Redline D4 ATF vs Type F fluid?

[CopperBronco]

I’m servicing my C4 auto trans… not sure last time was done, only had this Bronco for a short while, PO didn’t know, had never swapped fluid. So at least 5 years, fluid came out a bit dark, but better than I expected.

I have no idea what type of fluid is in the C4 currently… Type F, Mercon, Dexron, etc… Toms Offroad sells the Redline D4 ATF, and am curious if I can mix that with whatever is in my transmission? Or any mixing at all okay? Or do I need to essentially fill, start it up briefly, drain, refill, and so it again until I’ve diluted whatever the old stuff is? Curious if it’s cooling properties they claim are true as well for redline?

When I drained pan I got 4.5 quarts out… figured you could just mix, but after reading a few threads on here I figure I better ask before I screw something up. Redline claims D4 ATF meets Type F specifications… help is appreciated!

 

[Yeller]

ATF fluid mixes just fine. When you drain the pan you don't get the oil out of the converter so 4-1/2 quarts is about right.

 

[CopperBronco]

ATF fluid mixes just fine. When you drain the pan you don't get the oil out of the converter so 4-1/2 quarts is about right.

So I got my C4 trans back together, all I did is add new filter and new oil pan… put in trans fluid via the dipstick while engine was hot and after going through all the gears. I’ve always had a bit of a clunk when shifting into reverse, and at lower RPMs a bit of a clunk from 1st to 2nd, but if foot is on pedal it would shift smoothly, PO said it had a shift kit in it.

With new Redline fluid in it seems like the shift from 1st to 2nd struggles more… like 1-2 seconds of struggle, enough to make it feel like engine is nosing down for a quick second… I only drove around my neighborhood for 10 minutes maybe… hoping hotter fluid would help.

Any ideas? Don’t worry about it? Drain and switch to Type F? Hate to waste redline fluid, but hate even more to futz around with transmission function. I am not transmission literate, so could use help.

Should also note from a pan drain… I added 4.5 quarts before driving, but ultimately added 6 quarts, as it had drained slowly with the pan off for a number of days… any chance driving even the tiniest amount under 15mph when checking for any leaks I could’ve damaged something when a quart and a half low?

 

[CopperBronco]

I should add I replaced my vacuum modulator as well with a new one from TBP… are those parts prone to failure new? I have old one and might swap it on… it’s the push in style so super easy to swap.

 

[Broncobowsher]

1-2 upshift in drive, or manually going from 1-2?
In drive, that would be a strange one as it is only a band apply and no other clutch changes. Might be an engine tuning issue.
If from manual 1 to manual 2, you might be getting the intermediate band to apply faster than the low/reverse clutch is releasing. The easiest fix is to double check the band is adjusted correctly.

 

[CopperBronco]

1-2 upshift in drive, or manually going from 1-2?
In drive, that would be a strange one as it is only a band apply and no other clutch changes. Might be an engine tuning issue.
If from manual 1 to manual 2, you might be getting the intermediate band to apply faster than the low/reverse clutch is releasing. The easiest fix is to double check the band is adjusted correctly.

1-2 up shift in drive… it’s a C4 automatic trans… has always done it some, PO said it’s due to shift kit… but is usually smooth if foot on gas pedal mod to heavy… if light on gas it’s always lurched a little, I thought it was slippage first time I test drove it… but PO insisted just from shift kit, but with trans fluid, filter, and modulator replaced it’s just a bit worse now. Might go back to old modulator (no, I did lose pin, or the filter detent spring).

 

[CopperBronco]

1-2 upshift in drive, or manually going from 1-2?
In drive, that would be a strange one as it is only a band apply and no other clutch changes. Might be an engine tuning issue.
If from manual 1 to manual 2, you might be getting the intermediate band to apply faster than the low/reverse clutch is releasing. The easiest fix is to double check the band is adjusted correctly.

Real question is can I damage transmission if I drive it a bit? Would like to get transmission hotter from driving to re-test fluid levels. Make sure I’m not low or high… no bubbles so far. If anything I might be a tad low with new radiator, maybe trans cooler is larger than old radiator… how sensitive are C4’s to fluid? Off by 1/2 a quart and it misbehaves? 1/4 quart?

 

[CopperBronco]

Update: took for a drive again tonight… got it hot, then checked fluid, halfway between markings on dipstick… I can add a bit more, but I’m close. Not sure if that’s the problem… I’m a bit suspicious of the vacuum modulator… if I get right to point of shifting and feel it steer to shift and let off gas it up shifts almost smooth… but I keep on gas it’s struggles a bit, and if I hit gas heavier it tends to get worse… does that sound like a vacuum issue? I might just pop old one back in and see what happens… I did update the metal line from trans to engine as well… it was super rusted… I did have to bend the line to get it to fit with my lift… but I was careful and never kinked it… but if line has too many twists and turns maybe it’s restricting a bit?

 

[bmc69]

I did update the metal line from trans to engine as well… it was super rusted… I did have to bend the line to get it to fit with my lift… but I was careful and never kinked it… but if line has too many twists and turns maybe it’s restricting a bit?

As long as its not totally kinked shut, the twists and turns don't matter because there is no flow. Twists and turns only create losses when there is actual flow in the line.

I'd definitely do the modulator swap next..

 

[CopperBronco]

As long as its not totally kinked shut, the twists and turns don't matter because there is no flow. Twists and turns only create losses when there is actual flow in the line.

I'd definitely do the modulator swap next..

I swapped to old vacuum modulator and fixed! I’d love to know why part didn’t work… are there different types of modulators for C4’s, my old one has the green strip wrapping around it.

 

[matts460]

Yes there are different modulators! I believe with different colored stripes. And adjustable ones too.