schwanyGT

Have 07 Gt 5 speed....wanna change tranny fluid.....thought RP synchro max was the stuff I was gonna go with from what I read. Then I heard absolutely not gotta run a atf like redline.....can someone clarify this for me or send me the link where it is clarified. My tranny has harder shifts into 2nd and 3rd but not bad at all but think it's time to make the fluid change now. 50 thos miles btw.

Derf00

The 5R55S tranny on the mustang is meant to have the fluid flushed every 30K. At 50K the fluid is probably shot which is part of the reason for hard shifts.

You should also know that 2-3 gear hard shifts can also be caused by a faulty solenoid/servo assembly or an ovaled servo shaft in the tranny. A fluid change will help ease the hard shifts if it just started but once the servo shaft has started to oval, only a repair sleeve and/or new servo/solenoid pack will fully resolve the issue.

algregory

I've been running Amsoil ATF in my '05 GT's trans and changed it each 30k, and I wanted to get synthetic in it early on, so the first change was "early on" and I don't recall the mileage. Additionally, I've been using "Tufoil" as an additive since a machinist renown in the BMW world recommended near 20 years ago. It takes some doing since its viscosity his heavy out of the bottle, but I run a 10% mix in the trans. I do it by putting the "10%" in a bottle then cycling the Amsoil ATF through that bottle until the Tufoil has all gone into the trans. I'm now at 69k miles. I think if you go Amsoil and Tufoil that it may well take awhile before you need to operate on your trans. FWIW

The "BMW" thing, he had custom built my engine at 132k, sold it at 269k still purring like a kitten, the engine was pushed hard in mountain driving extensively seeing redline and near redline regularly and as an indicator, I used 29 sets of tires on that car. You simply can not push our Mustangs that hard.

outceltj

You should also know when traveling in a highway that kick downs are really hard on these transmissions. I know a lot of guys do it but it's not good on them. Now from stop or a very slow roll you will be fine buy going 40 or 50 then mashing the pedal should be discouraged

jz78817

the OP didn't specify auto or manual trans; both were 5 speeds. The TR3650 5-speed manual has ATF as the factory fill.

Nuke

Amsoil, IMO.

schwanyGT

Sorry guys i have 5 speed manual. That changes things a little

BlindGUYnAR

I changed mine in my manual last Monday. Used redline. I used the pump method and all went well. We only drove it 10-15 miles, but it seemed to drop into gears easier than before.

The trans has Mobil 1 from the factory.

schwanyGT

So should I run RP synchro max or redline atf?

stags

RUN from RP. That's a race day only fluid. It will work for 1000 miles or so before it degrades. Killed the third gear synchro in my 09 within a week.

Replaced synchro and ran amsoil... Better shifts all the time, never had a problem