Mushy/No Brakes

[pavochavo]

Hey everyone. I finally got my 91 GSX Automatic from Florida today. It is pretty decent but has a few issues. The largest of which are brake issues. It has the following upgrades for brakes:

Dual piston caliper front brakes, SS brake lines all around.

Rotors appear to be stock/OE quality all around.


The guy I bought it from warned me the brakes were "mushy". That was an understatement. There are almost no brakes at all. The car will drive fine down the road but it barely will stop. I floor the brakes and it barely stops. The firmness I expect does return when I turn the car off. I can also pump the pedal several times after the car is off with increasing stiffness. The consensus locally is that there is air in the lines. I will be bleeding it this weekend thoroughly.

I checked the fluid and it is fine. I checked for leaks and cannot find any.

Anyone have any suggestions? I did search here and other forums and found mixed suggestions. Brake booster possibly or the master cylinder. I have limited tools or ability so any suggestions or help would be greatly appreciated.

Thanks!
Aaron

 

[GRAVEDIGGER]

It sounds like you need to bleed them real good and see what happens. If you bleed them and are confident that you don't have any leaks anywhere then you can move on to other areas of concern like the brake booster and master cylinder. Good luck.

 

[LiquidX]

Put speed bleeders on the calipers and you might as well put one on the slave cylinder too. Makes bleed jobs a 1 man job and it's VERY quick and efficient.

Just need to loosen the bleeder a quarter turn and start pumping the pedal. Keep an eye on the fluid level and when you are done, just tighten the bleed valve. No need to use a vacuum pump or constantly turn the valve.

 

[pavochavo]

Ok some interesting notes from driving down the road to get an out of state inspection.


First and foremost... holy crap that thing pulls like a s.o.b. and I only went up to about 8 psi before letting off and coasting due to the brakes. The turbo in the car is laggy as hell but pulls like crazy once it hits.

On to the brakes...

Some interesting things here that might help in all of your thoughts and opinions.

There is strange on and off pedal pressure when I drove it down to the dealership for the inspection. No matter what the pressure wasn't great but it definitely varied as I drove. One press would have next to nothing pressure or brake wise and the next would have noticably better pressure but still bad. It varied on and off like this the whole drive. Again the brakes still were bad, very bad, but there was a noticable difference in pressure. I'm definitely thinking air in the lines but I may be wrong as I'm an obvious novice. I also spoke with the previous owner and he stated that the brake master cylinder was brand new with only 200 miles on it. I checked under the hood and just from appearance it does appear to be brand new. Definitely thinking air in the lines.

Feeling the little power I felt really makes me want the brakes fixed!! I'm hoping the bleed this weekend will solve it.

Pavo

 

[knochgoon24]

The pressure varies because the temperature of the air and fluid changes. Once the air in the calipers warmed up, you ended up with a larger volume of air in the caliper. You also might have water in the fluid.

If I were you, I'd completely replace all the brake fluid you can. Just bleed them until you see clean fluid, then bleed them a little more.

 

[pavochavo]

The pressure varies because the temperature of the air and fluid changes. Once the air in the calipers warmed up, you ended up with a larger volume of air in the caliper. You also might have water in the fluid.

If I were you, I'd completely replace all the brake fluid you can. Just bleed them until you see clean fluid, then bleed them a little more.

Definitely a good idea. Might as well do that since I'm bleeding them any ways.


Pavo

 

[knochgoon24]

Even if you brakes weren't mushy, I'd do it since you just got the car, and you don't know how long it's been since it was last changed.

 

[Kickerbeast]

Quit driving the car and bleed the brakes before you kill yourself.

 

[pavochavo]

Quit driving the car and bleed the brakes before you kill yourself.

I've driven it three times since I got the car on Tuesday. Once from the car hauler (one block down the road) to the garage and then a trip to and from a car dealership to get it inspected so I could transfer the title, which was also a block away. I only drove on both trips because it was 100% necessary. Believe me I don't want to crash or hurt anyone or myself. I'm not that stupid. The car will sit now until the brakes are bled.

Aaron

 

[motozachl]

Quit driving the car and bleed the brakes before you kill yourself.

This. Bleed your breaks already and stop making posts on every forum

 

[MIdsm]

Has the master cylinder been upgraded as well? If the calipers have been upgraded the master should have been upgraded as well. Bleeding may help some, but the if the master is too small the pedal will have long travel and give a mushy feeling even if bled properly.

Good luck.

 

[pavochavo]

Just an update for those that care...

Flushed and bled brakes thoroughly over the weekend. Also noticed some goofy bends in some of the rubber hoses that looked like it could be hindering flow. Fixed those and a bit of brakes returned to the car. It definitely stops now but not until almost to the floor.

