The 700R4 Transmission, Chapter 2
2018 summer: A few weeks ago, as I was headed to Round Rock to see a new buddy of mine who has a '62 Cadillac (HUGE), I got stuck in traffic in 100 degree heat. At about the same time, I noticed that I had lost 4th gear on the transmission. I pulled into Advance Auto and checked the trans fluid level. It was low. (Later found out I had a leak at the trans cooler behind the grill, and the leak only occured while driving). Anyway, since the fluid was low, I threw a quart in, but still no 4th gear.. Turned around and drove home. After the modifications I made to the cooling system (See the Gallery named "Under the Hood Modifications", scroll all the way down). In any case, I posted some questions on The H.A.M.B and Hotrodders.com, and got some concenses on the fact that the 2/4 Servo is subject to o-ring leakage, and since I noticed/thought that the Corvette servo in the trans seemed a bit loose when I rebuilt it, I decided that I would go "full blast" and upgrade the servo system to a Sonnax 2 and 4 Servo Upgrade Kit. So here it is. BEAUTIFUL ! It has double o-rings and D-rings to seal it, and the piston diameters are even larger than the Corvette Servo. You can't get a more powerful (pushing force) on the pin to clamp the band on the drum than this servo.
April 19, 2021. Lately, with warmer temperatures, the shift point for 4th gear would gradually rise from 35 mph to nearly 60 mph the warmer the fluid got. Since I knew that the corvette servo had a very loose fit on the 4th seals, I bit the bullet and finally decided to install the Sonnax 2-4 servo. Figured that the floor would have to be cut out anyway, so here goes. I had cut the floor a few years ago and fabricated a patch when I replaced the external cooler lines, so that comes off first.
The pin that pushes the band is supplied longer than any of the 3 stock pins. Procedure requires installation of the assembly, but with no O-rings and measure how far it pushes in. I started by measuring my existing pin and grinding to match that length.5.092 inches..took doing that 3 times since the tolerance is 0.075 to 0.125 of pin travel. End of pin must be rounded and semi polished.
An entire afternoon trying to get this son of a bitch to go in. Disassembled again and installed one of three pieces at a time, but the last cover/4th gear piston would NOT go in with the o-ring on it, but would without the o-ring. Eventually assembled with Brake Caliper grease on the o-rings and had to tap on it to get it to seat and get the snap ring on... WHEW!
DAY 3 !!!! DONE!! The feel of the shifts is measurably better, except that the 3-4 shift still varies between 35 and 60 miles per hour for some damn reason, but it is specifically connected to transmission temperature. Right after startup, whether the weather is cold or hot, it shifts perfectly through all the gears at the expected speed and throttle position. However, in warmer weather, the further I drive, the higher the shift point clear up to 60 before it goes into 4th gear. I thought the culprit was the 2-4 Solenoid, but after installing the Sonnax servo, and taking a recommendation from Dana at ProBuilt Transmissions in California, an incredibly knowledgeable 700R4 expert who builds racing transmissions, I added a gallon of Caterpillar gear oil to the transmission, but it had little to no effect. The gear oil is supposed to stabilize the viscosity.So the next step is to increase the cooling capability of the heat exchanger mounted in front of the radiator/condenser.
Installed, and piped in series with the original cooler, on the left of the picture. That one is a 5" x 11" out of a Jeep, the same car that I got the condenser out of. Not much capacity to cool the transmission fluid. Not particularly pretty, but it's behind the grill, and you can't see it. You can see the fluid diverter valve on the left, which is supposed to divert the fluid through the radiator heat exchanger when the fluid is cool, and at about 160 degrees, is supposed to change the flow through the heat exchanger(s) in front of the radiator/condenser. ... well....
UPDATE: IT WORKS ! ! Noticeably better/lower shift points by keeping the fluid cooler. 4th gear engagement occurs between 45 and 50 even in 90 degree weather and thoroughly warmed up ! ! !......................Installation complete. I had to cut even more out of the back edges of the "bullet" surround and the driver's side middle bar to clear the fan. Nominally, this should triple the cooling of the transmission fluid. If this doesn't completely correct the 3-4 shifting problem related to fluid temperature/viscosity, the next step is to remove/repipe the fluid flow to bypass the radiator heat exchanger completely, and remove the diverter valve from the system so that the fluid flow only to these two new heat exchangers.. The theory of the radiator heat exchanger is that it is supposed to help "heat up" the transmission fluid to around 160 degrees, which the "literature" recommends, but I don't believe it. I think the fluid should be a cold as possible. In addition, though very rare, is that if the radiator heat exchanger fails, the transmission will get pumped full of water. NOT good. Repiping the radiator circuit is going to be a lot of trouble, as the space is very tight to get to the fittings, requiring taking apart some very hard to reach fittings. We shall see......
5/30/2021 - The other day, I noticed the dust pattern on the underside of the hood looked like a LOT of air seemed to be passing between the rubber seal and the hood, and noticed that the rubber "flap" on the top of the radiator support structure was leaning backward just a little bit, so I got to thinking, maybe I put it on backwards. Since I'm presently investigating how to keep everything under the hood as cool as possible, I also bought a 4 channel thermocouple electronic thermometer (Chinese made, of course, and it's not worth a damn.... you get a different reading every time you turn it on.). That's what the little blue wires are in the video. Notice the "flap" angle in the video. Then watch the next video and notice the angle of the flap in that one. FOR 5 YEARS I'VE HAD THAT FLAP ON BACKWARDS ! ! !
