NOISE IN 4TH GEAR?

[Lancer99]

To start off with I was driving fine on the highway for about 30mins and when I was about to exit, I rev match into 4th and heard like a rattling/grinding noise coming from the transmission area and somewhat of a grinding noise from the rear diff. area. Every gear is fine including reverse but 4th gear is still making the noise even when double clutch and I made sure theres MT90 in there and theres no leaks. Anythoughts?

Scoops

 

The intermediate shaft 4th gear is very close to the intermediate shaft bearing which is on the end of the shaft. They are known to go bad. It's possible the bearing is getting loose and making the noise in 4th. Hard to say though...

Jack

 

[Hertz]

When my 4th "went out" it would only make noise under acceleration load (I could downshift through it without any bad noises). Is that consistent with the shaft bearing, or is it (what I thought) a chipped tooth on only one surface?

 

Anytime I have seen 4th gear have an issue it usually completely blows apart. They are too small and under too much load to survive in a damaged state. Here is a pic of a broken 4th gear:

It is difficult to diagnose noises without looking at the car. An intermediate shaft bearing would be my best guess as it is becoming a pretty common problem. Another thing to note is if it makes noise under acceleration load and not deceleration load you could most likely be looking at bearing. A helical trans will put load on one bearing during accel and load the bearing on the other end of the shaft under decel as the gears helical design will push the clusters one way or the other.

Jack

 

[Lancer99]

It makes noise all the time accelerating or decelerating. It didn't make any noise while I got on the high way. As soon as I got up to 70mph and cruised at 70mph it was fine until I got off and I wasn't puuting any stress on it until I rev matched into forth to slow down and after that and on my way home it just made that grinding and rattling noise from the transmission area and rear diff made a grinding noise. But the trans I bought two years ago but rarely drive the car, within the two year period I put on just under 20,000 miles and I bought it from J spec auto and this is the first to go wrong with the trans. Oh well just got to buy another built trans then.


Scoops