My '77 with L-48 engine and TH-350 tranny has some shifting problems. I've checked corvettefaq and found nothing. It seems to do very well on take off but will not shift until the throttle is lifted. Then if the throttle is opened a good bit it downshifts and the engine revs away until throttle is lifted again. I changed the modulator and it didn't help. Today I thought something may be wrong with the kickdown cable and disconnected it. When I dove the car I found that is seems to be shifting from first to third gear, skipping second. If it is put into second manually, it just seems to slip and the engine revs away. This is the case no matter if up or downshifting into second. Could this be a blown valvebody gasket? I know almost as much about transmissions as I do about building jet airplanes (nothing)! Really lost on this one, suggestions please.

 

Get Ron Sessions book called Turbo Hydra-matic 350. It is THE book to have when it comes to these bad boys. But be ready to do a LOT of reading. That boy reallly covers a subject thoroughly.

 

A Lot of reading is cool with me, I'm an information junkie. Thanks for the tip!

 

It's hard to diagnose without actually driving it myself but the first thing I would do is check the fluid level and the strength of the vacuum to the modulator. There is a restrictor on the line itself up on top at the engine. That can become clogged. You can cut this restrictor out of the line if it's there. The rubber hose could be cracked up top or at the bottom. It should be connected to the intake manifold vacuum port since this is where the strongest vacuum is located. Second gear is operated by a clutch pack if not in manual second. If in manual second it uses a band. If the modulator, vacuum signal and fluid levels are okay, it might be the accumulator spring in the servo on the pass. side. It might be a stripped governor gear on the driver side but then you'd have no third gear either. Valve body gasket seldom "blow" or at least I've never seen one blow. The sense that the trans. is slipping while in second may be that it is simply still in first gear. Pulling the pan off and looking at what's in the pan may reveal how serious things are. A thumb nail sized deposit of gray material (normal wear) is not unusual if it's been a while since the pan was off. Pieces of clutch or band material (looks like brown pieces of thin paper) though indicate it's time for an overhaul.

 

If you've lost second gear, I can almost assure you that you need to pull the tranny and rebuild it - it has likely smoked the clutches. Pull your tranny dipstick and look at the fluid color and smell it. If the fluid is brownish and smells burnt, you need to tear the tranny down. If it's bright red and smells like regular tranny fluid, you may be able to save it with a stuck valve body component.

 

While most of the above suggestions seem appropriate, I'd start with the vacuum hose. Very cheep, very easy and very fast. If this doesn't solve the problems, then work down the list.

 

I agree. It sounds like a vacuum leak. Check the line on the passenger side at the transmission. There is a rubber boot that presses into the transmission. I knocked mine out by accident once and it acted just as you describe.

 

I'm going to check the things suggested, pretty sure the fluid is not burnt. Haven't smelled it but it looks just like new. Still going to give it the sniff test just to be sure. Will advise of the findings in a bit.

 

Check the stupidest simplest stuff first... cuts down on bills and headaches!

 

Yep............the K.I.S.S. method (keep it simple stupid). Checked the fluid, not burnt. Hose is connected to modulator, no problems there. Hooked up vac gage to steel line going to intake and vac bleeds off very quickly. The only thing I can think of to cause this is the steel line being cracked between manifold and modulator. Bleeds from 15 to 0 in about 3 seconds, could this be the cause of the shifting problems? If so, why would it only seem to affect second gear?

 

Ttt

 

Hrm.. when I last remember driving my car (a good while back - before I stripped it down).. I had the same problem with my automatic- it takes too damn long to shift out of first to 2nd! My boot on my transmission shift control cable is basically non-existant.. I wonder if this is the problem (how exactly does this boot work - I thought it was just to protect the cable or something)? Also, where can I find this boot?

Edit: I'll post a pic later on tonight of what I'm talking about.

 

I think lars is right (as usual)...

if it just a missing/disconnected/leaking vaccume line, you can normally put the car in low and it will shift when done so manually...

 

What about this.. could this be causing a problem?



Please excuse my transmission leaks... I'll be getting to that soon enough

 

Just rebuild the whole thing and go on with your life....smoke a Mustang, you'll feel better!

 

Actually, rereading his previous post... my problem is different from his in that mine shifts into second fine manually - just doesn't do it automatically.

- Michael

(sorry for hijacking the thread but what could be the cause of this?)

 

if yours shift fine manually, then the vaccume line from the engine to the passenger side of the tranny probably came off/loose/or broke..........