Another JR

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I’m curious why you ask. The owners manual for my 2021 gas 3500hd says that transmission grade braking only works in tow haul mode. On mine, grade braking works in normal mode on descents.

Just to clarify, I’ve had the truck since last April. Understood about not having the dealer do an alignment. It tracks nicely as delivered. I’ll have to research doing the height adjustment, but I’m assuming I can take measurements before and match them after.

Hi All, I ordered my 2021 3500hd SRW gas truck with the heavy duty camper spring option (5600 FGAWR rather than the base 5200). I don’t need them for my pop-up camper, which weighs just under a ton fully loaded for travel and literally only puts 100 lbs of weight on the front axle. I had thought I might someday get a heavier hardsided camper, so I ordered camper springs, but have already decided we won’t ever do that. I’d prefer the front suspension be a little softer. So I’m interested in changing the springs to the standard 5200 lbs part number as a DIY job, and I’m trying to scope the work and price. The bars cost $220 each. Two questions: 1) Has anyone done this job on one of these trucks, and if so do you think a person who typically does light to medium mechanical work should attempt the job (I pulled engines and transmissions on simple smaller cars as a teenager, but wouldn’t attempt that today). I have the equipment to safely raise and support the truck indoors, and I have a strong son to help with lifting the heavy bars. 2) If I take careful measurements to restore the same height after the swap can I avoid having to do an alignment, or should I plan to have a height adjustment and alignment done by the dealer after the change? Thanks

Tha Thanks for the detailed explanation and for making the extra effort to educate me

I personally have not experienced such a large drop in mileage in the winter, but I am in the PNW, which has mild winters. I was under the impression that the winter fuel blend here has ethanol at approximately the 10% limit, where the summer fuel has much less ethanol. Wouldn’t that much of a difference in ethanol content cause an energy density change greater than 1.7%?

Think about this. What fraction if your operating time is spent with the oil temperature below the stabilized operating temperature, which is pretty much the same regardless of outside air temp due to the cooling system thermostat? To what extent does “oil drag” compare to your total actual engine power output needed to move the vehicle? A few percent? So how much difference does even a large change in cold oil drag really make in overall fuel mileage? How does that compare to the several percent change in volumetric heating value of the fuel when they change to the winter fuel formulation, recognizing that fuel is sold based on volume? To say the seasonal mileage effect drivers see is not dominantly driven by the fuel characteristics doesn’t make sense to me.

Looks like maybe it’s leaking from the connections at the top of the tank. Should be covered by warranty. Why not take it to the dealer?

The wire supplying the power pin of the 7 pin connector is inadequate to supply a 30 amp dc to dc charger. I don’t remember the exact gage, but it’s 10 awg or smaller. While ampacity charts will show 10 awg can handle 30 amps without overheating, the voltage drop will be excessive for a charger located in a camper and the engine running detection of the charger won’t function properly. Multiple people on a truck camper forum I frequent had problems trying to use a 30 amp dc to dc charger with 10 awg wire due to constant cycling if the charger on and off from low voltage. 6awg definitely works well with a 30 amp dc to dc charger from my direct experience. 8awg might work, but I haven’t tried it.

Are you sure you properly seated the large tailgate electrical connector? The use of the gray swing arm that pulls the connector in and latches it is counterintuitive. I had to review a youtube video and watch how the connector worked because it had been a few months since I pulled it off. If you do it wrong it kind of seems like it seats but it isn’t really connected. Unless you are positive you did it right, I would suggest reviewing a video and then remating the connector. Edit: Another possibility is the tailgate is locked. Do you have the truck unlocked (not just the drivers door) or a fob in your pocket when you try it?

Just to give you an idea of a ballpark empty axle weight if you haven’t weighed your truck, my empty GMC 3500hd SLT CCLB SRW gas, aux battery single alternator, camper springs, with full tank and 220 lb driver has front axle weight of 4440lbs and rear axle weight of 3340 lbs. i have the stock 18” Michelins and I run 55 psi front and 60 psi rear for general driving around including moderate loads of up to a ton or so. I get no tire messages at those pressures.

