2019 Silverado cabin rumbles when slowing down

STX30MAC · February 28, 2020

Mine was bad today. I feel like it is worse when it’s warmer. It got to 73 degrees today and had to hit brakes hard in traffic. Hard vibrate then kick forward. Tried putting in L2 while in slow traffic. Did not seem to help much. What’s really weird is that if you let the gears slow you down in L1 it lets loose at about 5-7mph and rolls resistance free. Plus 1500rpms it grabs like I hit the brakes but didn’t. My dealer noted it and will notify me when something comes up from GM. I have 6in bds lift with 35 x12.5. My drive shaft angle seems a little strong. RC rear blocks are tapered to reduce angle. Curious to hear if RC lifts have the issue.

Sent from my iPhone using Tapatalk

hotrodz37 · February 28, 2020

Maybe we can all measure our pinion angles and get a general consensus of which angles are worse. That being said I feel like it doesn’t describe why it would be better or worse with ambient temp.

Sent from my iPhone using Tapatalk

STX30MAC · February 28, 2020

I also wanted to note that the first 3 stops after starting in the morning I dont feel it. 4th stop and after you start feeling it. It is also weird that some days are worse than others. Not sure if it is related to this issue but once I hit 75mph and over I get a hum/Roar that slightly vibrates the gas pedal. The only way I can think of explaining it is when you ride in a air plane near the engine. Loud enough hum that it vibrates the chair ever so slightly. Passengers say they cant hear or feel it. Its worse driving into the wind. Goes away when you let off the gas pedal. Im going to clamp open the exhaust flappers and see if that does anything. Still love this truck and will drive it any chance I get.

HondaHawkGT · February 29, 2020

Engine braking + DFM/torque converter clutch modulation

STX30MAC · February 29, 2020

I found an issue. The rear lift blocks were installed backwards with the tapered part facing the rear. I am having the lift installer turn them around Monday morning. Hopefully this fixes my current issues: shake to a stop, roar at 75+, and vibration in rear at 65-75mph despite having tire balanced multiple times. Pissed that they installed blocks backwards but happy to have found an issue that I can correct. I will report back Monday night. Crossing my fingers that nothing was permanently bent or damaged.

hotrodz37 · February 29, 2020

I found an issue. The rear lift blocks were installed backwards with the tapered part facing the rear. I am having the lift installer turn them around Monday morning. Hopefully this fixes my current issues: shake to a stop, roar at 75+, and vibration in rear at 65-75mph despite having tire balanced multiple times. Pissed that they installed blocks backwards but happy to have found an issue that I can correct. I will report back Monday night. Crossing my fingers that nothing was permanently bent or damaged.

I just went out and checked my truck, stock Denali and there are shims with the tapered part facing the rear as well. Is this normal? Guessing they’re oriented that way to increase pinion angle as the opposite decreases angle when you lift a vehicle. Not quite sure what is the right orientation for a stock truck.

Sent from my iPhone using Tapatalk

lapoolboy · February 29, 2020

3 hours ago, STX30MAC said:

I found an issue. The rear lift blocks were installed backwards with the tapered part facing the rear. I am having the lift installer turn them around Monday morning. Hopefully this fixes my current issues: shake to a stop, roar at 75+, and vibration in rear at 65-75mph despite having tire balanced multiple times. Pissed that they installed blocks backwards but happy to have found an issue that I can correct. I will report back Monday night. Crossing my fingers that nothing was permanently bent or damaged.

This will do nothing to solve the issue. I tried blocks in both directions, different height blocks, and shim vs. no shim. The issue is something else with these trucks....not the lift blocks.

lapoolboy · February 29, 2020

1 hour ago, hotrodz37 said:

I just went out and checked my truck, stock Denali and there are shims with the tapered part facing the rear as well. Is this normal? Guessing they’re oriented that way to increase pinion angle as the opposite decreases angle when you lift a vehicle. Not quite sure what is the right orientation for a stock truck.

Sent from my iPhone using Tapatalk

The trucks have a stock shim on the bottom of the spring back (thin end of shim toward rear of truck).

Adding a tapered lift block cancels out the shim. Believe me, I tried EVERY combination and the rumbling/vibration is ever-present.

hotrodz37 · February 29, 2020

The trucks have a stock shim on the bottom of the spring back (thin end of shim toward rear of truck).

Adding a tapered lift block cancels out the shim. Believe me, I tried EVERY combination and the rumbling/vibration is ever-present.

