Sound coming from brake booster

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reznunt

reznunt

Massive Metal Shop
Supporting Vendor
10 Year
Joined
Nov 14, 2011
Threads
84
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1,799
Location
SoCal
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massivemetalshop.com
Hi guys. I'm completely new to 100's and I just picked up a 98 TLC. I hear a whizzing sound similar to a small electric motor winding when I turn on the ignition. It sounds like it's coming from the booster beneath the accumulator. I also hear it sometimes while driving when I press the brake pedal or a few seconds after I release the pedal. The sound is sort of faint, not screeching like in the other posts I've read. I also have a soft pedal on first pump but I wasn't sure if it was just air in the lines (since I just bought the rig). I've read the posts about the MC and booster, but I still am unsure of how to approach this.

Is this sound normal to a functioning 100 series braking system? If not, how do I get rid of this sound and get the brakes functioning normally? I was about to do a complete front/rear brake job and bleed, but I want to address the sound first. Thanks in advance.

BTW, I probably wouldn't have bought a used LC if this site didn't exist!

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Yes normal. That's an expensive system to replace so take care of it (maintenance and proper fluid).
 
sdnative said:
Yes normal. That's an expensive system to replace so take care of it (maintenance and proper fluid).
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Ya, so I've read! The first post I found had "$2400" in it and I almost shat my pants. I'll meticulously maintain her as I do all my vehicles.
 
What you've described is the booster accumulator motor/pump running to charge the system for brake assist, abs etc. A very simple system health check is to discharge the accumulator pressure and check how long it takes to recharge. With ignition OFF pump brake pedal 40+ times, at around 20 pumps you should feel the pedal go soft. The fluid level in the reservoir should raise about 12mm when the accumulator is discharged. Now turn the ignition ON and the motor pump should run for 30-40 seconds and the fluid level drop back down about 12mm.
 
PADDO said:
What you've described is the booster accumulator motor/pump running to charge the system for brake assist, abs etc.
Click to expand...

That's what I thought, just didn't think it should be that loud. I can hear it clearly in the cab.

PADDO said:
A very simple system health check is to discharge the accumulator pressure and check how long it takes to recharge. With ignition OFF pump brake pedal 40+ times, at around 20 pumps you should feel the pedal go soft. The fluid level in the reservoir should raise about 12mm when the accumulator is discharged. Now turn the ignition ON and the motor pump should run for 30-40 seconds and the fluid level drop back down about 12mm.
Click to expand...

Thanks! I'll give that a try and see what I find. I'll also do the brake bleed process to try and get rid of the soft pedal on the first pump. Before I posted here, I thought the loud motor sound and the soft pedal may have been related.
 
reznunt said:
That's what I thought, just didn't think it should be that loud. I can hear it clearly in the cab.



Thanks! I'll give that a try and see what I find. I'll also do the brake bleed process to try and get rid of the soft pedal on the first pump. Before I posted here, I thought the loud motor sound and the soft pedal may have been related.
Click to expand...
At the risk of inviting a "guess this sound video" I'd describe the accumulator motor sound as more of a gentle, rhythmic purr....;) not loud by any means. But my hearing is a product of nearly 3 decades of exposure to 5" naval gun fire and marriage and the selective deafness that comes with that.
Changing out the brake fluid with a purge and bleed is inexpensive and worthwhile and may well improve your pedal feel.
 
I think I am hearing the same noise in my cabin on start up. I thought it was ahc related until reading this thread.

Before I start the vehicle my brake pedal has no firmness to it. However, after I start it is feel the pedal becoming firmer within seconds. Is this normal?
 
It'll say it's normal for the brake accumulator to bleed off pressure after standing for a period of time. I just checked mine and after standing for 24 hours there was very little pedal resistance with ignition off. Holding in the pedal and starting you should feel the pedal push back pretty much instantaneously as the accumulator charges. Just one guys input FWIW.
 
Same here. Soft sound. Cross between a hiss and a buzz. Normal.
 
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