1985 4+3 OD Sluggish
Safety Car
Joined: Oct 2007
Posts: 4,426
Likes: 229
From: Pennsylvania
If your tps is adjusted and working correctly I'd then think maybe the filter not seated all the way. If it's first in line and getting an air leak it could be allowing for wonky pressures. Again it could be the kickdown cable but I haven't dug deep enough into these to really know for sure. If it's like a regular transmission having the cable out of adjustment will make it slip and do all sorts of things.
I also question the filter not being seated all the way on, the "o" ring missing or deteriorated. It only started this jumping in and out right after you changed the fluid, correct?
Melting Slicks
Joined: Feb 2003
Posts: 2,677
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From: Saskatoon Sask.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
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From: Nashville TN
2017 C4 of Year Finalist
Drive it until it warms up enough to "disengage" abnormally as you describe in your post I quote.
Make it "disengage" by giving it throttle. Does the light stay ON when it drops into direct?
Again: Does the light stay ON when it "disengages", or drops into direct?
If the light is staying ON, the overdrive clutches are burned up. That's why the seriously-black fluid. It needs to come out and be fixed. If the light is staying on, the ECM is not "disengaging it", the overdrive clutch-pack is slipping.
"Too much information" and baffling you with BS from a guy who's owned one of these for 33 years, has worked on it, and is trying to help.
Make it "disengage" by giving it throttle. Does the light stay ON when it drops into direct?
Again: Does the light stay ON when it "disengages", or drops into direct?
If the light is staying ON, the overdrive clutches are burned up. That's why the seriously-black fluid. It needs to come out and be fixed. If the light is staying on, the ECM is not "disengaging it", the overdrive clutch-pack is slipping.
"Too much information" and baffling you with BS from a guy who's owned one of these for 33 years, has worked on it, and is trying to help.
I was afraid the OD clutches might have been burned up. So that would cause it to disengage? And to not want to engage? The light will come on on the dash panel, but nothing changes and it stays in direct drive. When I let the throttle out completely, THEN the RPM will drop and if I give it just enough throttle to maintain speed it will stay engaged. If I try to accelerate AT ALL it will immediately go back to the direct drive mode. All this while the dash light says the OD is on.
I guess what I'm asking is if burned up clutches would cause it to switch back to direct drive, or just slip? Because it is still engaged in direct drive. It doesn't 'thunk' back into DD like it normally does, just kinda slides RPM up until it's back in DD. I hope that makes sense, and it's what makes me believe it might be the clutch. Just want to make sure you understand what's happening.
Also, I really hope I didn't imply I didn't like all the information? I know there was an argument about too much info above but I love all the info!
EDIT: Just thought about this but I drove it to town this morning and engaged the OD. When I got there it smelled kinda hot-could easily have been from slipping clutches in the OD. The manual clutch is NOT slipping
Last edited by Bfenty; Feb 17, 2018 at 01:12 PM. Reason: more info
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 165
From: Nashville TN
2017 C4 of Year Finalist
Also, from my understanding, as long as I keep it in direct drive, I'm not really using the OD clutches and so it shouldn't cause any problems to just drive it in direct, now that I have the right amount of fluid? I only ever drive it around town anyway and not above 55 mph, really. I'm asking because it may be months before I can get the OD serviced.
Also, I'm wondering if it might be easier/cheaper for me to drop the OD out of my parts '85, as I know it is in good working condition, and put it into my driving '85. I've never dropped a transmission before so I have no idea how hard dropping TWO transmissions will be, but I intended to drop the OD out of the parts car anyway, so this might just give me some extra incentive. That way, at least, is probably free-just labor intense.
Also, I'm wondering if it might be easier/cheaper for me to drop the OD out of my parts '85, as I know it is in good working condition, and put it into my driving '85. I've never dropped a transmission before so I have no idea how hard dropping TWO transmissions will be, but I intended to drop the OD out of the parts car anyway, so this might just give me some extra incentive. That way, at least, is probably free-just labor intense.
Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.
yeah the light stays on. So the ECM is not disengaging it.
I was afraid the OD clutches might have been burned up. So that would cause it to disengage? And to not want to engage? The light will come on on the dash panel, but nothing changes and it stays in direct drive. When I let the throttle out completely, THEN the RPM will drop and if I give it just enough throttle to maintain speed it will stay engaged. If I try to accelerate AT ALL it will immediately go back to the direct drive mode. All this while the dash light says the OD is on.
