25-20 mph vibration or "rumble" while braking

fireaxxe · July 21, 2021

I purchased a new 2021 RST and shortly thereafter added a 2" RC front lift kit and a 2.25" ready lift rear block. I wasn't satisfied with the ride quality, too stiff. I also wanted to keep my warranty in case I had to make any future dealer visits. So I went back and purchased the GM 2" suspension upgrade from Chevy Performance. The install was smooth and I even ended up using the 0.25" top strut mount steel spacer from the RC kit to give me a little extra lift. Right away I noticed the ride was much better however I had a vibration when I slowed down, most noticeable between 25-20mph, that was not there before. So back to the drawing board.

From my experience this was a clear indication that I had misaligned my drive shaft working angles. I measured everything and I could see where the problem was. The rear suspension seems to be on a elliptic travel pattern with the front of the leaf spring mounting position being much lower than the rear mounting location. The GM 2" suspension kit comes with a square 2" rear lift block and the ready lift block is a 2.25" tapered block. The square block put the rear pinion angle much more negative (or pointing downward) than the tapered lift block. I removed the 2" GM square block and also put two 0.10" washers between the transmission and the transmission mount to give me a more positive (or upward) tail shaft angle, then reinstalled the ready lift 2.25" rear lift blocks. The 25-20mph vibration is gone. So if you have this issue this may be your problem and solution. How did you miss this GM?

EarlsSilverado · July 21, 2021

It’s most likely that your tires are oversized as well. I installed the Readylift kit and still had the stock tires. Drove perfect, I added larger tires and noticed a rumble when braking. It wasn’t enough to make marks on anything but it was the sidewall ballooning from the added weight of braking.

If you think about driveline angles, your front axle shafts would be at a lesser angle when the front end is squatted from braking.

In my case the sidewall of the Nittos was barely making contact with my upper a arms. The sidewall has work slightly and only the hardest braking scenario does it.

The tires that I have are Nitto Ridge Grappler LT285/75R18 E 129/126Q basically 35x11.50x18.

Another thing is that the Trail Boss wheels have .25” more offset than all the other stock wheels. I’m running these and it still would balloon and touch under hard braking.

Hope this helps.

fireaxxe · July 22, 2021

1 hour ago, EarlsSilverado said:

It’s most likely that your tires are oversized as well. I installed the Readylift kit and still had the stock tires. Drove perfect, I added larger tires and noticed a rumble when braking. It wasn’t enough to make marks on anything but it was the sidewall ballooning from the added weight of braking.

If you think about driveline angles, your front axle shafts would be at a lesser angle when the front end is squatted from braking.

In my case the sidewall of the Nittos was barely making contact with my upper a arms. The sidewall has work slightly and only the hardest braking scenario does it.

The tires that I have are Nitto Ridge Grappler LT285/75R18 E 129/126Q basically 35x11.50x18.

Another thing is that the Trail Boss wheels have .25” more offset than all the other stock wheels. I’m running these and it still would balloon and touch under hard braking.

Hope this helps.

Actually I have the stock tires so that's not a possibility. I think in your case you are describing the typical rubbing noise and vibrations due to larger tires.

The driveline angles that I am referring to are dealing with the driveshaft only. The constant velocity shafts have a different dynamic when it comes to working angles altogether. The reason the rumble gets worse with braking is due to the fact that the front end dips and the ass end raises causing the axle to wrap under the braking force thus increasing the negative pinion angle causing a vibration.

For those of us with this issue one easy to diagnose is to put the transmission in neutral while braking if the "rumble" goes away the problem is your pinion angle.

EarlsSilverado · July 22, 2021

I hope you get it figured out. I was hoping that it was a simple issue like it was for me.

fireaxxe · July 22, 2021

16 minutes ago, EarlsSilverado said:

I hope you get it figured out. I was hoping that it was a simple issue like it was for me.

Yup! all good now.

10 hours ago, fireaxxe said:

I purchased a new 2021 RST and shortly thereafter added a 2" RC front lift kit and a 2.25" ready lift rear block. I wasn't satisfied with the ride quality, too stiff. I also wanted to keep my warranty in case I had to make any future dealer visits. So I went back and purchased the GM 2" suspension upgrade from Chevy Performance. The install was smooth and I even ended up using the 0.25" top strut mount steel spacer from the RC kit to give me a little extra lift. Right away I noticed the ride was much better however I had a vibration when I slowed down, most noticeable between 25-20mph, that was not there before. So back to the drawing board.

