This is a new one to me.

A non-forum member friend of mine was driving his 1990 NA tonight. Ported intake, custom catback, and an intake are his only mods.

On 1-2 shift, he said eh heard a LOUD clunk sound, and the pulled over.

I went and checked it out for him (I'm his mechanic). The engine runs, no codes, but stalls when you let the clutch out, even in neutral.

The transmission makes a "clunking" sound when we manually push the car by hand, in gear, clutch depressed.

Obviously something broke internally to the transmission, since the input shaft is obviously seized.

The trans fluid was fresh GL5 15W90, non synthetic, and was full.

What could have caused this? I am think terrible pilot bearing caused some major flex of the input shaft, or he shifted too hard and bent something internal...
Is this common for NA transmissions?



Finally, the important question: I can use any NA trans from 83-92 in replacement, correct? I am aware of the different gear ratios from the GSL-SE, and will use that trans if possible.
Any compatibilty issues?


And finally: good news! I am going to pull the engine and trans attached for this job (since I find it easier, and we have other engine work to do). This will give me the chance I need to re-do that engine R&R write-up that is going around, complete with all bolt sizes and tools, as well as a huge series of pictures. Sound good?

 

I am pretty sure the only difference between the FB and FC tranny is the location of the shifter housing, Which I also heard is interchangeable. Never have checked to see if they can interchange though. Marc

 

Keep in mind that the NA and TII trannies have the same internals.

That in mind, I killed my first NA transmission going up a hill @ 100MPH @ 10 PSI in fifth. Oh, and the fact that all the tranny fluid leaked out onto the highway a few minutes before probably had something to do with it. Snapped input shaft. It seems that I lost a seal (output shaft) just after I got on the highway.

The tranny that I have in now has noisy bearings from being chronically low on fluid. The input shaft seal is bad. It's going to the shop for a rebuild.

Draw your own conclusions.

 

You can use any 83-85 transmission, but you have to swap the tail housing so the shifterand transmission mount will be correct. Also swap the speedo gear while the tail housing is off. Any 86-91 transmission will bolt right in.

Just FYI, the 89-91 cases have extra bracing on the bellhousing, so you might want to swap that too.

I have 84 12A internals in my 90 GTU transmission. I gotta say, I LOVE the .825 5th gear

 

how hard is rebuilding a manual tranny? I have access to a free 88 tranny and a free 84 tranny and I hate my .69:1 5th.... I'm also pretty sure my synchros could be healthier too. I rebuilt my engine with no help, so is a tranny any harder? I do have access to a press for the gear swapping too.

 

All of my syncro's are officially dead after 144k miles. The pilot bearing is thrashed, and the clutch slips to all hell. The synchros are made of brass and are designed to wear...

Have you tried letting the clutch out in a higher gear, 2nd? 3rd?

 

15W90?!?!?!?!?

If I am not mistaken that is 15 weight (very thin) oil with additives to make it act like 90W? Isn't 80W90 the recommended weight? Synthetic or not, 15 weight oil with additives to make it 90 . . . Yikes!!

Yep the trans is broke. They sell in Ebay (mostly s4's though) for like $100-200, cheap I must say.

 

huh? that doesnt mean its 15 weight that is made to act like 90 weight. It means when the oil is COLD it acts as 15W as to help lubricate the parts efficiently during startup/early driving. It then thickens out to 90W when completely warm.


and ..he might have meant 75w90?

 

What proof do you have of this? The internal part numbers are different, and the turbo transmissions have different gearing. While the internals may be physically similar, the mettalurgy could very well be different.

Example: A Ford C4 and C5 3-speed automatic differ only by the torque convertor, and an accessory to the valve body in the C5. However, the planetary gears, sun gears, and clutch sets are made from a much weaker alloy than used in the C4.

With proper clutch paks, the C4 can withstand 500 ft-lbs of torque and up, whereas the C5 with the same torque figures would at anything above 300 ft-lbs.

Where does the extra 30 lbs come from in the turbo transmission, then? Just the extra bracing in the housing? I don't think so.

I disagree with you here.

As well, why would Mazda bother making a turbo transmission, then, if the N/A transmissions where identical, save gearing?

 

'

Gear does not change a thing. We KNOW the input shaft is seized, since the engine stalls when we let out the lcutch with the trans in neutral.

I know what is wrong. I just wanted to confirm compatability, and find out if this was a common problem.

We may have found a couple trannies... all from first gens though. Does anyone have a first gen listing of gear ratios?

 

Hard is a relative term.
It is far more complex than a engine rebuild, but by no means impossible.

The question should not be difficulty, but budget. Is it really worth the money to do this?

 

other than the synchro's and seals it would cost nothing.

 

FWIW, I beat on my na Tranny, at 223K, really bad on a daily basis and still no sign of death to come. Now this Is where I jinx myself and findout I need a new one.

 

Budget? Where do you expect to spend money, besides the tranny itself? Its easy to use an FB transmission. Follow the haynes or fsm on removing the tailhousing, and bellhousing if you swap that also. The speedo gear is held on with a pair of snap rings, and is a piece of cake to swap with the tailhousing off.