I guess what I'm asking is if burned up clutches would cause it to switch back to direct drive, or just slip? Because it is still engaged in direct drive. It doesn't 'thunk' back into DD like it normally does, just kinda slides RPM up until it's back in DD. I hope that makes sense, and it's what makes me believe it might be the clutch. Just want to make sure you understand what's happening.
Also, I really hope I didn't imply I didn't like all the information? I know there was an argument about too much info above but I love all the info!
EDIT: Just thought about this but I drove it to town this morning and engaged the OD. When I got there it smelled kinda hot-could easily have been from slipping clutches in the OD. The manual clutch is NOT slipping
I was afraid the OD clutches might have been burned up. So that would cause it to disengage? And to not want to engage? The light will come on on the dash panel, but nothing changes and it stays in direct drive. When I let the throttle out completely, THEN the RPM will drop and if I give it just enough throttle to maintain speed it will stay engaged. If I try to accelerate AT ALL it will immediately go back to the direct drive mode. All this while the dash light says the OD is on.
I guess what I'm asking is if burned up clutches would cause it to switch back to direct drive, or just slip? Because it is still engaged in direct drive. It doesn't 'thunk' back into DD like it normally does, just kinda slides RPM up until it's back in DD. I hope that makes sense, and it's what makes me believe it might be the clutch. Just want to make sure you understand what's happening.
Also, I really hope I didn't imply I didn't like all the information? I know there was an argument about too much info above but I love all the info!
EDIT: Just thought about this but I drove it to town this morning and engaged the OD. When I got there it smelled kinda hot-could easily have been from slipping clutches in the OD. The manual clutch is NOT slipping
What you describe here confirms IHBD's thoughts. What you think is "disengaging" is not so but probably slipping. It sounds much like when you have to baby the throttle on a car with a burned out clutch. You are probably right on the edge of no OD whatsoever. Under limited throttle, the clutches are barely holding in OD. Upon increased application of power, the clutches slowing start to slip to the point of the sprag slowing reengaging, hense no "thunk" as it would do by the OD clutches actually releasing.
PS - I don't think anyone doubts your sincerety. I think IHBD was not directing anything at you.
Thread Starter
Drifting
Joined: Mar 2017
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From: Nashville TN
2017 C4 of Year Finalist
What you describe here confirms IHBD's thoughts. What you think is "disengaging" is not so but probably slipping. It sounds much like when you have to baby the throttle on a car with a burned out clutch. You are probably right on the edge of no OD whatsoever. Under limited throttle, the clutches are barely holding in OD. Upon increased application of power, the clutches slowing start to slip to the point of the sprag slowing reengaging, hense no "thunk" as it would do by the OD clutches actually releasing.
PS - I don't think anyone doubts your sincerety. I think IHBD was not directing anything at you.
PS - I don't think anyone doubts your sincerety. I think IHBD was not directing anything at you.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
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From: Nashville TN
2017 C4 of Year Finalist
I've edited my post about 10 times since you two responded.
I describe how the sprag grabs at 1:1 when the OD clutch slips.
I was pretty sure that fluid and pan contents indicated a burn-up. Probably smelled bad too.
My GUESS is that this began with a hanging thrust washer. That will cause the delayed engagement, BUT it also could prevent full application of the OD clutch. And without full application pressure, it will slip. Then the burn-up, and what you have now.
And no, the snide comments are not directed at the OP.
I describe how the sprag grabs at 1:1 when the OD clutch slips.
I was pretty sure that fluid and pan contents indicated a burn-up. Probably smelled bad too.
My GUESS is that this began with a hanging thrust washer. That will cause the delayed engagement, BUT it also could prevent full application of the OD clutch. And without full application pressure, it will slip. Then the burn-up, and what you have now.
And no, the snide comments are not directed at the OP.
For it now I’ll just drive without OD, and fix it when I can.
Thank you everyone with with all the help! I’ve learned a ton!
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Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.
that sounds exactly like what’s happening. Ok, so I think I understand the problem. Next up is to figure out how I’m going to fix it. Disassembly of the OD is probably out of my skill set. I’m thinking swapping in a known good OD is my best bet, just going to be time consuming. Man I wish I had a lift-anyone in the Tennessee area want to let me use theirs?
Thread Starter
Drifting
Joined: Mar 2017
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From: Nashville TN
2017 C4 of Year Finalist
There's one other indication of burned-up OD clutches: There is NO engine-braking when you let off the throttle. RPM's go to idle.
