Synchromesh GM Part Number
 

Asked over on TeamSwift as well, but thought maybe someone here would know.

I'm looking for the part number for the GM Synchromesh fluid.

I understand there to be two formulations... and old and a new. I'd obviously prefer the new formula.

The parts folks behind the counter at the GM dealership here are clueless. I want to make sure I'm getting the right oil for my ol' '98 metro.

Thanks!

You can get it from Advance Auto, among other places I'm sure. It's not dealer-exclusive. Same deal with GM's Dexcool fluid.

no advanced auto's around here. we have kragen and napa.... do they sell?

think i found it:

GM part # 12345349

Don't get it from GM if you can help it. It is THE most expensive place you could get something for your car.

any online dealers? you're absolutely right... they want 20 bucks a quart. no wonder they're going broke!!

Napa should have it for around $5/qt. This isn't a GM-only part because it doesn't go in a GM transmission. It goes in a Isuzu transmission, and possibly others.

i called napa... they had no tranny fluid with the name synchromesh in it and hadn't a clue what i was talking about. sucks living in the sticks i guess (sticks compared to major metro area i should say).

anyway... is there any specifics i can tell napa to clue them in on what it is i'm looking for?

Why not go for a nice synthetic amsoil blend?

The GM and Chrysler synchromesh gear oils are very light gear oils ... formulated specifically for synchronized manual transmissions (tuned to have the right coefficient of friction). They are about 9.0-9.5 cSt in weight @ 100 degrees. But these dealer-fluids are NOT the only game in town.

The cheapest replacement would be to get Pennzoil Syncromesh which is a replacement formula found in many of the big-box auto supply retailers:

http://www.pennzoil.com/products/gea...cro_fluid.html

Or Honda MTF:

http://www.manchestermotorsports.com/index.cfm?pid=210

Me? My next change on my '06 Honda Civic is gonna be Amsoil MTF, I think:

http://www.amsoil.com/storefront/mtf.aspx

Here are the types of Syncromesh I know of that work great in these transmissions. The Part # is on the one bottle...................

http://i75.photobucket.com/albums/i3...TransFluid.jpg
http://i75.photobucket.com/albums/i3...esh_bottle.jpg
http://i75.photobucket.com/albums/i3...tf/Syntrax.jpg

thanks gents!

my search continues for either the Penzoil or the Amsoil. I use Amsoil in my big toy-hauler and like it a lot. good news is that i can at least buy the amsoil online if i have to.

btw... is it pronounced A-M-S-OIL, AMS-OIL, or AM-SOIL?? just curious. lol

I have had the GM magic synchromess fluid in my tracker(2nd gear grind is a common problem, it didn't help).
Now I have the stuff from Canadian tire for 1/4 as much and I can't tell the difference. There might be some efficiency gains to be had but at operating temp I don't think the viscosity is much different.
Buying the good stuff can't hurt though, just don't pay way way more for it.
Ian

i called every auto parts supplier in town. not a single one has the penzoil or amsoil synchromesh fluid. i'm SOL for local supply. looks like i'll be ordering online. i can get the amsoil for 8 bucks a quart so i'll just do that. will cost me about 30 bucks w/ shipping for the 3 quarts. not too bad.

pretty surprised that i can't find it from anyone in town.

found some!!

royal purple is making some now. replacement for the GM synchromesh.

http://www.royalpurple.com/manual-tr...ion-fluid.html

and

http://www.royalpurple.com/transmission-chart.html (click on GM for the part number cross reference)

picked up at the local schucks for 9 bucks a quart.

With rare exception, specific gears grinding is a symptom of poor driving technique. ie: downshifting into said gear without double clutching for the last 50K miles. Synchros will take only so much abuse and no fluid is going to fix that.

Well, I guess the tracker/vitara is the rare exception, the problem is that the ratio change from first to second is big, 4000rpm in first equals about 2200 in second, and they didn't double synchro 2nd gear. It hasn't really changed since new and I guess I could've been an ass about it and got a new tranny(which would probably be the same) out of GM but I didn't. I do rev match my downshifts but never double clutch, that's what synchros are for;). I'll try double clutching once in a while but I need to practice. Most of my driving is highway so normally I use 2nd gear maybe 10 times a commute and I don't take the tracker most of the time. If its the biggest problem I have with the gearbox I'll be happy with that!
I didn't have my scangauge when I had the GM fluid in there so unfortunately I can't post any before and after data. I suspect with my car unless I changed all the fluids to synth and back it would be undetectable. The loses at the rear dif and transfercase are much bigger I would think than the gear box, especially in 5th gear.

Ian

SirKeats, RP Synchromax is not really a direct replacement for GM or Chrysler synchromesh fluids. It is too thin: 7.7cSt versus the 9.0-9.5 cSt you should be looking for (both @ 100 degrees).