The FC transmissin has a dynamc damper on the output shaft, which the FB transmission does not. The car wont be as smooth with an FB transmission. Also, the synchros arent as good on the Fb transmissions. And 3rd gear is in a weird spot on the FB transmission. It just takes some getting used to. But if you can live with all of that, its not a bad choice. All of the gears, with the exception of 4th, are shorter than the FC transmission.

With the FC tailhousing, the shifter and transmissoin mount will be in just the right place, and it will bolt right into the car. You might need to swap the nuetral switch and such, I cant remember if the plugs are the same. But thats a piece of cake.

If you have any more questions, feel free to ask. I have done it before.

 

I don't know how common it is, but here's what mine started doing a few days ago out of the blue. have a look and tell me what you think...

Onward...

 

I agree Adam, but if you read the quote I was referring to, the guy was talking about a complete rebuild, which means synchros, seals, and replacing any shafts that are bent or worn beyond specs.

I, personally, would not rebuild a trans. When somethign breaks, it takes out a lot of stuff with it. I agree with adam about swapping to a FB trans... makes more sense if you ask me.

In the end, adam, my point is this; I am not arguing swapping trans on a budget, I am talking rebuilding a trans. I don't think it's worth it... most shops don;t either.

 

If your tranny was fine and not grinding in to gears before this bumping problem and stalling in gear problem occured then it is just your pilot bearing. I just had this same exact problem that you are describing and all it was was my pilot bearing disintegrated to the point that there were only 2 needle bearings to be found in the eccentric shaft and just a hollow pilot bearing casing. The bump that you are feeling is the input shaft missing its mark and hitting the loose needles or the pilot bearing casing. Go visit MazdaTrix.com and get a new pilot bearing and the pilot bearing seal as well as the other highly recommended tranny seals that you should replace while your transmission is out of the car. MazdaTrix has their recommendations as to parts to be replaced while the tranny is out listed on their site.


I replaced my: clutch plate, pressure plate, flywheel, pilot bearing and seal, front transmission seal, rear transmission seal, throwout bearing, shifter bushings, and transmission fluid. Car runs like new now.

Again.....if you were having problems before this incident where the tranny was gradually (over a couple years) getting harder to get in to gear cleanly without "chunking" in to gear because of bad syncros then you might as well just swap in a new tranny.
BUT I had the same exact problem as you did and after replacing the pilot bearing I was golden.

Good luck and PM me if you want n e more details.

 

GL5 will disolve the syncros in our trannys. You must use GL4 or GL5+ (that specificly says safe for trannies requiring GL4).

I am assuming that you meant 80W90 and not 15W90 which would also distroy the tranny.

Your buddy killed his tranny because he didn't read the owners or shop manual.

 

to my knowledge theres nothing wrong with the FB tranny and my tranny still functions properly with the exception of the occasional grind when doing the 2-4 shift. I'm not sure of the condition of my parts FC tranny though. I was told mine was a rebuild when I bought the car and there is signs of someone having been in it. (pretty sure they didn't use blue rtv at the factory) So I would be trying the mods with the two unknown trannies first. Are synchros really all that expensive?

 

My tranny blew with only 68,000 miles on it..this happened only 4 hours after i got done swapping my motor that had a bad coolant seal in it.

 

it is a lot more expensive to rebuild a broken tranny ($300 countershaft) vs one that has normal wear (bearings and synchros). building the tranny is not that hard but it is very picky about getting everything back together right. you also have to know how to asses wear, how do you know when to replace something?

mike

 

I'm thinking about rebuilding an extra tranny I have laying around, from what I've heard the bearing and syncros are pretty cheap, I don't know about shaft and gears though but I imagine that shaft is pretty strong and shouldn't break. I've heard lot of speculations about GL5 gear lube dissolving the syncros because of high sulfur content but the fatory manual suggests GL4 or GL5 lube so I don't know the extent of the truth, I've been running mobil 1 synthetic GL5 gear lube in my tranny and didn't have any problems but I've also heard of people having trouble with same lube. I don't think NA transmission is same as TII transmission, housing is completly different and gear ratio is different execpt for 4th gear, I believe that TII transmission is built lot stronger also. I would try to find a TII transmission if your NA transmission if broken, far as I know TII tranny has same bell housing bolt pattern as NA but it has shorter drive shaft, correct me if I'm wrong.

 

Oops, I thought you were directing that at me, not the other guy. I agree, rebuilding a n/a tranny is not worth it. You can get good ones about anywhere for $100.

 

A short story... I was getting used to my 91na 127000mi – shifting from 5th to 3rd at 70mph without going through 4th. It worked fine, but as I slowed down to about 50, I downshifted to 4th, and BANG SCREEEEETCH, the wheels locked up. I popped it out of 4th >BOOM< and limped home in 5th. I had that sinking feeling – this is going to be expen$ive. I pulled the tranny in the driveway, took it apart, and found the lock nut on the main shaft had come loose, backed up & jammed 5th so tight I had to chisel the thrust collar off. It cost me $60 for the parts (2 lock nuts, thrust collar & retaining rings). I'm sure some parts were hurt, but I drove it agresively for 2 years before the input gear spit a tooth. A used replacement cost me $400.

 

Actually, I meant 75W90. Whoops.

I did not do the tranny fluid change.