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Old 05-16-2006, 10:17 PM
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Turbo 350 Shifting Problems

I've (been) driving a '75 Chevy G20 Camper-Van (3/4 ton) with a Turbo 350|350 Automatic 4B, and have been having a few problems lately. It's not exactly anywhere near a hotrod, but I'm restoring it just the same (it's very clean to begin with, and sleeps four . I'll be as specific as a I can, and ANY suggestions are appreciated.

The transmission is stock, and has about 90,000K on it, (but I hear they can last much longer than that.)

I was driving on a short trip out of town last weekend, and about 5 miles down the interstate it shifted from 4th down into 3rd, and wouldn't go back up. Another mile and it shifted down and stayed in 2nd. It would get up to the point where the 2-3 shift should be and just rev. I backtracked about 15 miles down back roads (and lots of hills) to get it home, and no change.

It did not loose ANY fluid. It did have an ochre color to it, though. No odor.

Since I bought it about a year ago I've put about 5,000 miles on it with no shifting problems/leaks at all; everything has been smooth with the exception of the U-Joints, which have been replaced. P/R/N/D and 1-2 is still working fine.

*The vacuum modulator had blown, so I replaced that (with a slightly used one off a rebuilt 350 I've been keeping around for the occasion, but without the tools to put it in), and thoroughly cleaned out the line and the connection to the engine with carb. cleaner. There was trans fluid in the lower part of the line, but it did not at all appear that the fluid had made it up to the engine.

It did appear that it had mixed with the grime that had been in the line, though, so I replaced what fluid I could drain (which was a bit murky, but not unusual), the gasket (which still looked good) and the filter. I'd done this when I'd first bought it a year ago, and there was a little bit of gunk that had accumulated in the bottom of the pan since then, but no metal shavings to speak of (either time).

There was no change. Still revving at the 2-3. I just gave it a go earlier tonight and it gave a slight "kick" when I hit the gas hard (I was getting impatient), but still back at square one.

I also manually reset the clutch. I guess I'll note that one of the springs is slightly stretched about 1/2".

The engine is completely clean, and runs smoothly. I've put on about 600 miles since my last change and the oil is clear and at the level it should be. The firing is fine, though the timing may need reset. This shouldn't be the problem. The cooling system is also clean.

I don't know much of anything about what to look for when it comes to the governor. That's a bit more delicate than what I'm used to. That and the fact that all the work I do is outdoors because my garage door doesn't have 9' clearance I have to assume that the problem started with the modulator, and that I might be missing something related. Any help is appreciated.

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Old 05-16-2006, 10:34 PM
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I am going to go out on a limb here and say it is not a simple fix. I think the transmission is "DONE". Take it to a shop and have it rebuilt.

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Old 05-17-2006, 06:19 PM
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More Information.

This is a three-speed, not a four (my mistake).

I assume the 3rd gear is about 50mph, (correct me if I'm wrong), and my trouble is after 30mph (2nd gear?) New modulators are cheap, so I put one in today and I can now feel it shifting into 2nd, but thereafter it revs (but I can go about 15mph faster). This makes me do a double-take on the situation; it's not much fun to pour money into something if it's not absolutely neccessary.

There's an unsual "hiss" to it, and this sound has happened before on a rare occasion with both the van and my nova, but I assumed it was just the carbs. being mal-adjusted, which I haven't gotten around to messing with (on the van, it likes to kick in all four barrels all the time after 45mph.) Now this noise is more sporadic and will even keep up after I've let off the gas. Any ideas on this?

I've already scheduled an appointment to have the rebuilt checked out and put in next week, but I figured it was worth a shot finding some experienced/varied opinions. It hasn't been easy finding someone local who actually knows how to troubleshoot before doing the overhaul.

Much appreciated, at any rate.
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Old 05-18-2006, 04:18 PM
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I've concluded that it's the third gear clutch. Eh. It happens.

It's old and very standard, so won't cost too much ($200) to have someone do the job on the van, even if it is an automatic. Never had much trouble with trannies up 'til now. Everybody's gotta learn sometime.

More on the Nova: '79 Rally, (not really a muscle car, but apparently more rare than a Delorean), clean mechanically, body needs work. I'm just going to do what I want to it; it's damn near impossible to find the right Nova parts, especially with 2-doors, so there's not much hope of restoration.

It's currently in several pieces due to some idea I have in my head that involves replacing the rear end with that of a '77 hatchback, giving it crazy suspension, and a medium block engine (which would involve another tranny anyway; currently has a 305, which still runs good).

Interior is gutted and ready for some truck bed coating, everything else refinished in black, and hopefully leather seats to match.

Finishing it off with no paint, just primer with black stripes (vinyl, currently brown with gold stripes). Might put a big jolly roger on the hood, though

Last edited by Lepidus; 05-19-2006 at 01:39 PM.
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