swapping to synthetic gear oil

[dlb]

i picked up some synthetic gear oil on sale and want to put it in my all trac (errrr, i mean tercel...) but am reluctant due to the mixed reviews synthetic oils get from people using it in older cars. the topic has come up a few times but i want to consolidate the conversation into one thread here. here is what i've gleaned from some searching and talking to peeps on this forum. there are several main points.

- switching to synthetic can improve mileage due to lower resistance (the main reason i want to try it)
- synthetic can cause old transmissions/engines to leak, but it's not really the oils fault. with old transmissions/engines, some seals get stiff, crack, or shrink, but gunk and deposits from old oil can prevent those seals from leaking. synthetics contain detergents which break old sludge down, so any seals being held by gunk may start to leak. no way to tell until you try it.
- some people, including forum member petros, have found synthetic gear oil causes problems with syncros which leads to grinding when shifting into gears. from what i've read, it seems like this shouldn't occur as long as the viscosity (75-90, 80-90, etc) and oil rating (API GL-4, API GL-5, hypoid, etc) are the same between the traditional and synthetic oils. however, people have experienced this so i want to explore it more.

there is a great wikipedia article about gear oil and its ratings for anyone who is interested in it. it's pertinent to this topic.

http://en.wikipedia.org/wiki/Gear_oil

anyone with any experiences, insight, info, or questions, please throw your two cents in! i'm on the fence right now and don't want to put synthetics in my trans until i feel more confident one way or the other.

[Petros]

I do not think it has to do with the weight of the gear oil, but rather its lubricating properties. If it was just the weight of the oil than thinner oil should make the syncro work better, I think it has to do with the internal friction of the oil. Even thought oil is slipperly, it has internal friction, which causes heat and drag (consumes hp, therefore less fuel economy). When I worked for the Nissan race shop, we built a engine that was driven by a cog belt but had no pistons or connecting rods, we were testing various configurations of valve springs and cam timing and just needed to spin the engine up to 10,000+ rpms to check for harmonics, interferance, etc. One interesting effect of this was the oil temp in the driven engine would heat up to over 200 deg F, even through there was no load on the engine, and there was not even any combustion occuring in it. It was merely internal friction of the motor oil that caused it to heat up. That heat on a normal running engine comes from the fuel that is burned in combustion, the more friction in the engine, trans and drivetrain, the more fuel is burned to drive the car.

Synthetic oil has lower internal friction, and it means it should run lower temperatures, and consume less fuel since it should take less power to spin the engine, trans and diff. This is all good. But the syncros depend on friction to operate, and the more slippery (less friction) in the oil, the less effective they will be. It is not a matter viscosity at all, but rather the ability of the syncro to spin up the next gear to "synchronize" the gear to the drive-train speed so they mesh without clashing. with slippery oil it will be less effective in spinning it up. You sometimes experience this on a cold day with normal gear oil, when you start off with a cold trans, the syncros will clash when you first get moving until the trans warms up and the oil thins out some. in this case the viscosity is higher than normal, but the thick oil is also more slippery. Normally synthetic oil is lower viscosity, which means lower internal friction, and lower temperatures, this can occur because it is more slippery, the "film strength" is higher (prevents metal to metal contact).

Our transmissions were designed for the friction properties and weights of gear oil that were available at the time, it should operate normally with these types of oil. If you put in synthetic gear oil that has very different properties, it will not operate nomally. It may have lower friction, but the syncros were designed to operate with gear oil. I also suspect that the seals leak becasue the synthetic is lower viscosity and more slippery, so it can slip past the seals easier that were designed to work with regular gear oil.

If you use the same viscoity synthtic oil you will not get all the benefit of the synthic since the high viscoity oil will also have higher drag. And likely the syncro problem will be worse, just like on a cold transmission with regular gear oil.

I ran the costly purple synthetic gear oil sold as "MTF" (manual transmission fluid), and found the sycros suddenly acted like they were worn out, and it leaked out all the seals like crazy. The trans has well over 200k miles on it, but it shifts smooth and runs quite before, and no noticable leaks (there may have been some slight seepage, but nothing serious). After I leaked out about $30 worth of MTF I filled the transaxle with about half and half gear oil/MTF and the shifting returned to normal, and the leage slowed down so I did not feel I had to check the trans oil level every two weeks, but every six months or so instade, with oil having to top it up once a year or so.

