When To Change Diff Fluid When Speed Running Exclusively?

[GTRider610]

I was searching for an answer on this topic and I didn't find a ton of information. I was curious to when/ how often you guys who do speed runs change your diff fluid. I added 300k from stock about 20-30 passes ago and I feel like it may not be as thick or effective as when I started. I also notice the car seems to stay less straight on roads with a slight angle, that before on the same setup didn't seem to affect it. I was going to swap out to 500k when I rebuild the diffs. Any information if worn out diff fluid could effect the linear abilities of the car would be greatly appreciated. For reference I'm nothing crazy with my runs PR is a 139 Mph ATM. I'm sure the answer varies greatly the closer to 170+ you go.
Thank You.

 

[Kingleo619]

Hardcore full throttle aggressive mud slanging sand blasting basher id say after 5 packs regular bashers 8-12 packs low end regular basher after 20

Forgot speed runs i change fluid after 3-8 packs
Im 60r 100f fluid may have

 

[LibertyMKiii]

I'd love to hear @vwturbowolf and @phildogg 's responses to this and how often you re-grease the ring gear.
I have neglected mine although doing 2s and 3s challenges I have only been in the 90 - 124 mph range.

 

[vwturbowolf]

I'd love to hear @vwturbowolf and @phildogg 's responses to this and how often you re-grease the ring gear.
I have neglected mine although doing 2s and 3s challenges I have only been in the 90 - 124 mph range.

This is something I do when I change my input bearings. Which is fairly often on the limitless.
I pull everything out inspect clean and regrease.
Tbh with my single motor limitless and now my dual motor on I basically take them apart after every session, less chance of any failure

 

[rccar4life]

if you have your rig strictly for hardcore speedruns only
and want i go straight like an arrow.
Then you want spool in center , and locked front diff like this

You have only the rear diff with oil.

Also you need have Ceramic bearings

Depending of what speeds you run, maybe change rear diff oil every 10th pass.
This is about one lipo only.
Then also clean and oil the bearings in whole drive line also all diffs, and input gear bearings. Important. Wheel bearings also

Speedruns, you don't calculate MAH run time, only Passes.

https://scorchedparts.co.uk/collect...a-through-shaft-diff-locker-front-rear-centre

https://scorchedparts.co.uk/collect...ts/arrma-titanium-centre-drive-spool-assembly



https://scorchedparts.co.uk/collect...suitable-for-general-use-and-ceramic-bearings

https://scorchedparts.co.uk/collect...oducts/ceramic-hybrid-arrma-wheel-bearing-set

https://scorchedparts.co.uk/collect...etal-shield-bearing-set-complete-drive-system

 

[GTRider610]

Thank You everyone for the input so far. I think its about time I redo everything in the diff department. Think I'm going to try 500k before I go full locked and I have the ceramics already. May change my ceramic spool bearing too since that is feeling a bit looser than when I first installed it.

 

[Moirae]

I checked the wifey center diff recently after not checking it for MONTHS. It was still perfectly fine and seemed like the 500k I had put in there was still doing it's job. That's with her driving it like every other day for months too.

 

[jkflow]

My $0.02, diff fluid is not really utilized during speedruns as you are only going straight, unlike bashing etc. where it's constantly being taxed.
Greasing and having clean bearings is more important.
As noted above, you should lock them, which eliminates fluids altogether.

 

[Panther6834]

if you have your rig strictly for hardcore speedruns only
and want i go straight like an arrow.
Then you want spool in center , and locked front diff like this.
You have only the rear diff with oil.
Also you need have Ceramic bearings

These are things I've been thinking/wondering about.

Starting with the ceramic bearings, I run ceramics in all my race vehicles, except (until recently) in my NPRC drag cars. The "reasoning" is/was that, at those speeds, the ceramic balls could crack...and, if they did, that could (would?) be the end of that car. The damage caused from a bearing seizing up, due to cracked balls (yeah, I know...I'm just waiting for comments related to those two words...lol) could be catastrophic. However, knowing that other drag racers have switched to (quality) ceramic bearings, and haven't (yet) run into problems, I've felt confident to do the same in my Outlaw class car (but not, at least yet, in my Eliminator class car). As speed run cars are exceeding 150mph, with some breaking 200mph, seriously, how safe is it to use ceramic bearings? I don't mind spending the money, if they've already been "proven" reliable...but, before I do, I'm curious how many others have been running ceramic bearings in their speed run cars, and how many of them have never had problems. Also, I'd like to hear from those who DID have problems.

