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Need some help... blazer shuddering

MudFrog

MudFrog

1/2 ton status
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Feb 23, 2000
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Daleville, Va
I just picked up my blazer from getting the cracked spring replaced. I have a 14 FF, 4" suspension (blocks in rear), 33x12.50's. I'm pretty sure the wheels need to be balanced but for some reason I'm getting a constant vibration. Some times it is worse than others. I have a custom Denny's HD driveshaft with 1330 joints. the ujoints are fine. I'm thinking the vibration might have something to do with my brakes?!? I completely redid my brakes with new shoes/springs/wheel cylinder. I think I got everything right...haha. Anyway, when I did the brakes I did one side at a time and compared the other (original) side. Any ideas on the vibration? Oh yea... the vibration just started and I just did the rear axle swap.

Now to top it all off, I picked the blazer up and right before I got to work the blazer shudders when I hit the brakes. However it's only when I press the brakes hard... which I have to do right now cause I don't have the rear brakes fully adjusted. Anyone have an idea what might be causing the blazer to shudder?

89 K5 Silverado
<a target="_blank" href=http://mudfrog.rockcrawler.com>http://mudfrog.rockcrawler.com</a>
 
My 12 bolt shudders as well in similar situations which I've identified as my rear 4" lift blocks. The larger weight of that 14bFF I'm sure would exagerate the problem. Hows your pinion angle?

What, Me Worry?
<a target="_blank" href=http://www.echobit.com:81/k5/> The 'BEFORE' pictures</a>
 
My pinion angle is good. I have dropped the tcase and all.

I did not upgrade my master cylinder. Do you think having the stock master cylinder could cause this? Granted I still have 1/2 ton front axle.

89 K5 Silverado
<a target="_blank" href=http://mudfrog.rockcrawler.com>http://mudfrog.rockcrawler.com</a>
 
I don't think the master cylender would be the problem, more likely the proportioning block or the adjustment of the drums. Did you say this problem started after you upped to the 14bff?

What, Me Worry?
<a target="_blank" href=http://www.echobit.com:81/k5/> The 'BEFORE' pictures</a>
 
Yes... the problem started after going to a 14 bolt. And like I said. I don't think the brakes have completely adjusted, they squeel when I stop but it really does not feel like they are helping out very much.

89 K5 Silverado
<a target="_blank" href=http://mudfrog.rockcrawler.com>http://mudfrog.rockcrawler.com</a>
 
I'd start by tracking through your rear brakes and making sure everything is aligned properly and engaging properly. Then walk through an adjustment with the back axle jacked up and rotate the wheel while adjusting the drums from the access hole on the back side of the drum. Keep in mind that the rear brakes only provide 20-30% of your overall braking while the front handles the rest. If the drums are getting more than that, you might be able to tell by rolling forward and doing a few lock up tests with the brakes and seeing if the rear locks before the front, and if so, do they lock up premature. If they do, that could be an adjustment at the drum or even a proportioning block problem (although I think the stock proportioning vavle should be fine unless you convert over to disks.)

What, Me Worry?
<a target="_blank" href=http://www.echobit.com:81/k5/> The 'BEFORE' pictures</a>
 
Check your transfer case mount - once they get the least bit of slop in them, they'll cause a shudder like that.

Of the 5 toughest dogs in the neighborhood, my cat's ranked #3
<a target="_blank" href=http://pugsley.alloffroad.com>pugsley.alloffroad.com</a>
 
First off a 14 bolt has larger diam tubes. The pinion is also not in the exact same place. So you problem amy be all driveshaft angle. Second Lift blocks in the 4 inch range usualy have a wedge on one side. They may not be in correctly and again screwing with the pinion angle. Blocks will always make a vibe problem worse becuase of the extra leverage they give the axle on the spring (and the probable cause of your cracked spring). Most of the time warped drums and rotors will not cause shake in the truck. most of the time you feel it only in the brake peddle. The shudder seems to be most felt under light braking but not always.
Now what may be happening is when you brake hard the axle is rotating because of those blocks and screwing with the pinion angle again.
Can you tell I don't like blocks?

I don't need no damn shop manual, I got a pornographic memory.
<a target="_blank" href=http://communities.msn.com/OffroadK5s>communities.msn.com/OffroadK5s</a>
75 Jimmy, Dollar
Grim-Reaper
 
So Grimmy, what's your opinion on blocks?
smile.gif



Of the 5 toughest dogs in the neighborhood, my cat's ranked #3
<a target="_blank" href=http://pugsley.alloffroad.com>pugsley.alloffroad.com</a>
 
Hmm.... So you think blocks are the culprit. Well to tell you the truth I'm not sure if my blocks are on right or not. My blocks are weird. They have the center pin hole offcentered and diagnally away from the nub that goes in the spring perch. Because of this I did not know which way was right. The blocks are also bigger than my spring perch. So as they sit now I have about an inch of block overlapping the rear of the spring perch. If I flop it the other way I'll have an inch of block overlapping the front of the spring perch. The lift is a Superlift Softride. Anyone have any idea as to whether or not I have the blocks on right? Maybe I'll flop them around and see if that helps.

89 K5 Silverado
<a target="_blank" href=http://mudfrog.rockcrawler.com>http://mudfrog.rockcrawler.com</a>
 
I agree that it is probably all driveshaft angles. The block should be orientated so that the block has less height in the front than it does in the back. I don't see any real problem with the block overhanging the spring perch as long as it all goes together correctly. Just don't use blocks that are narrower than the spring or not as long as the perch.

If you want to know if a shudder is coming from the rear brakes, do a test while you are going slow and not around traffic. While HOLDING the parking brake release lever out, slowly apply the parking brake pedal until you feel it drag. Then just see how the rear brakes alone feel compared to all four.

<font color=green>Does a Dyslexic Insomniac Athiest lay awake at night wondering if there's really a Dog?</font color=green>
 
With my Superlift blocks, they are turned so that the shorter side is toward the front.

Of the 5 toughest dogs in the neighborhood, my cat's ranked #3
<a target="_blank" href=http://pugsley.alloffroad.com>pugsley.alloffroad.com</a>
 
The only other idea I could offer to you is that possibly have drums that are out-of-round? Mine are badly out of round right now, and the thing shakes like a wet dog when braking hard... I too have the previously blamed 4" blocks... but mine don't hang over the perches or anything else suspicious like yours...

<font color=red>Just give me a tank, and point me in the right direction!</font color=red>
<font color=blue>DONT MESS WITH AMERICA!</font color=blue>
454/TH400/NP205 - 14BFF/D60/w/ 4.10s
 
This is the same as mine... the short side is facing the front and the long side is facing the rear. I was getting ready to go out and try the other way but if yours are the same then maybe it's right.

89 K5 Silverado
<a target="_blank" href=http://mudfrog.rockcrawler.com>http://mudfrog.rockcrawler.com</a>
 
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