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Old 03-06-2014, 09:18 PM   #1
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Default DIFF FLUID GUIDE INFO

Been racing asphalt on road for about 5 years now and running ball diffs front and rear. switching to gear diffs this spring and have no clue on the fluid weights and what i would notice going thicker or thinner. i heard or read racers using anything from 40wt shock oil in the rear gear diffs to putty in the fronts. thanks for and input anyone can share.
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Old 03-06-2014, 09:33 PM   #2
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When running on asphalt, most guys run locked diffs or spools upfront. Gear diffs in front, even with putty, tend to be lazy when coming off the corner. At the rear the oil depends a lot on the kit (1000 diff oil will feel very different between a Tamiya diff and an AE diff) and the racing conditions. But generally you want to run a softer oil if your car is too slow around the corner off power or fishtails when you put on power.
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Old 03-07-2014, 06:02 AM   #3
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Rick - I'm running gear diffs all around this year in my TC. I've tried running spools in different chassis and classes, they just don't fit my driving style or our track conditions.

That said, I'd stock fluids from 100,000wt to 2.5mil or putty. The idea is to get it close to a spool, but gain the extra turn in and stability, at the expense of a bit of exit speed.

As VooDoo said, if the car pushes too much off power, lighten the fluid. Like a ball diff, lighter fluid will allow the rear to rotate more easily. If you loop out when getting on power, lighten the fluid, because if it's too thick, once you get on power, both rear wheels are putting more power down, breaking loose. Lighter fluid would let it diff out more before breaking traction. Do the opposite if the car gets too loose off power, but pushes on power.
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Old 03-07-2014, 07:02 AM   #4
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run 500 to 3000 in the rear and 500k to putty in the front. if you putty the front mix in a couple drops of oil with the putty before you put it in so its not completely hard.
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Old 03-07-2014, 08:12 AM   #5
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Instead of what oil...maybe a better question should be why first. Gear diffs can be a very useful tuning option for modern day touring cars. Now that companies have figured out how to get them to be light enough you can now pretty much run them in both the front and rear of the car exclusively. First lets start with the rear diff.

Rear Gear Diffs:

It is important to understand how the gear diff is constructed so that you can make a good plan on how the diff should be filled. Some gear diffs have a small cavity and others much bigger. As reference I will use the Xray gear diff as an example as I think that is about in the middle volume wise. Most drivers run 1K to 2K in the rear gear diff for stock and super stock racing because it helps the car carry speed through the corner, but limits the amount of forward grip. Mod drivers tend to go thicker to keep the rear end more planted and provide additional forward traction. A good place to start in mod is 2k-3k. Based on traction or tires you can continue to go up in weight until the car feels balanced. Temperature will have a big impact...so if you are running in hot weather it is best to go thicker to accommodate the thinning effect you will get. it is not unusual to run 5k or 7k in mod to help calm down the rear of the car.

Front Gear Diffs:
The thinner the oil the more turn in you will get while losing traction out of the corner. 100K in the front will give really good turn in and mid corner steering but will diff out when you get back on power coming out of the corner. Putty sometimes will feel too much like a spool. My recommendation is always to start with Gravity 2.5million CST in the front. This is almost always the right place to start because it provides more turn in then a spool. Coming out of the corner it wont have as much rip as a spool, but it provides great forward traction. If you need more turn in go to 1million cst in the front but understand that what you get coming in you will lose going out.

Some gear diffs you can run with 4 satellite gears or two. Two gears will make the oil feel thinner, so in some cases you might want to adjust for that, but this can also be used to adjust feel without having to go thinner on the oil. In the Awesomatix a two gear diff feels much lighter on the track then a four gear diff with the same oil.

Last point on gear diffs...they require some driving adjustment to get used to them. They will allow you to drive a bit more aggressively coming out of the corner, but going in might need a little bit more finesse. Since a spool will push while initiating the gear diff might oversteer, so be ready to adjust for that. Keep in mind that team drivers tend to have some insight from the designers that force them to pick a certain diff oil. So I would check some setup sheets or PM some people to find out where to start with your specific car.

Good luck and Hope this helps!
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Old 03-07-2014, 04:29 PM   #6
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Who makes this putty that everyone talks about? I'm gonna order a bunch of different weights of diff fluid and experiment some.
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Old 03-07-2014, 06:44 PM   #7
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I don't run putty up front, I prefer the gravity oil. On the rear i only use associated.

http://www.reflexracing.net/Fluids-a...ants_c_87.html
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Old 03-08-2014, 05:55 AM   #8
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Quote:
Originally Posted by touringdriver View Post
I'm gonna order a bunch of different weights of diff fluid and experiment some.
If it's in your budget, get several diffs and fill each with a different oil so you can easily swap them out. It's really yucky to be messing with those things at the track.
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Old 03-09-2014, 09:17 PM   #9
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just orderd diff fluids from 1,000 to 2.5 mill. weights. something should work
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Old 03-10-2014, 10:39 AM   #10
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Who makes this putty that everyone talks about? I'm gonna order a bunch of different weights of diff fluid and experiment some.
RIDE have some good putty which was developed by Hara. I've used it and it's pretty good.
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Old 03-10-2014, 04:38 PM   #11
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RIDE have some good putty which was developed by Hara. I've used it and it's pretty good.
RSD just released their new putty too.
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Old 03-16-2014, 08:14 PM   #12
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gonna start with 2.5 million in front diff and 3,000 in rear and test and tune from there.
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Old 03-16-2014, 10:58 PM   #13
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I tend to prefer a spool up front over a gear diff. Turn in is great with a gear diff with 2.5million oil, but the drive out just isn't nearly as good as a spool. Besides, in general, I find it easier to find more turn in rather than find more exit steering. I'd rather have the exit steering there and play with other things to get more turn in.

2.5million front/3k rear sounds like a pretty decent starting point though. I've found that in the rear diff, as you go softer on the oil, you gain off power steering. The opposite can be true in that thicker rear oil will generally increase on power steering.
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Old 03-17-2014, 10:38 AM   #14
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I'm trying the Mack's moldable silicone earplugs for putty. A couple drops of diff lube on the seals to lube the outdrives and the putty itself doesn't stick to the gears. Once the case was properly packed and not over or under full, a couple of twists of the outdrives with some wrenches in the blade slots and all was moving. It takes quite a lot to move it, but it does spin. Can't wait to try it.
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Old 03-17-2014, 05:30 PM   #15
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What is the best way to clean out a diff with putty? I want to try 2.5 million in there. I heard alcohol works. What is your method besides buying a new diff.
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