Gear Oil Questions

5561 Views 14 Replies 9 Participants Last post by Don L., Jan 6, 2010

forbiddenera

Discussion Starter · Dec 22, 2009

Two questions, opinions and facts please (preferably facts!):

Okay, so I know the LSD takes Hypoid gear oil or regular with a friction modifier added.

I bought some Castrol Hypoy C today and the bottle says it's fine to use in LSD's and manual transmissions.

I mean, if it says it on the bottle I'm assuming it should be fine, wouldn't it be false advertising if it wasn't?

Secondly, I only bought 3 bottles (need about 4x1L bottles to fill LSD & transmission) because I had a bottle of Castrol SYNTEC Gear Oil kickin' around.

I would've bought 3 bottles of the SYNTEC, but it's about $15 a bottle where-as the Hypoy is $8, as much as I love my car I can't always afford the "best", and I put that in quotes because maybe synthetic is worse for our cars?

So, the SYNTEC, on the bottle, says it'll mix with conventional oils just fine. Again, I'm assuming it should be fine, wouldn't it be false advertising if it wasn't?

Now, while I'm sure everything will work, and there probably wouldn't be much noticeable difference between using regular gear oil in the transmission vs hypoid, or using synthetic all round, or mixing, I want to know the details. I've done some searching on the net and I have an idea on how it works and a few people mentioned it could be bad, but this was all speculation.

I want facts, smooth shifting and a LSD that chatters less. I'm probably going to do the change tomorrow either way, but I figured I'd post and see what CS thinks.

1 - 15 of 15 Posts

Road Ripper

· #2 · Dec 22, 2009

What are the exact words that Castrol used on the back of the bottle that lead you to your conclusion? It may "work" in an LSD, but it may still need the friction modifier added.

I've always seen the "...for makeup of oil in limited slip differentials." - - In other words, it would need the friction modifier.

forbiddenera

Discussion Starter · #3 · Dec 22, 2009

Road Ripper said:
What are the exact words that Castrol used on the back of the bottle that lead you to your conclusion? It may "work" in an LSD, but it may still need the friction modifier added.

I've always seen the "...for makeup of oil in limited slip differentials." - - In other words, it would need the friction modifier.

I'm glad you pointed that out, it's worth reading it again to be sure.

But....I don't think it says that, I just went out in the snow and grabbed the bottles from my car.

Let's read! (warning 8 megapixel photo!)

Bottles

Syntec:
- Exceeds the service fill requirements of conventional and limited-slip differentials.

- Fully compatible with all conventional and synthetic API-GL5 gear oils.

Hypoy C:

- Meets the service fill requirements of conventional and limited slip differentials.

- Engineered for passenger cars and light trucks operating under high-stress conditions.

See less See more

forbiddenera

Discussion Starter · #4 · Dec 22, 2009

Oh yeah, my friend keeps telling me to go get GM Syncromesh.. I've done some reading and it seems like mostly hype..

Road Ripper

· #5 · Dec 22, 2009

Yup, your oil will work just fine as-is!

StanS

· #6 · Dec 23, 2009

Per the founder of SOGI use any name brand dino 70W-90 and FORD and only Ford for smoothest and quietest operating LSD.

I use M1 transmission oil in the transmission and find that it works well giving quiet and smooth shifts.

forbiddenera

Discussion Starter · #7 · Dec 23, 2009

Okay, so it took about 2 hours to get the fill plug out..

Tried big ass wrench with extension, big ass socket, impact gun, putting a wrench on it and putting a jack under the wrench, shoving jack into wrench and then smashing it with some propane fire.

I have only driven it about 25 feet but the shifter feels loose and grindy? I hope it gets better with some time.

Haven't had the chance to do the diff yet.. Shrug.

forbiddenera

Discussion Starter · #8 · Dec 25, 2009

Well, I can tell it was needed but there's not much improvement, but I can't expect a transmission with almost 300k to shift perfect every time (I rarely use the clutch, always shifts perfect when I do)

alfun

· #9 · Dec 25, 2009

forbiddenera said:
Well, I can tell it was needed but there's not much improvement, but I can't expect a transmission with almost 300k to shift perfect every time (I rarely use the clutch, always shifts perfect when I do)

You rarely use the clutch pedal? Maybe BillyM's Shifter-Bushing Kit will help?

82toy

· #10 · Dec 25, 2009

Do not use GM syncromesh,not enough viscosity for our older trans.

SilverMk2

· #11 · Dec 25, 2009

Redline MT90 in the transmission and 75W90 with the limited slip is what I recommend. The MT90 stuff is like magic for Toyota transmissions. I had to put some generic synthetic gear oil like Castrol or Valvoline in my Corolla since it was the only thing local and it shifted like crap after using Redline.

rsdeo

· #12 · Dec 26, 2009 (Edited)

I've been using Mobil1 75W90 synthetic hypoid gear oil in my transmissions manual ( ATF in auto), transfer cases, differentials and with the Ford additive in LSDs for years with great results. I always was concerned about one thing though.

The syncro's in a manual transmission operate with the use of friction. Would using a lubricant that significantly reduces friction in a system be detrimental to the proper operation of the syncros? Thus increasing the time for gears to match speeds.

DreadyDiggs

· #13 · Dec 27, 2009

That's a good question. I guess that depends on how much friction is needed for the synchros to function at their best. Maybe the factory setup provides more than enough, and now your swap over greatly reduces friction but greatly reducing more than enough could cancel each other out?

forbiddenera

Discussion Starter · #14 · Jan 6, 2010

alfun said:
You rarely use the clutch pedal? Maybe BillyM's Shifter-Bushing Kit will help?

Yep, like never, well, as soon as the tranny warms up.. And sometimes if I'm driving hard just to be nice to the car or when I know I'm gonna fuck up the rev match. Really, I mostly just use it for drifting or sometimes racing to put some extra power down at the cost of clutch wear (hey, it's a racing clutch), or clutch braking (combining engine braking with clutch slip to slow the rear wheels more) but never shifting.. (PS: Don't try this at home, your drivetrain will hate you - mine does)

I was actually going to try the Marlin Crawler bushings, but I'll check those out too!

82toy said:
Do not use GM syncromesh,not enough viscosity for our older trans.

Yeah, I don't think I ever will.

SilverMk2 said:
Redline MT90 in the transmission and 75W90 with the limited slip is what I recommend. The MT90 stuff is like magic for Toyota transmissions. I had to put some generic synthetic gear oil like Castrol or Valvoline in my Corolla since it was the only thing local and it shifted like crap after using Redline.

I'll give it a shot, as I said I'm using the castrol and it's not that great.

Don L.

· #15 · Jan 6, 2010

SilverMk2 said:
Redline MT90 in the transmission and 75W90 with the limited slip is what I recommend. The MT90 stuff is like magic for Toyota transmissions. I had to put some generic synthetic gear oil like Castrol or Valvoline in my Corolla since it was the only thing local and it shifted like crap after using Redline.

Exactly what I've been running for almost 10 years. The 75W90 in the rear works fine for the Trutrac LSD, although it really doesn't need it being a gear drive, but I like Redline stuff.
Don't confuse the MT90 with the MTL for the tranny. MT90 a bit more viscous, works better in our old trannies.

Don L.

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