ed's85irocz28

If i'm in drive, my car will top out at about 125 until the rpm's get too high and i have to let off.

When i shift to overdrive, i do see the rpm's drop......but then it still tops out at the same mph that the drive gear does and i still have to let off at about 125 because the rpm get too high.

Z28SORR

125 is not very fast. Sounds like you may have some sort of trans. slipping problem.

antoine

is your transmission upshifting into overdrive at full throttle?

ed's85irocz28

It wont go into overdrive until i let off the gas.

FruityOne

If your Z28 is a 1985 model year then you have had an engine swap correct? Or the motor was swapped before you bought the car. 85' and 86' TPI cars only came with the 305.

Sounds to me like you are confusing the shifter location and what gear the transmission is actually in. All 700r4's require you to let off the gas before they will shift into 4th. I'm not sure, but I think if the transmission sees over 66% or 75% throttle (not quite sure which one) it will not shift into 4th gear, no matter how fast you go. If you want to go faster you'll need to let off the gas till it shifts, and then slowly give it more gas, taking care not to give it so much as to cause the transmission to shift into 3rd because its seing a "WOT" position.

V8Rumble

I don't think that's quite correct. I'm going to double-check on it right now, but I'm pretty certain that there's a different (servo?) on some cars that allows WOT upshifts into 4th. I know that my GTA will do that, & I'm pretty confident that the 43-yr. old woman that owned the car before me didn't do any mods...

In any event (getting back to the original question), 4th isn't a "power" gear anyway - when you go into OD, you're essentially giving up torque in order to get lower RPMs (and thus, better economy).

FruityOne

My bad, I should've have mentioned it. Some TPI cars such as the B4C police interceptros received a modified upshift valve that allowed the 3-4 WOT upshift, however it is extremily rare to find one. Not all GTA's have it, its pretty much limited to the Players Challenge(1LE) cars, and the B4C's.

97WS6SCharged

A normal 700R4 won't shift into overdrive above 3/4 throttle. It's to protect the transmission since the overdrive gear isn't very strong. Trust me, you bark the tires in 4th and it's all over.

Dirt Reynolds

I agree - my L98 GTA will do this also. In fact I had it out on the highway just yesterday on the way to work, and was running a little behind, so I hammered it out on an open stretch. At about 105-110 MPH or so I felt it shift under WOT into OD. From what I understand, some L98 IROC-Z and GTA's recieved the upshift valve that allows 3-4 under WOT. It might have to do with other options the car has, perhaps? Mine has the aluminum driveshaft and dual cats (N10) option.

antoine

my car goes into overdrive at full throttle also you may need to install the upshift valve kit that gm sales,do a search on thirdgen.org for upshift valve

V8Rumble

You ran it up to 110 (or so) when you were "running a little behind"?!?
I'd hate to see it when you were really running late...


Interesting. Mine has the aluminum DS as well, but only the single cat (which has since been replaced w/ a 3" high-flow unit...)

That really surprises me. If it's really rare like that, then as a single-cat car, you would think that mine wouldn't have that... But I've found one or two other... factory curiousities with this car that don't make sense on the face of things. For right now, I'm blaming them on paperwork mix-ups when the car was built!

Heh - that falls under the category of "Problems I'd to like to have to worry about!"

FruityOne

I wish I had installed the upshift valve when I was rebuilding my transmission. I had the whole thing apart for new frictions, steels, seals, and all. When with some upgraded frictions, shift kit, vette servo, .500" boost valve. Though money was tight and I regret not putting in some hardened internals, but I had no idea at that time I'd have all the goodies I have in the engine now.

Now she should make about 280rwhp with a good tune, and I'm seriously wondering if the transmission will hold at all. I've got a nice stacked plate transmission cooler, but I really need hardened internals to take the abuse this engine will make. The first time I get traction I'll either blow the rear-end, or the transmission.

I wish I could bark 4th gear. lol, that would be cool!

97WS6SCharged

Nah, you really don't want to do that. I had one in my 77 Z28 that I had during high school. I was going to work one day waiting to get on the expressway and some retard in a 5.0 was behind me revving like an idiot. So I (being younger and even more nieve) nailed it getting on the expressway. At the top of 3rd around 100 mph, the car finally shifted to fourth and barked em nice and hard (cool). I coasted back down and hit the gas again and the car kept slowing down (not cool). I put it into 3rd and went to work, then over to my friend's transmission shop. Turns out the governor had stuck which is why it shifted so late. Anyhow, it stripped all the teeth off 4th gear, broke one of the planetaries, and messed up some of the clutch packs. $500 dollars in parts and quite a few thankyous later I had a working tranny again.

Oh yeah, the mustang guy did a flyby and I drove by him about 5 minutes later as he was receiving a ticket from a state trooper in a FHP Camaro of all things.

V8Rumble

LOL - expensive, but funny as hell...

antoine

take the valve body down and install the upshift valve the part you can get at a gm dealer,also i never herd of someone barking the tires going into fourth gear i a automatic.