RP Synchromesh too thin?

[deebee]

Service Manual calls for GL-5 75wt.
No problem with shifting but
I get a 5th gear whine. Should I go back
to 75-90wt dino gear oil?
92 Geo Metro XFI
thanks
deebee

 

[Herz]

isnt synchromesh 5-30 weight?

 

[Kiwi_ME]

Are you sure about that spec? I think it should be a 75W-90 GL-4.

 

[deebee]

Yes, I have read that 75wt gear oil is equivalent to a 10-30 motor oil.
I also own an 87 Chevy Turbo, 3 cylinder, and its factory service manual says GL-5 also.
For the Geo metro I went from the Chilton's book. Both engines are a 1.0L 3 cyl. Suzuki engine.
Again I have no problem with shifting up or down.
Just a whine in 5th gear.
thanks

 

[unDummy]

RoyalPurple Synchromax is a 7cst fluid which is a great substitute if you require ATF.

Synchromesh fluids are usually ~9+ cst.

GL5 75wt? I would put Redline MT90 or Amsoil MTG into that transmission which are ~14cst. And, if you're looking for a little MPG, then the Synchromesh substitutes which are ~10cst are Redline MTL and Amsoil MTF.

GL4 fluids were very difficult to find. So, its easy to spec a GL5 since every store has GL5 gear oils are available.

If you truly want that GL5 rated fluid, find a GL5 gear oil without LSD additive. Something along the lines of Motul Gear300, Redline 75w90NS, Synlube, Eneos, Ford, Toyota 75w85, BG, Neo, Silkolene, Torco, Lubromoly, Wynns......

 

[Jim Allen]

The RP is 7.7 cSt.

Is there actually a straight API 75 Grade? If so, I've never heard of it (I did a quick search and didn't find it). If there is, educate me!

There is a straight 75W, which is a cold weather gear oil of approximately 4.1 cSt @ 100cSt according to the API chart I looked at. That equates to about a grade 5 or 10 engine oil. Thinner than ATF. An 80W is around 7 cSt and 85W around 11cSt @ 100C. 90 runs 13.5 cSt.

deebee: I suspect unDummy is right and you may need to get more info on the car's requirements. I found one source that listed 75W90 GL5 gear oil for the Metro but recommended GM's Synchromesh fluid (which is around 9+ cSt) as a slightly thinner replacement for the gear oil. If a 13.5 cSt grade 90 is spec'ed, the 7.7 cSt RP is likely way too thin, hence the whine. You might get away with that in the frigid north, but I don't think Portland fits that description ( : < ). Since the GM Synchromesh is obscenely expensive (IMO), I'd recommend a good syn 75W90.

This is all assuming that you know something we don't... specific to Metros.

 

[cchase]

I believe all 75w-x gear lubes are synthetic, but I may be wrong.

 

[deebee]

Hey thanks you guys, I am a newbie when it comes to translating all the specs on these oils. I know in the Teamswift and Geo groups, many use the Penzoil Synchromesh and swear by it. I kinda thought it would have the same "thinness" as the RP synchromesh.
Excuse my ignorance, but is "cst" a measure of viscosity?
thanks again
deebee

 

[Jim Allen]

Originally Posted By: deebee
Hey thanks you guys, I am a newbie when it comes to translating all the specs on these oils. I know in the Teamswift and Geo groups, many use the Penzoil Synchromesh and swear by it. I kinda thought it would have the same "thinness" as the RP synchromesh.
Excuse my ignorance, but is "cst" a measure of viscosity?
thanks again
deebee


Yes, cSt stands for Centistokes and is the actual measurement of viscosity. The "90" part is the API Grade, which runs a range of cSt. An API (American Petroleum Institute) 90 Grade, for example, runs from 13.5 to 18.50 cSt. I suggest you Google "API" and download the latest info on gear oil grades.

The Pennz Synchromesh is 9.08 cSt, which would fit into the new API 80 Grade (7.00-11.00 cSt). The RP fits there too, but at the lower end of the scale and might be a bit thin for your application. FWIW, if it were mine, I'm not sure I would go with the Synchromesh fluid. If you are getting a whine now, I can't imagine going up one cSt is going to help much (it might but you have to pay to find out ( : < ). If I had to dump out fresh (expensive) fluid, I'd go with a 75W90. Either that or run the RP and see what happens.

I am assuming the whine started with the fluid change, by the way.

