'88 RCLB C3500 "Roscoe P. Coltrane"

[stutaeng]

I'm hoping it's a hydroboost, but I'm a little short on C2500/3500 knowledge - was that standard on 3500s? The truck originally had a 454, but when it conked out, the previous owner sold the motor.

All the 96-00 GMT 400 3500s had hydroboost as far as I know. That's not necessarily true of the early GMT 400 3500s. I've read some guys here saying their 3500s (again, early production years) have vacuum.

Maybe it was a BBC vs SBC thing? I'm not too familiar with early models. Even if yours doesn't have it, it can be swapped I'm sure.

I wonder what rear axle ratio it has? I believe the early 3500 trucks had a Dana 70 variation? Late models were all 14bolt/10.5"/4.10s standard, but early models were as low as 3.42...if you go with a 6 speed, probably wouldn't be too bad.

 

[letitsnow]

The part I'm not looking forward to is spending $600 on tires, but that's also why I wanted a SRW instead of a dually.

Even $600 might be a little light, for decent E rated tires.

 

[Erik the Awful]

Even $600 might be a little light, for decent E rated tires.

I found tires on Discount Tire's site for about $560, but that's without tacked on fees and installation. Probably just under $700 out the door. This morning I looked and they were gone.

All the 96-00 GMT 400 3500s had hydroboost as far as I know. That's not necessarily true of the early GMT 400 3500s. I've read some guys here saying their 3500s (again, early production years) have vacuum.

Maybe it was a BBC vs SBC thing? I'm not too familiar with early models. Even if yours doesn't have it, it can be swapped I'm sure.

That got me curious, so I went outside and tucked my head up under the bumper. It's vacuum. The truck originally had a 454, so it's not a big/small block thing.

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I wonder what rear axle ratio it has? I believe the early 3500 trucks had a Dana 70 variation? Late models were all 14bolt/10.5"/4.10s standard, but early models were as low as 3.42...if you go with a 6 speed, probably wouldn't be too bad.

Dana 70. My little bit of Google research this morning says they only came with 5.13s. The two extra gears in a 6L80 would be necessary for any long-distance towing. I also learned that it likely has either "Power-Lok" or "Traction-Lok" limited slip, and that makes me happy. Is that accurate, or is there a chance it has an open diff? Towing the truck out of the pasture with a open diff half ton was an adventure. We used a tractor to gently push the trailer to get the truck out of the mud.

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[0xDEADBEEF]

You could get an aftermarket underdrive and a junkyard 4L80 or TH400. Not sure if that would be cheaper than the 6 speed and controller though.

 

[frito-bandito]

Dana 70. My little bit of Google research this morning says they only came with 5.13s. The two extra gears in a 6L80 would be necessary for any long-distance towing.

Man I’m glad i passed up on the Dana 70 I was previously considering buying. 5.13 ratio has no place in my truck’s future plans lol

 

[stutaeng]

5.13s?! Are you sure on that?

From my limited knowledge of older trucks that had row-revving engines and no overdrive transmissions, the axle ratios were actually numerically lower that trucks that came later.

 

[Erik the Awful]

5.13s?! Are you sure on that?

Absolutely not. I googled it this morning. What do I know?

That said, you have to remember that when this truck was built the nationwide top speed limit was 55 mph. I'm thinking that a 454 with a TH400, 5.13 gears, and tall truck tires would run down the highway just fine if you're not going more than 60, but I haven't done the math. Reading a little more, it appears that 2.xx and 3.xx were common gears as well, but I can't find a spec on early GMT400s with Dana 70s. Anybody got a link to better info?

 

[frito-bandito]

Absolutely not. I googled it this morning. What do I know?

That said, you have to remember that when this truck was built the nationwide top speed limit was 55 mph. I'm thinking that a 454 with a TH400, 5.13 gears, and tall truck tires would run down the highway just fine if you're not going more than 60, but I haven't done the math. Reading a little more, it appears that 2.xx and 3.xx were common gears as well, but I can't find a spec on early GMT400s with Dana 70s. Anybody got a link to better info?

That’s the same issue I had when I was looking at the Dana 70 I was considering buying. There’s like NO definite info on them

 

[letitsnow]

I found tires on Discount Tire's site for about $560, but that's without tacked on fees and installation. Probably just under $700 out the door. This morning I looked and they were gone.


That sucks. I will need tires for my k2500 next fall and am budgeting $800 (just for the tires themselves). Not that I like that, but that seems to be where they are for only middle of the road tires.

 

[stutaeng]

2500 rpm = 45 mph in direct gear? Is that correct? 3,000 RPM gets you to 53 mph.

I would think you have 3.42 or 3.73. Maybe 4.10?

The 6 speed splits the old 4 speed into 2 gears, about 10%ish higher and lower than the old OD. And the deep 1st is good of course to get the heavy trucks going. 3.42s and 3.73s is what was offered in the Vans and trucks. Only the special Cab & Chasis vans (maybe also equivalent trucks?) DRW got 4.10s I believe.