what do you guys recommend for the diff. i've read lots of tranny recommendations but hardly any diff. ones.

 

tranny and diff take the same thing. The only difference though is that if you have an LSD make sure you add some LSD additive in there or make sure what you're getting already has it in there

 

Yep, or if you're using something like Synchromesh in the trans, just use a standard gear oil in the diff with the additive if LSD eqipped or a good synthetic in which you wouldn't need the additive

 

I like the Redline Heavy-Duty Shockproof fluids.

 

I bought the Castrol Hypoy C gear oil it has a label that says limited slip performance do I still need to add the LSD additive that I bought?

 

A lot of today's lube oils have the friction modifier already in them, so no additive is required. If it is labeled for limited slip you should be good to go.

Been thinking about changing the differential fluid in my Montero, but I hate to throw away perfectly good fluid. I know it is good fluid because it has 325,000 mile on it, the limited slip still works and it is quiet, so I am tempted to just leave it alone.

I have owned a lot of 1st gen RX-7s and have gone as far as 180k miles on them, never changed trans or diff fluid. I have never had any trans or diff problems with any of them. I do put magnetic plugs on the fillers, and so that gets checked regularly. I should mention that I also have several FB trannies and LSDs in my shop, just in case.

I have a friend who has made his living working on Mazda rotary cars since 1970, and his comment about all this was "If it ain't broke, don't fix it."

I do change engine oil on all my cars at 4k miles.

 

I used Royal Purple when I installed my LSD rear end. It states that no addative is needed, but I had quite a bit of chatter with it. I added a tube of the lsd addative, and haven't had any issues since.

 

^That's what I was looking for Kentetsu. I just put AMSoil in my rear end and tranny, but the rear end still chatters and the tranny actually shifts worse than it did before the change. Even with the clutch to the floor second gear still gets caught up. Perhaps the synchro is on it's way out. I'll try adding some LSD additive to the rear and some ATF or Synchromesh to the tranny. Maybe that will help

 

all went well so far. I put the Redline MTL in the tranny and i ended up adding the LSD additive for good measure to the rear end.

 

REDLINE MT-90 FTW it has cured grinding syncros in many of the cars that I have owned. I use Redline 75w-90NS in the rear end with redline additive. nothing better. I have used royal purple in the rearend and it's just as good.

 

I can vouch for this. Tried it in a tired old S2 tranny that I needed to use temporarily. It was pretty much impossible to shift into second without it grinding horribly, and getting it to shift at all took some skill. Long story short, I'm still using that tranny and the only reason I'm planning to change it is because I want to upgrade to a TII unit. After giving it that treatment, second gear doesn't grind at all unless I really slam it (though I do still have to be careful when downshifting).

 

You actually drained out some of the 80/90 and poured some ATF into that tranny? I don't think I added any when I filled it up last year, after changing the front seal and cleaning out the broken gear chunks.

 

If I remember right you put a mixture in it the first time because you didn't have enough 80W-90. Later some of it got drained and it was replaced with straight 80W-90.

 

Oh yeah! The ATF was diluted a little but you are correct. That means it still has perhaps a 50% mixture in there, or close enough to have improved the driveability so noticeably.

I had to drain some out to take the front hub off in order to change the seal, and I recall it was quite red as it came out.

It's actually quite pleasant to drive hard and shift it fast, yo. A major improvement over when it was in the blue car (constant grinds), and over what was previously in the white car (noise city).

Who knows... it may live for a long time behind the turbo.

 

I use 75-140 in my racecar in both the trans and rearend. Usually use Amsoil but have Royal Purple in the trans right now. I change it once a season or as necessary when making repairs. The heavier weight helps deal with the heat generated in racing - the trans shifts better at the end of a race. Not necessary on the street. I won't use dead dino oil - not worth the cost savings

Not sure about the ATF mix. I'm pretty conservative so I tend to follow manufacturer recomendations. So, I am not sure I would experiment in this way but what the heck - thinner lubes don't suck up as much power so at least it will feel better for awhile. Frankly it has been my experience that you can't hurry a shift in a Mazda gearbox - just ruins them faster when you do.

Get one of these to make the job easier

http://automotive.hardwarestore.com/...p--648771.aspx

I have seen them at autoparts stores too. They fit Amsoil containers the best.

I always use teflon tap on the trans fill plug and the rear end plugs. Seals them and makes removal easy.

 

Thanks for posting up the positive results on the ATF. Most people look at me like I'm crazy when I tell them to use half ATF in their manual tranny..

In case I didn't post this earlier, this trick comes from the Datsun Z race teams who swore by it. Information came from the book "how to hotrod and race your Datsun".

 

How much are redline/royal purple compared to valvoline?