Replaced transmission fluid, now it's causing problem
 

Hello,

I recently replaced both manual transmission fluid and rear differential with Amsoil products. Prior to changing, I rarely had grinding but it's now grinding when I downshift from 6th to 5th at speed above 65mph. No noise at speed below 55mph.

Mileage: 13000
Trans fluid: Amsoil Manual

Rear Diff fluid


The funny thing is that it started to grind right after changing the fluid. I am kind of stumped right now why it's happening. I've searched but most thread shows the common problem in 2nd, 5th gear grinding, but that's with the factory fluid. Should I try some other lubricant? I've also read that some people here with BRZ use GM Synchromesh manual transmission fluid or Pennzoil. I don't find a possible way to mess up a transmission while doing a flush. It's simple as drain and refill. Any suggestion/help is appreciated.

Sorry I don't have a solution, but I can at least give you the satisfaction of assuring I just read this entire post in Kevin Malone's voice. That should count for something.

I miss the office. I'm going to watch some funny moments.

I think you'll find it's a coincidence. Mine was the same and the gearbox is being replaced this week.
The factory oil isn't special and you used good to oil to specification.

You changed the oil to hopefully fix the grinding you were experiencing and it didn't work. Take it in under warranty and you should get a new modified[hopefully] gearbox too.

one more note, I've overfilled the fluid by .3 liter.. not sure if that could cause too much lubrication, resulting in "slippery" when downshifting?

How did you manage to get 2.5L in it through the filler/level hole?
I doubt it would cause any problems, especially synchro problems but it's easy enough to take the level plug out and drain off the excess[on a hoist].

the car wasn't 100% leveled. Front was a bit higher than rear, so I guess the trans box took more fluid in the back.

Here is an update. Replaced fluid with Redline MTL and the noise is gone.

Since the grinding sound came RIGHT AFTER using Amsoil, it had to be the fluid.. So I decided to wait for about a week thinking that the fluid had to be "broken in". Well... still same grumpy downshift from 6th to 5th. I did some research about oil weight/viscosity/lubrication stuff and concluded that Amsoil is providing too much lubrication, which could lead to too much slippery in synchronizer. I may be wrong on some points./ but tried Redline MTL. I've read from a thread here that it provides a grip to synchronizer. I guess it works!

Amsoil was great, providing smooth shifting, but it just didn't work on downshift and I don't know why it only happened on 6th to 5th downshift.

Well that's interesting. Strange though, that it should only affect 5th gear?

It makes my new gearbox for the same problem look like overkill!

I have no idea if it's affecting only 5th gear. I think I'm the only one who is experiencing this problem after replacing trans fluid with Amsoil GL-4 (not synchromesh). I also noticed grind when I upshifted from 4th to 5th gear above 4000 rpm. I've read numerous threads where people had grinding on 5th gear, but those people are with factory fluid. So the overall problem with this gearbox seems to be 5th gear. I'm wondering if anyone who still has problem with 5th gear and with stock fluid can try using Redline MTL (75w-80) and see if the problem disappears. It's only around $50 for 3 bottles, but not sure if anyone is willing to try before taking the car to dealer.

You said in your case it was only affecting 5th gear which was what I was referring to.

The problem with that oil is it's not to the 75w-90 spec if you get any problems in the future. I supplied the oil to the dealer and they changed it for no cost after approving the spec.

Very interesting still that oil caused and cured the problem.

Yeap, it was only affecting 5th gear.. I'm confused with Amsoil product. I know some people here use Amsoil in their transmission, but I haven't seen any problems or complaints.

Maybe a bad batch slipped through?

It's difficult to imagine how the oil has such a marked affect on the operation of the synchros?

I doubt its a bad batch.. More like the correct formulation of friction modifiers were needed.
My old camaro had issues with the diff.. The posi traction aspect wasn't working
Most of the time.. Only one wheel would spin during hard launches.. Like a non posi diff works.. I changed out the fluid and used redlines diff fluid with their friction modified formula.. It was like new again! Both wheels hooked up and cars tail went sideways and left two nice rubber tracks.. I then became a believer in the power of fluids! I have been using Redline fluids in the trans and rear ends of all my cars... With excellent results for the last 30 years..
Their stuff is pricey, but it works and lasts a long time..

