Transmission Swap, Electrical Issues, and More!
 

So first, this is one thread with three questions and... here they are:

1. The transmission on my 1980 RX-7 is on its way out. 2nd gear synchro is nearly dead and 3rd is on it's way out... There are grinding noises and clunks (and it's not the rear end as I just rebuilt and replaced everything there). I have an '82 transmission from my parts car that is still good and I have found some threads that make it sound as though a swap is feasible:

https://www.rx7club.com/1st-generati...tions-1089939/

https://www.rx7club.com/1st-generati...ans-sa-612876/

From what I have found it sounds like all you need to do is swap the shifter tower, rods and such, and perhaps the tail housing. Could someone confirm this? This car is somewhat a dd so I'd like to know if everything will play nicely before I tear out the trans.


2. Recently while driving with the headlights on (and occasionally when off), my radio will shut off randomly and all the lights dim. It's worst when you just let off the gas. According to a local shops tester, my battery and alternator are just fine. Like I said this is a recent thing and has never happened before. I've cleaned the battery terminals, and looked for loose or broken wires that might be bouncing around but no change. Another thing to note is that my right headlight pops up after the left, and sometimes not at all. Thoughts?

Edit: The radio is an aftermarket head-unit and sub. It also happens if the radio is "off" which means the sub is shut down and there is no input selected.


3. On the last two drives I've taken, when I shut off the car there is a fairly loud grinding sound. It's only when you shut it off and I honestly have no clue what it is. I've heard it could be a bad fan clutch but I haven't had time to check it out yet.

Thanks,
Ben

2. I would disconnect the radio stuff and see if the problem still exists. To many unknowns for us unless we can see/touch the wiring.

3. Could also be the alternator bearing or maybe alt pump that is not happy. Just thinking of things that go round-and-round when car is not moving.

So I was trying to think what had changed since I had messed with my ignition system and now (as I believe the radio thing has only happened since) my theory is that the alternator capacitor - or condenser - is to blame. I changed it out with a unit that I did not know if worked or not just as something to try and fix my ignition issues. Now I'm wondering if that's what's causing the problems. From what I can find (which is very little), that capacitor helps to smooth out power coming from the alternator when load scenarios change, high/low spikes, like letting off the gas and such. I'm about to change it back to the original one and see if that fixes things.

No progress on the other problems yet. If this doesn't fix it I'll look into the radio wiring even though I just re-did it a couple months ago to clean up all the random junk the PO had installed. Thanks thus far.

I've had a similar problem, though I don't think its random: Its whenever the output from the amp (built into the head unit in my case) exceeds a certain level, like when I'm listening to a podcast and someone gets excited and raises their voice. The radio then powers up a few seconds later. I'm planning to replace the radio with a newer unit and check out the wiring. I haven't noticed my lights dim at the same time and it doesn't cause any other problems or me, but it sure is annoying.

Also I broke my 2nd gear synchro today, so bump on the transmission questions.

See the issue with mine is that it happens even if I'm not listening to anything. Last night after I changed the capacitor I thought I fixed it but instead it only did it seemingly less often (although it probably was just chance). It also doesn't line up with bumps in the road or anything that I've noticed. The most common time for it to happen is right when you let off the gas or are sitting at a stop. Tonight I'll check out what unplugging it will do for the headlights, and with that I'll also take another look at my wiring. My head unit does have problems - for some reason buttons change what they to, like the off may become the source, etc. - so perhaps it's just damaged and messing stuff up. It did come in my parts car so... Anyway, I'll post an update if I figure anything out tonight.

Also, the transmission noise is getting slowly worse, so if we can start getting that figured out that would be awesome. I'd like to do the swap within the next week if the parts will match up.

You need to check for loose or bad connections near the alternator and/or the battery. When you let off the gas or idle the engine is probably moving the most and it would aggravate any wiring issue and may be causing this for you.

I suspect the grinding noise may be your fan, You need to have someone turn off the car with your head in the engine bay to see what it is. Or you can try spinning the fan by hand to see if its dragging or anything.

