T-5 Transmission Fluid - Vintage Mustang Forums

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post #1 of 11 (permalink) Old 12-28-2008, 12:28 PM Thread Starter
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T-5 Transmission Fluid

What is the best type of fluid to put into a
TREMEC T-5? I know some people put in ATF into them. Any suggestions

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post #2 of 11 (permalink) Old 12-28-2008, 12:45 PM
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T-5 Transmission Fluid

WC T5 uses ATF. NonWC T5 uses 90 weight gear oil.

1965 Mustang 2+2
1968 Mustang California Special
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post #3 of 11 (permalink) Old 12-28-2008, 01:32 PM Thread Starter
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Re: T-5 Transmission Fluid

What is the best type of ATF to use. I know there are a few different kind. (Ex. GM DEXRON® II, III & VI Ford MERCON®, MERCON® V & SP
Chrysler ATF+ through ATF+4®)

Which should I go with?
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post #4 of 11 (permalink) Old 12-28-2008, 01:57 PM
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From the T5 service manual:

transmission models use DexronÒ II automatic
transmission fluid. Refer the vehicle owner’s manual
or service manual for lubricant specifications

1965 Mustang 2+2
1968 Mustang California Special
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post #5 of 11 (permalink) Old 12-28-2008, 07:59 PM
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Re: T-5 Transmission Fluid

Using ATF in manual trannies had been an old drag racers trick for years before the car companies started doing it. Use a Dexron type fluid.

John Wilson

My factory GT '66 Fastback (photo circa 1984, and I still have it!)
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post #6 of 11 (permalink) Old 12-28-2008, 08:05 PM
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ALLLL T-5s use dexron mercon (older model GM auto fluid) atf fluid...do not run 90 weight gear oil in them.......not type F ford auto fluid...its no trick,,its what they came with originally...
lost of guys also run GMs synchromesh trans fluid which can be had over any GM parts counter...its essentially a synthetic fluid designed for Gm version T-5s and T56s...
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post #7 of 11 (permalink) Old 12-28-2008, 08:10 PM
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T-5 Transmission Fluid

I had been using Dexron III but recently had the transmission out of the car. I refilled it with Dexron IV (synthetic) and it works fine.
FYI, it technically takes 2-3/4 quarts to fill.

http://home.comcast.net/~stangg/vmf/stangg_516_1_sig.jpg>'68 Highland Green fastback clone. 331 EFI, AFR heads, tube chassis, Cobra brakes, Fox rack & pinion steering,T5z, 8.8" Auburn limited slip w/ 3.27:1 rear gears, triangulated 4 link, QA1 coil overs, run once in the 1/4: 13.3 @ 107.5
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post #8 of 11 (permalink) Old 12-28-2008, 08:39 PM
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I use Mobil 1 ATF in my T5.
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post #9 of 11 (permalink) Old 12-29-2008, 11:03 PM
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Re: T-5 Transmission Fluid

Borg Warner and Tremec recommend using old style Dexron II/Mercon.
Some people use synthetic or newer type ATF. For some people it seems to work for some not. In many cases it works fine for a while then later (like six months or so daily driven) they find the gears begining to grind a bit when shifting. This is because many synthetics are a bit TOO slippery. The WC T5 has carbon fiber blocking rings. These function like miniature brake shoes. The function of blocking rings is to slow the next gear to close to the speed of the shaft so the synchronizer and gear you are engaging don't grind. If you know how to "double clutch" you can get by without the blocking rings because you would be performing the same function. (All a basic and simplified explanation).
The upshot is that old Dexron is generally the safeest bet, particularly if you want to speed shift. If you tend to drive your car rarely and shift rather slowly and gently, you can run synthetic or what have you and likely will never experience gear clash.
Note that some gear clash going into reverse in most T5's is unfortunately pretty normal and what fluid you choose to run will likely have no effect on it.
I personally know of a healthy 185K mile T5 that has been running B&M "Trick Shift" fluid since about 1986. I can't swear that the B&M fluid was benificial or not, but it sure didn't seem to cause any harm. I've tried Trick Shift in other type manual transmissions for like 20K miles or so and couldn't really tell any difference or benefit.
I put Dexron III/Mercon in my T5's and Mercon V in my AOD's, but that's just me.

.... it wouldn't be the first time reality took theory and conjecture out behind the woodshed and gave them a good thrashing.
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post #10 of 11 (permalink) Old 12-30-2008, 09:55 AM
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Originally Posted by VictorII
I use Mobil 1 ATF in my T5.
Me too. That is what Modern Driveline recommends.

John Bednorz

1967 Shelby GT350, dark green, 347 stroker, 5-speed, inboards, #2206
1973 Mustang Convertible, white/white, black stripes, Q-code (351C-4V), ram air.
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"If you find the car of your dreams, ignore the price guides and pay whatever you have to in order to get it."
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post #11 of 11 (permalink) Old 12-30-2008, 10:16 AM
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Re: T-5 Transmission Fluid

I used Pennzoil synthetic ATF then switched to Amsoil synthetic ATF and noted a much smoother shifting transmission.

1965 C code fastback with; 306 c.i. w/Keith Black 9.3:1 CR; ARP; Edelbrock Performer RPM big valve heads, Air Gap intake and Performer 600 cfm carb; Hooker comp headers; MSD; mild performance cam; roller rockers; windage tray; 3.55 trac-loc rear; T5; Unisteer Power R&P; Ididit tilt column; Scat Procar Rally seats; LeCarra steering wheel; JME bezel with Autometer gauges; Tinman SFC; 265 RWHP/289 RWTQ.
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