Hey guys im still trying to figure out why when I am running the a/c it blows through all the vents but as soon as I push the gas in drive, the air stops blowing through all vents and only blows through the defrost vents, as soon as I let off the gas the air starts blowing through all the vents again. I checked all the vacuum lines and the vacuum ball. I didn't find anything unusual. I converted the Bendix 9 anti lock brake system on this 89 Laredo over to just a vacuum brake booster and master cylinder. I am wondering where I am loosing vacuum at and how do I tell if my vacuum canister is bad. I noticed on a 91 at the junk yard there was some kind of thing that the vacuum lines ran into with a electrical connector plugged into it. The vacuum lines ran to this device and then into the passenger side firewall. I was wondering if this was some kind of vacuum assist device that was needed to compensate for the extra vacuum that was being pulled for the brake booster or something. What is this part called and do I need to add this part and can I connect it without having to do a bunch of electrical work?

 

I had the same problem, I had a leak right where the line went through the firewall. I started by pulling lines off and seeing where i had vacuum and where I didn't.

 

The first thing to check is the vacuum reservoir just behind the front bumper on the passenger side. They crack, or get hit or the fittings get knocked loose.

 

Problem solved found two little holes by firewall. Used my vacuum tester and found them.

 

i have the same problem, can you throw some pictures please? Im new to the ac repair

thanks

 

I followed the line from my firewall to the vacuum bulb and then pulled the line off. I first hooked the vacuum pump to the bulb and it didn't loose any air after pumping it up so then I connected it to the end of the line going to the firewall and I could hear a leak so I cut the line at the hole and put some hose on and connected the two ends back together. Then I tested it again and still heard a leak so I found another hole and did the same thing, spliced in a little piece of hose. Checked the vacuum again and didn't lose any air. Now everything works

 

Im getting ready to swap out the Bendix ABS system in my 91 for just a standard booster.

Can you tell me what parts you pulled out of the donor XJ? Was it just the booster and MC? That's what I've heard, but I can't seem to find a write up on it with the search function. (which is how I found this thread)

Thanks for any help.

Dutch

 

I pulled the prop valve and the booster and also the master cylinder, also the hose that goes from the booster to the engine, the brake switch was a little difficult to figure out on mine. No one I have talked to has a brake switch like mine so u might get lucky. I also bought one new brake line from Napa. My brakes suck still because I am running 35s so what I recommend is that you find a brake booster that has the dual diaphram I have read on here that it make a big difference.

 

You will need a double flaring tool and some new fitting so I suggest that when u take the stuff from the Doaner to cut the brake line so that way you have all the fittings you need already attached if you need them

 

This was a very tricky task to switch out this system it took alot of thinking and I ran into a bunch of problems that I shouldn't have but it works