Preparing truck for towing

[TrybalRage]

Hey everyone, I have a 1985 C10 long bed, 305/TH350c with 2.73 gears according to the glove box sticker. It also has the HD brakes for that year, so the thicker discs and slightly larger drums in the back. It also has the factory tow bumper which is stamped for 4000lbs trailer/400lbs tongue weight, if I recall correctly.

I had the transmission was rebuilt a few years back when I bought it, not sure of any details but it has nice firm shifts. Probably less than 5000 miles on it. Engine runs Ok but it's 100% stock so it's a gutless vintage 80's motor.

I am planning on getting it into shape to tow my 17' center console boat, which when fully loaded with trailer is ~2500 lbs., so it's not a ton of weight. I'll be towing up to say 150 miles each way (with lots of hills) depending on where I'm going fishing or crabbing. The trailer does not have brakes.

With the 2.73 gears my truck is a dog on hills as it is, so first thing on my list is to get them changed out. A local driveshaft/rear end place quoted me ~$1400 to change the gears to 3.73 and add an Eaton Posi along with all new bearings and what not. I asked for a limited slip since I'm concerned about slipping on a wet ramp with 2WD. It seems a little high but labor is what it is and I don't have the knowledge or tools to attempt this work myself.

Any opinions on gear ratio or differential choice?

I also want to add an external transmission cooler, and a dedicated frame-mounted receiver even though the numbers work for my planned load.

Anything I might be missing? Any other recommendations? At some point, maybe next winter an LS/4L60E or 80E swap might be in the works, but not yet.

[biketopia]

Sounds like you have a pretty good list. The quote on the rear doesn't seem too outta line, 3.73 is a great ratio especially for towing up hills. Trans cooler in tandem with the factory cooler so the fluid stays at an operating temp is good. Good wiring hook up, don't use scotch locks, heat shrink butts or cut and solder the wiring. Other than that fresh trans fluid and make sure the engine is running the best it can with good plugs, wires, fluids etc. You won't be working that truck too too hard.

[mongocanfly]

3.73s will make it come alive....and that price you got for the axle rebuild is about right..although I would suggest looking around for a axle that already has 3.73s and g80 in it if your concerned about the cost...there are still a few out there in wrecking yards..but I wouldnt waste a lot of time looking...
If your going with the LS and od trans in the future I would work my gear choice around having the od vs the t350...
I would look into the tru-trac diff...its alot more forgiving than a posi locker is

[Tom]

Id buy a used axle for much cheaper myself.

[TrybalRage]

Originally Posted by mongocanfly

If your going with the LS and od trans in the future I would work my gear choice around having the od vs the t350...

This is something I've wondered about, I don't want to spend money twice... I thought a 3.73 might still be a good ratio even with an OD. For towing/off the line performance it would be the same, just the overdrive would give better fuel mileage, no?

[LS short box]

I'm kind of in the camp of if you plan to keep the truck long term bite the bullet and have your rearend rebuilt with new gears and quality parts. Then you will never have to worry about it again. The new posi cases are much stronger than the "old" chevy stuff. A used assembly is just that used and they are over 50 years old. Many are sold as rebuilt with a new coat of paint.
Also a receiver hitch is a must in my opinion. With the right drop on the ball you can tow your trailer nice and level.

[truckster]

You'll want to make absolutely sure those brakes are working well. If you're going up and down hills and your trailer doesn't have brakes, you don't want to find out the hard way that the brakes weren't up to snuff.

[TrybalRage]

Originally Posted by truckster

You'll want to make absolutely sure those brakes are working well. If you're going up and down hills and your trailer doesn't have brakes, you don't want to find out the hard way that the brakes weren't up to snuff.

New rotors, pads, drums, shoes, and cylinders along with new front bearings were installed right around the time of the transmission. They don’t have a ton of miles but I was planning on giving them a visual once over soon.

[Dead Parrot]

I have a 75 C10 with the HD springs, mostly stock 350/TH350 and 3.42 standard rear end. Had plenty of power to tow a 16ft Glastron + a few hundred pounds of boat related stuff in the bed while running the AC.

Don't be too surprised if the master cylinder goes bad after a few stops with your boat in tow. Been there, done that. That trailer didn't have brakes either. The extra weight pushing on the truck = extra foot power and the MC goes into rusty rarely used bore and destroys the seals. Might want to do a few local test tows before hitting the hilly roads.

If you haven't already, swap out the turn signal flasher for a heavy duty unit to avoid the rapid flash problem.

Never had much problem with slipping on the boat ramps but if you are doing a gear swap anyway, the limited slip seems a good idea.

Make sure your e-brake is adjusted properly.

[burnin oil]

3.42 or 3.73 gears. Look at the junkyard for an axle. You can also get the rear out of a 4x4 and swap the axle shafts. Probably best luck looking in trucks with an OD trans for an axle. O e thing is any factory posi is probably shot and ready for new clutches.