You might have a different experience with a fresh transmission, but I would be surprices. Lubrication engineering is like anything else, they design the bearing clearances to work over an area that produces a lube film strength over the metal surfaces. they syncros are soft brass rings with small metal "teeth", like find threads on a the inside of a pipe, that slip over a cone shapped surface. those teeth have to cut through the oil film to spin up the next gear to match the speed of the drivetrain. If they can not cut through the oil film, they will not operate properly. They were designed to work with 90 wt gear oil. Going with lighter weight synthic might make them work better (lower friction too), but it would likely leak past the seals faster. You also might consider putting some synthetic Auto trans fluid with it, since auto trans clutches operated in an oil bath and must be able to grip through the oil. So the ATF would have friction properties that might allow the sycros to work properly, but I would not put more than 25 percent. 3 quarts MTF, one quart AFT in a Tercel4wd trans? Might be risky, but it also might work better on our older transmissions. On the Nissan 300zx turbo that we ran in the '80s (over 1000 hp from 3 liters), we ran 50/50 mixture of gear oil and ATF in the close ratio 5 speed manual trans, it improved the function of the sycros which means faster shifting (that was before synthetic oils were available). You might want to install all new seals as well, at least on all the output shafts.

You might experiment if you want, but I have found that 50/50 synth/gear oil works well in my very used Tercel4wd transmission.

Good luck.

[dlb]

4wdchico has talked about a synthetic gear oil with no friction modifiers in it that has worked well for him:

https://tercel4wd.com/forums/viewtopic.php? ... 885#p43503

this is the stuff i got on sale at canadian tire. it's their house brand.

http://www.canadiantire.ca/AST/browse/4 ... ?locale=en

and here is what is written on the back:

"motomaster synthetic gear oil SAE 75w-90 continues the motomaster tradition of premier quality synthetic products and meets API GL-5 and MT-1, mack GO-J plus, as well as the requirements of military MIL-PRF-2105E/SAE J2360 specifications. this product can be used where an API GL-5 SAE 80w-90 or 90 are specified and provides excellent performance under demanding conditions where normal mineral gear oils will break down."

so it looks like this stuff is going back. i will look into the redline NS stuff that 4wdchico tried.

[splatterdog]

I switched from mobil1 to redline NS and noticed hardly any difference. The NS is the stuff to use if you are worried about shift quality.

I just want to get every mile out of my T4 tranny's and will run nothing but syn. Actually all of my machinery gets syn. Just because I could, I put this BMW M spec oil in my 85 http://www.redlineoil.com/product.aspx?pid=130&pcid=21

If it's dirty and/or metallic, flush with reg until it comes out new. Then syn. Your T4 is worth it!

BTW, ester based syn is the only true syn.

[dlb]

SD, have you had any trouble with leaks after putting synthetics in?

[splatterdog]

Slight drips, but nothing out of the ordinary for a quarter century/million miles +. 4wd shift shaft and tail shaft seal mainly.

[CathodeRayTube]

I have been reading up on this subject all day now, and as a result have a serious headache...started when i realized i supposedly put the wrong type of gear oil in the Yugos transmission...basically im finding out/remembering that any type of EP/Hypoid gear oil has sulfur additives in it to give it that property important for actual hypoid gears (as in the differential cases)...but said additives are bad for the synchronizers in manual transmissions. regardless of weather or not the oil is synthetic. Im puzzled because the Yugo,the Tercel and my corolla obviously all have synchromesh transmissions...The Yugos owners manual specifically says "Do not use hypoid/EP gear oil"...but the Tercel manual says you can use GL-5 hypoid oil...

Im thinking this difference could be use of different metals in the different transmissions? bronze vs brass sychronizers? would the EP additives/sulfur affect one metal but not the other? does anybody know which metal the tercels synchros are actually made of?

I had put Valvoline SynPower full-synthetic 75w-90 gear oil in the Yugo...and i had put Supertech synthetic blend gear oil in the Corollas gearbox...I havent actually touched the gearbox oil in any of my Tercels yet...but figure this is all still relevant. I havent had any transmission trouble with anything, but im still worried now after reading up on this...I never consulted the manual for the Corolla but the Supertech gear oil i put in it also says EP/Hypoid on it...

As for synthetic vs mineral oil that is specifically meant for use in manual transmissions...iv been reading good things about the Redline brand of oil...which supposedly addresses the hard shifting issues everybody is saying syn oil gives older transmissions...and it also specifically mentions that its safe for synchros and doesnt contain the EP additives which eat brass and/or bronze...so im considering switching to this in all my manual gearboxes..