I am also extremely dumb and realized that the abs has been deleted from the car. The person that owned it just did a hack job. The abs proportioning valve and hard lines are located where the abs used to be and not on the back firewall. I'm going to trace the lines sometime in the next couple of days to see if that is part of the problem and also see if there is another valve on the firewall as suggested by Motozachl locally.

Hopefully that may reveal some problems. I did have a couple of experienced DSMer's come over on the weekend and both believe it is a bad brake booster. I ordered one from Mitsu Graveyard and will be hopefully replacing that this weekend just in case. I suppose it can't hurt to rule that out.

Not too many more things I can replace.

Pavo

 

[GRAVEDIGGER]

Just an update for those that care...
Not too many more things I can replace.
Pavo

Yeah, you'll eventually get it fixed one way or another. Good luck once again.

 

[pavochavo]

Just an update for those that care...

Flushed and bled brakes thoroughly over the weekend. Also noticed some goofy bends in some of the rubber hoses that looked like it could be hindering flow. Fixed those and a bit of brakes returned to the car. It definitely stops now but not until almost to the floor.

I am also extremely dumb and realized that the abs has been deleted from the car. The person that owned it just did a hack job. The abs proportioning valve and hard lines are located where the abs used to be and not on the back firewall. I'm going to trace the lines sometime in the next couple of days to see if that is part of the problem and also see if there is another valve on the firewall as suggested by Motozachl locally.

Hopefully that may reveal some problems. I did have a couple of experienced DSMer's come over on the weekend and both believe it is a bad brake booster. I ordered one from Mitsu Graveyard and will be hopefully replacing that this weekend just in case. I suppose it can't hurt to rule that out.

Not too many more things I can replace.

Pavo

Just a quick update and a little help needed. I apologize for the lack in updating the thread as I've been VERY sick the last two and a half weeks with recurring strep and sinus infection. Two rounds of antibiotics later and back to the car.

I ordered a replacement used brake booster thedsmgraveyard.com (nice guys and great service btw). I went to install it this weekend and there is a distinct difference between the one they sent and the one in the car. The one in the car is very thin front to back, almost frisbee sized by comparison. The one I was sent for a 91 GSX was a lot thicker front to back and the brake master cynlinder they left attached was much bigger than the one in the car.

I've been searching for two days on the net for a clear picture of an OEM 91 GSX brake booster so that I can compare what was in the car vs. what I was sent and cannot locate a clear picture of the one. Usually just engine bay pics of people's cars with partial pics. It's way too difficult to tell.

Does anyone have a 91 GSX brake booster lying around that you could post a picture of? Also does anyone know the part #? I tried looking for that as well with no luck.

One thing of note is that it appears the booster in the car has been replaced. There were two bolts missing inside the car and the smaller booster was very clean and newer looking. The master cylinder looked different also from the one thedsmgraveyard.com sent attached to the booster. The autozone parts pictures online lead me to believe the guy installed an NT or FWD booster/master cylinder into the car and not a AWD.

Anyone have any pics they can post or send me? I appreciate the help as always.

I did post a similar update to Columbus DSM forum but no one has answered so I'm trying here.

Thank you all for the support and assistance.

Robert

 

[motozachl]

Sounds like the previous owner replaced the brake booster with the incorrect one. In my 91 awd the booster was rather thick as mentioned so I would just replace it with the one you just got from the graveyard IMO.

 

[pavochavo]

Sounds like the previous owner replaced the brake booster with the incorrect one. In my 91 awd the booster was rather thick as mentioned so I would just replace it with the one you just got from the graveyard IMO.

Would you replace the master cylinder with the one attached to the replacement booster? They are definitely different in size. I'm thinking I'll just drain the fluid totally and fix the crappy abs delete, master cylinder and booster all at once this coming weekend. There's nothing else it could be I don't think.

I'm just not 100% sure the master cylinder on the one I got it good. Bit risky...


Robert

 

[kenamond]

If there are bolts missing, there's a helluva lot of force on it and it may be flexing away from the firewall.

Also, I had a very similar problem that turned out to be siezed guide pins on the caliper. The torque plate couldn't "float", so when you push on the brakes, you are only pushing on one side of the disc, and that's not enough, because things flex out of the way. It ultimately warped my rotor a bit, too. I screwed around with bleeding for a weekend, and it didn't help (of course). But in my case, the car would pull to the left under braking which made it a bit more obvious that something was wrong on the passenger front corner.

Good luck!

 

[volcomsnow245]

I had the same problem but I didn't have abs to begin with so it didn't matter but when I push the pedal it wouldn't stop. I replaced the front brakes and the pedal still goes to the floor but acuatlly stops now. I'm going to bleed the front brakes today to see what happens.