Good deal, thanks for clarifying! Still anxious for you to try the range and rule that out too haha

Sent from my iPhone using Tapatalk

STX30MAC · March 1, 2020

The trucks have a stock shim on the bottom of the spring back (thin end of shim toward rear of truck).

Adding a tapered lift block cancels out the shim. Believe me, I tried EVERY combination and the rumbling/vibration is ever-present.

That’s how the blocks are installed now. .25in higher towards front. So you are saying that’s correct.
Well still excited to try it. But I do think the problem is with the torque converter or trans. Could be the programming of these. Have any of you put a speed calibration accessory. Maybe that would fix it. Or at least help a little.

Sent from my iPhone using Tapatalk

hotrodz37 · March 1, 2020

That’s how the blocks are installed now. .25in higher towards front. So you are saying that’s correct.
Well still excited to try it. But I do think the problem is with the torque converter or trans. Could be the programming of these. Have any of you put a speed calibration accessory. Maybe that would fix it. Or at least help a little.

Sent from my iPhone using Tapatalk

I think for stock trucks the tapered end should be towards the rear and for lifted trucks it should be towards the front to decrease the driveline angle from the lift.

I believe yours are in backwards like you originally thought.

Sent from my iPhone using Tapatalk

STX30MAC · March 2, 2020

DONE fixed it!!! The blocks and shims were installed according to BDS instructions. The rear 5in lift block itself is flat but BDS directions say to use the factory shim the same direction as it came on the truck. tapered end facing rear. Had my lift installer flip the shims this morning so the tapered end faces the front. I can't even believe what a difference it made. SMOOTH STOPS ARE BACK AGAIN. It also cured my roar at 75+. Smooth stops and no more roar. I couldn't be happier. A little ticked at BDS but letting my installer deal with them. Even the acceleration is smoother. I am curious to see if my mpg gets better because of it as well. If you guys will tell me how to measure the driveshaft angle to axle I will get you that info. I have to go back to driving the truck around now. LOL

lapoolboy · March 2, 2020

1 hour ago, STX30MAC said:

DONE fixed it!!! The blocks and shims were installed according to BDS instructions. The rear 5in lift block itself is flat but BDS directions say to use the factory shim the same direction as it came on the truck. tapered end facing rear. Had my lift installer flip the shims this morning so the tapered end faces the front. I can't even believe what a difference it made. SMOOTH STOPS ARE BACK AGAIN. It also cured my roar at 75+. Smooth stops and no more roar. I couldn't be happier. A little ticked at BDS but letting my installer deal with them. Even the acceleration is smoother. I am curious to see if my mpg gets better because of it as well. If you guys will tell me how to measure the driveshaft angle to axle I will get you that info. I have to go back to driving the truck around now. LOL

So, you're saying 1/4" taper on a 5" tall block solved all your issues? Interesting. I tried the OEM 1/4" shim in both directions with and without lift block installed and the issue persisted through all configurations (my block was only 3" tall too).

I believe the issue is in the driveline somewhere but I'm going to have to take it to a shop with more experience measuring and correcting angles to figure it out.

hotrodz37 · March 2, 2020

So, you're saying 1/4" taper on a 5" tall block solved all your issues? Interesting. I tried the OEM 1/4" shim in both directions with and without lift block installed and the issue persisted through all configurations (my block was only 3" tall too).

I believe the issue is in the driveline somewhere but I'm going to have to take it to a shop with more experience measuring and correcting angles to figure it out.

TRY THE RANGE TRY THE RANGE [emoji1787]

Sent from my iPhone using Tapatalk

STX30MAC · March 3, 2020

So, you're saying 1/4" taper on a 5" tall block solved all your issues? Interesting. I tried the OEM 1/4" shim in both directions with and without lift block installed and the issue persisted through all configurations (my block was only 3" tall too).

I believe the issue is in the driveline somewhere but I'm going to have to take it to a shop with more experience measuring and correcting angles to figure it out.

Yes. Technically it raised the axle connection to driveshaft probably over an inch or 5 degrees. Removed .25in from front and added to the .25 to rear of the block raising the axle connection point a considerable amount. Essentially by turning the shim around it made the u joint angle almost zero. On really hard stops I can feel it slightly but I think that’s the axle nozzle rotating downward putting extreme pressure on the U joint and drive shaft transmission not wanting to downshift smoothly that causes the vibration at shift points. This all bs that makes sense in my head but I’m not a mechanic and have never replaced a u joint or drive shaft. Just happy the truck stops smooth again and I can think about other mods like rock lights and mufflers. Already got the rock lights. Lol

Sent from my iPhone using Tapatalk