JaNusSolSumnus

Well I have been researching the idea of a swap ever since I bought my auto FD back in April. The idea has mixed views of complexity but one standing view that everyone agrees on is that it is the best mod for an auto-FD. I've read through these two threads below including a couple others on NoPistons and there seems to be some inconsistancies of how much has to be done to swap.

Some say with the harness that complete replacement or rewiring is needed in order to make a manual trans and ECU work in an auto car. Others say that just wiring up the reverse lights, clutch safety switch and speedo/tach is all that is needed.. and that the tach/speedo use all the same stuff the auto did so no real modification to these or their wiring is needed at all.

Some say the swap was a breeze and that the harness was the only hard part, while others say they have run into some major issues such as: trans bolt patterns DIFFERANT, starter mounts leave a gapping hole on rear housing, front counterweight is differant and will ruin engine if not changed... What is true about any of this? I mean this car was MEANT to be a manual and yet in strapping an auto to it seems Mazda changed EVERYTHING except the automatic itself.

AT to MT swap:
https://www.rx7club.com/showthread.p...l&pagenumber=3

Auto to Manual Harness Conversion:
https://www.rx7club.com/showthread.p...06#post2569106

I have collected the folllowing parts for my transition.

5spd trans
5spd shifter
driveshaft
engine counterweight (front)
ACT street/strip clutch kit
5spd starter
M2 stage 3 ECU
clutch master cylinder
clutch slave cylinder
clutch mst/slv lines

Now I know in addition to this I will need the 'companion flange' for the rear differential as well as the manual gauge cluster and clutch/brake pedal assemblies. Possibly new wiring harnesses or modification of my current ones may also be needed.

Here are my questions that I'm looking for solid answers on as there is a lot of vagueness around this swap.

Wiring Harness:
~Can the auto harness be reused without extensive modification as mentioned in the above thread? By that I mean can I just wire the reverse lights, and clutch safety and call it a day as far as getting the car started and drivable?
~Speedo + Tach, is any modification needed for these to function normally with the manual trans? I wouldnt think the tach would need anything as it runs off the motor and the speedo should connect to the manual trans the same as it does the automatic. Please correct me on this if I am wrong. Would I need the manual gauges? Or would the auto gauges function normally? (Sans the indicator and offset redline)

Trans-to-Engine
~Bolt pattern, are they differant? If they are, how are they differant and how was this overcome by other swappers?
~Starter 'hole', is there really a large hole left in the rear housing when using the manual starter? If so how is this overcome or covered? Is it even a concern that it is there?
~Front counterweight, some say a lightweight flywheel will resolve the issue others say no modification needed. What is true, what harm will come if I do not change the front counterweight? I want to avoid this if possible due to it being behind the front cover.

I dont want to go into this modification with one eye closed, I am trying to collect as much information as possible whilst trying to fill in the 'holes' of previous posts.

Thank you,
~Kris

speeddemon7

ejmack has done the swap and so has zyon13b
you can also talk to rotary extreme and also rx7store for more info regarding the auto to 5 speed swap. Im in the same boat as you. Although i dont have the parts yet like you do. I would suggest getting the 5 speed differential as well.Better rear end gears. 3.9 in the auto vs 4.1's in the 5 speed.

JaNusSolSumnus

I'll have to PM them and see what they have to say, maybe give Jason at RX7store a call and see what his thoughts are. Thanks for the info...

As far as the rear-end I'm just gonna stay with the 3.9 for now, once I can afford it I'll probably just have the ring/pinion swapped up to 4.33 and call it a day. Right now I want to be shifting through 5 gears at ANY rear-ratio.

~Kris

Badmfer

iTrader: (4)

DUE THE SWAP!!!! make sure you change the flywheel on the back to compensate for the different counter weight. Racing Beat 17lb flywheel is optimal for this, and yes do not use the stock 5spd flywheel or you will ruin your engine. and i know this cause it happened to me.

ejmack1

please search my posts... I have a lot of information spread out in a few different threads.... if you read the posts, you can use the auto harness like I did... If you look through my Wiring Harness rewiring thread... you might get an idea of what needs to be changed. but i would just get the manual dash and engine harness...

ejmack1

well mine worked for over a year just fine... So I think you should watch the information you are giving out....

ejmack1

The difference between the 3.9 and 4.1 is like night and day.

You will have to drill the flange on the Auto diff to mate with the manual driveshaft...

I ended up buying a used 4.1 differential and selling my 3.9 differential and nearly breaking even...

