is it ok on the tranny to use 5th at the track?

in my S10 i have a blown 4.3L bolted to a T56 from a '96 camaro. im building a new rearend and trying to decide on a rear gear ratio. im thinking 4.88 so i have a good first gear ratio to get off the line. right now i have a 3.73 and they kinda suck not having much power till the boost starts to build. even with the 3.73 5th gear pulls pretty hard so im not worried about a bog and the motor recovers from the shifts pretty fast

im looking to trap about 110mph. the truck weighs 3000# or a little less and the tranny has some upgraded parts cant remember what exactly, id have to look that up but the gears and input and output shafts are stock

i also have a 6000rpm redline but im shifting at 5500rpm to keep the stock preped rods inside the block

the guy who owned the tranny before me seemed to be OK with the 4.88 and using 5th with his nitrous fed 4.3L. i was just wandering it it was really hard on the tranny

also i drive mostly on the street and do about 10 passes a year

 

For what its worth, I remember hearing that 1-4 are cut for strength, and the 5th and 6th overdrive gears were cut more for quietness, thus sacrificing some strength. Although on a blown 4.3 you might be ok. I'd think the weakness of 5th might only become an issue at the 500+ rwhp/rwtq levels.

Sounds like a cool project btw!

 

I've wondered the same thing, but here's my take. I've worked on a number of T56's, and one of the weakest spots on them is the mainshaft splines for the 5-6 driven gear. I've seen a couple that were completely rounded out (trans lost 5th and 6th), and several that were on their way out. The only fix is to replace the mainshaft and the 5-6 driven gear itself (it happened on my own car also).

The 5-6 fork is pretty small also - don't shift it hard.

I would not 'set a car up' to shift in to 5th if you're racing it. You'll just hurt your times (and likely your trans). I'm actually dropping back in rear gear ratio (probably going to 4.30's, from my 4.56's) just so I don't have to hit 5th on the spray.

That's not saying it can't be done... yes, guys do it. But it's not very good for the trans, and odds are good that the mainshaft will wear out faster.

 

As One that also had a 5/6 gear failure also. I have to shift into 5th at 130mph. I guess I have to deal with it.. I have to use that gear while road racing. Most tracks I raced at have staight's long enough to do that. Road America is a 150+mph track. Later John

 

Uh yup. Bent two so far trying.
I would not do it again. It was accidental (not enough valve spring) but trying to use 5th killed my MPH and aborted half the runs.

 

thanks for all the replys, this truck is alot of fun only problem is like everything has to be custom made. its a combination of parts that just arent intended to go togather.

my trans was upgraded to the viper 3-4 shift fork and the viper blocker rings. im also using the mcleod street twin with the mcleod C5 vette master( real fun to get mounted on my firewall) and a pro5.0 shifter

you guys really think my mph and ET will suffer with using 5th and a 4.88 gear? id be shifting into 5th at 83mph (5500rpm) and the rpms would drop to about 4000 and by 110mph id be spinning 5200rpm. my motor would be fully recovered from the shift and id be making good boost by then

if i keep it in 4th id have to use a 3.73 gear and i was thinking that would hurt my time more than going with more gear and using 5th

with as many passes i make a year id probably not notice any extra wear. the shift stops in the shifter will prevent the fork from breaking? or is that still a huge gamble

here are a couple links to pics
bofore teh blower went on

 

I can't guarantee that your MPH will suffer, but I think it will because mine did. My ET actually benefitted from a better launch with the 5.13s.
No, the shift stops won't prevent breakage. I have a Pro 5.0 with the stops adjusted and the fork breaks going into 5th. Problem is, it will go easily into 5th if you let the RPM drop to match. Otherwise the slider stops against the synchro and the fork bends if you push. The long delay until you get it into 5th kills your MPH. About 10 MPH in my case. I understand where you are coming from. It seemed like a good idea to me too, but it turned out that it didn't work. I even proshifted 5th after I replaced the first fork. That helped a bunch, and I got a few passes before the fork broke again. Even proshifted, the MPH was lower with the 5.13s and 5th than it was with the 4.11s and 4th.

 

that is one damn fine s-10!! i just looked at all 154 pictures lol. i used to have a 94 s-10 blazer that i wanted to build up. i had plans for a forged 383 stroker on dope / th350 combo but i got the camaro instead. i needed somthing more drivable.

just a question, that front plate on the tranny, that looks like another place for a shifter, what is that? it is in the same location as the stock hole in your floor. i've always wondered whats under that plate.

 

thanks, the truck is fun, but ive got F-body runnign through my blood. i cant wait to get back to working on my '71 camaro protouring genIII/t56 project. i also got a '95 z28 convertable for beating around town

im not real sure whats under that plate, never had a t56 that far apart. maybe just an inspection hole?

you want streetable, use a t56. that alone gained me 10 more MPG. i drove out to kansas city for the s-series nats, 8-9 hour drive most of which was in the rain with drag radials, got 27mpg went to the track left the tires at 35psi and went 14.8@95 with a 2.3 60'. next pass i left above idle and went 15.8@95mph, LOL. that was before the blower went on

ive decided to go with a 4.10 gear to prevent the 5th gear shift. should be alot easier to make these nittos work. ill save the 4.88s for when i decide its time to minitub and 4link with 30x13.5 ET streets

again thanks to all for the help