Hi I don't know if this is the write place to post this but I was trying to find out the top speed of my GTA in it's current state so when I finish with the tune-Up I can go back an check if it made any difference at all.

I put the pedal to the metal and close to 110 the Trans start to shift on an off Overdrive. I forgot that I could put it in Drive so it wont shift to OD but I think that shouldn't Happened. so if anybody know why this happened?

This is the Vid.

 

The 700R4 is designed to shift out of OD at a certain % of full throttle, I want to say 70% or something like that. There are parts you can buy, TCI has one, I saw it in my summit magazine, that will allow it to run to 80-85% of full throttle before shifting. To my knowledge, there are no OD transmissions that will stick in OD all the way to 100% throttle.

 

That may be the vehicle speed limiter that is being hit. Unless the car was factory equipped with Z rated tires that is about the speed that it is limited to. To be sure, drop the ECM, open the small cover, and get the 4 letter code from the top of the PROM (on the silver label). And post it here.

With that myself or someone else can tell you if there is a speed limiter.

As far as staying in OD, that is an easy fix. I used the GM b-body fix kit and once over 85 MPH or so I can mash the pedal to the floor and stay in OD (4th). Unfortunately that kit is no longer available. There is also a different solution posted here:

http://www.joby.se/corvette/mods/2002-0X02_tranny_wot/

Dana (pro-built) also shows this mod but uses two set screws that are self threaded into the holes.

RBob.

 

The B4C police cars as well as the Corvettes would do a full throttle 1-2-3-4 gear just as a person would expect. Same TH700R4 in all of them. That's why the Corvettes would do 150 mph back in the 1980's while every road test for an L98 F-body would list "estimated 140 mph top speed."

The 1987 and earlier F-bodies will do a top speed run with the automatic, but the 1988-91 cars would not. Sometime in 1991, GM changed it so that F-bodies would do a top speed run. I've always found this odd because the 1988 700R4 was upgraded and that's the same year they stopped doing the top speed runs.

The reasoning behind this is that 4th gear is weak in these transmissions and you don't want to be putting too much throttle on a vehicle while in O/D without getting a downshift into 3rd. This makes sense when you're towing a boat or when you're driving up a steep highway. But it sucks for high performance driving.

The stock 700R4 will automatically do an upshift from 4th to 3rd at aprox 2/3rds throttle. And it won't do a 3rd to 4th gear shift at wide open throttle. I found this out myself when I had my foot to the floor in 3rd gear and noticed the tach was at 5700 RPM and it wasn't shifting into 4th.

Letting off the the throttle lets the car shift into O/D, but even if you feather the gas pedal. At some point around 120 mph, it will make a downshift back into 3rd.

B&M makes a different plunger and sleeve that changes the stock 4-3 downshift from 66% throttle to 85% throttle. I don't like this idea, because it changes the point where you get a downshift from 4-3 from 120 mph to probably 135 mph (when a downshift would send you waaaaay into the red line). On the plus side, it allows you to do high speed driving in the 90-110 mph range (not racing, just gently accelerating and slowing down) without the transmission constantly shifting back and forth. Because you're going to be around 60-70% throttle at that speed anyways.

The better route is the Pro Built Automatic setup that Dana sells. His setup blocks the holes on the plunger sleeve. (Ask him to add it onto his modified Trans Go kit if you ever buy one from him). This blocks the part throttle 4-3 downshift. You still get a downshift when you slow the car down. And you still get a downshift when you're heavy on the throttle. But it takes more gas pedal to get a downshift. And it takes progressively more gas pedal to get a downshift the faster you go. So once you're at 85 mph or faster with his plunger sleeve, you won't get a downshift out of O/D unless you manually pull the gear shifter back. His sleeve also allows the car to shift 3-4 at full throttle as well.

The only difference you'll see under normal driving with Dana's sleeve is that at 60-75 mph you probably won't get a downshift from O/D unless you're really on the gas pedal (say 90% instead of 50% throttle). It's actually nicer this way, because unless you're racing, most of the time you don't want a downshift. More gas pedal or manually pulling the shifter back will get you the 4-3 downshift at 60-75 mph if you really want it.

Sonnax also makes a sleeve that has no holes at all. Accomplishing the same thing that Dana's plugged holes do.

 

Thanks Every one for your imput.

What I'm Concern about is the shifting back and forth when at 100% Throttle. it didn't stay either in 3th or 4th it switch back and forth from 3th to 4th. Something most be wrong. I was thinking about the Throttle cable that go to the trans but all the info you have brought is very helpful.

Before modifying my car I'm Planning to take it back to the best stock specks and then upgrading as I needed. but what Reid Fleming Post is very tempting to do. Can you tell me how much this cost? or a link where I can find this kit?

is this what you are referring to?
TransGo 700R4 Street/Strip Shift Kit w/accumulator pistons Late 1987-1993
Part Number: TGSSSKWACC88UP700

This "modified" Trans-Go Performance Shift Kit is very streetable, nice part throttle & firm WOT shifts. For all Late 1987 & up 700R4's. Works best with 10" or smaller diameter torque converter. I use this kit in all of my Performance transmission build ups. An external trans cooler is recommended.

Also will check the numbers on my computer and post it so We can find out if this is a limiter thing.

Thanks again for the info you people are the best.

 

I doubt it's a limiter thing. As far as I know, all GTA's came with 245/50/16 Z-rated tires (or V-rated tires in the earlier years) and no computer controlled limiter.

You're close on the link for the modified TransGo. I would go with this one instead:
http://www.700r4l60e.com/store/produ...&cat=65&page=1

It looks to have more things. Essentially he has 3 products.

Heavy Duty (meant for S10 trucks, ambulances, trucks that tow)
Street/Strip (higher performance for F-bodies, Corvettes)
Elite (major HP drag race type stuff. Out of our league)

I went with the Street/Strip. I've had this in the car for 6 years now as a daily driver. You will never get tired of it. It's a quicker shift, but not a harder shift. And it's a progressive shift. So the more gas pedal you give, the faster it will shift. Pulling the shifter from O/D to 3rd will result in firmer shifts than leaving it in O/D would. And pulling it to 2nd gear will result in a very firm 1-2 shift. The result being that the shift gets firmer when you want it to be firmer. His kit does NOT bang into every gear at low speeds (which gets annoying very fast)

Unfortunately my knowledge of transmission internals is limited. So I can't say exactly what your transmission is doing wrong. In my car, putting the gas pedal to the floor will result in it staying in 3rd gear until it gets to 5,000 RPM and then it will shift into 4th (with the sleeve from Pro Built). Before that, it would just stay in 3rd until I left off the gas pedal.

I'm guessing it's some band or spring that needs replacing (the kit has this stuff). It could simply be something that needs tightening. It's probably the 3-4 band on it's way out. The shift kit from Pro Built has a stronger 3-4 shift band. After the kit is in, the 3-4 shift won't be as firm as the 1-2 shift, but it will certainly be firmer than the stock 3-4 shift. It's just right. You'll like it.

 

Thanks for the info. This is what I was looking at so as soon I gou the mony I'll be buying one of these.

 

Reid, thanks for this description. I'll be getting a rebuild kit from Dana this winter and this is good to know. I will definitely ask him about this part. By the time I'm doing 70mph on the Highway I'm basically "in" the early stages of the powerband of my motor (2600rpm @ 70) and downshifting doesn't generally do much for me at this point.

On a side note, when I was in Germany running on the Autobahn, I managed to feather my throttled into OD at 100 mph and rode it all the way until I backed out of it at 125 when I ran into traffic.