The tranny swap may be possible. I've heard of being able to swap tail sections from the 80 tranny to the right model later year tranny to get a fit in an SA. Not sure about the exact year required and so forth. Hopefully someone will come forward with details for you. Also keep searching, I know I read about this before.

Tonight when I get home I'll check out the fan. It spins freely when cold, but I suppose that that's not the case when you would normally shut the car off and it's hot. That's also probably why it only does it once the car is warm. We will find out tonight.

As for the electrical issues, I have another theory. The positive terminal for the battery has a split cable, and an obviously not original clamp. The one for the starter runs to, well, the starter, and the other runs to the fuseable link box on the strut tower. That wire is what supplies all power from and to the battery to the rest of the car. As the clamp has a small and short wire, the PO took a wirenut and another wire to connect the clamp to the fuse block. Tonight I'll also check that connection as perhaps that's causing issues.

I'd just replace that whole feed wire. IMO wire nuts have no place on a car...

That's what I'm planning on doing. Last night I found a length of what I think is 6 gauge wire from a previous sub install. I'll probably go get a new clamp and redo the connection. Hopefully that will fix it.

As for the transmission, any advice appreciated.

Didn't have time tonight to go buy a new clamp so instead I just cleaned up the connections and such. Problem seems to have lessened, although when attempting to reconfigure my radio (due to the loss of power), it didn't feel like cooperating. Perhaps I should look for a new head-unit. None of the buttons would do the same thing twice and I couldn't even get into the menus to change settings. I only had the loss of power/shut off thing once when I put on the turn signal to pull back onto my street after the test drive - headlights were on and this was after some low rpm driving.

As for the grinding sound on shut down, it appears to be coming from under the car. Perhaps an exhaust rattle, or maybe it's just another part falling off of my already dying tranny. Who knows...

More trouble shooting to come this weekend so I'll keep this updated.

So after some investigation with the headlights I have figured out the following (thought process proceeding): If you use the lever on the steering column, which turns on the lights at the same time as raising them, I run into the issue with the right side not popping up. If I used the manual switch in the center console they work fine consistently. I figured this was due to the added load of the lights being on, causing there to not be enough power to raise both the left and right at the same time, and thus instead one after the other. I know the battery and alternator are good so I decided to check the resistance on the grounds. From the battery to anywhere (including the engine block) I read ~4 ohms. I made sure to clean where I tested before hand so rule out that possible variable. To me this seems a likely culprit to my power issues as the higher resistance would lower the current capacity, noticeably affecting higher loads such as the radio or lights. Thoughts? I didn't have time to clean stuff today, but maybe later in the week. What should I expect for a resistance reading from the battery terminal to grounding points?

In my previous post I mentioned the radio going kaput; not anymore! I checked all the wiring and it was clean, so logically I removed the unit and fully disassembled it :). Inside I found that a corner of the PCB was snapped off along with a lot of flux residue and grime that I then removed. I glued the PCB back together, reattached the broken trace, and cleaned the whole thing real well. Since then it's worked 100% normal, but I guess I'll find out how time treats it.

I confirmed the "rattle" is not the exhaust, so now I'm betting it's tranny related. It happens with the clutch in or out so it has something to do with the engine moving when it returns to idle. As for the swap, I measured everything and it seems all will work so long as I can swap the tail housings, otherwise it all looks good to go. Are the internals different enough that swapping the tail housing will not work? I still have to find some documentation on the transmissions to compare them.


Long post, thanks thus far.

Well I went ahead and decided, after doing more research, that a transmission swap was possible. And... now I have different transmission in the car and it's back on the ground. I have to admit, a transmission swap is not the most fun thing on jack stands. Anyways it's driving again while my original transmission is being inspected and dissembled by a friend and myself for a rebuild. All that was required to swap the tranny was the tail-housing , and the shift forks (the pieces that are moved by the shifter rod for lack of better terminology). Something I noticed on both transmissions while they were apart, was that the bearing for the output shaft seems to be spun. It spins quite cleanly in the center casting, almost like it was designed to. Is this supposed to be pressed in and is it a common thing for this to happen, or is this fine and will last for the foreseeable future?

As for the clunk, it's still present. Now with the swap it eliminates the trans mounts or the trans itself so what else would do this? Clutch, flywheel, engine bearings....? To reiterate, it happens when the engine returns to idle, and worse when it's shut off.

