Synchromesh GM Part Number

[SirKeats]

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!!

[Bror Jace]

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.

[SirKeats]

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

first my email to them:

I have been shopping around for an alternative to the GM Synchromesh transmission fluid for my 1989 Geo Metro and was pleased when I found Synchromax at my local auto parts store. However, despite the claims on the Royal Purple website that the Synchromax product is appropriate for vehicles requireing the GM Synchromesh fluid (PN12345349), I've just been told that the GM fluid (as well as the Pennzoil alternative) has a cSt @ 100°C of 9.0-9.5 while the RP Synchromax is only 7.7. I was further told that this could result in damage to my transmission.

This is a major concern as I've already put your Synchromax oil in my 5spd manual transmission. I'm worried now that I could be causing my vehicle harm.

Can you please explain?

Thanks,

Nick

their response

Nick,

Thanks for the email and for choosing to use Synchromax in your Metro.

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

Your concerns are not well founded and are probably being fueled by those on the internet that like to think of themselves as lube experts but hold day jobs in another field of work! I do this for a living and have traveled the world improving lubrication.

Although marginally lighter in fluid thickness, or viscosity at 100 C, the Synchromax has 300 percent greater oil film strength which prevents metal to metal from happening due to our advanced additive technology. By stopping friction and metal contact better, operating temps drop and the slight viscosity difference becomes negligible in the bearings.

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

RP stands behind the recommendation to use the Synchromax in your 89 Metro manual transaxle as the fully synthetic base oils and additives offers superior wear and high and low temp performance above that of the mineral based OEM fluid.

Email me direct if you have additional ?

Thanks,

David
Tech. Services
[omitted]
Sent from my Verizon Wireless BlackBerry

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.

[slopemeno]

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.

[Bror Jace]

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.

[Daox]

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.

[Bror Jace]

"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?

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.

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.

[Daox]

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.

[Bror Jace]

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).

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?

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.

[JohnnyGrey]

I do rev match my downshifts but never double clutch, that's what synchros are for.

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.