I would highly advise doing that.

ejmack1

you will have to keep the auto tranny computer if you keep the harness and just wire into the existing wiring. Take a look at my harness rewiring thread. I eliminated the tranny computer, while still using the auto harness.

There is 1-2 holes that wont line up on the auto engine and manual tranny. No big gaping hole at all. And i know some people say you can use the auto starter, but they are honestly full of ****... Its impossible. Front counterweight is fine, and you can use a stock flywheel. My car ran over 25K miles (50K on the engine) before I popped it because of a boost spike in 5 degree weather. Be careful what infromation you read about the swap, some people do not know what they are talking about Some people like to talk but in reality they have no experience doing the swap.

Rear Differential with 4.10 gears
Gauge cluster without "PRND21, Hold" Lights which is also calibrated to the 4.10 gears
5 Speed Wiring Harness

check above, you can use your existing gauge cluster, just make sure you use the correct speedo sensor. you dont need a companion flange, you can just drill new holes in the flange, until you get the correct differential Clutch and brake pedals bolt right up the holes in the firewall are covered with a plate that just unbolts.

all you have to do is wire the clutch safety switch in order to get the car to start... no other modification is neccesary. Of course you will not have 1-2 switch, reverse switch or neutrtal switch hooked up correctly The speedo sensors are different. Make sure you use the correct one, they look different (one is longer) but they will both work in either tranny. They will obviously just show the wrong speed.

Pretty sure I already covered all these questions... if not they are definately covered in one of my threads....

ejmack1

and finally a semi How to on the mechanical portion. Never got around to the rest, mainly because i really dont have much time and no one else wanted to help.

another thread whored out by ejmack

JaNusSolSumnus

What are the purposes of this the 1-2 gear switch and the nuetral switch? I know the reverse switch turns the reverse lights on, but I thought the nuetral switch was the switch under the clutch pedal to cut-off the starter.

As for the rear diff, couldnt I just take the yolk from a manual diff and stick it in my auto diff? No big deal?

As for the front counterweight, I may let it slide for a little bit but I honestly dont see how offsetting the motor balance can be a 'safe' thing... If it wasnt an issue why would Mazda create two differant counterweights?

As for the harness, I will have to do the heavy modification written in the 'rewiring thread'? I cannot just wire of the clutch switch for the clutch pedal and drive the car?

You said the speedo sensor from the auto works but it will be 'off' slightly, getting the manual sensor will correct this? I thought it wouldnt be effected unless I got the 4.1 rear as well.

Thanks ejmack1, I am gonna re-read the thread on the harness as I didnt put too much attention into the specifics on it... I just have time comstraints to get this done and it seems like its gonna be a nightmare/impossible without a lift and some airtools.

~Kris

ejmack1

1-2 gear switch I have never gotton an answer on the functionality of it, but it is there. Neutral Switch is what senses you are in neutral Probably adjusts somethin with the idle... not sure

Driveshaft is a different length... Just drill the holes, there is an inner lip on the flange that center the driveshaft so you dont have to worry about it getting out of line.

Out of all the people that have done this swap, I don't really know anyone that has changed it. If you want to change it then do it, but you really don't need to.

You could, just depends what your mods are and how in depth you wanna go. Check the wiring diagram and you will get an idea of where you need to wire the switches. I believe COsborne had a good thread with the pinouts and everything.

you can use the auto sensor in the manual tranny. I guess since you will be keepin the 3.9 gears it won't have an effect on the MPH.

I did mine in the driveway with a 98 piece tool set, and 4 jackstands.... of course i had to go buy a socket for the flywheel nut, and had to get some *****, to put 300+ lbs of torque on that ******

Badmfer

iTrader: (4)

you only help prove my point. my car ran fine for about 6 months until the engine went bad due to being unbalanced. better safe then sorry!

Badmfer

iTrader: (4)

you dont need to change the front counterweight but you should use a 17lb flywheel.

JaNusSolSumnus

What is the weight of the stock flywheel? All the aftermarket lightweights I've seen are 9.5lbs and 12.5lbs... I think RacingBeat offers a 7.5lbs. I honestly dont feel safe doing that, maybe for a couple thousand miles until I can pay someone to do the front-cover work but no longer than that.

Thanks,
~Kris

Badmfer

iTrader: (4)

stock flywheel is 19lbs....if u get the 17lb flywheel you dont have to change the counterweight on the front.

