Vaccume problem on Brake booster?

[Joelzme]

Hey all,

I have fixed a lot of my rough idle problems by replacing a faulty MAF. However I am still idling a little rough when stopped for more then a minute with the brake engaged.

I notice that when I press the brake pedal, the rpms drop down some. They recover a little bit when I let off. Is this normal or should they pretty much stay the same? The Brake booster is OEM (1991 2.3L) and I noticed a lot of these problems came on after doing a brake job and bleeding the system.

How do boosters go bad? Do they leak? Would I lose all brake power assist if they were bad? Is there a procedure for checking this out? I have alldata, but there is nothing listed there.

Thanks for the help.

Joel

 

[Mark_88]

Not sure of any actual proceedure for testing the booster, but if you hear a hissing sound when you press the pedal there is a good chance there is a leak in the booster...the seal around the push rod can break and that could cause what you're seeing, but you'd definitely hear something also.

If there was a leak in the hose you'd have other problems with the vac system so it's likely internal to the booster...but take the hose off and check it for cracks...and make sure it is plugged into the booster properly...might help to spray a bit of lubricant around the connector nozzle also, but not usually necessary (except they can be difficult to remove or install when the connector stiffens)...

 

[Joelzme]

I *definitely* get a hissing sound when the brake pedal is depressed. Come to think of it, it sounds like air being ford out of a small oriface. There is also some sponginess to the pedal. I can press it almost all the way in and when I hold it it will slowly start to travel in more.

Does this sounds like the culprit?

 

[Mark_88]

Yeah, the hissing is air by-passing the seal...is the hissing inside or outside the cab? Outside would mean the hose seal and that may be fixable by replacing the outer nozzle where the hose connects...inside would mean you likely need to replace the booster itself...

It's not actually difficult to replace these...remove the master cylinder from inside the hood (careful not to stretch the brake lines or you may need to replace them too) and there are four bolts holding the booster against the firewall...

If you do need to replace the booster make sure you get one from the same year as the push rods can be different lengths...and it may also help to lubricate the brake lines connecting the master cylinder too...I sprayed mine with WD-40 and let that soak in for a bit to try to prevent the lines from cracking...but ended up breaking the front line anyways...they were rusted pretty good though...

 

[Joelzme]

The hissing is loud and inside the cab. My brake lines coming off the master cylinder are in pretty good shape. I was thinking about just getting a replacement that comes with a new master cylinder as it would seem like it's easier to install and my cylinder is oem.

the only thing I am afraid of is the corrosion around where the booster mounts on my firewall. It's pretty rusty there and I dont want it to become a problem. How thick is that metal?

thanks!
Joel

 

[Mark_88]

The firewall actually is reinforced and the booster itself mounts on a column (IIRC) that is attached to the FW. Not to scare you or anything, but that is where my first Ranger had a major problem with rust.

When you take the booster out have a good look at the metal around where the reinforcement plate is and maybe prepare to do some sanding/refinishing/replacment. You can usually tell if there is excessive damage in that area by pulling back the carpet and poking around with your finger or a screwdriver...just not the easiest place to work from...pulling the booster will give you a better idea because it's pretty much open after that is removed...and if you have a clutch check around that as well...my clutch ended up going through the firewall mount even though it was also reinforced...

Fortunately, the new Ranger cab I have is solid...hope you find that out too...

It's a good idea to replace the master as well because they are mated and the depth that the push rod goes into the master is critical...when you buy them together they should already be setup properly so you won't have to worry about that.

 

[Joelzme]

That prompted me to take a look a little further down there. Seems good there is no rust inside and the area around the clutch seems good. Under the hood there is only rust in the top right corner where the reinforced plate attaches to the FW....all in all I think I will be fine with the corrosion.

On a hunch i did the following procedure. Engine off I pumped the brakes to relieve pressure in the booster. I then started the engine with the brake all the way down. When she started the pedal then traveled the rest of the way to the floor with a very noticeable change in rpms (like a vacuum problem). I then released the brake and she REALLY started to idle low, defiantly leading me to believe that it's a vacuum problem with the brake booster. SO I guess I know what I got to do.

Thanks for your assistance in this. This is my first vehicle that I have ever done any work on. I have learned a lot about auto troubleshooting with it and reading on here. I appreciate the help.

Joel

 

[Mark_88]

You're welcome...hope it helps...

Good to hear the firewall is solid..I was thinking about this post afterwards and then thought...gosh, if you change the master you'll need to bleed the brakes...then I remembered the problems I ran into doing that...the bleeder nipples on the rears on mine were shot...you can replace the nipples or for about $20 you can replace the cylinder and it comes with new nipples and everything...but then you have to bleed them.

If you're not familiar with this there is a one-man kit that you can buy for about $10 that works really well...don't need someone to help pump the pedal while you crack the bleeder...I used it for the first time this winter and it worked really good...but, anyways, that's only if you run into problems with them...otherwise, the bleeder kit is a good investment.