Redline transmission fluid compared to old castrol 75/90

Well I need some opinions.
My 4 speed snchro is shifting very smooth after the rebuild, but like my DB4 after the rebuild my transmission guys suggested the redline as others as well.
Yes it shifts smooth BUT I get the CHAIN RATTLE out of the gear box and have heard this in others as well.
He claims redline 90 synthetic is equal to a 30 weight synthetic oil, in conversion terms to mineral oil 75/90.
Im going to drain it and see if the sound goes away. I think it will.
Anyone feel the same or had this happen?

i think there was a post awhile back where a ford/motorcraft oil was better than redline for the trans.

I have used Redline MT90 in the E-Type for about 40,000 miles and for decades in Triumphs – seems fine to me.

If you have a leak it may leak more with the synthetic.

Not familiar with chain rattle. I’ll admit I have never been inside the E-Type gearbox so perhaps there is a chain I don’t know about.

I hope you’ll refill it or the sound will increase for a while😳

1 Like

Bone dry
The box is fine it sounds like more modern Porsche and ford Gt and viper sound
It goes away at speed
They had a name for it
I’ll try the 75/90 see what happens

Your funny
It’s a box of chains rattle
All newer cars with alum cases have the sound
It’s running great and it has to break in but will try this before the interior goes back

1 Like

As I understand it, RedLine MTF is used in any M/T that calls for motor oil, gear lube, or ATF. I was amazed at that, but that’s the story. And RedLine’s claim to fame is that their lube is less slippery than any of those other fluids so synchros work better. I doubt it’ll make any difference to the sound.

Just fitted a lighter flywheel to my 140 which has a Tremec T5 box using ATF.
From cold start the gearbox rattled for a minute or so until the engine evened out as it warmed.
Changing the ATF for a more viscous 75/90 fettled it.
The only down side as far as I can gather is that over time the 75/90 may damage the synchro mechanism, but probably not in my lifetime.

No chains. !! but chatter twixt layshaft and mainshaft perhaps, but more likely the baulk rings rattling in the selector hubs. Wasn’t the idle speed upped to 750 from 500 rpm to counter this ?

Yes it was upped during break in
And it is from the tail bearing side at idle cold
I have no rugs or console in so it’s more noticeable
I’ll have it changed my lunch today and will report back with another long drive😃

Joe, I put a synthetic in my S-2 trans. More idle rattles, shifting was…fine but I could feel more harshness through the lever. Whether placebo effect or not, it felt more metal on metal, as if the lube was thinner. I also experienced a bearing noise when cold & backing out of the garage. As if a bearing was dry and giving a shrieking noise. It was an “expensive noise” so I immediately drained it.
I went back to regular old hypoid gear oil, and preferred the shift change feel. The noise went away too.
The removed synthetic oil did make my BMW motorcycle shift better. It went from “agricultural” to “almost Japanese” transmission shifting.

If your gearbox has brass baulk rings you don’t want to use 75-90 gear oil with a high sulfur content. Redline MT 90 is an excellent substitute for motor oil in a gearbox. Don’t be misled by the seeming disparity in the numbers; motor oil and gear oil are graded differently

I thought Redline MTL was the recommended substitute for motor oil (as in the Moss box), with MT90 being preferred substitute for hypoid gear oil in the all synchro box.

1 Like

That’s correct. I’m amazed how often there seems to be confusion around this.

1 Like

Did my last post go through

Let’s try this again
I drained out the mt90 at 8am
Replaced it with old fashioned Castrol 80/90
As David had said
I had the same issues
It is now night and day and imho
Never put mt90 in the synchro 4.2 box
The rattle the rolling gear noise are all gone
It’s is 94 degrees with 100 percent humidity
It drive wonderful but the noises are gone!
Yes the stick feels a tad stick in the mud
But it’s a good stick in the mud
The other oil is way too thin!
Thank you everyone

You do not want GL-5 in the transmission. It will damage the synchro rings over time.
A GL-4 is what you need.

I understand
It will take 75 years instead of 109 years with the gl5 on the brass but
Who has low sulfur gl4?