Brakes work but car won’t stop - Ford Mustang Forum
Like Tree6Likes
Reply
 
LinkBack Thread Tools
post #1 of 18 (permalink) Old 09-16-2018 Thread Starter
Apprentice
 
mcc351's Avatar
 
Joined: May 2010
Location: Bridgewater
Posts: 195
 
Brakes work but car won’t stop

I just upgraded my front brakes to Wilwood 4 piston 12.19” discs. There are no leaks, they were bled, the mc is full, rotors were cleaned with brake cleaner. On jack stands the brakes worked. I just tried to take the car for a test spin and can’t stop the car. The e- coating on the rotors is scratched up so it is engaging at some point.
Next issue. Haven’t driven the car in a year. When I fired her up, the engine is racing at around 2500 rpm. When I go into gear, the car accelerates to around 25mph without hitting the gas. Not sure if this is because the choke hasn’t opened yet. So this isn’t helping the brake situation... but I would think the brakes should still overcome this. So maybe I have two problems.
Right now I’m relying on the steep slope on the driveway and slamming the tranny into park to stop the car (not good). Almost hit a tree, the house, etc.

mcc351 is offline  
Sponsored Links
Advertisement
 
post #2 of 18 (permalink) Old 09-16-2018
GT Member
 
Charles Reeves's Avatar
 
Joined: Sep 2010
Location: Knoxville
Posts: 1,434
 
Obviously you need to fix the 2500 rpm problem first (the brakes may be working just fine). If the choke plate never opens, then something in its mechanism is stuck. A quick press and release of the gas pedal is supposed to release it once the engine warms up. Spraying the mechanism with choke/carb cleaner might do the trick.

Hopefully I don't have to point out that you should NOT drive the car again until this is fixed. . .

Beechkid likes this.
Charles Reeves is offline  
post #3 of 18 (permalink) Old 09-16-2018
GT Member
Classic Member
5.0L Member
 
Grimbrand's Avatar
 
Joined: Nov 2016
Location: Sedgwick
Posts: 2,019
 
Garage
Send a message via Skype™ to Grimbrand
When you step on the pedal do they feel soft and spongy? Or is it normal pedal feel but they aren't slowing you down?

If your pedal is going to the floor but the car's not stopping, I'd bet it's air in the system, and you've got more brake bleeding to do. There are a lot of sneaky places for air to hide. Did you change your master cylinder along with the front brakes? Without more info about the changes you made, it might be hard to troubleshoot this with you!
Beechkid likes this.

I smile a lot. It makes people wonder what I'm up to...
Grimbrand is offline  
 
post #4 of 18 (permalink) Old 09-16-2018
PONY Member
 
Travis98146's Avatar
 
Joined: Jun 2016
Location: Seattle
Posts: 932
 
Garage
First off, it sounds like your carb/throttle linkage is sticking. Repair this problem first as 2500 rpm without using the gas pedal can override most of your braking power. Did you try the brakes while just rolling in neutral? You may also have a serious vacuum leak causing the high idle. I'd check all the vacuum hoses.
Travis98146 is offline  
post #5 of 18 (permalink) Old 09-16-2018
PONY Member
 
GT'sGT's Avatar
 
Joined: Apr 2018
Posts: 933
 
Brakes that don't stop the car cannot be described as "working"
Why do you use park? Does neutral not disengage the drive? Are the emergency brakes also not working?
Using park while moving will shear off the park pin in the tranny.
GT'sGT is offline  
post #6 of 18 (permalink) Old 09-16-2018
GT Member
 
Tony 64's Avatar
 
Joined: Sep 2012
Location: Sydney Australia
Posts: 1,050
 
Even if the choke was stuck closed, it shouldn't rev to 2500rpm. A closed chock will hover you around the 1000rpm area. As said above, after a minute or so with choke on, a quick blurt of the go pedal will bring the rpm down to normal idle.
A vacuum leak would not idle the car that high, in fact it would make the car run rough.
I believe your accelerator linkage is stuck near the carby or needs the idle screw wound out. Also check the throttle return spring, this should bring the linkages back to idle rpms.

Brakes,
Start simple and work from there.
Start by bleeding all corners starting furthest away from the MC and work towards MC checking fluid after each bleed.
Some MC's need to be bench bleed before installation and some don't.
Beechkid and Grimbrand like this.

