Towing with my '74 C-10

[roundhouse]

The Gear ratio should be on your SPID sticker.

Gearing is really the key here.  i tried towing a chevette and open 16' car trailer with 2.56 gears.    You can't.

Truck really struggled up hills and had difficulty maintaining 65mph.

the  ratio it left the factory with will be on the glove box if the glove box is still here and hasn't been swapped and the axle hasn't been swapped at some point


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[egleaves]

I've been searching for the axle code to no avail.  It seems like everywhere is should be, it's not.  I did the "spin the wheel and count the driveshaft rotations" check, but the math is rough.  I still want to verify the ratio with some certainty.  If I can't find a code, I'm just going to have to pull the diff cover.

Here's my SPID sticker.  Does anyone see something I'm missing here?

BTW....I appreciate all of the responses and comments I'm getting here.  It's been a big help.  Thanks.

[egleaves]

By the shape of the pan, I was able to verify today that I have a TH350, not a 400 as i had previously thought.

[Stewart G Griffin]

Ok, i guess not all SPID stickers have them.

Another thing you can do is bring your VIN# to a dealer and they can look up exactly what gear ratio you got.   3.07 was standard for your combo. With 3.40, 3.73 and 4.11 optional.

[roundhouse]

Assuming It hasn't been swapped at some point in t
he last 40 years

Only way to know for sure is remove the cover and count. Teeth or see if the number is cast into the gears


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[Irish_Alley]

How to determine what ratio you have without removing the cover

[Stewart G Griffin]

i would bet money it hasn't been swapped.

Since the SPID sticker did not indicate any axle options, then i'm going with 3.07.

[egleaves]

Ok. It's been a while since I brought up this discussion, but now it's real.

I went ahead and had a local GM dealer install a turn key, Vortec 350 crate engine (PN 19210009).  I'll try to get some pics posted.  I had this done back in September, drove it a couple thousand miles, and then started towing the camper.  Keep in mind that every component of this engine is NEW, not rebuilt.

Pulling the camper over the mountains of WV was a challenge.  I almost burned up the trans, but the engine ran well enough.  I'm now 7 weeks and almost 4000 miles into my cross-country adventure and she's developed a bad stutter under load.  With or without the camper, but it's most obvious with.

Here's what I know, and what I think.

The only thing I have done to this engine  since it was installed is minor adjustments to the base timing.  I don't know exactly where it is since I've been timing it by ear for a couple of weeks.  Probably 6-8 BTDC.

The stutter is very pronounced on a hill, in third gear (3spd auto), pulling the camper.  Kicking it down into second clears the stutter and pulls fine.  If it shifts before the top of the hill, the stutter is right where i left it.

Even without the camper I might pull out into traffic with my foot in it, but I get a hesitation and/or backfire before it springs to life.  Once it comes to life it runs like a scalded dog.

Once in a while, under light acceleration, I can feel the stutter quit and the engine comes to life.  Briefly.  This is leading me to a few possibilities. The cap and/or rotor are shot and I'm just not getting good spark, my vacuum advance isn't working correctly, or I've blown the power valve.  Or a combination of any of those.  Also, the vacuum advance is connected to a port on the carb.  I've read that it would be better to connect it directly to manifold vacuum, but that means I will have to install a port on the manifold.

I don't think it's fuel issue....if I had a fuel delivery problem it still wouldn't run well in second gear at 4000+ RPM.  It seems to get plenty of fuel, but can't use it all at certain times.  Overall fuel milage doesn't seem to be affected so you'd notice.

My next move is to pull the cap and rotor to see what they look like.  If that looks good, i'm going to switch my vacuum advance to a manifold source.  Any other ideas?

[blazer74]

Basic tune up first

[Irish_Alley]

one thing you might find is the gas switched from a summers blend to winter. i dont know what you might or might not have to do or even if it can cause your problems but its another option

[zieg85]

Pull and check the spark plugs.  Wrong heat range and timing could cause premature failure.

[Captain Swampy]

http://www.gmperformancemotor.com/parts/19210009.html

Are you running the 92 octane gas? Looks like a great engine, but for towing it could probably use an RV cam. Really to bad they didn't use a roller cam.

[egleaves]

I always run high octane gas.  I asked when I bought it if I could choose a different cam, but the engine was already built and there weren't options to choose from.

[Irish_Alley]

can you hear any ping or is it just a hesitation?

[egleaves]

Just a hesitation that sometimes feels like a dropped cylinder or bad timing. I had a slight knock a while back after advancing the base timing a bit.  Dialed it back a little and it went away as expected.  These are the timing adjustments I have been doing "by ear".