Hello again,

I thank you all with your help the other day with my starter issue... it turned out to be a relatively simple fix, thank heavens. In light of that, I decided to come back here looking for advice on my transmission as my car has had all sorts of transmission issues over the 4 years I have owned it... but its never, "not worked", so I have never really bothered to do anything about it. However, I would like to look into fixing it as all the issues it has do drive me nuts... that and I have basically been sitting on a repair price time bomb that I would like to get fixed when I can anticipate the price rather than all of a sudden when I will end up needing the car the most (as thats how it always happens)

My car is, from what I can tell, a bone stock 84 Auto. As far as I know this means it is a 700R4 and throughout the years, as I have gathered from a lot of reading, the appear to have remained fairly similar from vehicle to vehicle they were put in. The main difference I can surmise is that the ones for Corvettes had different valving for more aggressive shifts and they had a different tail housing (which might be able to be swapped from transmission to transmission?). Naturally I am not pretending to be an expert on any of this... this is just what I have gathered... none of it may be correct at all, and if not, feel free to correct me.

Anyways, my particular car, according to the previous owner when I bought it, has had both the engine and transmission swapped. Somehow he blew the previous engine, and then proceeded to have his mechanic swap not just the engine, but the transmission as well (he thought that blowing the engine might have somehow damaged the transmission, so he decided to swap it and not take any chances). He made some comment about the transmission being out of a newer car because they have 32 splines or something in that nature, so he had his mechanic do this because it would be stronger. If this is the case, I currently have no idea how to find this out. The only evidence I have that it is definitely not the original transmission is that the speedometer is about 8mph off at 70mph... so at 70mph, the gauge reads 62mph. This seems to be the mechanics only oversight... ended up getting me pulled over the first day I owned the car, but luckily, since I was very honest, the cop understood and believed me.

All that being said, whichever transmission the mechanic swapped in was either a dud or just adjusted really badly. When the transmission is cold, it never wants to upshift at all... the thing will hold onto a gear until 3500 to 4000 rpm before shifting, and when it does shift, it slams those shifts. This sounds like an improperly tuned TV cable. Let the transmission heat up some, and the shifts smooth out a bit and start to happen at a normal rpm... roughly 1200 to 1800 rpm (this all is at just normal driving conditions... nothing hard, crazy, or fun). Kick down under throttle seems to work fine, and TC lockup engages just fine in overdrive at the proper speed, (usually around 40 to 45 mph). Let the transmission get heat soaked (full operating temperature I would assume) after 45 minutes to an hour of driving, and the transmission starts to shift goofy again, but the opposite of what it does when its cold. At full temperature, the transmission shifts very early. It has no qualms about jumping to higher gears, and if you go to accelerate, occasionally it will just jump straight to 4th (OD) and lock the torque converter. Naturally, chugging around at 600 rpm isn't really great for the car, so when it does this I usually just grab the shifter and slide it back down into an appropriate gear for the speed (second or third, take your pick). When its this warm it refuses to downshift unless you come to nearly a complete stop, you are at full throttle, or you decide to downshift it manually yourself... naturally this isn't ideal.

As if this wasn't enough, it has more issues. When the transmission is this warm, if the shifter is in overdrive and you go to accelerate (highway passing speeds, so 70 to 80 ish) the transmission will slip in 4th gear and refuse to downshift into third. So I pop the shifter back into third, match the rpm's for the gear change, hit the gas, and everything locks up and the car takes off... no real issues. Then once I get up to speed, I can just slot it back into 4th and it will drive just fine. Above a certain speed it doesn't slip at all... but most times those speeds are frowned upon, so I will leave them out here.

Finally, to round it all off, this transmission also, "freewheels", or at least thats what I call it. This is my most hated problem with this transmission at the moment. Most cars, automatic or manual, you let off the gas, the engine is still engaged, so the car will use the engine to slow down some. Simple enough. My transmission, for whatever reason, does not do this. No matter what speed your going, unless you are in 4th gear (as that's the only one that seems to hook up), when you let off the gas, the engine will fully disconnect from the transmission and just return to idle. So if you are just coasting along and you want to accelerate, you need to gently bring it back up to the rpm you think it will be at (as you have no idea what gear it has decided to be in while you were coasting) so you don't shock load the system, find that rpm, and then accelerate as needed once everything has connected up again. Over the years I have come to find that this can be caused by dead, "overrun", clutches... but that's all I know about them. I have never found anyone talking about this happening in a Corvette, and only ever found one thread of a guy talking about his pickup doing this after he got the transmission rebuilt, and the guy messed it up...