The electrical issue is also still present. It happens as soon as you let off the gas, so perhaps something with the charging system where it looses power with the sudden drop in rpm. It also gets worse the more load that you put on the system. The most notable signs are still the headlights and the radio. The headlights still do the "one after the other" while the car is off, so perhaps that points back to the original thought that it was the main cables. I have since cleaned the ground and the resistance is back down to ~ 0.2 ohms but with no major changes. The resistance from the chassis to the battery terminal is still quite high though. Where is the main chassis ground? If I can access and clean it maybe that would fix some things.

Just looking for some input here. Also, when I get the transmission rebuild going, I'll be sure to document things for anyone who may need the swap information in the future.

Electrically, I would recommend brand new + and - cables to start with. This are not available from Mazda, but with the old ones in hand there are places that will build you a nice custom set. If yours are the originals, the amount of corrosion internally can well be a cause. I have heard of weird, untraceable electric gremlins "magically" disappearing when new cables are added. Regardless, at the cars age, this should be done....

Kudos on the TX rebuild! That would be like Black Magic or Nuclear Fusion to me :D

Stu Aull
80GS
AK>AZ

What ground did you clean,where are you measuring from/to?
Main chassis ground...follow negative battery cable from battery to main ground lug at driver side inner fender apron down by frame rail. The cable will be stripped of insulation for about an inch and a ground lug is clamped around cable and bolted to fender apron. Does your car still have this,is it corroded? Unbolt and clean up lug with sand paper and do same where it attaches to body. Reattach cable and check ground again.

Digital multimeter,are you zeroing meter before testing? Turn meter on,low ohm scale,touch both test leads together. What is the value?The reading is the internal resistance of the meter and should be subtracted from whatever readings you get.
Start resistance testing at battery. One lead on negative battery post,other lead on negative battery terminal.What is reading? Next,move one test lead to ground lug listed above leaving the other on negative battery post,what is reading? Next move one lead to end of ground cable by starter and leave other end on negative battery post. Post your test result numbers here.

Basic charging system output test:-
Turn multimeter on to low dc volts scale,20 volts?
Put positive test lead on positive battery post,negative lead on negative post. What is voltage read?
Leaving test leads where they are,start car(all accessories off)at a fast idle what is battery voltage? Let car idle,what is battery voltage? Move positive test lead to back of alternator battery post,what is voltage here?
Turn headlights,heater fan wipers on at idle what is battery voltage? Raise engine speed to about 1500-2000 rpm,what is battery voltage now?

Do all these tests in order given and post #s to each here. Results will help to guide you on what next to do.

Well I did those tests you outlined. The following are in ohms and have not been adjusted for the meters resistance:

Resistances:
Multi-meter Base Resistance: 0.2
Post to Terminal: 0.2
Post to Block Ground: 0.4
Post to Chassis Ground (after cleaning): 0.4 (it was over 3 before I cleaned it. Thanks for the location. It did not fix anything though) This was also measured at other grounding points on the chassis.

Voltages:
Alternator at Idle: 13.55 (stable)
Battery while Off: 12.67
Battery at Idle: 13.53 (climbed to 14.00 and stable)
Battery at 2K: 14.00 (stable)

Lights on, radio standby (no input, but turned on. Sub off):
Idle:

• 12.90 volts (dropped to 12.74 by end of test)
• Audible RPM drop
• Electronics stop clicking (relief solenoid and something under dash)
• Erratic turn signal (this happens all the time, but gets worse with extra loads)

1.5K:

• 13.15 volts
• No spikes or dips with quick RPM change (recorded up to 2K. It was late so I'll do higher RPM testing today)
• No other major changes

So that's what I've found. Nothing seems too out of the ordinary. I did find the origin of a grinding noise; it would appear something in the air pump is going out. I'll be fixing that today. I also had another idea of a ground that may be giving problems. There is one under the carpet in the rear (where the later cars had the bins), that doesn't look original that may be giving problems. I painted those cover plates for behind the seats so maybe it's not getting a solid connection now. It's the only major electrical change I can remember making before these problems started.