Moving onto the other part of the 'equation', as I'm preparing to start building my first 'true' speed run car (for the purpose of this post, I'm not going to consider my 4Tec 3.0 Corvette 'speed run' car as a TRUE speed run car, as it still hasn't broken 100mph), a "question" I raised in another thread (which I created) had to do with locking (or using a spool on) the front and/or rear diffs. In NPRC, we typically lock the rear (they are 2WD, so locking the front isn't possible)...and, as such, I was figuring the same would/should be done on a Limitless-based speed run car - I was figuring locking the rear, and either locking the front, or using extremely thick (500K-1M) fluid in the front.

In that other thread, the 'consensus' was to not lock either end...yet, here you are, mentioning locking the front (as opposed to the rear), and running thick 500K diff fluid in the rear. In another thread, one person mentioned running 500K up front, and 20K in the rear. I'm curious as to "why" locking the front, and not the rear. The primary purpose between NPRC & speed run cars is, essentially, the same - go as fast as possible in as straight a line as possible. The only 'difference' is that, in NPRC, you have a minimal distance (132ft) to achieve your top speed, and it's the quickest time...not the fastest speed...that truly matters.

So, I guess what I'm getting at is this:
1) What are the advantages/disadvantages of locking the front vs locking the rear vs locking front & rear?
2) Whether the front and/or rear are 'open', what's the difference between running a thick (500K-2.5M) fluid vs a thin (20K-100K) fluid?

I'm trying to 'learn' as much as possible before I start the actual build.

 

[LibertyMKiii]

These are things I've been thinking/wondering about.

Starting with the ceramic bearings, I run ceramics in all my race vehicles, except (until recently) in my NPRC drag cars. The "reasoning" is/was that, at those speeds, the ceramic balls could crack...and, if they did, that could (would?) be the end of that car. The damage caused from a bearing seizing up, due to cracked balls (yeah, I know...I'm just waiting for comments related to those two words...lol) could be catastrophic. However, knowing that other drag racers have switched to (quality) ceramic bearings, and haven't (yet) run into problems, I've felt confident to do the same in my Outlaw class car (but not, at least yet, in my Eliminator class car). As speed run cars are exceeding 150mph, with some breaking 200mph, seriously, how safe is it to use ceramic bearings? I don't mind spending the money, if they've already been "proven" reliable...but, before I do, I'm curious how many others have been running ceramic bearings in their speed run cars, and how many of them have never had problems. Also, I'd like to hear from those who DID have problems.

Moving onto the other part of the 'equation', as I'm preparing to start building my first 'true' speed run car (for the purpose of this post, I'm not going to consider my 4Tec 3.0 Corvette 'speed run' car as a TRUE speed run car, as it still hasn't broken 100mph), a "question" I raised in another thread (which I created) had to do with locking (or using a spool on) the front and/or rear diffs. In NPRC, we typically lock the rear (they are 2WD, so locking the front isn't possible)...and, as such, I was figuring the same would/should be done on a Limitless-based speed run car - I was figuring locking the rear, and either locking the front, or using extremely thick (500K-1M) fluid in the front.

In that other thread, the 'consensus' was to not lock either end...yet, here you are, mentioning locking the front (as opposed to the rear), and running thick 500K diff fluid in the rear. In another thread, one person mentioned running 500K up front, and 20K in the rear. I'm curious as to "why" locking the front, and not the rear. The primary purpose between NPRC & speed run cars is, essentially, the same - go as fast as possible in as straight a line as possible. The only 'difference' is that, in NPRC, you have a minimal distance (132ft) to achieve your top speed, and it's the quickest time...not the fastest speed...that truly matters.

So, I guess what I'm getting at is this:
1) What are the advantages/disadvantages of locking the front vs locking the rear vs locking front & rear?
2) Whether the front and/or rear are 'open', what's the difference between running a thick (500K-2.5M) fluid vs a thin (20K-100K) fluid?

I'm trying to 'learn' as much as possible before I start the actual build.

You will find no shortage of people on the internet offering advice who don't have real-world experience with this. If you go back far enough in the forum you will see me providing bad advice about locked diffs as my preference. What seems logical in your head does not always play out when the rubber hits the road...

