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Brendan Block
Brendan Block, Technician
Category: Car
Satisfied Customers: 260
Experience:  BMW Technician specializing in engine conversions, braking upgrades and race car prep.
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When I start the truck, I hear a compressor type noise coming from under the dash. I assu

Customer Question

When I start the truck, I hear a compressor type noise coming from under the dash. I assume this mmust be my brake booster pump. The booster light comes on until the compressor noise stops..about 20 seconds. If I step on the brake the Booster light comes on again and stays on when the brake pedal is held down. While driving if I step on the brakes the Brake booster alarm sounds. My power brakes are sporatic. Sometimes I have power and sometimes I don't. Any thoughts? what can I check
Submitted: 3 years ago.
Category: Car
Expert:  Pete replied 3 years ago.
My name is Pete and I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.

From what you have described here this sounds like you have a leak in the vacuum supply for the brake system here causing this issue.I would start with locating this pump assembly and trace any vacuum or pressure lines off of it to see if you can locate a leak.If a leak is found it will need corrected to correct this issue.Starting at the pump would be the best way to go here.

Thanks Pete
Customer: replied 3 years ago.

I am not able to find the pump and related hoses. I went on line to see if anyone call tell me and struck out. Where is this located in this particular truck?

Expert:  Pete replied 3 years ago.
Unfortunately my info doesn't show me the exact location of this pump.

I will opt out and put this question back on the list to see if others can help more.Don't reply to my last here unless it is a last resort as it will keep the question locked to me.I hope you can get this resolved with ease.

Thanks Pete
Customer: replied 3 years ago.


I was sent an e-mail with this link asking for me to rate service. I'm not un happy with you although no one else has responded to me. I contacted "Just" earlier; firist trying the chat optiion but no one respionded and then e-mail. I got a response by e-mail saying they would set this as a priority. I still havn't heard from anyone. Bottom do I rate you based on this situation. It certainly is not your fault

Expert:  Pete replied 3 years ago.
The email is an automated email sent out to customers.Most likely the reason no one has responded yet is this is a difficult question here and it may be the right person may not be on line yet to help.

If you rate my service here you would do that above but this could close out this question.I would leave it be if possible and see if you don't get a response soon.If you do not let me know.

Thanks Pete
Customer: replied 3 years ago.

OK. I will let you know if I hear Back

Expert:  Pete replied 3 years ago.
Sounds good.

Thanks Pete
Expert:  Walt-Mod replied 3 years ago.

I’m a moderator for this topic. It seems the professional has left this conversation. This happens occasionally, and it's usually because the professional thinks that someone else might be a better match for your question. I've been working hard to find a new professional to assist you right away, but sometimes finding the right professional can take a little longer than expected.

I wonder whether you're OK with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you.

Thank you!
Customer: replied 3 years ago.

Thanks for responding. I will be unavailable until Monday. I would like to leave the question out there until then. If I don't receive an aswer, I will withdraw Monday night.



Expert:  Walt-Mod replied 3 years ago.
Thank you for your continued patience. We will continue the search for a professional for you.
Expert:  Brendan Block replied 3 years ago.
Hi there! My name is Brendan and I'm a tech, hopefully I can help you! Based on what I can find in my literature (I'm a euro car tech so my books are somewhat limited) it sounds like the vacuum pump is on the back of the alternator. There should be a vacuum tank on mounted to the frame on the passenger side and a lot of hose in between. I would inspect all of the above hose but it seems like pump failure is fairly common so that's my initial hunch!

If this is helpful, please leave me a positive rating and if you have any more questions just let me know! If I can't help you please leave my answer unrated and I will back out so someone else can help you.

Thanks and good luck!

Customer: replied 3 years ago.

This truck has a tip up cab to access the engine. I found the pump on the alternator and traced the hoses to under the dash on the drivers side to a resevoir or someting like that. The hose then went to what seems to be a small compressor or pump under the dash.

Your info was helpful to finding the related parts but I can't fnd a leak. I guess you may be right and the pump is not working but it's hard to tell whether it is the pump under the dash or attached to the alternator.

Expert:  Brendan Block replied 3 years ago.
I'm assuming the pump under the dash is electric (based on the info I've been able to find) so if there's a wiring connector on it you can try disconnecting it and see what happens. From what I've been able to find it sounds like pump failure (the one on the alternator) is fairly common so that's where I would head at this point. Disconnect the dash pump (if possible) and I suspect things will get worse.

Thanks and good luck, keep me posted!

Expert:  Brendan Block replied 3 years ago.
Did you have any luck with unplugging the pump under the dash?

Please don't forget to leave me a positive rating, it's the only way I can receive credit for helping you!

Thanks and good luck!

Customer: replied 3 years ago.

Hi Brendan,

Thanks for your help. I didn't pursue disconnecting the pump but you have helped me get to the point of understanind the system and where things are located. I would like to close this out and give you a positive rating but I'm not sure how to approach it due to the following: A guy named Pete tried to help intitially and when he was unable to, passed the question on. He asked me for a positive reponse as well which I am happy to do because he was helpful in reviewing the problem and then reaalizing it should be pased on to someone else. How do I go about rating both of you?

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