Analysis appreciated. I'll keep this updated if I find something.

Base battery voltage looks ok. When car is running,system voltage should never drop below 13 volts. 13.5-13.8 is a good average charging system voltage. Your idle charge spec of 12.90 dropping to 12.74 is indicative of an imbalance in electrical system.

If 13.15 is the maximum voltage at 2k rpm with lights on that is too low. You mention the problem you're having is at low engine speed or when letting off gas,at night with lights on. This and low charge rate are not a coincidence.

Cleaning the chassis ground can only help your situation and by your numbers over 2.5 ohms is significant. Makes me wonder if there's a like amount of resistance on power side of system.
If there isn't,the alternator needs to be looked at more closely. Question,is the alternator drive belt slipping or is it adjusted properly? Did you ever replace the main feed wire from battery to main fuse link,if not,should be the next thing you should do.

1. The 80's SA's could have a split case transmission depending on the VIN number of your car. I have issues with my 79 gearbox but it is before the VIN that came with a seperate bellhousing/tailshaft, I believe it was the tailshaft? Been way too long to remember but I can do some digging. Also, if you are going to go the route of rebuilding the trans there are a lot of people who go for the Miata gearbox set in the RX7 case. There is a Miata shop across the street from Road Atlanta that can do this. Last I checked they did it for $600 if you brought both transmissions to them. This was in 2006-2007ish, so obviously prices are going to be different by now.

2.Your SA came with a 55amp alternator stock. Unless you have upgraded the alternator to a later model RX7 (S5 and S6 are best) then you are going to drain the battery faster than you can charge it with that alternator. Especially that you have upgraded sound system with a subwoofer, the sub alone will draw massive amounts of power. This alternator was barely enough to run the car, when I upgraded to a bigger fuel pump I had to run a larger alternator and a relay just so the blinkers wouldn't dim...

3. Engine peripherals. Doubt it would be a fan clutch because those lock up when they go bad (so you do not overheat). Like the above said, I would check the alternator bearings and waterpump assuming that you have the clutch pushed in when you shut it off. You can remove the alternator belt when the engine is running, and I believe the waterpump belt would be a lawnmower belt number 3L220? That way you can keep the pump running. Also a good failsafe, saved me once before.

EDIT: Had to re-read that last bit, please do not attempt to remove the alternator belt while the engine is running. I meant that the car can be started and ran with no alternator running provided it does not drop below 10.5ish amps from the battery. Those ignitors tend to have a very hard time firing when it drops below that.

About that alternator. What years had the same units? I have an alternator that was on an 82 rx7, and it's noticably larger than the one on my 80. Would there be any benefit trying to install the 82 alt on my car? Is there a way to tell if that alternator was even from an 82?

I was reading yesterday in the Haynes Manual that if you ever connect the battery backwards it can fry the diode in the alternator. It's been a long time, but when a friend and I started getting this car running about a year ago, he did flip positive and negative, blowing a fuseable link (his car was black positive, red negative). Could that have made much of a difference that's only showing up now?

If you have red battery cable, then it's not a stock cable. The 1979 and 1980 alternators have external regulators (on the drivers side fender well). If you swap to anew model, it's not that hard to do. You can take both alternators to your local auto parts store and they will test them for free.

Well the battery cable makes sense, it sure doesn't look oe. As for the regulator, from what I can find, only the 79 cars had the external one. I also don't see a regulator box on my fenderwell which would support that. The other alt is definitely different (photo), although it looks like it should just be plug and play, so should I just swap them quick and see if it changes anything? Can you tell what year it is from just by looking at it? It definitely seems like a charging issue, if not some other power delivery problem.