I despise asmoil for a reason...

So far after a couple months my Redline MTL has only improved and I'm going to stick with it.

Agree here especially after this happening. MTL is very smooth throughout every gear.

Why have you guys gone for the MTL 75w/80 instead of the MT-90 75w/90 which is to OEM specification?

MTL 75w/80

API Service Class GL-4 SAE Viscosity Grade (Motor Oil) 5W30 SAE Viscosity Grade (Gear Oil) 75W80 Vis @ 100°C, cSt 10.4 Vis @ 40°C, cSt 54.1 Viscosity Index 185 Pour Point, °C -50 Pour Point, °F -58 Flash Point, °C 232 Flash Point, °F 450 Brookfield Viscosity @ -40°C, Poise 120

MT-90 75w/90
API Service Class GL 4 SAE Viscosity Grade (Motor Oil) 15W40 SAE Viscosity Grade (Gear Oil) 75W90 Vis @ 100°C, cSt 15.6 Vis @ 40°C, cSt 90 Viscosity Index 185 Pour Point, °C -45 Pour Point, °F -49 Flash Point, °C 240 Flash Point, °F 465 Brookfield Viscosity @ -40°C, Poise 320

RL MTL into tranny as well zero issues only improvements.

So it seems the gearbox I had replaced might have been perfect but the oem oil had somehow changed/broken down to somehow become more slippery, stopping the synchros engaging correctly?

When I had the oil changed for a fully synthetic 75w/90 and the symptoms were the same it could have been because that spec was too slippery too?

Redline-
Appropriate coefficient of friction for most manual transmission synchronizers (other's synthetic gear oils are often too slippery for proper synchro engagement)

MTL is 70W80...

@sierra I went with MTL even though it's 75w-80. I read from somewhere in the forum during research and found that MTL provides less slippery which helps synchronizer to grab the gear better? I'm not too into specific details of each manufacturer gear oil's character. I replaced it and it's good as new, smooth.
(Response on 2nd post) So did the dealer replace your transmission this week? I'm assuming you now don't have 5th gear problem. When you say you "oil changed", was it before the transmission was replaced? If you had the grinding before you changed oil, then I would assume it's the transmission problem. If the problem is gone with new transmission, I wouldn't change the fluid again.
@Amir Ghadiri Did you read my first post? This never happened before changing the fluid. It happend literally right after changing the fluid. It had to be the fluid that was causing the slipperiness. I know a lot of folks experienced this 5th gear grinding, but those people didn't touch their fluid.
@roddy Redline makes 3 different GL-4 oils... MT-90 75w-90 // MT-85 75w-85 // MTL 75W-80. I noticed some websites state MTL 70w-80, but Redline website uses MTL 75w80. Link

The gearbox was replaced recently and of course it's fixed the problem. 2nd is as tight as but slowly freeing up.
5th gear grinding was there before the oil was changed and that didn't make any difference. To be honest it might have been worse after changing it.

As I said, it could be an oil problem and not mechanical. Who's to say the OEM oil isn't losing it's ability to allow the cones to grip somehow. If I could go back I would have tried Redline but it's too late now.

I was aware of the 3 different viscosities, and I originally went with the MT-90 because it was the recommended weight. It worked better than the OEM fill, but when outside temps got below 50 degrees or so, it wasn't that great. That's when I started experimenting with lighter weight fluids. So far, Pentosin (75W80) has had the best feel. I haven't tried the MT-85, but my current mix of MT-90 and MTL is working for me.

I looked at the link and I see where it says 75W80. I think that's a typo...it says 70W80 on the bottle.

I've never had a good experience with Amsoil in manual transmissions. Both the MTL and Ams. Synchromesh. Also, I believe you should have been using the Ams. synchromesh in this tranny and not the MTL but that is all moot at this point.

