it from sitting higher perhaps you could dent out the transmission tunnel in the areas they hit it specifically. Conversely, grind down the ridges or bumps a tiny amount if it would make all the difference?



If lifting the rear just a little can make up the difference after modifing transmission tunnel and lowering nose of the engine, and it isnt too expensive or difficult, maybe there is some merit in this. Perhaps you could explain why you want to avoid this?
On a side note: Lowering the front of a car and raising the rear in aero terms is known as rake. It can make more downforce through creating low pressure under the car. How this might help or hinder a mx-5 I couldnt begin to guess.



You say it is already very close and there isnt room to lower it enough. perhaps in conjunction with the other 2 solutions above it would be enough?


Again, I doubt this will help much but I find bouncing ideas around, even if they plainly wont work, often helps find a solution eventually.

lil_mike

we arent allowed to modify any parts of the transmission tunnel according to Queensland Transport. it must remain completely intact. plus with the car so small, any modifications would start to show through the floor pan.

the amount of lift required on the rear would be ridiculous. we're talking around 6 inches here. the car would be far too front heavy. downforce would be another issue but i wouldnt be able to test it without it running. it would lose its 50-50 weight balance though which would definately kill its handling.


yeah i know what you mean. any input is better than no input. hopefully we can sort it out soon.

to do a bit of each solution though would cost a fortune. a friend did bring up an interesting idea though. When the diff died we decided to put the new gearbox in as well as the old one was completely shagged (synchros were nearly non-existant). now they should be identical as they are both rx-7 boxes (pretty sure they are both series 6 ones). but is there a possibility that they could differ, or did some come out with slight changes?

lil_mike

well i just got off the phone with Mr Rotary. he went down and had a look at the car yesterday. he specialises in conversions.

i'll give you the good new first. he said he can make it work, its possible to make it all work.......for a price.

now the bad news. we have to pull out the entire engine, transmission, etc. then we have to lower the engine and position it properly in the engine bay. from there we have the problem of the turbo firstly. it has no room to move down to begin with, so we would need high mount manifold and new piping for IC setup. then there could also be the issue of the firewall as well. once thats done we'd have to have a hybrid gearbox made up comprising of a 12A-t internals in an MX-5 housing mated to original MX-5 driveline.

his words were "i dont know how this was driving on the roads before this, let alone legally. This is the worst conversion i've ever seen. The people that did this conversion obviously did a dodgy job"

so Duj, shove that up your ass you stupid assmonkey.

metalhead

That sucks mate, the 12at boxes are much weaker than the later model boxes too. I don't know how much power you're pushing, but if it's a reasonable amount I'd be looking at beefing up the internals of the box one way or another.

I can't believe the number of issues you've had with the car either, or that it was engineered setup the way you describe. Exhaust manifolds and intercooler piping can easily be changed, and if the engine needs to be remounted then that is unfortunate but it shouldn't be too much of a hassle. I'd be looking into whether the gearbox will be up to the task though, it'd suck to finally get it all sorted properly and find that it starts regulary smashing gearboxes. Probably not something you want to think about, but I think you'd better look into it.

The existing gearbox won't fit in the tunnel properly if the engine is lowered? The series 4/5/6 gearboxes are all slightly different I believe too, certainly the mounts for each box are different. With my 323 I have been working out gearbox and engine mounts the past few weeks, and with the engine and gearbox lowered enough there is enough space even in my little 323 tunnel for a series 4 turbo box pushed a long way back (oil filter barely clears the firewall) while still retaining a decent angle on the tailshaft. Certainly the mx5 housing box will be the easiest to fit, but have a look at your options.

Hope you get it sorted soon either way.

lil_mike

well, would the internals from the series 6 fit in an mx-5 casing? or maybe thats asking a bit much from a little gearbox

i may go with a series 4/5 box instead. i know the series 5 ones arent as much hassle to get in there, so that might be an option i guess.

i'll have to look into it and see what i can do. i would like to have the car ready before december though

metalhead

I don't know a lot about the difference between series 4/5 and the later boxes. I think series 4 and 5 are very similar, from memory they are basically identical, except one has a slightly taller 5th gear than the other, and the series 4 box is easier to mount as it has a flat mounting surface, and I think the series 5 requires a more complex mount. I'm not 100% confident on this, I got a good deal on a series 4 box already shortened to suit my use so didn't look into it a lot. On Ausrotary there is a big thread in tech reference about the difference between mazda gearboxes. It would be worth having a look.

I believe the 12at boxes are similar in strength to the other first gen rx7 boxes, which are pretty commonly broken behind any reasonable power. I also very much doubt series 4/5/6 internals will fit in an mx5 casing, I think the reason that is possible with the earlier gearboxes is that they are a similar design to the mx5 box. The later boxes are much beefier. If you've seen pictures or had the 2 of them side by side you'll see what I mean.

There may be other options for strengthening the 12at gearbox bits if that's the easiest way to go though. Be that by stronger aftermarket gearsets or by treating the existing components in some way. You'd have to talk to an expert about that though.