So, what am I hear for... well... advice. I personally think that this thing is going to need a new transmission or a rebuild at the very least. Any suggestions would be fantastic. Price wise... I am not really too concerned about anything at the moment... I have tried looking for ideas as to what all this could mean, prices on transmissions, all that fun stuff, but when you search, most of the threads are 10+ years old (no, I'm not kidding) so in that time, something that may have been common to get back then might be scarce now. So I am just looking for modern advice. Should I rebuild it? Swap in one from a junkyard and risk it also being messed up? Just go for a new one and make some performance mods while I am in there? (higher stall converter or something) Anyone do something like this to theirs recently that has a rough idea what the price was?

Any advice is good advice, and I am not in a hurry on this at the moment... I am just trying to plan my course of action for the future. This is my daily driver (even if I have other cars) and has served me fantastically so far, so fixing it right and not messing this up is kind of my goal here.

 

Thanks for the response... I can see how this would be a TLDR... Sorry about that. I have gotten better at it then I used to be, but it is getting better. If enough people tell me this enough times I am sure it will knock me down to normal post lengths. That said I will try to shorten this one up as well. Thank's for reading anyways, I definitely appreciate it.

Thank you for all the information, I definitely appreciate it. That cleared up a lot of things for me that I thought were potentially broken on this transmission.

I had no idea that over-runs were only active in D1, D2, and D3. I just figured it would work like most normal transmissions and be connected in all gears all the time. That is good to know, because if I would have swapped in another tranny and it did that same thing again, I would have thought I had gotten another dud. Definitely explains why I couldn't find anyone else complaining about it as apparently thats how its supposed to work.

Currently the only gear that the over runs work in is D4 when it shifts up into 4th gear. This sounds like it is actually normal operation from what you have stated, so that's good. However, in D1, D2, and D3, the over-runs don't work either. In D1 you can almost feel the slightest bit of resistance the first time you engage it and let off the accelerator, but after that, there is nothing. The rest of the gears, there isn't even a hint of resistance.

Again, thank you for all your information. It is very much appreciated, and over the next few days, I will try to get under my vehicle and see exactly what I have in the car so I can proceed from there.

 

The transmission is designed to only freewheel when the brake is depressed. That way there is no momentum working against the brake. I would suggest you have no cruise because it sounds like your pedal is resting on the unlock tc(if you will) switch. That is worth a check. If you have done the booster you will know what I mean. They are adjustable. Also I just went to the Corvette Mechanic(Canoga Park) to get advise about the TV cable. .
The thing has much adjustment, I push the throttle with my foot all the way. Keep in mind you may be able to open it more by hand. Use the pedal and mark how far it is going. Then put the throttle there and make sure
the button is pushed and you are pushing or pulling the inside rail of the cable to make it tight at your most forward throttle position by foot measurement. That is how I finally got mine perfect after my rebuild last year .
If you pull the rail out it will tighten, IIRC. I could not get the push the button and floor it thing to work at all. Good Luck!

 

That statement is totally incorrect. The switch on the brake controls TC lockup(+) and has jack to do with the overrun clutches. IHBG described it correctly above.

 

Well that is how mine works i can tell when driving. When on freeway and I can tap the brake and feel the TC unlock and it lasts a few seconds then connects again.
If it was doing it all the time may present a problem. Just another check.

 

What you are describing is an entirely different scenario than what is being talked about in this thread. What you describe does happen. Sort of. When the TC clutch disengages, it does not "freewheel" as you state.(otherwise, the car would come to a stop) There is still a fluid connection to the engine, just not at a 1:1 ratio. What is being discussed here is no engine braking. This involves the overrun clutches as has already been noted.

 

I realize that his transmission may be defective I was just giving advise on adjusting TV cable as my 700r4 was slipping in 4th gear under load. It took me
a couple of tries to get the cable just right. Mabey time for a rebuild.

 

You forgot to mention the accumulator.
since he didn’t have a trans without it, he never felt the car jerk into gear.
i changed my 86 trans to a 91 firebird 700, and was amazed at the difference!
i used to dread putting it in Gear.
i did have a worn band or stretched band problem, and bought a longer servo pin, resealed the servo piston, and readjusted the tv cable, and it works pretty well.
i had to change speedo gear for vss, and housing, and don’t remember much else as it was 10 years ago.