I'm also weary to run redline, not so much because of lubrication properties but because in transmissions where the bearings have plastic cages, which is common, the redline degraded (almost dissolved) the plastic cage and it would result in complete bearing failure and eventual catastrophic failure in the transmission. I don't think our transmission has bearings with plastic cages but nonetheless I've been weary about trusting their products since then. That's a significant engineering oversight if you ask me.

Thank you for the good information. There are significant others who use Redline products in this transmission, so we'll see what happens in the long run... "crossing fingers" This is my first manual car, so I'm kind of surprised how people (including myself) decide to use different weight oil depending on the region/temperature/purpose.

Anyone in the PNW make a change and if so what mileage did you do it?

I just want to resurrect this thread because I'm having the exact same problem and until now haven't been able to find someone who shares(ed) my pain. Mine is a 2015 BRZ. I changed the MTF around 25k miles with Amsoil (GL-4) and almost immediately I noticed it jumping a couple teeth when down-shifting into 5th or up-shifting into 5th at high rpm. I gave it a few weeks to see if it would work itself out and there was no change. I read that resetting the ECU would possibly make things better by a "re-learning" process. I'm not sure how much truth there is to that. Anyway it didn't seem to change after the reset.


On a side note, I did find that by holding the shifter directly under the 5th gear position (about half way between neutral and 5th) for half a second or so I could avoid the grinding for the most part. However, I don't want to have to continue driving this way in order to avoid the problem.


So I am going to change the fluid to Redline 75W-90 and report back.

Completely unrelated. Electrically, the only thing the car knows about is whether or not it's in neutral and whether or not it's in reverse.

Is it actually a grind, or is it the occasional "ka-chunk" from slipping a cog between syncro and gear engagement?

I honestly didn't think resetting the ECU would work but wanted to eliminate that option. I know the ECU knows what gear I'm in. You can select the option to display the gear next to the trip meter. So it's more of a passive system and I think that is the extent.


I'm fairly certain that it is a friction issue. I still haven't changed the fluid.

Motul ftw

Gear indication is calculated via engine/wheel speed ratio.

Got around to changing the fluid last weekend. I decided to go with pennzoil synchromesh. It is the only API GL-3 I could find. Immediately my woes disappeared. Every shift is smooth and happy, which makes me happy :)

I elected to replace MTF and LSD with Amsoil products at 30k. The shift lever feels lighter and more fluid though cold 2nd gear is still a disappointment.

5k miles after the swap the LSD started making a lashing/click/metallic sound when pulling away in 1st at any speeds. Feeling pretty well misled by this forum and lots of Amsoil fanatics saying it was the solution.

I'm not sure why, but results vary throughout any car. I once used Amsoil MTF, but never again. I've been happy with Pennzoil Synchromesh and Redline MTF/MT90.

I should also mention that I switched from stock to Amsoil early on when I got the car. Noticed the same grind 6 to 5 above 70mph. Reproducible too. Dealership didn't want to address it so I just switched fluidls to Motul 300 and it disappeared right away.

I have another very cool solution to this. go like 3 inch straight pipe with catless header and it will warm up gearbox with glowing red exhaust pipe, it's a true WIN/WIN!!!

There is actually a lot of truth in this

I've tried ALL MTF fluids you can think of in the span of 5000km. I was never happy with any until i settled with pentosin mtf2 (isnt perfect but the closest thing to it). One thing all fluids had in common was after some spirited driving the gearbox would perform to perfection, not even the slightest notch just pure butter.

After wasting 500+ dollars on fluid I've come to the conclusion that the tranny doesnt reach a temperature to achieve the consistent shift performance I desire. Being RWD, the transmission doesnt reside in the engine bay and the relatively flat underbody of the car would pull alot of air out from around the transmission area due to air pressure differential (relatively high pressure around tranny and engine bay, with relatively low pressure fast air under underbody).

P.S. it sounds worse than I say it, shifts alright now even in cold, you can feel the synchros catching in 2nd and 3rd though

THOUGH I loved the stock fluid performance, so everything I just said could be irrelevant... hmmm

I switch to a Amsoil recently, was previously using Motul. Can't say that it feels any worse or better. Don't have problems getting into any gear up or down shifting.


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