SkinnyG's 1977 Chevy Silverado

I haven't ever seen anyone balance brake drums before. It would seem that your aversion to vibration is similar to mine about oil leaks. 

-I've- never balanced drums before either.  You'd assume they -were- properly balanced, eh?

I hate driveline vibration, and I hate oil leaks too.  Been having a dickens of a time getting my TH350 to stop leaking.  Finally gave up with different 0-rings on the speedo bullet and siliconed the thing in.  Now THAT's dry.....

Do the easy thing and swap to discs. Impala SS rotors, 93-97 LT1 calipers and a pair of brackets to make them work. Done. Plus it weighs less. 

I'll do disc swap on the '61 with the 12-bolt I have for it.  Captain Fab sells brackets, but I'm sure I can design and CNC plasma cut my own at work.

How pronounced is this new vibration you speak of..........eye blurring??? Tailbone excruciatingly miserable? What? 

Oh no, it's not new.  It's been one of the nasty vibrations I've been trying to find.

It's like if the truck were a dog, and the tail was wagging too much.  You can feel it in the seat, and it kinda feels like a side-to-side wagging, at and around 80km/h (50mph) ONLY. There's nothing as you accelerate, then at 80 it's got the "wiggle-wiggle-wiggle-wiggle-wiggle-yeah" going on, and then it's gone.

It's kind of like a BADLY balanced tire, or a bent rim vibration, but it couldn't be found.

It seems to be gone now, but I need a few more days to be sure.  Last night I balanced the other drum which needed 0.75oz removed.

I've got to believe that all susp bushings have been addressed.....the drive shaft PROPERLY balanced.....engine/trans mounts addressed...correct??  

All suspension bushings are poly.

Driveshaft was new when I shortened the frame, and has since been re-checked. U-joints are routinely checked, and are currently Spicer brand.

Engine & Trans mounts have been both new rubber and new poly (using rubber trans mount now, poly motor mounts).

Pinion angle has been corrected.

Transmission mount has been raised.

You can bet no stone has been un-turned, but you can't argue with a drum that needed 3.75oz removed.

It's significantly better. But still ever-so-slightly there.

The other drum needed 0.75oz taken off.

Very happy with the new PCV valve (FV410 - empty with metered orifice).  MUCH less smell of burning oil.

A properly-functioning PCV also made it idle and run off-idle much better. It seemed un-tunably too rich for the longest time.  Also added a bit more fuel in the Q-Jet's APT.  I like it.

I might actually see an increase in fuel economy!

The truck started flooding out while idling in traffic recently. I figured the most likely culprit is the float.  Smack the carb with a hammer wouldn't fix it, maybe the float has taken on fuel?

Picked up a new brass float to replace the factory plastic one, but the problem is still there.

Checked timing next, and it's sitting at 36° at 3000, and about 33° at idle with full manifold vacuum advance. That seems normal.  Still idling in Drive at 650rpm and 8inHg. Gotta be needle and seat. Luckily I have an unused one.

Pulled the old needle and seat out, and stuffed in the new one, and it still was flooding out, just taking longer than before. DOH! The gasket slipped out and didn't get installed.  Took it apart again and replaced the gasket for the seat, and also checked the float level.

I -had- always been running the float as per Cliff Ruggles' Rochester book (great book, by the way) recommendation of 1/4" float level.  I have also struggled with a fairly rich off-idle, as well as flooding while parked hot (every re-start is a flood-clear). THIS time, I set the float to 15/32" as per GM for this carb.

WOW.

BIG difference.

No more flooding, for one, but boy the whole carb feels a lot happier. And I don't have to flood-clear at the end of work to go home. Interesting how this will be in summer.  If this danged extra-long winter will ever go away.

I did have to fatten the idle screws a quarter turn.  Interestingly, previously if the screws were a tick too fat (like 1/32 turn), tip-in was horrible, and if it was a tick too lean (1/32 again, very narrow window of "happy"), it would run-on and diesel.  Seems sweet now.  Yay!