From my experience this was a clear indication that I had misaligned my drive shaft working angles. I measured everything and I could see where the problem was. The rear suspension seems to be on a elliptic travel pattern with the front of the leaf spring mounting position being much lower than the rear mounting location. The GM 2" suspension kit comes with a square 2" rear lift block and the ready lift block is a 2.25" tapered block. The square block put the rear pinion angle much more negative (or pointing downward) than the tapered lift block. I removed the 2" GM square block and also put two 0.10" washers between the transmission and the transmission mount to give me a more positive (or upward) tail shaft angle, then reinstalled the ready lift 2.25" rear lift blocks. The 25-20mph vibration is gone. So if you have this issue this may be your problem and solution. How did you miss this GM?

Mcropper514 · July 22, 2021

I swear I have this issue and I have been looking for a good way to describe it. I've searched a lot of different things and came up with nothing. It doesn't happen all the time and it feels like the rear is going over rumble strips. I don't feel it everywhere, but when turning into my neighborhood, it seems to happen all the time. In that situation the road is slightly down hill. It seems to do it there every time. I am also turning in that situation as well and I feel it then also.

Truck is a stock Trail Boss. You think the washers alone might be worth a shot?

Any idea what size washers you bought?

fireaxxe · July 22, 2021

5 hours ago, Mcropper514 said:

I swear I have this issue and I have been looking for a good way to describe it. I've searched a lot of different things and came up with nothing. It doesn't happen all the time and it feels like the rear is going over rumble strips. I don't feel it everywhere, but when turning into my neighborhood, it seems to happen all the time. In that situation the road is slightly down hill. It seems to do it there every time. I am also turning in that situation as well and I feel it then also.

Truck is a stock Trail Boss. You think the washers alone might be worth a shot?

Any idea what size washers you bought?

I did the washers first and didn’t notice much difference. So I went ahead and put the ready lift blocks back in. I may actually remove the washers. When I initially installed GM kit I was wondering why the bump stop spacers were so heavy. Now after this issue and hearing that some TB have this issue I think GM are using this part for a dual purpose as a bump stop spacer and for vibration dampening.

matt grz · November 9, 2021

I put the gm lift on my elevation and have this rumble around 23 mph. I brought it to the dealer but they were no help. I’m a little confused what fixed your issue. Would you be able to add a picture of these washers you added? Did the other blocks alone fix the issue? Thank you in advance.

fireaxxe · November 14, 2021

On 11/9/2021 at 6:38 PM, Matt Grz said:

I put the gm lift on my elevation and have this rumble around 23 mph. I brought it to the dealer but they were no help. I’m a little confused what fixed your issue. Would you be able to add a picture of these washers you added? Did the other blocks alone fix the issue? Thank you in advance.

Yes I have driven awhile and the truck is still smooth slowing down from 25mph. The main thing that solved this problem for me was removing the SQUARE lift blocks that came with the GM kit. I then replaced them with a TAPERED 2.25” lift block. I have removed the 3mm washers I installed between the transmission mount and transmission and noticed little to no change.

matt grz · November 19, 2021

On 11/14/2021 at 7:23 AM, fireaxxe said:

Yes I have driven awhile and the truck is still smooth slowing down from 25mph. The main thing that solved this problem for me was removing the SQUARE lift blocks that came with the GM kit. I then replaced them with a TAPERED 2.25” lift block. I have removed the 3mm washers I installed between the transmission mount and transmission and noticed little to no change.

Thank you very much. I’m going to give this a go if gm can’t figure it out.

Ry363 · March 24, 2022

On 11/14/2021 at 5:23 AM, fireaxxe said:

Yes I have driven awhile and the truck is still smooth slowing down from 25mph. The main thing that solved this problem for me was removing the SQUARE lift blocks that came with the GM kit. I then replaced them with a TAPERED 2.25” lift block. I have removed the 3mm washers I installed between the transmission mount and transmission and noticed little to no change.

Do you have the tapered end (shorter end) facing to the front of the truck like ready lift says or the fat end to the front? I’m having similar issues when slowing as well and around 65. Have icon coils in front with the same 2.25 block in the rear. Driving me nuts.

4threeking · June 23, 2023

I have the same exact issue. If you guys want to keep the factory blocks just order 2.5 degree shims. This will angle the rear diff so the pinion on the drive shaft is inline with the transmission. Chevy should have these included but it took me forever to figure out the issue.

https://amzn.to/3pbzmdj

Throw these on your rear leaf springs and point the narrow end towards the front and the thick end towards the back