Spongy Brakes

[mikeyc4]

Hi guys, went out the vette today, the first real drive for 6months, i was concerned at how poor the brakes were, the pedal went almost to the floor, and the stopping wasnt good, although it will stop you. Could it be that its been standing? No visible signs of a leak, fluid level is ok, although the fluid looks a bit dark. Is this a sign of the dreaded master cylinder? If so, how much do they cost?

My cars a 86tpi coupe.

Cheers

Mike

 

[SPANISHVETTS]

Brake fluid attracts water and should be changed every 2 years or so. Dark fluid is a sure sign of water contamination. Purge the entire system adding new fluid until you have clear fluid coming out of all four brakes. If you still have mushy brakes after you have fresh fluid in the system it is time to suspect the master cylinder.



Master cylinders go for well under a C note. I found a new one on eBay for $25.



It only takes about ½ hour to change just be sure to follow the instructions to bench bleed the new master cylinder.

 

[mikeyc4]

whats the correct procedure for changing the brake fluid? and what kind of brake fluid should i use?

 

[SPANISHVETTS]

I just noticed that you were in the UK. What part are you located in?



Lake Chevrolet www.lakechevrolet.com has good prices on original GM parts, will ship to Europe and bill to a Euro credit card.



I have had good service out of the sponsors of this forum as well. I recently bought a booster from Corvette America. It arrived here in Spain in 3 days!!!



Use DOT 3 brake fluid.



I am late for the shop now. If nobody else answers the how to I will get back with you later.

 

[mikeyc4]

Hi, im located in the Midlands in the UK, so would you change the fluid before doing a master cylinder, just the fact it was stood for 6 months that made me think its the master cylinder.

 

[Hib Halverson]

Hi guys, went out the vette today, the first real drive for 6months, i was concerned at how poor the brakes were, the pedal went almost to the floor, and the stopping wasnt good, although it will stop you. Could it be that its been standing? No visible signs of a leak, fluid level is ok, although the fluid looks a bit dark. Is this a sign of the dreaded master cylinder? If so, how much do they cost?

My cars a 86tpi coupe.

Cheers

Mike

My guesses would be your brakes have ingested quite a bit of air, the master cylinder has a problem or your ABS modulator has air in it.

If the brake fluid has not been changed in more than three years, not only is it time for repairs but you need to flush the system. On an 86, being that the car is 18 years old, I'd service all the brake calipers. too.

Lastly, be very careful buying used master brake cylinders on eBay. You have no way of knowing the history of the part you buy. You might be buying a master cyl. in worse condition than the one you have now.

 

[taegdh]

Well yes, it could be the master cylinder, but I would change out the complete brake fluid first. Sitting six months might not be long enough for that much water to be absorbed. But in all practical application, it is probably 14 year old brake fluid.

I would recommend you have an assistant to pump the brake as you do it. This is also an excellent time to get "one way" valves for the caliper bleeders. Start at the Right Rear, attach a clear plastic hose and have a clean bottle to flush the fluid to. Make certain you have the master Cylinder Topped off before you start, and bleed out all the old fluid, by having the assistant pump the brake slowly, when they let up, make certain you close the bleeder valve unless you've swapped them out to the "one way valves" until the fluid turns clear. Then go to the left rear and do the same, right front and finally the left front. Toppping off the master cylinder each time. Then go and do each of them one time again to ensure you haven't had old fluid get sucked back into the master cylinder.

You might also check the condition of the brake hoses which lead to the calipers, if they are originals, they might be "ballooning" up due to age deterioration. If so, replace them with braided Stainless Steel covered hoses.


This is the less expensive way to do it. If it is still spongy, then you'll have to check the master and the power brake booster. That is quite the job to replace.

Lots of Luck

 

[mikeyc4]

Forgot to say, that the abs didnt kick in when i stamped on the pedal, does that change things at all?

 

[eleebid]

Just had this problem. I replaced all of the brake fluid and the brakes came back. I just checked the fluid today and it is black again. I will need to re-replace the fuid again.

 

[WhalePirot]

I routinely check the brake fluid color and replace when it is quite dark. Frequency depends upon local climate and driving factors. Heat aids in moisture absorption into this fluid; not a good thing.

Certainly, do the fluid change (cheaper) before spending big bucks on parts. A 'spongy' pedal means either air in the a line or a failing master cylinder.

A power bleeding tool can make it a one person job or you can ask a strong-legged helper to pump the new fluid through, pushing the old out. A clean hose, used as described, lets you see when the color lightens. Sequence goes from longest path to shortest, i.e., RR-LF-RF-LF wheel calipers, and DO NOT allow the supply to go dry.

I like Castrol (or others); DOT 3 or 4. Silicone fluid has a higher heat capability; absorbs almost no water but is very costly. It yields a softer pedal and is probably a waste of money for the street.

 

[mikeyc4]

So how come the abs didnt work either?

 

[SPANISHVETTS]

So how come the abs didnt work either?

The ABS only works when the wheels lock or slow down too fast. The same problem that is making them spongy is probably killing the ABS.



It takes an incredible amount of pumping and bleeding to get all of the air out of the system if it enters at the master cylinder. As the Welsh say ¨Benitdonit¨. Get a set of the one way bleed screws; they have trade names like easy bleeders, and save yourself a lot of frustration.



When we are in the UK we usually hangout around Northampton…Thunder is registered in Little Billing. My buddy’s family has an auto recovery service based there.



Tom at Clermont Corvette down in Snodland, Kent has always helped me out when I was in a bind. If it gets to the point that you would rather pay someone to make it right talk to Tom.



Keep us posted

 

[mikeyc4]

Ok, ive got an update on the brakes, apparantly its the servo thats gone, how easy are these to fit? Anyone know where i can get one from in the uk?

 

[SPANISHVETTS]

Spongy and Servo do not go together! If the servo is bad the brake peddle should be really HARD to push down. A long time ago I did a really silly demo for a long lost member named ¨RedHookGirl¨of how to suck on the servo to test it. I do not know if it is still archived or not….do a quick search on brakes or booster, (booster is what we Yanks call the servo) and see what pops up.



To test the servo pull the vacuum hose off of the booster and suck on it until your cheeks pull in. Then stick your tongue over the end of the hose and see if the servo holds vacuum, i.e. your tongue stays stuck to the hose, or not.



If your servo is bad an OEM GM part goes for about $300, rebuilt units go for $150 or so and Eckler´s, Corvette America, and a few others sell aftermarket units for +/- 170.



I have a brand new servo from Corvette America that I ordered in error. If it will solve your problem we can work a deal. http://www.corvetteamerica.com/main.cfm?function=LearnMore&CategoryID=3&PartNo=45491&LearnMoreID=&OrderBy=Description&CFID=2841305&CFTOKEN=41760545



If you would rather talk to a real voice call me in Spain on +34 956 54 34 44 any day after 1600 hrs.