gears grind only after car warms up

[juntjoo]

would I be wrong to assume this to be caused by too thin of gear oil? i'm in hot FL and i'm using RP 90-150 which is like the thickest no? thanks

 

[pauleyman]

90-150 isn't the right gear oil for the job. Please consult your manual.

 

[juntjoo]

thank you. you know, sometimes my little Haynes will surprise me. it's got some good info. API GL-5 75-85. but that's thinner than 150 and it seems my tranny is suffering from heat intolerance, so would logic tell you I'd need a thicker, not thinner oil? or am I not understanding how the oils work? thanks

 

[pauleyman]

Heat intolerance???? What on earth?
Use the right weight. If it grinds there is something else wrong with the clutch or synchros.

 

[garrettgoines]

check your clutch line/fluid also. If its old, flush it. Adjust your clutch pedal also.

 

[juntjoo]

Heat intolerance???? What on earth?
Use the right weight. If it grinds there is something else wrong with the clutch or synchros.

I guess I meant since it grinds after reaching a certain temperature, which is hotter than when the gears don't grind, during the first 10-15 min of driving, perhaps the gear oil is thinning too easily for this transmission, indicating a need for a thicker oil. it's great to get info from people who know more but just to take someone's word for something just because they know more, you don't learn anything. can anyone explain why the gears don't grind until after 15 minutes of driving? thanks.

 

[juntjoo]

check your clutch line/fluid also. If its old, flush it. Adjust your clutch pedal also.

thanks. was on my list. but still don't understand what it means that they only grind when warm. I think once that is understood, at least for me, it could shed some light on what the cause of the grinding could be and save me some time messing with different things. like... if for instance, your car uncontrollably crashes into things off the road only when your dog drives it. in such a case you would waste time inspecting the steering system before you investigate your dog as a possible cause.

 

[DSM1G90]

95/150 ... like molasses and coal tar in the tranny...major thickness !

75w/85 or 80w/90 (GF-4 fluids) is what you need for any outside temp.

If that 95/150 is a GF-5 gear oil, that stuff eats up the brass syncros since GF-5 is loaded with sulpher and is very corrosive to brass.

GF-5 is made for worm/spur gears in the rear end of a RWD vehicle since there is massive gear pressure and GF-5 reduces the friction and the sulpher sticks to the gears to aid in the anti friction.


when tranny is cool, the fluid is thicker to allow syncros to grip the gear cones. But, when things get warm, oil starts to thin, things expand (esp brass syncros that expands when hot) and have a hard time to grip the cones since they're all worn out in the first place, thus you get syncro grinding.

Do this simple trick: with the motor idling, gradually push the shift lever into first gear without dumping the clutch. If the motor slows down, the syncros are doing their job to slow the motor down with their braking down the input shaft. If the syncros grind, esp if you do this in any gear, that set of syncros associated to the pair of gears are shot.

Thus, two things: dump the heavy crap out and use Redline MT-90 to see if that helps. But if not, you got a tranny overhaul in store to replace the syncros.

-DSM

 

[juntjoo]

are you sure? I would imagine that if you performed that test on any transmission regardless of it's health will slow the engine down while grinding synchros/gears without using the clutch. thanks.

 

[pauleyman]

I don't know the dynamics of lubrication inside a transmission. I do know the recommended fluid for your transmission is not what you have in it. Another member has also expanded on gl5 gear oils. What I can tell you is viscosity doesn't always change just as a function of temperature. In oils (at least motor oils anyway) viscosity changes as a function of shear rate also. I can't tell you if this is whats happening in a synchro or if it even matters. Point is you should use the recommended gear oil for the transmission. If the synchros are grinding the only proper solution is to fix the root cause of the problem which is either the clutch or the synchros themselves.

 

[juntjoo]

alright, thanks for your responses. I'll update my progress as it comes

 

[DSM1G90]

regardless of it's health will slow the engine down while grinding synchros/gears without using the clutch. thanks.

Guess again - I learned this from a well known moderator here on Tuners, a few years back and I believed him, thus I do believe he knew more than the lot of us.

Give it a try - just barely push the shifter towards a gear without pressing on the clutch pedal. If the motor slows down, the syncros are doing their job, but if it begins to grind, the syncros are shot.

Here's a post on the topic I did 4yrs ago: http://www.dsmtuners.com/forums/new...hen-cold-search-didnt-help.html#post151625529

 

[And_44]

That oil is way to thick. It's not penetrating where it should. The lower weight oil will penetrate those synchro's and gears easily and allow them to work properly. If there still there that is. But if your already grinding you got other issues as well.

Put a thinner oil in and it will help cover up the other issues but won't fix them. It's to late to fix with an oil.

 

[DSM1G90]

You thin the oil and you water down and destroy the viscosity.

Do a drain and use correct weight of oil.

 

[juntjoo]

okay, so I need a lower weight oil, 75-85 as specified by my manual, gl 5, but the guy at amco said no GL 5, and I've read both opinions so... also, anyone know the weight of Pennzoil synchromesh? not stated any where

 

[pauleyman]

spec is gl4. Read the manual again. 75-85 should be a gl4 anyway.

 

[Spyderman7]

I can remember on one of the many cars I picked up had super thick gear oil in the trans and it would grind slightly into every gear .Changed the oil out with some Durablend 7590 and the grinding went away.

Im not saying changing the oil will fix it.But it could help