OK, this is a site for hypermilers, people willing to go to extremes. A thin oil would offer less hydrodynamic drag, right? And that can save a few percent in fuel economy? True, but you can damage the tranny too, depending on the conditions, driving styles, climate, etc ...

So, is that extra 2-3% more mileage worth the chance of a transmission replacement in a year or two? Each has to make his/her mind up on that one.

my intent wasn't to goto any extreme. RP though specifically states that this is suitable for trannys calling for the GM Synchromesh (PN1234359) which is the exact same part number called for in the geo tranny's.

RP even posts this exact part number for the synchromesh fluid in their compatibility chart.

i've emailed them regarding this as you've got me worried now... but just to clarify, are you suggesting they're being less than forthcoming with respect to compatibility?

SirKeats, pretty much.

The manufacturers each have their own comfort level as to how far out of factory spec they are willing to go. Red Line, Amsoil, RP and others do this as a way of expanding the potential customer base. I look at their recommendations and try to double-check

I am going to try Amsoil MTF for my '06 Civic's 5-speed manual tranny. Amsoil claims it is a direct replacement for Honda MTF (I & II) ... but I thought Honda MTF was 10-11.5 cST ... and the Amsoil is 9.6 cSt. I just can't confirm the Honda spec ANYWHERE. If the Amsoil doesn't seem right, I'll dump it in a year and go back to genuine Honda MTF.

While I've seen some people have good results with RP products, in my opinion they are short on engineering/innovation and long on bling-bling. If your tranny called for ATF, I'd say go ahead and buy the Synchromax as it is the only true synchromesh gear oil in that super-light weight now that Specialty Formulations has closed its doors.

However, if yours asks for GM-brand synchromesh, I'd try one of the several fluids available in the correct thickness. This is a popular weight and you have plenty of appropriate choices.

Remember, I'm using actual weight numbers ... not vague, brand-specific puffery.

well crap... i've already put the synchromax in the car though. i did check both the pennzoil and amsoil specs and they confirm your reports. i've no way of knowing what the actual figures are for the GM Synchromesh... but i'll assume you're correct.

i've emailed RP to see what they say. i want a refund from them if they're not willing to back up their product!!

Or if you already bought the RP Synchromax, you could thicken it up a touch with RP Max Gear 75W-90. 75% RP Synchromax and 25% Max Gear would give you a weight of about 9.6 - 9.7 ... your target weight.

Both oils are GL4 compatible, both from the same blender ... don't worry about mixing/compatibility.

here's what the RP guy said (i'll omit his personal info):

first my email to them:

their response

not trying to argue here... just wanted to share his opinion on the subject. i may end up switching out anyway. i don't wanna risk damaging my tranny.

He may have a very real point. There's a trend in lubes to thinner and better quality lubes in engines, trannys and even wheel bearings.

SirKeats, to sum it all up, I'm not particularly impressed with this guy ... although I'm sure he has gotten negative internet-driven feedback before ... so he knows what he's up against and his initial comments reflect that. Truth is, some internet discussion is good, some is BS. Often, telling the difference between the two can be hard.

I could put you in touch with a chemist/physicist who DOES blend oils as a day job ... or at least he did before he shut down his company due to logistical problems over a year ago. He'll tell you the same thing ... he's where I got a lot of my knowledge from. And if he was still blending, I'd recommend his syncromesh fluids (Specialty Formulations - offered in four (4) different weights) over every other brand ... it was the only stuff that made my Nissan 6-speed shift worth a d@mn.

And what I'm telling you is to more closely match your fill with what the factory uses and asks for … Now, does that sound nuts? Doesn’t it sound like common sense instead?

Now, to pick apart some of the RP dude’s response:

” First. How is it working? Excellent, right? Improved easier shifting - less noise, lower temps.”

The first thing you’ll notice is less shift effort … well duh! If the oil is thinner, there will be less fluid resistance! That says nothing about how it is protecting (or failing) your tranny. How would you know the temp before and after? (of course you probably wouldn’t) And when was the last time you heard noise from ANY syncromesh transmission? I don’t think I ever have. Unscientific gibberish!

” Although marginally lighter in fluid thickness, or viscosity at 100 C, the Synchromax has 300 percent greater oil film strength …”

Going from a 9.08 cSt fluid (Pennzoil) to a 7.7cSt fluid is a reduction of 15% … 20% if you use Amsoil instead of Pennzoil. That’s more than marginal in my book. And he’s talking about “300% greater film strength” … um, compared to WHAT? What a load of vague, marketing puffery!

” I'm using the same Synchromax in my personal vehicle which is putting 650 lb-ft of torque through the manual transmission.”

That’s probably a Corvette … or a car that uses a modern ‘Vette transmission which is designed to use a super-thin oil like ATF (factory recommended). RP Syncromax is perfectly appropriate for THAT application. But your car calls for a thicker fluid … that’s a fact.

