Tranny Slipping in 3rd?!

[Ludigdrums]

My '81 has the stock 350 Tranny (as far as I know), but all the computer stuff has been removed. The trans always seemed strong to me, it's just that it was always very lazy shifting, and couldn't decide what it wants to do at part throttle. I'm assuming this might have somthing to do with the lockup not working because of the missing computer?

The problem is, just last night I merged onto the parkway, and when I got into 3rd gear it was fine until like 60-65 the tach started reving without me moving any faster. It's like it wouldn't engage.

I've never had a transmission slip before, so I don't really know if that's what this is. I have a strange feeling that it might be vaccum related. Is that possible?

As I said before, it always took its time changing gears...very slow and smooth...not exactly what you'd expect in a performance car. I usually manually shift also because when you floor it, many times it won't downshift.

What do you all think? 1st and 2nd are fine, and it only seems to be 3rd above like 60mph. However, it seems like I can get it to engage by quickly stabbing the throttle in a short burst. I don't know.

Thanks in advance.

P.S. Just had my highest ever gas bill...$61.21 for 21.113 Gal of Amoco Premium!!!

 

[jdp6000]

Is it the tranny slipping? When it revs does the car excellerate? If the speed remain the same and the RPM's go up I would say 3rd is slipping. What color is the tranny fluid? Is it burnt?

Jim

 

[Ludigdrums]

The car doesn't seem to accelerate, although maybe a little. It doesn't rev the same way it would in neutral, and actually has a cool sound to it.

The tranny fluid is fine, and funny thing, I just checked it before I went out last night.

- Jeremy

 

[gmjunkie]

Vacume Modulater on trans can couse this Problem! Or a leaking Vac Line!! On a Tubo 350 & 400 gmjunkie!!

 

[Ludigdrums]

How do I go about checking those things?! - Jeremy

 

[jdp6000]

I've had trannies go. You'll know. Basically when you hit the gas the RPM's go up but speed doesn't increase. It may only do it in one gear at first but will progress to all gears. If the transmission is slipping you will notice a decrease in speed but not RPM. So in your case it doesn't sound like its slipping. It probably needs servicing. The old turbo transmissions are easy to work on. Bring it into a shop and get them to tune it up. Not just change the fliud. Drop the pan and do the full 9 yards. Maybe throw a Shift Kit into it. I had mild one installed in my 77 and you really felt a difference when you floored it.
Jim

 

[Vettehead Mikey]

If you want to save a few bucks and your engine is still stock or near stock, switch to regular gas.

Your engine does not need or benefit from using super/premium.

 

[wishuwerehere82]

Vacume Modulater on trans can couse this Problem! Or a leaking Vac Line!! On a Tubo 350 & 400 gmjunkie!!

I agree with the junk, as usual. Vacuum modulator is sticking, keeping the 3rd clutches from engaging fully. The Vacuum line is steel and is one piece from the Intake manifold to the transmission vacuum modulator. There is rubber tubing on both ends to connect it. Check for leaks or pulled loose hoses. If not, replace the vacuum modulator on the transmission and change the fluid.

 

[Ludigdrums]

Well, I changed the Vaccum modulator and made sure the rubber was not leaking...and unfortunately still have the same problem. I also check my vaccum from the manifold and it read 20 at idle.

To further detail the problem...it seems like I can sustain my speed in third, and the RPM reads what it normally does, and I can also accelerate, very very minimally. The second I ask for too much the RPM flies up.

Is this definitely the trans? I still feel likes it not (hoping also), because the trans always seemed to shift this way, the only difference is now it's not engaging 3rd.

Could it be TV cable, torque convertor? Both of those things I would think that I would have the problem in the lower gears too?!

Any other ideas?!

Much appreciated as always!

- Jeremy

PS Vettehead...that is a good point, and I used to use regular...but I've got my timing pretty advanced so I thought I'd be on the safe side. But next fillup, I'm going Regular and hope not to hear any knocking.

 

[wishuwerehere82]

My advice is to drop the pan and look at the fluid. Now that you have eliminated the obvious stuff, you have to see if your clutch packs are worn out. If the fluid is dark brown or if you see any metallic particles in the fluid or if it smells burnt or metallic then your clutches are worn down to the backing plates and need a rebuild. How many miles are on it?

 

[Ludigdrums]

As far as I know, and if the mileage is correct, 75,000 miles. Thanks for the advice...I guess that will be the next project! ;-)

- Jeremy

 

[black_81_vette]

Well from the sounds of it you have a direct clutch seal going bad for the apply pistion. Simply put the seal gets hard fluid gets past the seal and slippage occurs.I seen this happen quite a few times and the vac modulator wont cause a slip condition when bad just a delayed up and downshift with harsh shifts.So If I was you drop the trans and do a seal and clutch job on it . One thing else too,if you do not want the lock up feature most trans shops have older units that dont have the lock up junk,or they can install the proper parts in your trans.And make sure if you go that route you change the convertor it wont work with a non lock up input shaft ect.

 

[Ludigdrums]

So, as a last ditch effort I put a $12 bottle of the Lucas Tranny stuff just to see if it might do something. Well, it didn't...although I don't blame the product, I probably (as you've said) have physical internal problems!

I drove it a bit today and it seemed as if 1st and 2nd were much more ballsy. Could this be possible?! I don't think it's my imagination, could this be?

Although I would rather not spend the money now, I would like to go the 4 speed auto w/overdrive route. Especially since I have the stock 2.87 rear.

Any tips?!

Thanks!

-Jeremy

 

[wishuwerehere82]

You could upgrade to a 700R4 but without the computer to control the torque converter lock-up, it would run without the lock-up.

 

[Andy]

Check out this for the 700r4

http://www.700r4.com/

Andy

 

[81 Corvette]

i agree on teh gas thing...no need to throw premium at a motor with 8.5ish compression

just wasting money.

good luck on the tranny. you put an OD in with those 2.87 and that thing is gonna love the highway.