85 vette Auto Trans doesn't engage forward or reverse
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Intermediate
Joined: Oct 2005
Posts: 26
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From: Corinth MS
85 vette Auto Trans doesn't engage forward or reverse
I have a 85 Corvette Coupe. I was driving home one afternoon and as I stopped behind a car turning left, I went to give it gas and the engine ran but with no forward movement. I thought I might have bumped the auto gear shift in neutral. Nope! It would shift through all of the gears, but the only gear it actually engages is PARK. There was not any noise made as it happened. I was not even listening to the radio. I knew that since it engaged Park, then it wasn't the drive shaft. I pushed it off the road and checked the fluid and it was on the full mark. I have brought it home and I can crank the vette and give it gas, runs fine, just no forward or reverse engagement. What would be a good place to start on diagnosing the problem? Could it be a dirty transmission filter? Could it be the Torque convertor? Prior to that, I did not notice the trans shifting with problems prior to the incident. I would appreciate any assistance. Thanks!
Race Director
Joined: Aug 2000
Posts: 14,130
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Cruise-In II Veteran
I believe the trans is bad...you can drop your trans pan and see if theres a bunch of metal,shrapnel,clutch debris in the pan.
If you drop the pan and its pretty clean,drain it out and fill with new fluid and filter and "see" what happens...but what you described happened to me on a 86 Pontiac Firebird I had years ago with the 700R4 tranny...one day nothing worked except P or Park...it turned out I had a real bad trans.
The fluid was a very dark cherry red,almost burnt but not brown or black yet.Dropping the pan showed me the crap inside there.
Btw the trans fluid should be a pinkish red color,if its brown or black,its burnt and is no good.You can also do the smell test sometimes...smell a fresh quart of tranny fluid,then smell the fluid on the dipstick.If it has a bad odor,sort of burnt or smells like its very hot,theres a problem with the trans,could be TC or internal stuff.
Online troubleshooting isnt gospel,but hope it helps narrow down some.
If you drop the pan and its pretty clean,drain it out and fill with new fluid and filter and "see" what happens...but what you described happened to me on a 86 Pontiac Firebird I had years ago with the 700R4 tranny...one day nothing worked except P or Park...it turned out I had a real bad trans.
The fluid was a very dark cherry red,almost burnt but not brown or black yet.Dropping the pan showed me the crap inside there.
Btw the trans fluid should be a pinkish red color,if its brown or black,its burnt and is no good.You can also do the smell test sometimes...smell a fresh quart of tranny fluid,then smell the fluid on the dipstick.If it has a bad odor,sort of burnt or smells like its very hot,theres a problem with the trans,could be TC or internal stuff.
Online troubleshooting isnt gospel,but hope it helps narrow down some.
Race Director
Joined: Feb 2004
Posts: 12,518
Likes: 19
Reverse and foward gears use different clutch packs. To lose both points towards a massive hydraulic failure, broken torque coverter, broken pump etc. It could also be a lo-roller clutch(rear sprag). The bad news is that the unit is likely toast
. The good news is that I currently have 2 for sale in the c4 parts for sale section. The less expensive would make a nice upgrade for your stock 85. If you plan to make 600hp in the near future, I have another one for sale that will take it
. The good news is that I currently have 2 for sale in the c4 parts for sale section. The less expensive would make a nice upgrade for your stock 85. If you plan to make 600hp in the near future, I have another one for sale that will take it