SirKeats, you paid good money for that oil so I am not gonna suggest you dump it. If you want to be on the safe side, drain it into a thoroughly cleaned catch-pan. Buy 1 quart of RP’s gear “Max Gear” oil and make something close to a 25/75 mix (heavy on the Synchromax). And pour it back in (I’d filter it through a coffee filter first … or at least a clean, piece of cloth to catch any large particles.

BUT, if you are driving your car gently and putting only light loads on the driveline (like most Ecomodders) you might be fine with a 15-20% lighter fluid in the box. This is especially true if you live in the northern third of the U.S. or Canada where it is colder and a slightly thinner fluid has some benefits. It will be better shifting in extreme cold of morning … and the decreased hydrodynamic drag might give you a measurable increase in fuel economy.

However, this goes the other way if you live in the southern third of this country or Mexico where I’d want to use something a little thicker like Red Line Oil MTL (cSt 10.0-10.5) to protect the bearings, etc … in the intense heat that tends to thin out these fluids.

I still say the safest thing is to use the proper weight of fluid and off-the-shelf Synchromax ain’t it.

If the RP is designed to have a higher film strength then it very well may be just fine for your transmission. I work in the gearing industry and you can see large gains from changing oil specs. I'll admit I'm no expert, but if RP recommends it I'd be fairly secure that it'll work alright. If you are very unsure, use a magnetic drain plug, or drain the oil out in a few thousand miles and run a magnet through it. If you see metalic particles there is obviously wear going on. Keep in mind they may be remainders from the first oil change that weren't flushed out initially though.

"If the RP is designed to have a higher film strength then it very well may be just fine for your transmission. I work in the gearing industry and you can see large gains from changing oil specs. I'll admit I'm no expert, but if RP recommends it I'd be fairly secure that it'll work alright. If you are very unsure, use a magnetic drain plug, or drain the oil out in a few thousand miles and run a magnet through it. If you see metallic particles there is obviously wear going on. Keep in mind they may be remainders from the first oil change that weren't flushed out initially though."

To be honest, RP is one of my least favorite of the large oil brands. For years, they have been heavy on the gimmicky marketing and puffery, but short on real innovation. Currently they are a sponsor of the Iron Man movie ... WTF does that have to do with automotive lubricants? Are we to believe that Iron Man can do all the things he can in the movie because Royal Purple works so well? :rolleyes:

I just don't have a lot of respect for their claims of higher film strength. Most Royal Purple formulas are a mix of petroleum/mineral oil and PAO ... which is what most companies use these days. Talk of "higher film strength" sounds like they are comparing their current formula to mineral oils from decades ago. :rolleyes:

Here is a thread on BITOG where we discuss one person's experience using Max Gear in their car tranny (yes, I participated). He sent a sample of his used oil off to a lab to see how it fared:

http://www.bobistheoilguy.com/forums...93#Post1037993

It's best not to trust a visualization of metallic particles in used oil ... just not scientific enough ... and once the tranny is showing that kind of wear, most of the damage is done. :(

If you choose to run the lighter oil, fine. But I'd have a sample tested by a lab after 10-20,000 miles just to see how it's holding up.

Can't argue with hard numbers. It would be interesting to see the test in another 20k miles or so though to see how much was initial break in.

Yes Daox, I'd figure some of that wear is break-in ... and I don't have a baseline for that sort of vehicle.

But the one number issue that really stood out for me was the viscosity of this "premium" gear oil after less than 30,000 miles (recommended intervals for manual transmissions start at around 30,000 miles and go past 100,000 to 'lifetime' fills). :eek:

Oil starts off (supposedly) 16.5 cSt or more and it sheared to a 11.6. Imagine that oil left in that tranny for double or triple that time? Most Nissan trannies now call for a 12.5 cSt GL-4 gear oil ... this stuff started out high then sheared down to well below spec. I wonder how much Synchromax shears? :confused:

I've seen RP motor oil shear alarmingly before ... but some of that might have been fuel dilution. That's not the case with an oil in a tranny. The oil in this case simply couldn't take it. :(

Thanks, but I'll choose another brand ... plenty of good ones out there. :p

Synchros aren't there so you don't have to double clutch, they're there when you can't double clutch (racing). I've got 2 manuals (@92K & 121K) with all their synchros in tact. It's because I double clutch on every single downshift. If I need the synchros for occasional rapid upshifting, they're there, however they'll wear with constant abuse.


The 4000-2500 shift isn't as bad as you think because the synchros have the natural clutch spindown to work in their favor. When you downshift without double clutching, your synchros have to accelerate the clutch which is a lot more work.

What I'd do if my 1st and 2nd gears were that far apart is:
1. Not wind out 1st gear to 4K rpm if I could help it. A gear that short is probably designed for high torque climbing, towing or just barely getting the vehicle in motion after a stop. If you shifted at 2500, you'd have only a 1000 rpm drop to deal with.
2. Slip out of 1st without clutch, then clutch into 2nd halfway there.

Double clutch now on downshifts, or double clutch later, every shift. :)