I also just did a quick test with the headlights. Even if the battery is on the tender, they still do not both pop up. So it still seems like a power draw issue. Like I've said before, they both pop up consistently if you use the manual switch without the lights being on. I'm going to look at some more wiring diagrams to see if I can find possible bottle necks.https://cimg9.ibsrv.net/gimg/www.rx7...f1460bc3e6.jpg

Update: Now that the battery has been on the tender for a little while, both headlights are now popping up at the same time with the column switch. No major voltage bump, if any, but I'm assuming an amperage increase (although I have no way to test that). I'm going to go ahead and clean up the other alt and get it ready for install just to see if it changes anything. I started the car while on the tender and the voltage only dropped to 13.2 (no doubt thanks to the extra power from the charger), but that would mean the alt still isn't putting out enough for the lights. Turning on the lights also does kill my radio temporarily while they raise (if it's on, which means the sub is powered). Otherwise the screen just dims for a second if no input is selected (sub off). Aka, still not enough juice.

My mistake, you are correct. I just checked and the 1980 wiring diagrams shows the alt has an internal regulator.

Good to know I ain't crazy :). Anyhow, I've got the alt swapped and I'm seeing 14.5 idle no load. With lights on and radio playing it's about 14. So it's much better, but I'm still having issues where I'm driving the car, I let off the gas and the radio cuts out. Both headlights are popping up consistently now though. I can't see the headlights to tell if they're flickering, but since the radio is still acting weird I'm going to bet the lights might still flicker. It only happens if I let off the gas or sometimes if I put on a signal. But even then I'm slowing down for a turn so it's probably just the decel again. I just checked the idle switch/tps and it's correct so... I can't think of anything else that happens when you let off the gas. I'm not measuring a voltage drop either which makes it even more confusing.

Just now looking into the radio wiring again. Somehow never noticed before, but the PO has the radio being powered off the cig lighter outlet. I think I'm going to try and make this a bit more proper. It would also explain why my plug never works even though it gets power. The original radio power plug is still back there so I think I'll try connecting to that. The ground resistance to the cig lighter is also 5.2 ohms at the spade connector; that can't be helping anything.

Well I've made it better. I didn't end up redoing the radio wiring as it sort of makes sense how they did it. Also they were already using the original radio power as the signal wire for the radio to turn on with the key. I decided to check the resistance from the positive lead to the fuse block and then to the radio. At first I was seeing over 24 ohms; not good. I decided it would be worth cleaning the fuse connectors (it's got the glass fuses) as they were pretty corroded. I got the resistance down to 4.8 ohms after cleaning. I also cleaned the other fuses so they're much better too. Anyways, the lights are both popping up at the same time now, without the tender that is. The radio is also much less finicky.

I did come up with a theory. I don't remember for sure, but I believe that I had to do something with the ignition switch on this car to make it work properly when I first got it - to the tune of dissembling it and cleaning things. While testing the resistances to the fuse block (the battery ground was disconnected), and changing key positions, sometimes the resistance would be higher than others with only the movement of the key. Is there a chance the ignition switch is going out?

I also have noticed that when the radio goes "out", it doesn't reset which would imply that it's loosing its trigger power from the key, as opposed to it's main power feed directly from the battery through the fuse block and the cig lighter. Again potentially pointing to a faulty ignition switch.

Is this likely? I got the resistance from the battery to almost all the fuses down to 1-2 ohms after cleaning. The only fuses I couldn't get consistently lower than 12 are the ACC fuses (radio and something else; there's two). Opinions? The clunk does still exist btw.

Well there have been a few new things:
As of now, the transmission is waiting for time and a rebuild kit. Is there any real reason to go with a different transmission set up as opposed to rebuilding the one for the SA? This is just an off hand thought and I really haven't done any research into it; just curious if something else would be worth it while I'm doing the work anyway. Still looking for info about that output shaft bearing too, the one that appears spun.

As for the clunking noise, I believe I have narrowed it down to the cat. This was an exhaust I swapped from my parts car (it was used and "custom") so I guess that the internals have broken down and are now rattling around nearly constantly. It looks like I finally have a good reason to use that RB header I have lying around and redo my exhaust properly.

Last, but not least...! Since cleaning my grounds and other connections, I have noticed my temp gauge and, just recently, my fuel gauge have been reading much higher than normal. Is there a way to adjust for this, perhaps on the back of the gauge cluster? My temp gauge is high enough that it's nearly at the top at normal temp, and I darned near ran out of gas this last tank since I had though I still had nearly a 4th of a tank left. Obviously I could just get used to it, but if there's a way to adjust/fix this, I would be glad to do it.