type f vs. dextron III in 200r4


Empty Pockets
Feb 25, 2007
Not sure if this question has been asked before, but I just had my trans rebuilt and was wondering what type of fluid to use. I know some guys swear by type f in thier turbo 350-400s and say it makes harder shifts. Is type f ok in a 200r4 or is dextron a better choice?
Bruce uses Mobilube 424 hydraulic tractor fluid. I use it too, but since I can't get the mobil stuff here, I just buy a big pail of the wal-mart stuff. Works great and is cheaper than normal tranny fluid!
the person who rebuilt it should have told you whats best for it. Well at least the person who did mine did.
Yup. Ask the builder what he recommends. I don't like type F, but that's just me.

I use Type F, havent had any problems with it what so ever. If i would have known exactly what Bruce used in the beginning, then i would have probably went and bought that and put it in, but that doesnt mean i cant always do another trans fluid draining and all.

My torque converter builder said to never use the "tractor oil".
It and TCC's don't get along at all.
My tranny buider....

...told me to use Mobil 424 Tractor/Transmission fluid or Dextron. I am planning on getting some today from my local Grainger supply. Its $37 for a 2.5 gallon jug. [which for the mathematically challenged is $3.70 a quart]
Does the tractor fluid have a detergent package in it like tranny fluid? Reason I ask is I had TC solenoid and 4th gear switch act up and eventually stopped working. I changed the tractor fluid out to Dexron and they all started working again. Fluke?:confused:
I have used 424 in the past with no downsides at all. TCC, converters, no issues.
Infact, in a heavy duty application it is hard to beat. It will not break down like Dex 3 under severe situations like a trans brake launch, sitting on the verter stalling for to long. It will not save a failure, but it is better that "stock". Dex 3 can/does vaporize under extreme conditions rendering it totally useless.
Also, as a side note... in my experience 424 has slightly to marginally improved shift quality. Which is the reason some use type F to begin with.
If you feel the need, you could substitute a couple qt`s of 3 for F if you are so inclined. Some old timers add a qt of Synthetic 15w50 Mobil1 to their fluid, and swear by it.
B&M trick shift fluid is basically type F. (incase this gets thrown in)
I do not care for F as it seems to degrade any rubber seals. (but, if you have a leak you may want this, as it can swell them)

Mixing a few quarts of Dex 3 into 424 is a good idea, mainly to get color so you can tell if you have an oil or trans leak.
We all know, Buicks do not leak any oil though!;)

Good luck, HTH...
I agree with Brian,
I haven't seen any issues using tractor fluid.
I was using it in my Chevelle doing WOT 3-4 shifts with converter lockup happening after the shift with a stock type single disc converter. I bet I did 50 of these lockups over the course of a year and the $125 converter worked great through it all. :biggrin:
Never chattered, trans held up well.

The 424 fluid has a temp rating of 424* F and that is where it gets its name.
Dexron is about 380* IIRC.

The tractor fluid (I use cheap Walmart Super Tech stuff) doesn't directly cross-reference for Dexron but in a roundabout way it does cross-reference.

I suspect that the tractor fluid cannot legally be sold as ATF because it isn't red, and federal law requires ATF to be red.
As many different opinions here as there are fluids to choose from, with no real consensus. :rolleyes:

Might be better if one were to be very specific with a question like this. Like:
I have a built 2004R with billet parts etc. and running a vigilante multi disc that I lock in 3rd gear at WOT.
Anybody with a similar setup? What fluids?
I used Type F in my trannys since the first rebuild way back when...Kurtz recommended it back in the day....I understand he says used syn now. I just put a new tranny in my car today and am now trying full synthetic Merc V. So far what I have noticed is that the tranny seems to operate smoother and the shifts, yet quick and firm, are not violent like they used to be. My buddy Fast Eddie tried syn in his tranny and hated the way it shifted...says he got back 2 mph by switching back to regular Type F. I'm convinced that gain was due to the converter slipping with the syn fluid. IMO the clutch material did not like the syn fluid and was not as efficient as with Type F....I'm using a non-lock so that point is not valid in my case.