• Locked front and rear diffs generally lead to broken parts in this diff itself
• Locked front and rear diffs generally lead to unpredictable handling during hard acceleration at high speeds and will abruptly throw the car off the road (only recommended for 2wd cars or drag use below 110 mph)

Now with that said there are plenty of people with different preferences on setup. Short cars like 1/10 and 1/8 seem to like 500k fluid on the front and thinner in the rear. My experiences with that were never good. I now run think stock like diff fluid all around for all my cars.

When talking about a 1/7 scale thin fluid front and rear (OEM equipped) works best. Plenty of us on the forum with real experience can back up this statement after trying a few times. With that said I am not above 150mph yet and those guys seem to like the 200-500k fluids. (James McCoy's setup video referenced)

Ceramics are an unnecessary waste of money. They don't have the strength to handle high power for big 1/7 cars pushing 10+ horsepower. Regular rubber sealed bearings are fine just oil/service them often.

 

[Panther6834]

You will find no shortage of people on the internet offering advice who don't have real-world experience with this. If you go back far enough in the forum you will see me providing bad advice about locked diffs as my preference. What seems logical in your head does not always play out when the rubber hits the road...

• Locked front and rear diffs generally lead to broken parts in this diff itself
• Locked front and rear diffs generally lead to unpredictable handling during hard acceleration at high speeds and will abruptly throw the car off the road (only recommended for 2wd cars or drag use below 110 mph)

Now with that said there are plenty of people with different preferences on setup. Short cars like 1/10 and 1/8 seem to like 500k fluid on the front and thinner in the rear. My experiences with that were never good. I now run think stock like diff fluid all around for all my cars.

When talking about a 1/7 scale thin fluid front and rear (OEM equipped) works best. Plenty of us on the forum with real experience can back up this statement after trying a few times. With that said I am not above 150mph yet and those guys seem to like the 200-500k fluids. (James McCoy's setup video referenced)

Ceramics are an unnecessary waste of money. They don't have the strength to handle high power for big 1/7 cars pushing 10+ horsepower. Regular rubber sealed bearings are fine just oil/service them often.

Guess I'll (probably) be "playing around" with f/r set-ups. As I'll be going slow (less that 100mph) at first, I'll just have to test diff fluid viscosities, as well as the spool.

As for bearings, I'll try a 'trick' I use in my 1/10 race vehicles. For my asphalt & carpet vehicles, I use Avid RC Ceramic Revolution bearings. These are greased bearings, having a metal racer on one side, and a rubber seal on the other. I remove the rubber seal, completely clean out the grease, and replace the grease with bearing oil. Now, Acer RC does sell a bearing - Ceramic Metal Aura - that is exactly the same as what I end up with (oiled, metal racer on one side, open on the other side), but they charge considerably more for these (as they're charging customers for doing the same work that I do to the Ceramic Revolution bearings)...ie. the Ceramic Metal Aura bearings, and my 'end-result' of the Ceramic Revolution bearings, is the same, but I pay less doing the work myself.

When inserting the bearings into the vehicles, I place the 'open' side to the inside, and the metal racer side to the outside. Obviously, going this route requires more frequent maintenance...but, it's well worth it. Rubber seals produce a considerable amount of 'resistance', and even the metal racers produce some (albeit, fat less) resistance. By removing the rubber seal, the Resistance is greatly decreased...yet, the metal racer still provides a very good amount of 'protection' from debris.

Why does does any of what I said, above, matter...especially when the Ceramic Revolution bearings are ceramic, and you've established that (at least, when it comes to speed run vehicles) ceramic bearings are "a waste of money"? Because Acer RC also has a steel ball version - Revolution Aura - to which the same thing (ie. removing the rubber seal) can be done. Even better, these bearings are oiled (NOT greased), so the initial "cleaning out the grease, and oiling them" steps are removed. Acer developed these bearings for competitive racers who don't want, or can't afford, to spend lots of (wasted) money on ceramic bearings.

 

[Hector_Fisher]

Thank You everyone for the input so far. I think its about time I redo everything in the diff department. Think I'm going to try 500k before I go full locked and I have the ceramics already. May change my ceramic spool bearing too since that is feeling a bit looser than when I first installed it.

+1 for incremental change.

I'd say doing incremental changes like that and working towards and extreme (locked diffs) is better in the long run. Then you'd understand how they affect the overall performance rather than go to an extreme on one end with no prior experience.