In reply to SkinnyG :

Color me curious why Ruggles recommends setting the float level so high.  Was that for drag cars where he found that a lower level would uncover the main jets on a hard launch, or some similar application-specific reason?

I don't know.  Skimmed through the book again (I studied the book 4+ years ago when I built this motor), and all his "recipes" call for 1/4" float level. It might say in there and I just can't find it. It may very well be the jet issue and/or the wee float bowl.

He also doesn't recommend full manifold vacuum for the advance canister, which I prefer now that I've run it.

I'm ready for spring, but the snow keeps coming.

In the mean-time, the rear tires don't seem to last long on the truck (I'm surprised too), so even though it's snowing, I'm getting ready:

295/50's?

You bet!

I was running 275/60's for the past four summers, but at 30psi the centers wore down right quick.  Last two summers I ran 20psi to try and wear off the outers, but that wasn't happening quickly. We're wear bars on the middle 2/3 of tread.

I plan to do a better job of testing tire pressure on the 295's.

Fronts are still 235/70's, but if it looks visually too tall, I'd bring in some 245/60's.

SkinnyG your tire pressure conundrum is of great interest to me too. Currently running 275/45's on the 'V' . Am setting the pressure at 1+ above 'door guide' on the BFG SC2's, but with the last rotate I've noticed 'wear' in the middle at these PSI's. Not enough to run out and replace, but I am thinking droppingof PSI below 32 .....what say ye? 

AngryCorvair said:

In reply to SkinnyG :

Color me curious why Ruggles recommends setting the float level so high.  Was that for drag cars where he found that a lower level would uncover the main jets on a hard launch, or some similar application-specific reason?

Part of it is because the Q-jet has such a small float chamber that it's easy to suck the bowl dry.

He also recommends drilling out the fuel inlet and ditching the puny filter inside.

795NRG: I'd easily recommend 25, if not 20psi for a while and see.  It actually rode a WHOLE LOT BETTER at 20psi than at 32psi - it had been pretty bouncy in the back (much like too high a tire pressure, go figure). With the air ride low rider guys, the bigger the bag, the lower the air pressure needed at ride height.  Big tires = big volume = less air pressure.

I now have a tire pyrometer, and I'm not afraid to use it.

ShawnG: That was my main guess, but the driveability really suffered at 1/4".  I did have the larger size fuel inlet already in my Q-jet, so I merely tweaked the seat with an old ball bearing as per the book, but I switched back to a normal seat this time; I'm not really at full throttle all that long on the street anyway. I wasn't running the puny filter inside at all.

In reply to SkinnyG :

You need the 275/60's up front. 

For width, yeah, but they are almost an inch and a half taller than the 295's.  245/60's ordered last night.

SkinnyG thanks....the way these meats go from 32 to 44 per my ultra accurate in dash monitor thingy while on a long stretch drive .......I'm game to drop the PSI for the tread wear.....and see where this goes on my next trip back to H'town from B'Ham....

It was going to be rainy today so I took the truck to work (V8 Firefly doesn't have an effective defrost, and now has a leaky header gasket which I can't stand listening to), so I checked tire temps on the way.

Was about 40°F today, and the 295's were 62° - 62° - 63° at 23psi. Pretty good guestimate, eh?

Fronts (245/60R15) could stand to go up another 2psi or so.

Also fueled up today, after running the lower float level.

Mixed highway & city: 44.7L, $70, 128.6 miles.

Works out to about 13mpg (UK), 11mpg (US), or 21.5L/100km, depending on which way your door swings.

Not bad, really, considering lumpy cam (idle at 8inHg), 2500 converter, 3.73 gears, no lockup, no overdrive, Rochester carb.

First tank on the new engine for me netted 14.7mpg. Considering the same type of driving before was between 9.5 and 10.5 I consider that a win.