New brake booster without new MC

[NC Tom]

Basic question. Do I need to replace MC when replacing booster?

 

I know my booster is crapping out. I have the in-cabin vacuum hisses going on. I see them sold as a unit and individual. And, see folks online usually replace both. Just wondering why.

[Jeep Driver]

If your MC is good there is no reason to replace it. Just replace the booster. 

[HOrnbrod]

Run through the below tests. It may be all you need is a new booster check valve.

 

http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm#testbooster

[carnuck]

Run through the below tests. It may be all you need is a new booster check valve.
 
http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm#testbooster

It could also be the 4x4 or heater control vacuum leaking. Right above the gas pedal is one that was knocked off before I got my truck.


Sent from my iPhone using Tapatalk

[Knucklehead97]

I've bought 2 NEW boosters (not refurb) and they both hiss in the cabin. Its a bit upsetting. I haven't driven the Jeep with the hissing but with it just idling you can definitely hear it. It worries me for sure.

[cruiser54]

Good time to upgrade both. 

[NC Tom]

On 4/18/2018 at 10:28 AM, HOrnbrod said:

Run through the below tests. It may be all you need is a new booster check valve.

 

http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm#testbooster

 

Very helpful! Thanks! I hope messing with it doesn't really void my warranty! 🤣

[schardein]

If you installed a new M/C, and the next day your booster went bad and required replacement, would you replace your one day old M/C?  NO.  What about a month old?  No.  A year? probably not.  If the M/C is original to your 30 year old truck, it might be a good idea to go ahead and replace it.  I consider this a common sense approach.

 

 

[NC Tom]

On 4/18/2018 at 10:28 AM, HOrnbrod said:

Run through the below tests. It may be all you need is a new booster check valve.

 

http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm#testbooster

 

While replacing both is likely the way I'll go, I did some of the testing with these results.

Test 1: I think the pedal dropped more than 1/4"

Test 2: I couldn't tell much of a difference.

Test 3: Pedal did not drop after 30 sec. But, did slowly drop with continued pressure beyond 30 sec.

 

Power check valve was bad, replaced it BEFORE running the tests.

 

That's as far as I have gone as I don't know what "18 in. of vacuum" means.

 

[HOrnbrod]

Idle vacuum for most engines is about 18 to 22 in. You need a vacuum gauge to measure it. Low vacuum is probably not your problem with the brakes.

[NC Tom]

9 hours ago, HOrnbrod said:

Low vacuum is probably not your problem with the brakes.

 

Does that rule out the vacuum booster? It's a loud hiss in the cabin, reduces/stops when brakes depressed.

[HOrnbrod]

I'd rent a gauge at Autozone or somewhere and check engine vacuum. If okay, then replace booster, booster/master, or upgrade to double diaphragm booster brakes. Your choice.

[NC Tom]

On 5/3/2018 at 10:16 AM, HOrnbrod said:

I'd rent a gauge at Autozone or somewhere and check engine vacuum. If okay, then replace booster, booster/master, or upgrade to double diaphragm booster brakes. Your choice.