Failing Synchro - What Additive(s) worked for you?

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Akron, OH
1997 BMW 318i
M44 motor / 5spd trans / 199,000mi

I purchased this vehicle in June 2010, from the second owner. They had quite a few receipts to go along with the car, so I trusted that it was well cared for.

I first noticed the following...

When downshifting from 3rd --> 2nd, the gears would grind as they engaged. Rev-matching my downshift didn't help the problem. Actually double-clutching and matching revs would help. The problem did NOT happen when the car was cold -- "cold" is a relative term as it was summer then. Because the issue seemed to be related to operating temp, I hoped some fresh fluid would fix the issue. I put in Redline D4 ATF (popular with BMWs, I'd used it on several BMWs in the past) hoping it might help the issue.

NOW it's winter where I live. Temps are frequently in the low teens in the morning, down to single digits (F) on cold days. The transmission will now grind on the 1st --> 2nd upshift during the first 2-5 mins of operation. I've began to double-clutch that shift as well, which cures the issue. The 3rd--> 2nd downshift still grinds when I forget to double clutch.

I'm fairly certain that my 2nd gear synchro is on it's way out...my question is this:

Has anyone been able to "save" or "resurrect" a failing synchro with some sort of additive? If so, please share your experience.

This car is my "winter car", and I'm not interested in investing in a new tranny. Best case is I find some sort of additive that improves my situation and then I sell it in the spring.

Thanks in advance!
Matt
 
Try this usually at Napa or purchased online:
Lubegard

What transmission? what fluid requirement?

Bleed and/or adjust linkages. Verify power train mounts.
 
Originally Posted By: unDummy
Try this usually at Napa or purchased online:
Lubegard

What transmission? what fluid requirement?

Bleed and/or adjust linkages. Verify power train mounts.



Like unDummy said,bleed your clutch lines. Mine has two bleed points,on the passenger side fender well and on the slave. Be sure to bleed both points if your car has such.
 
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Originally Posted By: aquariuscsm
Try Pennzoil Synchromesh/GM Synchromesh maybe?


+1
IF your clutch is bled and adjusted properly!
 
Bleed the system as already mentioned, in fact I'd flush the fluid from the system and completely replace it. I would change out the fluid and add the LG product recommended for your application. If that doesn't work, you'll have to continue to double clutch or opt for some very expensive repairs. Please update us.

Are you certain the clutch is fully releasing? Can you go into reverse from a dead stop w/o double clutching or shifting into first before going into reverse? In other words can you start the engine, and shift into reverse w/o doing anything else, both from a cold start or a hot start?
 
+1 for what demarpaint said.

When the problem "migrated" to the other gears, it wouldn't seem to be synchros alone. Bleeding the clutch system may be the cure, and I hope it is. If not, look deeper.

The classic example is what demarpaint cited: engaging reverse, where there is no synchro, at stop. If it grinds or crunches, it could be the clutch release (aka throwout) bearing.

The synchros on the forward gears can hide a lot of that bearing failing until they can't past a certain point.

It doesn't mean total trannie failure, just clutch time.
 
Redline's Lightweight Shockproof is now marketed as a manual transmission oil. It has been known to 'mask' the symptoms of old synchros in Subaru 5mt's. I've used it, and it was smooth as silk. However, I'm not sure what fluid is spec'd for your tranny.
 
Originally Posted By: Matt_N
Has anyone been able to "save" or "resurrect" a failing synchro with some sort of additive? If so, please share your experience.


First off, you did not hear any of this from me. I deny it.

I had a similar situation with an old 1980 Mazda Rx7 I had back in the high school/college days. First gear would crunch every time, and worse in cold weather. An old timer told me to put 2 ounces of powered graphite into a quart of gear oil, mix it all up, and replace 1 quart of my tranny gear oil with this mix and the grinding would stop. Being young and naive, I did it. Within one days drive time the shifting was smooth as butter. I drove it for tens of thousands of miles with this mix in the gearbox with no problems until the engine quit a few years later and I traded it on a new 1986 Rx7.

You did not hear this from me.
 
Originally Posted By: expat
Originally Posted By: aquariuscsm
Try Pennzoil Synchromesh/GM Synchromesh maybe?


+1
IF your clutch is bled and adjusted properly!


+2, BUT, it could also grind even worse in the cold, since it has a thicker cSt than D4 (or ANY Dex 3).
 
Matt, you state the problem was not there when cold.
This means it likes a thicker oil.
But then you put the thinnest stuff you could find in there!

Anyway, get a lube that is made for manual trannys - one that is friction modified for good synchro action [grabbing].
Anybody's version of a Synchromesh type would be a good start. Synchromesh fluids are about a 5-30. Redline or Amsoil make thicker versions of great tranny fluids, if you need thicker.

And like mentioned, there are adjustments and bleeding that have to be made as good as you can get them , first. Not a big deal, but get that right. Also, linkage can get sloppy - check it out as well.
 
Synchros need friction to work (they are essentially a cone clutch), so adding more lubricity is often counter productive. You need to go into the other direction. Try an oil that's less slippery. You see the proof in that it shifts better when cold... the oil is more viscous and less slippery.

I had an old Datsun 510.. you know, one of those swift little IFS/IRS "Z" Like sedans of the '60s (with the Mulholland kit, it handled like a go cart!). Mine had a balky trans ( a few too many speed shifts ( : < ) that ground the gears. I tried all sorts of oils to band-aid it and it just got worse the better the oil I installed. I was working in a Mercedes shop at that time and one of the old Germans there told me what I told you above. I don't remember what I actually put in... I think it was motor oil... but it vastly improved.