JaNusSolSumnus

Where do you get these mystical 17lbs flywheels? I'm assuming if I got a 9.5lbs flywheel I could use the rear-counterweight for a 12.5lbs one?

Thanks,
~Kris

Badmfer

iTrader: (4)

Racing Beat sells a 17lb flywheel. When i called to order it whoever i talked to on the phone was very knowledgeable. If you go with a lighter one, you would think you would use the different counterweight, but you are going to have to get that answer from someone else.

maxpesce

Aftermarket flywheels DO NOT (generally) have a counterweight built in like the stock MT flywheel does - They use the same counterweight as the AT (note: AT cars dont have flywheels at all - just a flexplate w/ the starter ring gear that the torque converter bolts to and a seperate counterweight). The style/size of the counterwieghts is determined by the ROTOR weights and varies by engine type/series, NOT Flywheel size. For an at to mt swap you just need to get an aftermarket flywheel and stay with the counterweights that are already on the engine. If you want to use a stock (or lightened stock) flywheel you have to remove the at's REAR counterweight AND make sure the new flywheel was from an engine in the same series w/ the same style rotors. (ie for an fd you need a flywheel from a series 6 13b-rew)

ejmack1

please explain where you came up with this information... BTW, my engine blew to overboosting in cold weather...

how do you know your's went because of your engine being unbalanced?

ejmack1

So tell me this... how many people are running aftermarket flywheels without using the stock counterweight (nearly all, because anyone with a manual tranny car did not have a counterweight). So I guess everyone that has a lightweight flywheel better go get there engine balanced and there counterweight drilled out to the right amount so there engine doesn't blow

JaNusSolSumnus

My understanding is that both AT and MT motors have front and rear counterweights. The rear is the same on both, however the front has differing part numbers. I dont know the weight differance or at what degree i is positioned differantly, I just know it is differant. Now ejmack1 says it is safe and was safe on his motor with the STOCK flywheel, so I assume I can run that way atleast 5-7k miles.

BTW, RacingBeat's lightweight flywheel kit comes with a rear-counterweight... whether it is just an OEM manual one or not I do not know.

I'm still concerned about the rear bolts.. the trans is held to the block by 6 bolts correct? If two do not match up that means only 4 are holding it together... even with the other supports I dont know if I trust that. Whenever my motor DOES go I will certianly be getting a manual engine reman.

~Kris

Badmfer

iTrader: (4)

i bought the flywheel without the counterwieght

Badmfer

iTrader: (4)

I have this information based on experience. I am not saying you are wrong i just want to say what ive seen done. i know mine went to an unbalancing because i took the engine apart. The front housing has gashes in it from where the rotor was rubbing against it. The front rotor was also pinched together so much that the seals could not be removed. there were also spots on the rotor where it had been rubbed down. One of the rotor housings (rear one) was gashed to all hell from the rotor scraping against it. I dont mean to argue and i wish this topic had more concrete evidence on what exactly to do.

ejmack1

i understand the point your getting at, but look how many people run counterweights that were not made specifically for there engine....

Maybe we just solved the mystery of why the rotary is so unreliable

DaleClark

iTrader: (55)

On the counterweight deal - there's some confusion here. First off, manual tranny cars have a big, cast iron flywheel that has a counterweight cast into it. Automatic cars have a small counterweight with the flex plate bolted to it, and the torque converter bolts to the flex plate.

When you get an aftermarket flywheel, guess what? You buy an automatic counterweight to attach to the engine, then bolt the flywheel to the auto counterweight.

So, in doing the swap, just get any aftermarket flywheel that's designed to bolt to an automatic counterweight. Remove the flexplate, bolt the flywheel on, done. You don't even have to break the 54mm e-shaft nut loose.

I'm not doubting the experience of having the engine unbalanced, but really the rotors and counterweights are matched sets. If you run '93-95 rotors, which are all the same manual and automatic, the front counterweights SHOULD be the same, as is the specific weight of the rear counterweight.

Seriously, I would just get a good aftermarket light flywheel and be done with it - just makes the whole process far easier, and it's an upgrade. The weight of the flywheel itself has no bearing - it could be 5 pounds or 500 pounds, the balance is all in the counterweight. Get the flywheel weight that you feel comfortable with driving. Personally, I'd go chromoly or aluminum in the 9 pound range. An AL flywheel is NOT hard to drive at all - maybe if you're a total novice at driving a stick it would be. For the cost, you really don't get a lot of benefit with a steel flywheel - it's just not a lot lighter than stock.

Dale