Synthetic transmission fluid for a manual transmission?
 

I felt something in my transmission go pop a week ago. The dealer found gears missing a tooth or 2, they have decided to replace the transmission instead of just the damaged gears. In warranty.

So my question. Is Synthetic better in a manual transmission? And if so, Do I offer to pay for synthetic transmission fluid?





Side note: more info on same issue.
After I felt the transmission go pop into 5th gear it just did not feel right. Sliding it into gear was not as smooth, and when I got up to high speeds it would sometimes grind going into 5th. I found I could produce the grinding issue 100% of the time if I did this:
6mph+, shift to neutral, let the clutch out, push clutch back in, shift to 5th gear.

So now basically what they are telling me:
“You should not double clutch a car with synchro’s, it could cause damage. Double clutching should only be done in large trucks without synchro’s”
That sound like a bunch of bull shift to you also?
I have driven a stick on and off for 30 years, from a VW Bug to large truck. I am shifting as I always have – sometimes leaving the transmission in neutral. This is the 1st transmission I have ever had any problems with. I do NOT see how double clutching can cause any issue. IMO it helps.

If anyone can point me to any verifiable documentation on the issue of double clutching in a car with syncros PLEASE let me know. I would love to hand them verifiable documentation.

Here's the problem with double clutching -

If you're doing it, chances are, you're doing it wrong. The point of double clutching is to allow the gears to match the engine speed that will account for the next gear. Most people just clutch, remove from gear, let off, clutch, put in gear, then hit the gas and let the clutch out like normal. It's a pointless 'third step' in that case, because the synchros still have to work, albeit slightly less.

When double clutching is done properly, you don't need to hit the accelerator until after you've left off the clutch pedal entirely.

It will not, however, damage your transmission. That dealer is throwing darts at an invisible dart board, hoping to sound correct. Ask them to show you proof that double clutching will damage a synchronized transmission, and if they can't put up the evidence, to stop spouting non-sense.

Other than wearing parts unnecessarily, such as clutch master cylinder, slave cylinder, and release bearing - again, negligible - TBH, it's just not necessary, and serves no benefit other than peace of mind in some people's cases.

Synthetic fluid isn't necessarily "better" for your transmission, but it is usually less viscous, so less engine power is necessary to defeat the impedance to movement that a thicker oil will cause.

Yes, you should ask the dealer to install it anyway, even if they make you pay for it (They most certainly will) unless they tell you that it will void any further warranty.

Synthetic oils have a longer life, better lubrication over the long haul, are more heat-resistant, and aren't made from something we could be using for fuel (not necessarily true, actually).

Definately better, especially in cold weather. When the fluid is fully warmed up, dino and syn should be close. However, before that dino will be significantly thicker.

I remember once starting up my old truck at -40 degree F. It started fine, but I put it neutral to let it warm up and when I let off the clutch it lurched forward and died. The fluid was so thick it acted as if it were in gear. Also, moving the shift lever felt like it was full of molasses I switched to synthetic later and at the same temps it acted normal. Granted, this is a little extreme compared to most, but it illustrates the point.

There's no harm in double clutching with a synchro. One note though, when double-clutching while upsifting, you should rev match in neutral. Doing it the way you described, there will be a greater difference in speed making the synchros work harder. That's why you heard the sound every time. This still shouldn't have harmed your tranny significantly and certainly isn't the cause of the broken tooth.

One more thing I forgot in the earlier post -

I don't double clutch, but I do rev match. I only use the clutch pedal going into gear, never coming out of it.

IOW - If I'm making my 1st to 2nd shift, I'll gently pull back on the selector while letting off the gas. As you reach neutral throttle, the selector will slide out of gear. At the same moment that it slides out of gear, I'm pushing the clutch, sliding into the next gear, and letting the clutch back out. It's a nearly perfect gear match, so there is minimal work for the synchronizers to do.

Alternatively, on my bike and in my car, I usually shift without using the clutch pedal at all. If I'm starting off, I use it, but shifting up/down or stopping, not so much.

I'm a big believer in synthetics. Have Royal Purple in my Neon's 5 speed...

Thanks for the replies.

Sounds like everyone is confirming my thoughts. Synthetic even if only slightly will help. I will go with Synthetic if they allow me to.

...double-clutching 'tears' teeth off the SYNCHRO-rings not the actual inter-meshing GEARS (which are actually always engaged).

...whaich was the dealer actually talking about?

Unfortunitly I have only been told Teeth Missing from Gears.

I do not know how the synchro works….
So…
You have my attention, “ 'tears' “? As in Cry?
Or…
Dictionary.com
verb (used without object) -- to fill up and overflow with tears, as the eyes.

Center shaft may not be the correct term for it. But I thought Double Clutching (or Using neutral between gears) affects the center shaft by slowing it down.
This can help in large trucks bring the center shaft speed closer to the speed of the next gear making it easier to shift.

Is that center shaft speed difference due to using neutral VS going right to the next gear somehow causing the were on the synchro?

why is this different due to double clutching?
Can you elaborate a bit more? You may have the knowledge I am looking for.

Thanks.

tear = (1) to pull apart (verb); (2) drop of liquid from the eye (noun)
tare = (1) weed (noun); (2) container's weight (noun).

...I meant #1 of (1) above.

...synchro is abbreviation for synchronization-ring, which is an intermediary 'toothed' (usually brass) ring that initially engages the DRIVE rotator, then by friction due to its 'conical' inner surface, slows down the DRIVEN rotator until their two rotational speeds "synchronize" and then the DRIVE and DRIVEN shafts can be locked by sliding spline.

Wonderfully put! You did a great job of boiled that down to a short statement.
After your explanation and a link to HowStuffWorks.com I feel I understand how the synchronizers works!
http://auto.howstuffworks.com/transmission3.htm


I can also see how a poorly done Double clutch, could cause extra wear. I see the possible issue like this, let me know if this is close to what your thinking.

The frictional portion of the synchronizer is not meant to handle a lot of force. It could be over powered causing the soft brass teeth to encounter too much force, and causing excessive wear.

...correct, it's common to wear/chip synchro "teeth" but not the actual mechanically-engaged gear teeth...to break one of them usually means a piece of hard metal (brass might do it, but usually not) has broken loose from something and physically gotten between the engaging gear teeth, which if you notice in the illustrations, are always engaged with their mating gear...all engagement is via the synchro.

If someone told me that the teeth broke off the gear, I'd assume they meant the helical splines that engage from gear to gear, which transfer power between gears.

Probably the furthest thing from my mind would be the dog-teeth, or those things that engage the gear to the input/output shaft (whichever one free spins when gears aren't engaged, usually output, I think) so that it can begin transferring power from the input shaft, to the drive gear, which sends power to the driven gear (via the "teeth" or Helix Splines), which sends power to the output shaft, eventually going to the differential and driving the wheels.

The fact that you're getting an easily reproducible grinding noise suggests that you've destroyed a synchronizer, though.

...my diagnosis too. But, if there REALLY are pieces of "iron teeth" in there, that's BAD news.

Most definitely. In fact, I'd be inclined to say that if there are pieces of anything in there, trouble is afoot.

...both require tearing down the tranny, but IMHO swapping in new synchros is much easier and less costly than changing out a mating gear-set (because, then you really should refresh all the synchro too...ultimately too much money).

I used Redline in my 03 Matrix (came with it when I purchased the car), and I have Royal Purple in the Paseo. When I put the Royal Purple in the Paseo, it made a noticeable difference when the car was cold in the winter. It wasn't noticeable in the summer. I'd still highly recommend synthetic, whatever brand you go with.