Saw this warning in the owners manual for my 3500hd: { Warning Do not hold the brake pedal and press the accelerator pedal at the same time. Damage may occur to the power steering and power brake systems which could lead to reduced performance, up to and including loss of steering and brake assist. Not that I do that when I drive, other than briefly on a steep hill start maybe, but does anyone know how the steering system would be damaged by this?

Don’t know about manual release, but here’s what I’d try: 1) identify and check fuses, 2) disconnect and reconnect the big tailgate electrical connector just behind the bumper near the spare (it’s a complex connector mechanism so pull up a YouTube video if you are not familiar.). 3) disconnect the truck battery(s) for several minutes to reset computers, 4) call dealer; it’s under warranty.

Is there a slot you can use on the fuse block on the battery? Mine had three unused slots, on of which I used for my camper dc to dc charger.

You don’t need a dummy plug or harness just to protect the connector. It is quite easy to bag the connector to protect it. You also can get just a camera cable separately to hook up a replacement for the tailgate camera. I bought a gm tailgate camera of the same part number for $90, made an enclosure and installed it on the back of my camper. I bought my FAKRA cable from Pasternack.com for around $30.

Using the mile markers of a marked 5 mile highway speedometer test section, my 2021 3500hd with stock Michelin 18s seems to be almost dead on accurate. At 5 miles the number flipped about 100 feet after the marker. That’s just under 1/2% error. I have not been able to find out if there is a different calibration on trucks delivered with 20 inch wheels.

There is a law or regulation in CA prohibiting light arrangements that look like an emergency vehicle if you are not such a vehicle. Someone made a determination that roof marker lights on pickups violate that rule. So all pickups sold new in CA don’t have roof marker lights. However, this mandatory delete option is not associated with the CA emissions configuration. I live in WA and new cars and trucks here are required to meet CA emissions but they have the marker lights.

Agreed, particularly on heavy items. Those types of part my local Chevy dealer is often the best net price.

Don’t know whether the nonpower version frame is different. However, best i can tell the outer frame piece for the mirrors that don’t have the rear facing white lights that light up with the bed light are different from those that do have the lights. They have the same mirror glass shapes with the notch, but the notched area is flat instead of having the light shapes.

I’ve used a few of the on line parts sellers with no problems. I don’t think there’s any one that stands out. Maybe check with other GMC and Chevy dealers in your area. My GMC dealer where I bought my truck charges msrp for parts. However, I’ve been going to the Chevy dealer across the street from them for parts for my 93 chevy truck and 2004 yukon, and will for my new GMC truck. I get prices from them similar to the online dealers and get lots of free advice. You just give them the VIN and make sure they know it’s a GMC. They sold me an OEM rubber bed mat for less than I could get it on line. They both order from the same regional warehouse.

Here is a picture of the fuse block in case that helps. The 80 amp fuse was unused.

The fuse was an unused fuse on the battery mounted fuse block. It has a big fuse for the wire coming from the alternator, another going to the aux battery, one to the main fuse box, and this 80 amp unused one. I believe it is intended for this type of use powering a trailer or camper charging system. An 80 amp fuse is just fine to protect Ancor Marine type 3 6awg wire. The charger pulls about 34 amps when in bulk charge. It doesn’t need an 80 amp fuse but the fuse is adequate to protect the wire run. The wire is upsized to reduce voltage drop. The fuse is permanently attached to the fuse block bus bar. If you blow a fuse GM intends you replace the whole thing is my understanding.

I know I saw work trucks on the lots when i was test driving 2021s that had 17 Inch wheels. They might have only been on 2500s. The duallies have 17s as well. My understanding is the brakes are the same 2500 vs 3500. As folks above said trying it is the best way to know, but I think you are going to be ok.

Could depend on specific wheel dimensions, but the base model hd trucks have 17 inch wheels.

What the parts guy at my dealer always tells me for questions like these is go on the lot or go on line and find a truck configured with the parts you want to identify, and bring me the VIN for that truck. Then he can find the part in their system.