You can drive it in Direct. My only concern would be doing hard parts damage to an obsolete, hard to find unit. I know you have another OD unit, but....
One other thought I haven't brought up. My 85 developed an OD issue when it had about 7,000 miles on it. All of a sudden it didn't up-shift correctly either with the button OR after a forced down-shift with throttle. It was slow and mushy. Not right. Harry Mann Chevrolet drove it, and ordered a new OD unit for it. I still have the order slip. I really didn't want major surgery on my 5 month old car. Lo and behold it fixed itself. Everything was normal again. So I never let Harry Mann change it. I'll leave out how the OD clutches got burned up, but it was a valve-body problem that came back after Mr. Goodwrench worked on it a couple years later for an unrelated issue. The tech was cool, he fixed the OD and the valve body, and it's been pretty good until recently. The thrust washer hang-up is back, but I don't drive it much so I'm just letting it go for now.
You can drive it in Direct. My only concern would be doing hard parts damage to an obsolete, hard to find unit. I know you have another OD unit, but....
One other thought I haven't brought up. My 85 developed an OD issue when it had about 7,000 miles on it. All of a sudden it didn't up-shift correctly either with the button OR after a forced down-shift with throttle. It was slow and mushy. Not right. Harry Mann Chevrolet drove it, and ordered a new OD unit for it. I still have the order slip. I really didn't want major surgery on my 5 month old car. Lo and behold it fixed itself. Everything was normal again. So I never let Harry Mann change it. I'll leave out how the OD clutches got burned up, but it was a valve-body problem that came back after Mr. Goodwrench worked on it a couple years later for an unrelated issue. The tech was cool, he fixed the OD and the valve body, and it's been pretty good until recently. The thrust washer hang-up is back, but I don't drive it much so I'm just letting it go for now.
Thread Starter
Drifting
Joined: Mar 2017
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From: Nashville TN
2017 C4 of Year Finalist
Here is my suggestion. Since you say you have a spare unit, even if you think it is good, I would have a reliable shop open it up and check it since it would be a bench job. Put in new clutches and give it the once over. By the style of driving you describe, it will last as long as you drive the car. Then, either do the swap yourself or take it to the shop of your choosing and it is out and in in a short time.
Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.
Safety Car
Joined: Oct 2007
Posts: 4,426
Likes: 229
From: Pennsylvania
"Too much information" and baffling you with BS from a guy who's owned one of these for 33 years, has worked on it, and is trying to help. I had the exact same thing happen to mine. The overdrive clutch pack was fried, the light would stay on. When the OD clutch slips, the RPM increases to Direct ratio speed where the sprag grabs and it still drives the wheels, but in 1:1 ratio.
While I now totally respect your 33 year ownership (WOW) and your vast mechanical knowledge and workings of this old car,
I don't understand your obvious jabs at me and why you keep making smart comments about my "too much information" reply. I thought I explained my opinion easily enough. You must have had a car sometime where a mechanic fed you a whole line of baffling bullsh-t repairs just to make more money on a possible small repair if the car owner didn't know what was wrong. It happens. It happens alot. That's all I wanted to convey to the O/P. Especially on a Corvette as old as his. Instead you decide to take this as a personal insult and keep attacking my earlier suggestion. I just don't get it. I hope the O/P understood my first suggestion. We're all here to help each other. Even though we all don't all have 33 years ownership of a C4 like you.
Thread Starter
Drifting
Joined: Mar 2017
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From: Nashville TN
2017 C4 of Year Finalist
Le Mans Master
Joined: Aug 2017
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From: New Jersey
This is really making me want to top mine off....
If you were closer I'd lend a hand. Don't have a lift but have pretty much everything we'd need to do it.
If you were closer I'd lend a hand. Don't have a lift but have pretty much everything we'd need to do it.
Last edited by 84 4+3; Feb 17, 2018 at 08:43 PM.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
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From: Nashville TN
2017 C4 of Year Finalist
my buddy offereded to help me out once the weather is nicer.
While ive got the transmission off, I’ll probably do the clutch as well (it’s worn but not badly enough I’d replace it otherwise). Anything else I should maybe just do at that point? I’ve hear rear main seal is a good idea?
Im not looking to ballon the job too much, just thought it would be a good idea to poke around a little while the transmission is already out.
Thread Starter
Drifting
Joined: Mar 2017
Posts: 1,897
Likes: 165
From: Nashville TN
2017 C4 of Year Finalist
Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.