89IROCZ28

iTrader: (14)

Since I've owned it, my 89 IROC (L03 & 700R4) never made the 1-2 shift at WOT until it was over 5,000 rpm and way past peak hp/torque for the basically stock engine. Sometimes it didn't shift at all until I lifted off the throttle for fear of floating a valve or worse. I recently installed a Corvette servo to firm up the shifts, which it did, especially when I would get a part throttle launch just right. But, that only made the WOT late shift issue even more frustrating. It seems many others have had the same experience.

I was going to purchase a governor tuning kit, but it seems most were primarily designed to increase the shift points, not lower them. I also didn't feel like spending $40 or more for something that I could probably do on my own for a lot less. I'm not claiming to be all that knowledgeable on the 700R4 transmission. In fact, most of what I know came from others on this site or reading online articles.

Well, I successfully lowered the WOT shift point to 4500 rpm for just a few dollars and thought I'd share how it was done w/ my fellow TGO members.

First, good online resources:
DragRacing Online - This link provides very good instructions & pictures on removing, disassembling, modifying, and reinstalling the governor. Keep in mind, it was created for tuning a governor using one of the kits.
NastyZ28.com - I believe this is the thread that got me thinking of doing the recalibration on my own. But, it appears the link is no longer active. I've contacted the site admin to see if it's the thread I think it is and if it can be made available again.

Tools:
Jack & jack stands or ramps
Drain pan
Flat blade screwdrivers
Diagonal cutters
Center punch
Drill (drill press recommended)
1/8" drill bit (IMPORTANT - Drill must be for hardened steel - cobalt, tungsten carbide, etc.)
Pop rivet gun
Large vise grips
Hammer
Funnel

Parts:
1/8" x .500 stainless steel pop rivets (the next shorter rivets would probably work, too)
1/8" steel pop rivet washers (3/8" OD, 1/16" thick)
2" 6d finishing nails
1qt trans fluid

Procedure:

1. Following the instructions located on the DragRacing Online website to remove & disassemble one side of the governor. Be sure to place the drain pan under the area before removing the governor cover. Disconnecting the speedometer cable/wiring may allow more room to work.
2. On the lighter (inside) weight, as accurately as possible, center punch the recessed side of the spring perch. This will locate the hole to be drilled for the rivet. Use the attached pictures as a guide.
3. Using the punched location, drill an 1/8" hole through the center of the spring perch. This was unexpectedly the most difficult part of the entire process as the stock weights are made of hardened steel and a normal drill bit won't even scratch them. A carbide bit is probably the best route to go. I used a larger carbide bit just to get the hole started and used an 1/8 cobalt bit to actually go through. Even w/ cutting fluid, the cobalt bit broke while drilling the 2nd weight. It probably wouldn't have broken using a drill press.
4. Pop rivet one or more of the pop rivet washers to the weight using the hole drilled in the previous step. Two washers on each of the lighter weights dropped the 1-2 shift on my car from 5000+ rpm down to ~4500 rpm. I inserted the rivet from the raised side of the spring perch and placed the washers on the opposite side. File off the excess length of the pop rivet to avoid any potential interference, being careful not to remove too much. Using a shorter rivet would eliminate the need to do this. Inserting the rivet from the other direction may work, too. Compare it to the other side to check for any interference w/ the range of movement of the weight.
5. Again, using the DragRacing Online link as a guide, reassemble the modified weight to the governor, except use a 6d finishing nail as the hinge pin. With the finishing nail fully inserted, use vise grips to crush the end to lock it in place. I kept closing the vise grips tighter & tighter until the crushed area looked like the original pin. I also used diagonal cutters to remove the excess length of the crushed area.
6. Repeat steps 1-5 for the other side of the governor.
7. Reassemble the governor in the transmission. Once again, use the DragRacing Online website as a guide.
8. The governor cover must be properly seated all the way around. Again, having the speedometer cable/wiring disconnected may allow more room to get it seated. Reinstalling it may require lowering the rear of the transmission. If you need to do this: First, remove the distributor cap to avoid damaging it; place a jack under the transmission cross member; remove the four (4) transmission cross member bolts; place the drain pan under the area (additional fluid WILL drain out); and, lower the rear of the transmission. After seating the governor cover, reverse these steps for reassembly.
9. If it was removed, be sure to reinstall the speedometer cable/wiring.
10. Lower the vehicle and replace an approximate amount of transmission fluid based on what was captured in the drain pan. Error on the low side, but be sure there's a least some fluid showing on the lower end of the transmission dipstick while the engine is idling and the transmission is in park. Top off the fluid after the transmission has been warmed up.

I'll follow up with some pics and longer term testing.

89IROCZ28

iTrader: (14)

1. Stock governor w/ "C" weights installed.
2. Inner weight w/ hole drilled through spring perch.
3. Drilled weight w/ 1/16" thick x 3/8" OD steel pop rivet washers & 1/2" stainless steel pop rivet.

89IROCZ28

iTrader: (14)

1. Pop rivet inserted into raised side of spring perch.
2. Washers installed on opposite side of spring perch and pop rivet trimmed to avoid creating any interference.
3. Modified weight assembly installed on governor using finishing nail. Note the crushed end to lock the nail in place. The crushed end has also been trimmed to avoid creating any interference.

89IROCZ28

iTrader: (14)

I've had this mod in for a month now and I couldn't be happier with the results. The 1-2 shift is still occurring right about 4500 rpm and has made driving the basically stock L03 a whole lot more fun.

The 2-3 shift is coming in a little earlier now, but I can hold that shift back with the shifter. I may try some spring changes to see if the automatic 2-3 shift point can be raised a little.

Also, I have to imagine there's a slight increase in gas mileage with the slightly earlier shifts that occur during normal driving.