Another option might be to drain a quart or two, and replace it with RP 75W90 Max Gear. That might be enough to bolster the viscosity a bit without too much extra cost. The two RP products are most likely to be most compatible with each other. I know they both use the same anti-wear additives, but the 75W90 would have more. If you drain and add a quart at a time, you might find a perfect mix.

 

[Kiwi_ME]

I don't think a change of oil is going to "fix" a fifth gear whine on an 18-yr old car. As pointed out several times a GL-5 is a convenient choice for a mfg or Chilton to spec - not the optimum one.
For a transverse engine FWD use Redline MT-90 or other GL-4 75W-90.

 

[Jim Allen]

Originally Posted By: Kiwi_ME
I don't think a change of oil is going to "fix" a fifth gear whine on an 18-yr old car. As pointed out several times a GL-5 is a convenient choice for a mfg or Chilton to spec - not the optimum one.
For a transverse engine FWD use Redline MT-90 or other GL-4 75W-90.


Many syn 75W90s are dual GL4/GL5 rated. Right, no oil is going to fix a mechanical whine but it if didn't whine before and does now??? At least that is my assumption. Sometimes a lighter oil can bring out a slight noise that wasn't so apparent with a heavier one. I assume that even with a helical gear drive like a typical FWD car uses, that would still be the case.

 

[mechtech2]

Engine oil has it's hot rating at 212 deg F. Gear oil is measured at 150 F.
This is why a seemingly thick 90 gear oil really is not .
In any event, we can't readily compare the two.

With your Geo Metro, you don't need extreme lubes for protection.
The PS will serve you well.
If the noise bothers you, another fluid is not a sure cure.

 

[deebee]

Thanks again.
I will get back to you in a couple of days and let you know what I used and how it turned out.
deebee

 

[m37charlie]

Originally Posted By: mechtech2
Engine oil has it's hot rating at 212 deg F. Gear oil is measured at 150 F.
This is why a seemingly thick 90 gear oil really is not .


I am sorry, but you are incorrect. Both motor oil and gear oil are measured at 100C. (212F.) Check the viscosity tables in the front of the forum. Gear oil and motor oil viscosities are not on the same scale. If they were, a 90 viscosity gear oil would be a 40 or 50 motor oil.

Charlie

 

[mechtech2]

Gear oil is measured at 150 deg F. That is the 'hot' measurement.
This is why it is rated so thick.
Get it up to 212F, and it is comparable to engine oil.

 

[Jim Allen]

Originally Posted By: mechtech2
Gear oil is measured at 150 deg F. That is the 'hot' measurement.
This is why it is rated so thick.
Get it up to 212F, and it is comparable to engine oil.


Again, sorry, but no.
SAE J306 and the equivalent ISO test specify the same 40C and 100C (212F) viscosity specs for gear oil grades as with engine oil grades.

See Here: J306

There are many other references.

 

[Tremo]

My old WC Borg Warner T5 loves the RP Synchromax. It calls for ATF, but the Synchromax is for manual boxes that call for ATF. Shifting is very smooth. Never any grind.

 

[deebee]

Well I changed out the RP Synchromesh to Castrol Syntec 75-90wt gear oil, a full synthetic(so it says).
Still a whine most audible at around 55mph-64mph(no tach). After that, maybe these old ears can't pick up the frequency.
Is there an additive that might quiet down the whine? Lucas Oil Stabilzer?
The car has 140K on it. Not an uncommon problem with Geo's.
some have state.."5th gear and the countershaft gear is not meshing right. could be the bushings in the countershaft are worn allowing a separation of the mesh." Another mentioned a tappered roller bearing going bad. All beyond me. I guess I will put up with it until it falls apart.
Thanks all, for your inputs.

 

[Jim Allen]

Well, as mechtech2 said, oil (or an additive) can't fix a worn out part. The best idea is to stay tuned to the noise and when it changes pitch or starts to get worse, be ready for some repairs. Often these kinds of things go on for a long time before anything needs to be done... though that's not something you should count on too highly (like plan a drive to Alaska or something.

BTW, do I remember incorrectly or didn't you say the noise started after you put in the RP?? Maybe its my old BRAIN! ( :< )

 

[mechtech2]

A 75-90 gear oil is comparable to a 10-40 motor oil.
Of course you can measure any lube at any temperature, but they are way different when comparing numbers.
This is basic and obvious.