[hberdan]

I've been using 5W-30 full synthetic oil for over a year. I don't see any improvement in mileage, but the car starts much easier in the cold. No additional oil leaks, or increases in the current minor drip here and there.

[Jarf]

Back in the early nineties I used to work at a Suzuki dealer, back in the day when GTI swifts were all the rage.
We had several customers switch over to redline for gear oil.
The first one that failed got a new tranny under warranty (that tranny went back to Suzy for inspection) but after that first occurrence they refused to pay warranty unless the customer could verify dino oil changes.
-The issue at the time was synchro's burning out.

I have been wary of synthetics ever since.

Hardly a scientific approach but I figure those hi-paid engineers did their jobs well and designed things to work best on what was available at the time.

Now if I had a NEW car that came from the factory with synthetics, built and designed to run on it, that would be an entirely different story.

[splatterdog]

Hardly a scientific approach but I figure those hi-paid engineers did their jobs well and designed things to work best on what was available at the time.

Sometimes they do their job well, other times they should be forced to work on their handywork for eternity. Oil has come a long way in the last 20 years too. Do you remember which redline oil was used back then?

Might have been a suzuki thing. I rate them at the bottom of the jap pile for cars. I used non synchro safe syn(mobil1) for about 100k without problems on the 84, from a starting point of 160k. Still going too.. Swift GTI drivers might be a little harder drivers than most of us too. Driver skills/habits can really mess with a manual. Factory warranty covers that right?

[TURTCEL]

I have been considering an additive for my manual trans. I have read a few posts in reference to trans clunking and grinding. I thought I may have had a bad motor mount since when driving, usually in 3rd gear at 25 to 30 mph the trans will clunk when first accelerating while driving and letting off the gas while driving...usually always in 3rd. I checked motor mounts and they are totally fine.

I have read that other members have had similar issues. I almost thought I had a carb/fuel or timing issue but I think it is in the trans.

I don't want to change gear oil but was considering adding Lucas Trans treatment in place of some gear oil that I would drain out. I had an '85 S10 4x4 with a 5 speed trans that clunked every shift. I thought I had bad u-joints but turns out the trans was the issue. The S10 tranny was actually known as the "clunker" around the Chevy dealerships come to find out. It worked fine but would just make a crappy sound. Anyways, I added Lucas to it and the clunking completely went away.

I would think that it would work similar in my Terc. Any suggestions on my plans? Could I cause more harm than good? Could the problem not be in the trans, something else?

Peace

[dlb]

from my experiences turtcel, i have found the clunk when starting from a stop or shifting gears to usually be worn strut mounts. others have had other experiences but after replacing the clutch, engine mounts, CVs, various bushings, and all other front end components, the strut mounts wound up being the regular culprits for my shifting clunks. not too hard to remove the strut to thoroughly inspect them, either.

[TURTCEL]

Are the strut mounts the ones that are at the top and look like a big rubber chunk...visibe under the hood? At the top of the strut correct? How do I know if they are bad? They look fine up top, if that is the correct parts I am looking at.

Peace

[dlb]

yes, that is them. you can't tell their condition by looking at them because what you are looking for is slop or play in their bearings.

the best way to inspect them is to remove the strut. break the CV axle nut while the car is still on the ground, jack it up and remove the wheel, remove the steering hub by undoing the ball joint, tie rod, and hub-to-strut bolts, and slide the hub off the end of the CV. then undo the three nuts at the top of the strut in the engine bay and pull the strut out. the mount is the top part that you just undid the three nuts on. it spins but should not wobble at all when you press down on alternating sides from the top. if there is play there, that mount needs to be replaced. you need spring compressors (be extremely careful when compressing springs!) to swap out the mounts.

like i mentioned, others have found that the strut mounts were not the source of their mystery starting/shifting clunks but i have found them to be the cause of mine with multiple tercs. it actually doesn't take long to remove the strut, maybe an hour to remove and replace each side, so i think it's worthwhile to check.

[CathodeRayTube]

Undoing all the front end stuff like that and ten putting it back usually means having to get everything re-aligned also...wich iv managed to do somewhat accurately with strings, cinder blocks and a measuring tape...and alot of spare time & patience...but the laser alignment for $60 something at my mechanics is a decent deal i guess..