Towing with 5 speed and clutch upgrade questions

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SalahHH83

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So I found an 88 C1500 for a steal and bought it to use, among other things, to tow my BMW track car. It's a 5 speed manual with a 305. I found a nicely rebuilt 350 from a guy locally who needs money and is willing to sell it pretty cheap. So I've started thinking about swapping in the 350. I'm curious about a couple things from those who tow with their manual GMT400s:

1) When towing a light car trailer with about a 3000lb car on it, do you think I should shift into 5th or leave it in 4th? Where I live it's pretty flat, but I can encounter areas where there are hills. I figured I should be fine in 5th on flat ground once i'm up to speed. I figured I'd shift at higher RPMs to minimize stress on the clutch. When encountering hills, I'd prob go down to 4th. Of course I don't want to be shifting a lot while pulling a trailer, but I think this should be okay. Thoughts?

2) I'm considering swapping the 350 for a fresh engine with a little more power. It's a TBI engine out of a 91. I've done some research and it seems like all I'd need are 350 injectors, 350 knock sensor and the 350 computer. Any advice on this swap would be appreciated.

3) I've also researched whatever I can regarding a more heavy duty clutch for towing. All I could find is it seems the 350s came with a 12" clutch whereas the 305s came with an 11" clutch. Is this true and is this the only "upgrade' available for a better clutch for towing? I know there are clutches out there like centerforce etc. but other than that, are there any larger GM stock clutches I can use? If I went to the 350, I would certainly get the corresponding 12" clutch. If I could use a larger clutch out of a 454 or something, that would be great too.

I'm typically a BMW guy as that is my track car, but I have a history with American cars as well. My first car was a 76 Jeep CJ5 which I totally rebuilt back in high school. My parents had an 88 2500 GMC Suburban with a 454 which I did a good bit of work on as well. Any info/advice would be much appreciated!
 

K15 Blazer

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install a vacuum gauge. that will help tell you when to downshift for hills and how to cruise for the best power and economy.
its easier on everything to have higher vacuum at a higher RPM than the let it strain in a higher gear.

the 350 would certainly be an improvement.

not sure about the 153 tooth flywheel, vs the 168 tooth fly wheel... but... with a good clutch it shouldn't matter much... I have a clutch pressure-plate with levers, not a spring steel pressure plate.... DO NOT GET MY CLUTCH lol
seriously, don't. it hurts. apparently they are good for towing but its the heaviest clutch ever ever felt.

the only thing I would really suggest upgrading or at least inspecting would be the rear end... make sure its in good shape, the gear wipe is good, and maybe even install a high capacity cover to help keep it cooler... other than that.... maybe re-gear or add in a Detroit locker...

and good brakes. obviously. lol
 

SalahHH83

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Thanks for the responses, guys. I had a centerforce dual friction on my CJ5. The best way I could describe that clutch was “clamped” or “open”. It didn’t allow for much slip. The clutch the truck came with (i’m sure it’s been replaced given the mileage) is a very very hard to depress. Honestly, I don’t mind it as this truck is pretty much just for towing and hauling. I was drawn to this Sachs clutch kit (the $108 SBC 350 one)

http://www.partsgeek.com/catalog/1988/chevrolet/c1500/clutch/clutch_kit.html

I’ve had good results with Sachs clutches on BMWs but don’t really know too much about them on Chevys. I bought this truck for $900 so i’m not trying to spend a ton on the clutch. Honestly the current clutch is perfectly fine (albeit, for a noisy throw out bearing) but if I go to the 350, I’ll want to put in a fresh clutch while I have the bell housing off.

I’ve priced Sachs flywheels for the 350 and it’s only 60 bucks for a new one (it costs bat $40 to resurface a flywheel where I live so i’d rather spend 20 bucks more and have a brand new one).

I’ll likely do nothing to the 350 for performance mods. This truck is simply going to be for towing, so HP means almost nothing to me. I’ll sacrifice the fuel efficiency of the 305 for the easy/cheap to build 350 and its increased power, but this truck is by no means sexy haha
 

LS2Goat

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I'm assuming you will have the getrag trans or an nv3500. Neither of which I would advise towing in 5th. They just aren't build to withstand that kind of abuse.

Sent from my XT907 using Tapatalk 2
 

SalahHH83

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I'm assuming you will have the getrag trans or an nv3500. Neither of which I would advise towing in 5th. They just aren't build to withstand that kind of abuse.

Sent from my XT907 using Tapatalk 2

I believe I have an NV3500 (I'm going to confirm today after work). That was really my concern as, from what I understand, it's not really a robust transmission. I can't really justify the money for an NV4500 on this truck and can't bring myself to swap in an auto.

When I bought the truck I just assumed I'd be towing in 4th but would play it by ear and base it on the load I was feeling in 4th with the trailer behind me. I've freshened up the brakes to where I feel comfortable towing, but I'm still going to be using trailer brakes as it's still a 1/2 ton truck with drums in the back.

Eventually, if I find a suitable 14 bolt to swap in, I might do that. I also want to figure out my gearing in the rear end. I figure if I do swap in a different rear axle with lower gears, maybe that will help protect the transmission for 5th gear towing. I'll say this... as the truck sits today, 5th gear is a very high gear and the engine is sitting at almost too low of RPM...
 
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