sk87

So, I bought an 85 about three weeks ago, and long story short, without really understanding what the 4+3 transmission was all about, I bought the car and later come to find out the overdrive is not working (i deserve any berating that follows for my retardation).

Here's my symptoms/current status. The manual part works very well; shifts are smooth and easy, and goes into reverse with no problems. The light on the dash comes on when I activate the switch (console). However, instead of down shifting into overdrive, RPMs stay the same, but when the accelerator is released, it freewheels (no resistance/deceleration from motor) and drops to idle speed. As pressure is applied to the accelerator, rpms increase, but does not engage drive line until the engine and tranny speeds are matched. Forgive the terrible explanation...

Funny thing is, I had a 1998 Monte Carlo that did the same thing in overdrive. I seem to recall it had something to do with clutch packs or some other wizardry that I haven't the faintest understanding of when it comes to automatic trannys.

So, my impression is I'm looking at a failure of an internal component of the OD. Does this seem correct?

Assuming that's true, what will be my cheapest way of getting my overdrive back in service? I am a novice, but I am willing to turn some wrenches. I do not have a lift though.

Could I just buy an OD unit and take it to a shop and have them R&R it? How familiar are shops with these transmissions? Would that be cost effective?

Not having that OD is going to kill me on gas. 3000rpm on the highway = bad times.

Thank you for any help!

vetteoz

"If the light comes on and the unit freewheels that means the overdrive is burned up. This is a common symptom. The clutches for the overdrive are slipping so it reverts to a direct mode with a freewheel condition since the sprag in the unit is not locked."

Few shops knew how to work on them when they were current

Brian at SK Speed
http://www.skspeed.com/

has been the 4+3 builds and parts go to man for CF members for years on but there was recent talk he was getting out of doing them.
Worth a shot

Another 4+3 contact is
http://www.pipersauto.com/4speeds.html

sk87

Thank you for the info. So if I buy a new OD unit, is it even in the realm of possibility for me to do myself with a decent set of tools but no lift?

vetteoz

Dropping the trans out while on the car is jack stands is no biggy

The factory service manual (FSM ) for your year would be a aid into splitting the O/d from the 4 spd case and reasembly

This article is more on how to rebuild the unit
http://www.corvetteactioncenter.com/...t#.UnGqJVNNW34

sk87

In your opinion, would i be better off rebuilding it myself or buying a new or already rebuilt one whole. Keep in mind my utter lack of experience with transmissions.

ProjectC4

I have a 4 + 4 in need of some work, too. Spoke to Brian at SK speed in Long Island, NY 2 weeks ago. He's still doing them. Quoted me I think 2,500 for both units, 1,400 or 1,500 for just the OD unit. He was working on his 900th or so unit when we spoke. In think he is the most recognized rebuilder for that transmission there is.

sk87

Good to know he's sell doing them...

anyone know... Will i have to remove the entire transmission, or will i be able to pull and swap just the od unit? Estimated time to R&R? Trying to plan this before i dive in

c4cruiser

You're going to have to pull the entire unit.

If you don't have th expertise or the tools, you would be better off by having the work done. Many shops have access to online repair guides (ALLDATA is one system and their sections on C4's are duplicates of the FSM) so it may be worth checking around with some reputable shops that have experienced transmission techs.

sk87

Well thank you for the input everyone... Now I start my search for a shop that's not thing to cause more damage than they fix. Sigh...

vetteoz

You could ask Brian to recommend someone local?
I'm sure he has sold parts to trans shops that work on 4+3's as well as the members here.

frank j. moran

That is a good idea. My personal experience having done two of these units is getting hard parts. In both cases I had $500. in parts tied up in each unit, they are really not hard to repair if you follow the manual. If you cannot do it yourself and you can negotiate a price with Brian in the long run you will be better off. My last one I bought parts from Brian. I can almost guarantee you will need the large thrust washer, annular bearing very possibly the front adapter plate, a soft kit with clutch plates. My first one also required a pinion gear. Luckily I know Dave Fulcher and I picked through his old parts stash and salvaged a set. Good luck, let us know how you make out.

DanielRicany

If you don't care about it not being stock, since it's coming out anyone, maybe considering swapping in a ZF6? That's what I'm doing when mine blows up!

sk87

That would be ideal, but I think that's more of an investment than I can make right now :/

sk87

Just wanted to follow up and say thank you for all the advice especially the hookup with Brian at SK. He was super helpful and immensely knowledgeable. For reference, the rebuilt OD unit from him was $1250 + core. Found a local shop that R&R'd it and she's working great. Like a totally different car, and driving down the highway is not breaking the bank.

One more quick question if anyone has any ideas... The OD switch (on the console) is on it's last leg... there are cracks in it, and it flexes every time I activate the OD. It is any day before it comes apart and gets pushed down into the console. What can I do to repair this switch? I don't care if it is stock or OEM necessarily. I don't know much about electronics so any help would be great!

Thanks again.