about 5k miles ago i changed my differential and transmission oil to redline

i changed my transmission to MT-90 to be more specific

earlier today i realized this as i drove down the highway (i do not usually drive on the highway) ------if i push the clutch in all the way and shift into 4th gear, it will grind in as long as the speeds stay up high, the same thing happens if i shift into 5th but there is less grind. during everyday driving, there is no grind.

any idea what could be wrong? my transmission is at 75k so bad synchros isn't totally out of the question......but i want to avoid getting a transmission rebuild or a new transmission.....

will lucas oil stabilizer help any? i saw the little demonstration gears and i have been thinking about that

thanks!

 

What about SS clutch lines? I read somewhere that they fix grinding at high rpms?
You could get them from RP down in garland for about $30.

 

google "rev matching"

 

lol i know how to rev match! i was talking in context of upshifting

 

i get this as well, between 3 and 4..

after i realized it, i second guessed that i wasnt clutching all of the way, but the next day i purposely clutched all of the way and it still made the grinding noise.

 

hmm well that's no good either

 

Does having the transmission hot vs cold make a difference? I had horrible grinding, changed out to Pennzoil Sychromesh with a couple squirts of Lucas oil stabilizer to thicken it up. Now I only have grinds when I drive aggressive when the transmission is cold (which I don't routinely do!) and it shifts like butter at all other times. If I was to guess I would say that the weight of the oil you used does not suit your driving habits. Someone else should be able to give more info.

 

when it's cold, the gears are a little harder to get in...it just feels like thicker oil tho and after a couple minutes it's fine. like i said before, i do not usually drive very fast (in terms of local roads vs highway).

is the oil stabilizer gl-5? i remember people saying that i had to use redline mt-90 because it is gl-4 and it doesn't contain the sulfur that eats away the brass synchros

 

ever since my transmission fluid change i also had trouble getting into reverse and it wouldn't go in all the way at first.....i let out the clutch and i hear the gear grind on the idler gear

only until the second or the third time it goes in


it doesn't happen everytime but occasionally it does that

 

Lucas oil stablizer is for engine oil. It's neither GL4 or GL5, but it does not contain sulfur. Do NOT use GL5 gear oil in your transmission. It will cause gears to grind and make you think you need a new transmission. I made that mistake and fixed it withing 500 miles. If all this happened after the gear oil change out I would try a different weight. Also, stupid question, have you checked your clutch petal play?

 

clutch pedal play? as in my driving habits or the actual clutch?

i am probably going to open the transmission fill plug and top it off with the lucas oil stabilizer (probably the heavy duty one, not the pure synthetic)

i just remembered that i filled it up with race ramps on the front tires so the transmission was tilted when i filled it...i think 2 full quarts of the fluid went in.....i have actual jacks now so im going to lift it and top it off tonight and see what happens

 

M A Z D A
Clutch petal adjustment, it's under drivetrain
NEVER fill the transmission or diff without the car level. It will change how much it can hold before overflow. Do not put in too much lucas, it will change the weight of the oil. I probably put less than 6oz in mine. I was using a hand pump to fill so I put in a couple pumps of the lucas before topping off with GL4.

 

Bump for interest. I've been having the same issue, it only happens to me when I'm up-shifting from the top of 2nd gear's powerband to 3rd.

 

Change fluid first. MT-90 has a large following around here, haven't tried it myself. The 1st gen 6speed tranny seems to be temperamental when it comes to oil weights. Use the wrong one for your environment and you will think your syncros are gone. Oh, one other thing, after changing mine it did take about a month for it to start shifting like butter, I think whatever gunk that was left over had to get flushed off the bearings. Transmissions are kind of a mystery to me, I've never had one apart to really understand everything going on there. Maybe someone else can provide some more insight.

 

well first let me have a quick update:

i know i said earlier that i would put some heavy duty oil stabilizer in "tonight"...but it ended up being on 1/20/13....

anyways, i put it in and i went on a test drive: it works! (so far so good)
i only took it up to 60mph where previously it had a "little" grind; it used to be that it didn't have a noticable grind until 70mph

4th & 5th still feel a little different and "notchy" compared to the other gears, but at least there is improvement

due to the the weird infrastructure up here in the NW dallas metroplex, i would have to drive 20 miles just to get to a highway where there arent any tolls, when i get the chance, ill post another update


interesting note is that during the filling, i used about 1/4 of the bottle of oil stabilizer; the level of the fluid now is where the taper of the bottle ends
this is weird because the specs show that i only need 1.8L of fluid to fill the transmission...when i had the front end of the car higher than the back end, i managed to get exactly 2L in before it started overflowing
I checked for leaks from then on and no leaks (i used a torque wrench and properly torqued the bolts in)
when i opened it up today, none came out and i put in 1/4 of the oil stabilizer until it started slowly dripping out.
1/4 of the bottle of oil stabilizer is on par with what the label said about how you can mix 25% oil stabilizer with the transmission fluid

 

There are some nice youtube videos that have nice explanations, but essentially,the large gears with the actual gear ratios are always meshed together

there is an input shaft and an output shaft....self explanatory, the input shaft connects to the clutch/flywheel while the output shaft connects to the driveshaft and the rear diff

the gears that are on the output shaft always spin with the output shaft. since they are always connected to the gears on the input shaft, the gears that are on the input shaft always spin as long as the gears on the output shaft spins

the gears on the input shaft, however, spin freely on the input shaft UNLESS you connect the shaft with the gear. this is what you are doing when you shift gears:

there are teeth that stick out of the gears that go on the input shaft and teeth that stick out of the input shaft. rings can align these teeth and then make the input shaft spin at the same speed as any of the gears are spinning. when you are shifting gears, you are just moving around the rings to select which gear the input shaft should spin at the same speed with

these rings are called synchros because they need to "sync" the speed of the input shaft with the gears before the inner teeth can be engaged to each other. the synchro rings have a cone shaped brass ring that mates with the gear right before the two teeth align....it is these cone shaped rings that can wear out over time


oh and dogboxes are different...