Fixing the M5OD/M5R1 Gear/Transmission Whine in a 1994 Mazda B2300

[alansb1982]

I just picked up a cheap 1994 Mazda B2300 2WD with the M5OD/M5R1 manual transmission. It whines in all gears but fourth, and the whine increases with RPMs in pitch and volume. The whine is not present in neutral nor when the car is not under acceleration.

I've looked around, and I've heard the following fixes: change the transmission fluid, input shaft, input shaft bearing, throwout bearing, and pocket bearing. I've tried changing the fluid, and no dice.

Has there been a clear consensus as to what causes this; and has anybody successfully fixed it? Would a full transmission swap pretty much guarantee to nip this issue in the bud? I know there are people who can tear down one of these transmissions and find the part that needs replacing for much cheaper than a swap, but I'm no mechanic and, at best, just mechanically inclined.

 

[adsm08]

Almost guaranteed to be the pocket bearing. All the bearings move in all gears except the pocket bearing. That lets the input and output shafts move at different speeds, because the front of the output shaft sits in a pocket at the rear of the input shaft. In 4th gear a collar just locks the two together at the joint and that bearing doesn't spin at all.

 

[4x4junkie]

It's possible the gears themselves could be damaged too (you'd only hear them noticeably while under a load, which they aren't loaded in 4th).

Your best bet here is to pull the trans, pop the top cover off and do an inspection on it, as there's really no other sure-fire way to know exactly what's going on inside it.

Be sure to also check the 3 shift-rail plugs at the top-rear of the trans, as it's common for these to shrink and leak with age (bearing & gear issues on the M5OD almost universally result from lack of lubrication/low fluid level due to the plugs leaking). Replacement with metal freeze plugs is a common mod on this trans.

 

[tyrn]

I've got the same whine! 1997 3.0 ranger 5 speed. I have read that the 5th gear was a late BAD addition. I notice mine in 3rd but REALLY bad in 5th to the point I don't use 5th at all... even on the interstate at 70+mph. It is commonly reported this will eventually cause a catastrophic failure (complete lock up) This happened when driving a friends Ranger in a neighborhood at approx 20 mph... the 3 hispanic laborers in the back were NOT happy amigo's! I found a used tranny for $200 that reportedly did not have that whine when pulled. It is out of a 94 4.0ltr and I joined this group to see if I could get an answer to the compatibility. What years/engine combo's are compatible with my 97 3.0 5spd manual? I figure I'll go ahead and put a new clutch/pressure plate, throw out bearing and slave cylinder in it (and fresh lube) prior to bolting it in there. Anyone got any suggestions for me?

 

[alansb1982]

I thought I'd check and replace the fluid today, just in case I might be able to avoid further work. Of course, no dice. There might've been less than a quart of fluid in there. No chunks, but a fair amount of metal sludge/shavings.

Given that I probably don't have the require know-how and tools to attempt a rebuild, I'm going to start planning for a transmission swap. I've watched all the videos I could find, and I'm fairly confident, with an extra set of hands, I could do it. I'll keep this thread updated with my progress to serve as a resource from the point of view of an incompetent novice.

Anybody have suggestions for sourcing a transmission? It seems like the best price from established vendors is from Smart Parts Auto (http://www.smartpartsauto.com/manual_transmission_m5r1_mazda.html). This will be $595+$250 freight (one way for the reman and return shipping for my core). Anybody have any experience with these guys? Anybody have any other alternatives? If it makes a difference, I live in South Florida.

 

[tyrn]

Youtube... you just made me think of when I was 13-18 at our shop... the benches filled with books, guides, manuals, dripping with grease and sludge...lol... But, two things. First, I have read that those metal shavings are indicative of that "catastrophic failure" I was talking about, and 2nd, like adviced passed, and reminded of here, don't forget to lube your yoke... as in life... there is NEVER too much lube on your yoke...

 

[alansb1982]

Alrighty guys, I'm getting ready to order a rebuilt transmission from Smart Parts Auto (http://www.smartpartsauto.com/manual_transmission_m5r1_mazda.html).

While I have the transmission dropped, what else should I do? If it's shifting fine and all that's there is the gear whine, should I bother replacing the clutch at this time?

 

[redhurricane]

Unless the clutch was near new I would replace clutch, pressure place, and slave cylinder, and the pilot bearing. you're already in there, and for another $150 or so in parts you won't have to think about pulling the trans again for a long time.

Kind of like the same mentality of doing a water pump on cars that need timing belts changed. You're in there already, do the preventative maintenance.

 

[alansb1982]

Okay, so to make sure I've got my shopping list right, here's what I have:

(1) Rebuilt M5R1 Transmission
(2) Valeo Clutch Kit (https://www.rockauto.com/catalog/moreinfo.php?pk=1326337&cc=1137967&jnid=511&jpid=5)
(3) Dorman Pilot Bearing (https://www.rockauto.com/catalog/moreinfo.php?pk=593272&cc=1137967&jnid=513&jpid=1)
(4) Dorman Clutch Slave Cylinder (https://www.rockauto.com/catalog/moreinfo.php?pk=963625&cc=1137967&jnid=512&jpid=5)

Is this all of the parts that I'll need?

 

[4x4junkie]

Sounds like you should be good to go, nothing else is coming to mind, outside of the 3 trans plugs I mentioned earlier...
Be sure to flush out your master cyl with clean fluid too, so you don't have any dirt in the system that could potentially ruin the new slave.

Also, put a little extra grease in the throwout bearing before you install it (lithium-base wheel bearing or chassis grease is fine), I've found many bearings don't contain enough grease to last the life of the clutch (the center isn't sealed on ones I've seen, so it's easy to force some grease down into the groove into the bearing with your thumb).