1980 Corvette Shifting Problem with Vacuum Hoses
Thread Starter
6th Gear
Joined: Jun 2011
Posts: 6
Likes: 0
1980 Corvette Shifting Problem with Vacuum Hoses
Hi all,
Lately I've been having problems with my Corvette shifting properly. First off, I cannot get my car to drop into reverse unless the engine has fully warmed up. Secondly, my car does not want to shift into 3rd gear unless I really get on the gas and when I let off the accelerator (to maintain a proper city speed limit) it drops into neutral or downshifts into 2nd gear.
I recently had the transmission rebuilt, so I highly doubt anything within the transmission is the issue. After a little research, and consulting my mechanic (I cannot go see him because I am away at college) I think I've narrowed the problem down to something within the vacuum hoses. Which vacuum hoses should I check to resolve this issue? Or are there any other components I should check? Thanks!
Lately I've been having problems with my Corvette shifting properly. First off, I cannot get my car to drop into reverse unless the engine has fully warmed up. Secondly, my car does not want to shift into 3rd gear unless I really get on the gas and when I let off the accelerator (to maintain a proper city speed limit) it drops into neutral or downshifts into 2nd gear.
I recently had the transmission rebuilt, so I highly doubt anything within the transmission is the issue. After a little research, and consulting my mechanic (I cannot go see him because I am away at college) I think I've narrowed the problem down to something within the vacuum hoses. Which vacuum hoses should I check to resolve this issue? Or are there any other components I should check? Thanks!
Pro
Joined: Nov 2012
Posts: 672
Likes: 0
From: Chesapeake Virginia
there is one hose that runs down to the vacuum modulator on the tranny, it's on the passanger side all the way on the very back of the tranny, it should be hooked up to MANIFOLD vacuum. there is also a TV cable that attaches to the carb, if that is not hooked up and adjusted correctly, you will burn the tranny up in no time. do a google search for how to adjust the cable, it's easy to do.
2026 Loser of the Year
Joined: Sep 2013
Posts: 36,555
Likes: 7,006
From: New Or-leens Loo-z-anna
If you have the knowledge, buy a $20 transmission "direct pressure" gauge ( a gauge that uses a high-pressure nylon tube to actuate it).
Install the gauge temporarily near the console area where you can easily read it while parked or driving. There are charts that show what the gauge should read in PARK/REVERSE/DRIVE/ETC.
Write down the readings call the guys at www.TransmissionCenter.net (I hope it's OK to post the site)
Tell them what the trans is doing/not doing
There is a "ton" of free info/how-to's/etc on the site.
I did a "$1,200 trans overhaul" with $60 worth of their parts and a $30 700R4 specific transmission rebuild manual!
I told the guys my skill level and the exact problems/pressure readings.....
They sold me the individual parts that they recommended.....
I followed the manual to install the parts with the trans still in the car..........
PROBLEMS SOLVED!
It's worth a try...Hopefully your problem is low-cost also..other members know of dependable trans repair shops also.
Install the gauge temporarily near the console area where you can easily read it while parked or driving. There are charts that show what the gauge should read in PARK/REVERSE/DRIVE/ETC.
Write down the readings call the guys at www.TransmissionCenter.net (I hope it's OK to post the site)
Tell them what the trans is doing/not doing
There is a "ton" of free info/how-to's/etc on the site.
I did a "$1,200 trans overhaul" with $60 worth of their parts and a $30 700R4 specific transmission rebuild manual!
I told the guys my skill level and the exact problems/pressure readings.....
They sold me the individual parts that they recommended.....
I followed the manual to install the parts with the trans still in the car..........
PROBLEMS SOLVED!
It's worth a try...Hopefully your problem is low-cost also..other members know of dependable trans repair shops also.
Last edited by doorgunner; Nov 14, 2013 at 09:42 AM.
Melting Slicks
Joined: Mar 2008
Posts: 2,666
Likes: 289
From: Spring Park MN
Definitely internal problems. It should engage reverse even if the kick down cable and the vacuum lines aren't hooked up! If this was the only problem it had, I would still tell you it needs to be pulled and gone through properly. To me it sounds like the rebuild is the issue.
The 80 has a 350C that is just a 350 with a lock up clutch. There is nothing really special to setting this tranny up in the car. As stated, vacuum from manifold to the modulator. There should be one electrical connection to the tranny for the lock up clutch. It comes from a vacuum switch on the firewall. It also has a switch on the brake pedal feeding this same wire. The vacuum switch on the firewall also needs manifold vacuum to it. The kick down cable is setup just like any other Turbo 350, fully extended with the throttle wide open.
The 80 has a 350C that is just a 350 with a lock up clutch. There is nothing really special to setting this tranny up in the car. As stated, vacuum from manifold to the modulator. There should be one electrical connection to the tranny for the lock up clutch. It comes from a vacuum switch on the firewall. It also has a switch on the brake pedal feeding this same wire. The vacuum switch on the firewall also needs manifold vacuum to it. The kick down cable is setup just like any other Turbo 350, fully extended with the throttle wide open.
Advanced
Joined: Dec 2012
Posts: 59
Likes: 1
Definitely internal problems. It should engage reverse even if the kick down cable and the vacuum lines aren't hooked up! If this was the only problem it had, I would still tell you it needs to be pulled and gone through properly. To me it sounds like the rebuild is the issue.
The 80 has a 350C that is just a 350 with a lock up clutch. There is nothing really special to setting this tranny up in the car. As stated, vacuum from manifold to the modulator. There should be one electrical connection to the tranny for the lock up clutch. It comes from a vacuum switch on the firewall. It also has a switch on the brake pedal feeding this same wire. The vacuum switch on the firewall also needs manifold vacuum to it. The kick down cable is setup just like any other Turbo 350, fully extended with the throttle wide open.
The 80 has a 350C that is just a 350 with a lock up clutch. There is nothing really special to setting this tranny up in the car. As stated, vacuum from manifold to the modulator. There should be one electrical connection to the tranny for the lock up clutch. It comes from a vacuum switch on the firewall. It also has a switch on the brake pedal feeding this same wire. The vacuum switch on the firewall also needs manifold vacuum to it. The kick down cable is setup just like any other Turbo 350, fully extended with the throttle wide open.
I have a TH350 in my dirt track Camaro, and we don't bother hooking up the kickdown or the vacuum modulator because it's not needed for racing purposes. If it's not a TH350 (like say a 4 speed retrofit) disregard this - the 700R4 needs it's stuff hooked up.
A disconnected vacuum modulator = the trans thinking you're at full throttle and not upshifting until it hits it's "redline" - you can drive all day long at 4900rpm and it won't shift out of first and then the second you hit 5000rpm it bangs 'er into second.
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From: Oxford MA-----You just lost the game!!!!
Scott
Safety Car
Joined: Dec 2012
Posts: 3,775
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From: Summerville SC
If you haven't changed anything since the rebuild, it might be time to take it back to them and ask them to fix a problem that didn't exist before they FIXED things. Politley, of course.
Pro
Joined: Jul 2007
Posts: 664
Likes: 1
From: Orlando, Florida
It's funny how differently people look at things. For instance, the phrase "I recently had the transmission rebuilt," makes me think the complete opposite of what the OP thinks. As in "Awww, man! I just had the transmission rebuilt, and now it's giving me problems! They must have screwed something up in there!"
Scott
Scott