If you don't regear consider an RV cam and try to bring those factory torque numbers up. This isnt as good as a gear swap but should help immensely with 2.73 gears.

[mongocanfly]

My 99 with 5.3/4l60 and 3.73s was a great combo..I pulled a trailer and tractor many a mile thru hills and such..no trailer brakes...loaced trailer was around 7k gross...just had to be careful with no trailer brakes..
I think you'll be happy with 3.73s

[kwmech]

3.73s with the t350c---have the rear rebuilt with the true-trac. Factory G80 posi is junk over with 100k+ miles on it. It will eventually blow everything out in the diff, then you're back to square 1. Have it rebuilt and forget about it

Still not enough?? put a 350 in it when the time is right

[cadillac_al]

I would go with an E-locker. Locked up when you need it and nice and open when you don't. I used to tow plenty of cars with an 85 C10 and gutless 305, never had to back it down a boat ramp though.

[TrybalRage]

Originally Posted by kwmech

3.73s with the t350c---have the rear rebuilt with the true-trac. Factory G80 posi is junk over with 100k+ miles on it. It will eventually blow everything out in the diff, then you're back to square 1. Have it rebuilt and forget about it

Still not enough?? put a 350 in it when the time is right

You're not the first person to say truetrac... It was the shop who recommended the eaton posi when I told them what I wanted. It seems like they do the same thing, just using different mechanics (posi=clutches that can wear out but be rebuilt, truetrack=??).

Why one over the other?

[mongocanfly]

Theres no clutches to wear out in a trutrac...look up a video of how it works..

[kwmech]

Right---no clutches to wear out on the Tru-trac. From the day you put it in it will always perform the same. No 'breaking it in', no special additives needed, just a clean quality oil and an occasional service every 30k or so.

Just put one in my Suburban 14 bolt

[TrybalRage]

Thanks everyone, got an appointment to drop the truck off next week for a Trutrac and 3.73 install. Can't wait to see how it feels compared to the current gearing.

[tdangle]

You are going to love it. Years ago I had a Dodge pickup with 318 and 2 something gears. Went to a 3.55 gear and it made all the difference. Mileage even up up believe it or not!

[burnin oil]

Originally Posted by tdangle

You are going to love it. Years ago I had a Dodge pickup with 318 and 2 something gears. Went to a 3.55 gear and it made all the difference. Mileage even up up believe it or not!

This happens alot more than you think. Same goes for a bigger motor. Years ago guys were swapping 350tbi motors into S10s and gaining MPG since the motor wasn't working as hard to get it down the road.

[TrybalRage]

Picked up the truck last night. Only made the trip home, my thoughts so far:

- Low-speed driving around is much more responsive. Lots of back roads in my area, and even though I was taking it easy for break-in, it has a totally different feel. Doesn't feel like so much of a slug anymore. Definitely cool.

- There was a short section of highway that I was on.. oh dear. Engine was roaring keeping with the speed of traffic, which I can only assume was around 55 since my speedometer is way off right now. I have a cheapo unlit tach that I couldn't really see, but it appeared that I might be around 2200-2500 RPM? That sound right with these gears? I wonder if I need to replace my fan clutch or try to swap in the electric fans off a 93 firebird that I have sitting in my garage...I've noticed the noise it before but since the RPM's were normally so low (under 2k) its much louder now.

[biketopia]

22-2500 isn't terrible, you could like you said be hearing the fan going full on for whatever reason. Sometimes they sound louder at different RPM's my camaro with 3.55's sounds louder and more of a drone at 60-65 than it does a 70.

[rpmerf]

You can calculate RPM based on tire size, rear ratio (3.73), trans ratio (1.0 in 3rd), and speed. If you post up your tire size, I could calculate RPM at a hand full of speeds for you.

[kwmech]

Originally Posted by TrybalRage

Picked up the truck last night. Only made the trip home, my thoughts so far:

- Low-speed driving around is much more responsive. Lots of back roads in my area, and even though I was taking it easy for break-in, it has a totally different feel. Doesn't feel like so much of a slug anymore. Definitely cool.

- There was a short section of highway that I was on.. oh dear. Engine was roaring keeping with the speed of traffic, which I can only assume was around 55 since my speedometer is way off right now. I have a cheapo unlit tach that I couldn't really see, but it appeared that I might be around 2200-2500 RPM? That sound right with these gears? I wonder if I need to replace my fan clutch or try to swap in the electric fans off a 93 firebird that I have sitting in my garage...I've noticed the noise it before but since the RPM's were normally so low (under 2k) its much louder now.

What do you have for tire size? Is the convertor locking up?

[TrybalRage]

235/75/15 on it right now. So when I plug that into an RPM calculator seems like ~2400 is about right.

[tdangle]

2400 is not bad at hwy speeds. You can download a GPS speedo app on your phone to verify your speed.