Should I swap my t5 out while the engine's out? Or just see if it lasts?

SadbutTrue

Founding Member
May 1, 2002
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Granada Hills, California
I’m planning (as I’ve repeated to people at least 100 times on this forum in the last few months… I swear it’ll happen and I’ll stop talking about it soon!) on swapping new heads/cam/intake on to my 351, expecting it to push 425 hp/tq (351w, 9.5:1, Trick Flow TW heads, Stealth, compcams 274xe… the same combo but with a roller 331 made 438 hp in a magazine article.. its on AFR’s site..).

I have a t5 in my car now out of an 89 GT. It works great now. However, I have my doubts as to how it’ll handle the engine. That’s basically the question… while my engine is out at the shop is the easiest time to swap in a new transmission (and pull the current one while its worth something, whereas if I break it…). Should I do this? Tony at Astro transmissions says his super-alloy t5 (essentially a T-5z) will be fine for the aforementioned application, and that real high-end T-5s (gforce, A-5, etc) are overkill.

There are a number of factors that might help my current T-5 live a lot longer than it would in most cars. My 66 is really light. I have relatively tame rear gears (3.25). I do not plan on running drag radials or slicks (though I may put cal-tracs on it to reduce wheelhop… I hate wheelhop with a passion). I don’t race the car (the nearest track is 2 hours away, and is LACR… which sucks). I don’t powershift the thing or drop the clutch at 3k rpms. Its abuse will be limited to things like spirited country road driving, having fun on highway onramps, etc.

So yeah… what would stangnet do? A new T-5z is about 1500 shipped from summit (if anyone knows anyplace cheaper please let me know), and I figure I could still get 500 for my T-5, so a total outlay of roughly $1,000.
 
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I have a blown 302 with a little over 400 rwhp and I have been advised that my 1988 T5 should be fine. I plan on driving my car a similiar way that you plan on driving yours. I will replace mine with a TKO 600 or T56 (if gas prices continue to go the way they have) if I have problems down the line.

There is a guy in my club that is running an 88 Fox mustang with the stock tranny. He is putting out about 450 rwhp without any problems. I think a lot of it comes down to how hard you drive your car.
 
I have a blown 302 with a little over 400 rwhp and I have been advised that my 1988 T5 should be fine. I plan on driving my car a similiar way that you plan on driving yours. I will replace mine with a TKO 600 or T56 (if gas prices continue to go the way they have) if I have problems down the line.

There is a guy in my club that is running an 88 Fox mustang with the stock tranny. He is putting out about 450 rwhp without any problems. I think a lot of it comes down to how hard you drive your car.

Your last point is another thing Ive thought about. There are tens of thousands of hot 5.0/fox body mustangs out there and I highly doubt they ALL go out and upgrade their transmissions (Tremec would be a fortune 500 company if they did).

Maybe we could have a pool and see whose lasts longer...
 
You could have your t-5 rebuilt to t-5z specs for under $500.00 and be just fine. When I rebuilt my t-5 I added the cobra tapered bearing/alloy lower gear set and had more tranny than my basically stock 302 could handle.

Do some research on the cobra input shaft tapered bearing...can be done, if anybody says no..they're yanking you around...
 
Maybe we could have a pool and see whose lasts longer...

The Cobra T-5 I had in my '65 behind a blown 306 making 445rwhp lasted about 2-years. That's more than I'd originally expected. In that time, it never saw a drag strip, ran on street radials, and did maybe 8-10 open track events. One day on the street (not on a track), while shifting into third (spirited, but not abusive), it clanked loudly and then was no more. The insides looked like a grenade had gone off - hard to tell what failed first.

It's not a matter of "if" in the 400rwhp+ range, it's "when."
 
:D Just a little "salt in the wound" but I wonder how much longer the 40 year old Toploader in my Ranger will last ? :rlaugh: As far as I know, it's never been rebuilt, other than the blocker rings being changed.:nice: My son sold his 94 GT Stang to his freind two years ago and it's T5 has never been touched and both my kid and his friend has put that one through hell. It's amased me it's lasted this long. The car has well over 100K miles on it.
 
It may be more fun to see who can blow their tranny up first.:D

Sounds like Red65 already won that one though :( But why not.. how much of a head start do you have on me?

Originally Posted by mrmustangman357
LACR closed last year, no?

Well, thats just awful. Not sure what I'll miss more, the absolutely awful track surface, the altitude that added half a second to your ETs, or the fact that its in the middle of nowhere...

And I don't think I'll have 400+ rwhp. Probably more like 350. I know...
 
You won't break it on street tires if you don't bang shifts like an idiot.

An aftermarket shifter w/ stops will go a long way from bending the shift forks and hanging it between gears.

I have the pro 5.0, so hopefully that'll help. wasn't really sure on how to set the stops, just sorta checked to see how much room i needed to shift and set the stop screws right up against that with a few paper widths of clearance... :shrug: