Hello all you happy people!

The last couple of weeks have uncovered some issues with my 84' RX-7's gearbox.

The synchronizers are at the end of their lifespan and I uncovered evidence today that indicates the input shaft bearing is on it's last legs. I'm not quite sure what to do.

Are there rebuild kits for these gearboxes, or should I just try and find a whole new gearbox?

I'm open to any and all ideas.

 

There are no rebuild kits. You would just have to buy each individual part that you need. Its cheaper and faster to buy a known good transmission. Stick with an 84 or 85 trans.

 

Curious to know what makes you think the syncros and front bearing are bad? Is there a specific noise? Crud in the fluid?

 

I rebuilt my 83 gear box with this kit:

Mazda B2200 RX7 Transmission Bearing Kit 81-89 20.5mm | eBay

I believe it will also work for yours. All bearings and synchros seemed to be of good quality and I have had no issues thus far.

 

First gear and reverse gear do not like being shifted into unless you force it, or turn the car off and then shift it into gear and then turn it back on with the clutch depressed. The rest of the gears can be entered only if you double de-clutch, but that's not easy - or fun - when you're in traffic. When my local mechanic took a look at it, he found chunks of metal floating around in the trans fluid. He thinks it's the synchros and I have no reason not to believe him.

I replaced the fluid and tried flushing the gearbox as best I could to remove as many of the metal chunks as I could, but the gearbox is already ruined. I'm just trying to extend it's lifespan a bit until I can find a new gearbox or get the parts to repair the original.

And I found out about the bearing when I noticed a new grumbling sound coming from under the center console. When I lifted the car up, I noticed scratch marks on the drive shaft. The bushings in the suspension had all been replaced shortly after I got the car and the drive axial is in good condition, apart from the few scratch marks where it hit the heat shielding. I figured that if it wasn't the axial itself or the rear suspension, then it must be the output shaft bearing.

 

Darn it. I was hoping for a rebuild kit. Good condition transmissions for 84-85 RX-7's are also a bit rare and will be hard to find.

How about a NA or NB Miata 5-speed transmission? Would it be possible to swap in one of those with little to no modification?

 

I'm sorry to hear about your transmission problems, those are never fun to deal with. It definitely sounds like you are having some syncro issues that will need to be addressed sooner rather than later, but if you are interested in getting a few more miles out of the trans before a rebuild or replacement, I've had tremendous luck with Pennzoil Syncromesh in multiple cars of all ages. It's an additive for the trans fluid.

I'm​​​​ currently running almost straight syncromesh in my 1990 Nissan 240. It was very hard to get through the gears, and just wouldn't mesh up. I drained it dry and refilled with straight syncromesh. It shifts smooth now.

Again, the above is just food for thought. It might not work out for you, but wanted to share my good experience. It's like $9 a quart so it might be worth a shot to add some to see if it makes a difference.

 

I'm agreeing with Mr. Farrell that you're mis-diagnosing this problem. The 'input shaft bearing' you refer to; do you mean the Pilot Bearing (located in the end of the eccentric shaft that centers the input shaft from the trans)? That would cause the difficulty shifting into 1st or reverse, because it's dragging and causing the transmission to spin the clutch disk along with the flywheel when in Neutral. That's a $20 bearing and an $8 grease seal to fix - though it's a pain to pull the trans to get to it...

That said, the Series3 transmissions hold up just fine even under racing conditions, so unless you're of the mind that If-You-Can't-Find'em-Grind'em! crowd, then it's probably not your synchronizers.

Also, I would look into finding a different mechanic.

 

Synchros typically show wear when grinding is present and do not prevent shifting into a gear. Their job is to ai in smooth grind free gear changes. If an input bearing is worn you'll typically hear growling from the transmission when driving in all gears. I would look into replacing the pilot bearing and seal as stated above before replacing the transmission. The trans can be dropped in an hour or so, even without a lift and air tools, though having those makes it easier. I would also make sure your clutch hydraulic system is in good working condition and bled properly as well. A faulty hydraulic system will cause the exact symptoms you are describing.

Metal shavings found in the gear oil is normal, especially if it hasn't been changed in some time. If there were a lot of metal shavings, I feel as though there would also be bearing noise from bearing wear, causing the metal shavings.

 

I agree with the above suggestions, but if you decide to rebuild try this supplier for rebuild kits:

Mazda Car's Manual transmission Rebuild Kits | Mazda 323, 626 manual transmission parts - Drivetrain

This have kits listed

 

that is a symptom of the clutch not releasing completely, most likely to be the hydraulics

 

How old is the clutch? I had an issue with my pressure plate in which it wouldn't fully disengage, causing problems when shifting.

 

Clutch hydraulics,pilot bearing,pressure plate not releasing fully are three things to be examined fully before condemning transmission. Slave cylinder should move release fork at least 1/2" to fully release clutch-try bleeding clutch to see if pedal improves or symptoms are better. Any further diagnostics require transmission removal to investigate. Seized/grenaded pilot bearing can cause exact symptoms as does a pressure plate not fully releasing clutch. Recommend be prepared to replace clutch,pressure plate pilot and to bearings-regardless of miles,more due to age of car. Were the problems op posts about internal to the transmission they would be accompanied by grinding,possibly jumping out of gear,bearing noise,etc. Feel pretty certain problem will be found external to the transmission. I have destroyed more than a couple of these gearboxes in different 1st gens and for a light(duty) transmission i marvel at how much abuse/power they'll take without complete failure-at least for a short while and never without giving notice something's not right. Maybe take car to a 2nd shop for a second opinion...

 

I'll look into that Pennzoil Synchromesh. If it'll help me eek a few extra miles out of the gearbox; I'll do it.

 

I went and got a second opinion by Rotorsport in Santa Clara. You were right; it's the pilot bearing. They also verified the synchromesh being an issue, so I'm still on the hunt for another gearbox.

 

The clutch has about 10K miles on it. It's fairly new.

 

If the gears don't grind when shifting, the synchronizers are generally in good working order. The pilot bearing can cause binding when shifting. Just hate to see you replace your transmission if you really don't need to.

 

DUDE, REPLACE YOUR PILOT BEARING AND GREASE SEAL!

There, I just saved him a few hundred bucks.

 

I agree but its hard to tell someone something different than what they themselves have been told/believe. I would feel bad if this guy bought a trans and tossed it in to find that it was not faulty in the first place.

 

They do grind if I shift normally. Every single time. The only way I prevent the grinding is by double de-clutching everywhere.

 

I used a 75/25 mix of gear oil and automatic transmission fluid and no more grinding. One of the best mods I’ve done.

 

+1
OP's issue sounds way to familiar. Yup, a new pilot bearing & grease seal did the trick.
Replaced the clutch while it there was access.

 

He even points out the key factor of it grinding UNLESS he double-clutches it, which is because the bearing is dragging.

The good news is that the bearing is slowly grinding itself to dust in there and will eventually disintegrate, fixing all of his problems! Unfortunately, the pilot head on the Trans Input shaft will then be unsupported and ruin the input shaft bearing on the trans, but at that point he'll have a spare transmission,...