I'm not sure what to recommend exactly, only something that's less slippery than what's in there now. I would say avoid synthetics and stay near to the recommended viscosity. Remember also that you can't put metal back on an synchro with an oil change. That's just a band-aid that may, or may not work. Ultimately, the trans needs to be repaired.
 
Originally Posted By: Jim Allen
Synchros need friction to work (they are essentially a cone clutch), so adding more lubricity is often counter productive. You need to go into the other direction. Try an oil that's less slippery. You see the proof in that it shifts better when cold... the oil is more viscous and less slippery.


My position in this reply is similar to Jim's which I quoted above. There are multiple factors in MT lube - viscosity AND friction modifier properties. Crunching and grinding occur because the transmission shafts were not synchronized when the gear was engaged. There are multiple causes for this. The answer may not be as simple as "See, it likes thicker lube". If you give the synchros more "grip" then you may solve (or delay) your problem, assuming that the clutch is not actually at fault.

I would stick with dedicated synchromesh fluids - MTL from Redline instead of D4, MTF from Amsoil, Pentosin MTF2 (a very close if not identical match to factory fluid).

As others have suggested - check your clutch and linkages. My BMW's shifting has become notchy over the last couple of years because of linkage wear (I think). The catch is that I have been unsuccessful at swapping the last few components without dropping the transmission which is not a casual Sunday afternoon honey-do for me
smile.gif
I get crunching or grinding extremely rarely.
 
How about the GM Friction Modified Synchromesh fluid? How does this stuff differ from the regular GM Synchromesh fluid? Is the FM for better synchro engagemant,or for front wheel drive units that share tranny/diff per se?
 
Friction modified means just that. It doesn't tell if its modified for more or less traction.

The tire contact to the road surface is friction modified.
A patch of ice can modify the road so that you do crash into that tree.
A sander tosses sand on the ice to modify that slippery road so you don't crash into that tree.


A FM can be a traction modifier, the sand.
A FM can be a slippage modifier, the ice.
 
Thank you for taking the time to respond. I wanted to provide some info that will clairify your questions, as well as ask a few of my own.

- ATF fluid is what is spec'd by BMW for this transmission. I've used Redline MTL in the past on BMWs, but have found that D4 ATF is better in the cold temps

- During the summer months, the grinding would not occur until the transmission was warmed up. That lead me to believe that maybe the fluid that was in there has lost viscosity, and fresh fluid would do the trick. Now that winter is here, it seems the cold temps bring the problem out when the fluid is cold. This is different than what I was experiencing in the summer...when "cold" (60-80F) fluid was good, and warmed up fluid brought on the grinding.

- It does NOT grind going into reverse, nor do I have trouble with any of the other gears. I agree that it's a good idea to be sure the clutch is bled properly, but if this were the issue then wouldn't I have problems with more than just 2nd gear?

- QUESTION - Has anyone ever nursed/improved a failing synchro with an additive, or some other type of trans fluid?? If so, what was it??

Thanks for the suggestion of graphite in the trans fluid. I may try that come Spring.

Any other suggestions?
 
Matt, I think you may have missed the point in that INCREASING lubricity, with an additive like graphite or a more slippery fluid, is counter-productive to your problem.

Since ATF is spec'ed, trying changing to a mineral ATF, maybe even a Type F, which has minimal friction modifiers. It's cheap enough to try for a short period. As I said before, IIRC from 25 years ago, I think I used motor oil in my Datsun 510 tranny to mask a synchro issue.
 
Originally Posted By: Matt_N
Thank you for taking the time to respond. I wanted to provide some info that will clairify your questions, as well as ask a few of my own.

- ATF fluid is what is spec'd by BMW for this transmission. I've used Redline MTL in the past on BMWs, but have found that D4 ATF is better in the cold temps


Are you ABSOLUTELY positive of this? I know that all of the aftermarket fluid companies like RL and RP say to use their ATF but if you look at the viscosity of MTF-LT-1 (the factory fill for BMW in the time frame your car was made) it's closer to 9 cSt like RL MTL and Amsoil MTF.

I could swear I saw a VOA of MTF-LT-2 indicating that it was also in the 9s but just in the last couple of months someone here pointed me to theirs which showed it in the 7s. I still haven't found the first post I read years ago showing VOAs of LT-1 and LT-2 for comparison.

In my E39-oriented forums, there are lots of folks running 9cSt and even thicker MT lubes (like MT-90) and loving it as long as their temps stay in a good place. I've used D4 ATF in my E39 and it worked "fine", but when I switched to MTL I thought it worked even better even in the cold.

My point about MTL was, again, that it's a purpose-blended synchromesh fluid tuned for synchronized transmissions and nothing else. D4ATF may tout itself as an auto/manual fluid, but it is primary an AT fluid. Back when I used to drive an Acura, RL MTL *was* the magic fluid to eek the last out of tired synchros. Those transmissions speced motor oil, not even ATF.

Clutch factors are not just limited to bleeding. There are a number of different ways that a supposedly disengaged clutch can continue to transmit a fraction of power through to the transmission. The negative effects will happen to 2nd first because it is always the most-abused synchro in any MT. Anyone driving an MT looking to move fast winds it out in first and then tries to jam it into second - high revs, large difference between the gear ratios, hamfisted shifting = synchro wear. It's good that your car passes all of the other tests but it was certainly worth checking or you would continue to make things worse.
 
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