I have done a ton of searches on the subject of ATF. There have been things going both ways wether to use synthetic or not, from what I found on the net Dexron VI is a synthetic and has a lower viscosity than Dexron III but has better shear strength better high temp properties and better oxidation resistance and GM approved for a 700R4 from what I could figure out. The had a bunch of RPO codes and specific vehicles not to use it but again none sounded like a 91 Vette.

Following a bunch of old threads i found doing a search most went back to 2007 and hoping there is some new info since then. Petek mentioned odd failures with synthetics in general that sounded like the friction material was ok but bearings bushing washeres etc. I was wondering and hope pete might off his thoughts if the difference in viscosity lowerd the oil pressure but the improved, according to gm friction properties saved the friction material but bearings and bushing suffered from low oil pressure.

The reason I ask is this summer I had the fluid and filter changed at the dealer for just a little above the cost of parts and oil so i thought why jack it up spend the time and mess and disposal issues for a few bucks. When I got the bill I noticed there was Dexron VI was the proper oil now and Dexron III is being phased out, basically did exactly what GM said to do. It did not seem right when I picked it up and they ended up dropping the pan again to verify that the filter was installed correctly and no issues with the pump pick up. It was still different Then ended up changing the TV cable and adjusted it for the cost of the NAPA cable that I provided. It still seems to shift different than it did though firm but slightly delayed for my taste even after following the FSM for adjusting the TV cable. It sems to shift at the factory setpoints for speed and does brake the engine when you lift. It just feels like delayed shifts and you can force an upshift by relasing throttle position if fairly close to the correct speed for the shift.

OK all that has been changed is the fluid filter and TV cable. Does all this sound normal for a 75k miles car everything stock? Is it worth doing the fluid change procedure just discussed here through the trans cooler lines and switch back to Dexron III? I also found a link here that was all about TV cables and adjustment. Under possible things mentioned was the TV spring being too long or too short from wear and listed driving tests as well. I will see if I can do them mid week as the weather is not going to be good for it until then.

Sorry for the long post but thought I would anser all the possible questions that might come up ahead of time.
Dave who should have bought a 6 speed...

 

There is nothing wrong with owning a C4 Corvette with an Automatic Trans.

The 700 R4 Trans is more Consistant shifting than most individuals can be 100 % of the time. Including myself.

I love driving a Muncie 4-speed M-20, M-21, M-22 Rockcrusher equipped Car myself.

But You cant make quicker shifts than a good factory stock Corvette 700R4 unless You keep your Right Foot planted hard on the gas and never lift off the gas while making lightning fast upshift gear changes.

Also takes a perfectly setup and performing HURST shifter and linkage on that manual trans too.

I found my 87 Vert about 4 years ago now.

Looked through the window at the council and then seen it had no 3rd clutch pedal.

I was dissapointed. Till I took the Corvette for a test drive.

I was amazed at how fast and consistantly the Corvette 700 R4 trans shifted and consistently fast and clean.

A convertible, Red Paint, and Red sport leather interior, I was hooked and in love. I bought the car, my vert. No regrets !

I dont believe there is anything wrong with using Dextron VI "6" ATF myself.

I know Pete K. hates synthetic fluids also. From my own posts to him last year.

Dex 6 ATF is factory recommended in the new 2010 and 2011 Corvettes with the 6L80E transmissions. I dont believe GM is incorrect in there recomendations.

I am a Royale Purple ATF fan. I am using Royale purlple ATF in my 87 700R4 trans after rebuilding it this year.

7,000 miles later after the trans rebuild, absolutley no problems using the full synthetic Royale Purple ATF. The fluid is still as clean as the day I put it in.

I rebuilt my 700 R4 with factory GM 4L65E planetaries, Full Alto Red Eagle Frictions, Full Kolene Steels, New Sprags, Beast Sun Gear Shell, New bushings throughout, Billet Steel Pump Rotor, Parts from PATC, Sonnex, Trans Go, Custom Converter, ect.

Spared no expense. Built a the same or better 700R4 the pros built and charge $4k - 5K thousand for.

For a cost of around 2K including finding every single Factory Kent Moore Tool required for proper rebuild- shopping on ebay at night last winter.

Built a 700R4 trans myself to take the power of my 410 CI smallblock I will transplant into my 87 Vert.

A freind of mine runs a 8-second Renegade Mustang. 306ci Vortech Supercharged, 22-25psi Boost.

He has made over 500 passes to date at Route 66 in Joliet, IL.
Runs Royale Purple ATF in his built Ford C4 Transmission. Absolutley no TRANSMISSION Failures.

I dont drive my 87 Vert easy. Foot is down on the gas every chance I get. I often run it to over 150MPH on the didgital dash.

I belive in synthetic trans fluids. Royale Purple ATF myself.

The TV cable is probably adjusted properly on your Vette, the Throttle Valve may be sticking. Might have to remove it from the valvebody for cleaning and inspection.

If the TV valve itself hangs up, you wont have proper shift points and the usual shift feels you are acustomed to in your Vette.

The Trans Go Jr. and The Trans Go Sr. aftermarket shift kits address the sticking TV valve problems and others too.

BR

 

Thanks for all the info! I will see if I can do that this winter. I am a real good machinist engineer and used to be race engine builder but to be candid I left everything after the belhousing flange to a trans shop other than balancing flywheels and clutches and never had any interest in what they were othere than balanced. How hard is it to do the shift kit in the car with zero trans experience?
Dave

 

I swapped to fully synthetic fluid and shortly after that my 700R4 blew. I cannot prove that was the cause, but I sure was suspicious.

 

Try this link I asked the same question not long ago and this what Pete K answer.

http://www.corvetteactioncenter.com/...fluid-atf.html

 

Thanks for the link that is the info I wanted from someone that while I have never met I trust as he has always presented himself a pro. I also have more faith in actual results rather than studies. Form what i read one of the driving forces in Dexron VI is mileage something I could care less. I also suspect something is done differently in a 2009 trans compared to 1991 as far a materials and clearaces and all those no doubt optimized around Dexron III.
Dave

 

If you had a lot of miles on that transmission without a previous fluid flush or regular change of pan-contained fluid and filter it was not the fact that you changed to synthetic but the fact that you changed the fluid at all. Some transmission places won't do a complete flush (or even change the fluid in the pan) if they see very old and dirty fluid, since the new ATF puts particles in circulation that will ruin the trans very quickly -- and then the customer will come back complaining that they did something wrong.

If your fluid was black or smelled cooked, you would have been better off getting a rebuild right away, or driving it until it died and then getting a rebuild. Changing fluid just hastened its demise and wasted $$ on synthetic fluid.

Don't ask me how I know...