Stupid question. What kind of trans fluid are you putting in your 350/400 these days? It seems that dextron 2 is history?
Trans fluid?
Brian_d
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Dextron 3 will work fine
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Use a Dexron/Mercon fluid. The Type F myth is still perpetuated, lol. Do some searching on this topic, and look into when Type F was formulated and why. Times have changed, and there is no real need for Type F in a modern performance trans. 
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myths perpetuated? some of us have used type F with great success. I'm wondering if the clutches would have last longer in the new th400 had I run type F, I did as the builder suggested though. This almost as bad as oval vs. rectal not to mention B&M shift kits
not to mention B&M shift kits 
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What myth perpetuated? The manufacturer of the shift kit recommended type F so I used it. Would you call a 1969 Chevy pickup TH350 with a shift kit a "modern performance trans"? Or is it just that you don't like B&M?Originally posted by Oldani Motorsports:
Use a Dexron/Mercon fluid. The Type F myth is still perpetuated, lol. Do some searching on this topic, and look into when Type F was formulated and why. Times have changed, and there is no real need for Type F in a modern performance trans.
I have done some research and found that Dextron and Dextron II are much "softer" fluids used to make the transmissions shift smoother and softer, not exactly what we want in a performance application. The Ford fluid was designed with much less of a slush quality and is readily available and not overpriced like products like a B&M Trick Shift fluid (which from what I can tell is slightly modified F-type fluid).
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Type F has friction modifiers that were first blended to be used with auto trans clutch friction materials that contained asbestos. The Ford fluid requirement was for a fluid that had a differing need with these clutches. Most all of the current technology used in auto trannies has the friction materials cellulose-based and thus no need for the older thought of requiring Type F to keep clutches applied without slippage. I have nothing against B & M. You do NOT want a harsh shift quality in a trans. It does NOT help trans life to beat it apart this way. You are much better with a smooth, properly-timed shift, even in a race-only trans. I can tell you that for as long as I can remember I have not only recommended Dex/Merc fluids but used them in my own stuff. I ran it in a 6-second 2200+ pound car with a supercharged small block and Glide and never had friction wear out of the norm, or any fluid problems. The short of it all is that the F fluid was engineered for materials whose time has long since ended, yet many places do still recommend it. I just happen to be one who does not...and have guys running my TH-400s for close to three seasons of weekly racing with the same frictions in them.
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That all makes sense. My trans was all original inside thus likely had the older style of friction material. After 115,000 loyal miles it needed new frictions and they were replaced by a reputable shop that also recommended Type F fluid even if I hadn't had a shift kit in it. We didn't install anything fancy since it's just a work-a-day truck so I assume the friction materials used are the same or similar to the OEM stuff that's been used for years.
I agree that brutal shifts out of an auto aren't good for anything in the drivetrain, but original equipment-style shifts out of a '69 TH350 certainly can be improved upon without damaging anything along the way. The B&M Shift Improver kit I installed did a great job improving the shift quality without making it harsh and also recalibrated when it shifts to some extent. When just cruising it shifts up a lot earlier but when pushing it it holds each gear longer than it used to. It was intended to improve the shifts for towing applications and I've found that it has done a great job doing just that as it now tows the Chevelle with much less fuss from the drivetrain and the trains runs cooler to boot.
I guess ultimately, to answer the question originally posed, we should be asking if his TH350 has been updated with modern friction materials or has older style friction materials. Or does Dex/Merc fluid also work well with the old stuff too?
I agree that brutal shifts out of an auto aren't good for anything in the drivetrain, but original equipment-style shifts out of a '69 TH350 certainly can be improved upon without damaging anything along the way. The B&M Shift Improver kit I installed did a great job improving the shift quality without making it harsh and also recalibrated when it shifts to some extent. When just cruising it shifts up a lot earlier but when pushing it it holds each gear longer than it used to. It was intended to improve the shifts for towing applications and I've found that it has done a great job doing just that as it now tows the Chevelle with much less fuss from the drivetrain and the trains runs cooler to boot.
I guess ultimately, to answer the question originally posed, we should be asking if his TH350 has been updated with modern friction materials or has older style friction materials. Or does Dex/Merc fluid also work well with the old stuff too?
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Yes, any fluid will mix with no problems. It will ultimately have the properties of the blend of the two, but not enough to cause issues. There are some other foreign and domestic trannies out that use other fluids and are more sensitive to mixing or misuse of fluid type. The only one thing about some B & M stuff I personally do not care for is the disabling of accumulators in three speeds as that is the beginning of the end for them IMO.
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I used the harsh shifting B&M kit in my th350 for over 4 years,when the trans was taken apart and rebuilt by my neighbor across the street he found nothing wrong except slight burning on the 3rd gear clutches,which should be expected when racing a 3900lb. car with 3.73 gears. This is the second th350 that I've used and they held up fine,some may not like the harsh shift,but if it shifts hard the clutches aint slipping. This is just from my personal experience,my son is currently using a B&M shift kit in his car and so far so good.
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That is the one thing the trans shop that did the rebuild didn't like either. The B&M kit said to remove the spring behind the accumulator altogether so I did. They didn't like that idea so they put one back in when they rebuilt it. I noticed the change immediately and asked them about it. They said that if I wanted the best of both worlds they suggested an accumulator spring that has half of it cut off so that's what we put back in. It now shifts like it did before but I suspect will be more long lived and reliable.
Woah! I had no idea this question was going to stir up such a debate! I also have heard that type F fluid would give you a firmer shift & that's basically what "trick shift" is (this was back in the '80's). I'm not looking for a whiplash inducing shift nor a smooth one - just firm. (it has a trans-go shift kit) So the question now is, new or old friction material? I have no idea. Would the date of rebuild be of any help?. The trans was rebuilt in the early '90's w/extra clutches (somewhere) & a HD sprag from a 700r4 (i think - its been awhile). I guess its been awhile since the last fluid change when I find out they don't make dextron 2 anymore... So I'm stuck on a fence...What kind of fluid?
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This is a bit late but here is the Castrol page for Dexron-III / Mercon:
http://www.castrolusa.com/products/productpageo.asp?product_category=3&product_id=8
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