15/5/1964 260 Manual Coupe.
23/3/1965 289 Manual Fastback.
Tony 64 is offline  
post #7 of 18 (permalink) Old 09-16-2018 Thread Starter
Apprentice
 
mcc351's Avatar
 
Joined: May 2010
Location: Bridgewater
Posts: 195
 
Ok I checked all vacuum hoses. Checked intake manifold bolts and carb bolts for tightness. Checked PCV valve. Cecked choke and its wiring. Checked choke valve and throttle linkage... nothing seemed off. I will look into the other items previously mentioned. I should’ve hit the accelerator pedal... sometimes that would do the trick in the past.
The car originally had functioning disc brakes so I stayed with the original style MC already in place.
I bled to he brakes using Mityvac. This is a pump that suck the fluid from the calipers... I bought this so I don’t have to bug my wife to help. But I will re-bleed the old fashioned way in case that is a factor.
E-brake does work and wish I had thought of that. The car was flying back to the garage and I sort of reacted without thinking.
The pin that is supposed to engage the flexplate is most likely shot anyway. When I started the car in park, I got out to check for leaks... then removed the wheel chocks and got in. As soon as I got in, the car started accelerating in park. Silver lining- at least it accelerated out of the garage instead of into the house.
mcc351 is offline  
post #8 of 18 (permalink) Old 09-16-2018
GT Member
Classic Member
5.0L Member
 
Grimbrand's Avatar
 
Joined: Nov 2016
Location: Sedgwick
Posts: 2,019
 
Garage
Send a message via Skype™ to Grimbrand
I don't think you could bleed brakes very well with a Mityvac, honestly. There's just way too much volume of fluid/air that needs to be moved to do it with a little hand pump, useful as that pump may be.

So - that brings me back to my original question: is the brake pedal soft, or firm when you step on it? If it's springy, you almost certainly have air in the lines.

I smile a lot. It makes people wonder what I'm up to...
Grimbrand is offline  
post #9 of 18 (permalink) Old 09-16-2018
Apprentice
 
slimpanama's Avatar
 
Joined: Sep 2012
Location: pcb
Posts: 136
 
Garage
Did you get a larger master cylinder to go with the calipers? the calipers with more pistons need more fluid to make the pistons travel. with out it, the pedal will go to the floor before enough fluid is moved to stop the car. go ahead and plan to get stronger booster to go with the larger master cylinder. pushing more fluid is harder and you will have to stand on the pedal hard to do a regular stop.

Windsor Jr. heads, 4.10 gears, bored to 306, cam, headers, h-pipe, line lock, shift kit, 24lb injectors, and cold air induction
slimpanama is offline  
PONY Member
 
baylensmanfl's Avatar
 
Joined: Feb 2017
Location: largo
Posts: 572
 
Quote:
Originally Posted by mcc351 View Post
nto the other items previously mentioned. I should’ve hit the accelerator pedal... sometimes that would do the trick in the past.
The car originally had functioning disc brakes so I stayed with the original style MC already in place.
I bled to he brakes using Mityvac. This is a pump that suck the fluid from the calipers... I bought this so I don’t have to bug my wife to help. But I will re-bleed the old fashioned way in case that is a factor.
.
The original style master cylinder does not push enough fluid for modern multi piston brakes!There are several bolt on styles that will work with bigger calipers check summit and CJ and the rest of the usual suspects.

Bled the brakes again the old fashioned way , then let the car sit and bled them again!

I'D RATHER GO SLOW THAN NOT GO AT ALL
baylensmanfl is offline  
post #11 of 18 (permalink) Old 09-17-2018 Thread Starter
Apprentice
 
mcc351's Avatar
 
Joined: May 2010
Location: Bridgewater
Posts: 195
 
The brake pedal did feel somewhat soft and spongy. The stock MC has a larger reservoir for the front brakes. I can check with Wilwood on this to see if I need to upgrade the MC. I was planning on upgrading at some point anyway for the rear disc install.
mcc351 is offline  
Apprentice
 
slimpanama's Avatar
 
Joined: Sep 2012
Location: pcb
Posts: 136
 
Garage
its not the size of the reservoir. its the diameter of the MC. the larger the diameter of the piston in the MC, the more volume of fluid that is moved. it wouldn't matter if you had a 5 gallon bucket for a reservoir since the MC is only capable of moving a certain amount.

Windsor Jr. heads, 4.10 gears, bored to 306, cam, headers, h-pipe, line lock, shift kit, 24lb injectors, and cold air induction
slimpanama is offline  
GT Member
Classic Member
5.0L Member
 
Grimbrand's Avatar
 
Joined: Nov 2016
Location: Sedgwick
Posts: 2,019
 
Garage
Send a message via Skype™ to Grimbrand
There is a relationship between piston diameter and braking force. Smaller piston = higher pressure, but less fluid being moved. All of this stuff is really determined by the manufacturer, and it's a pretty close balance. You mess with one thing, and the other thing has to be changed.

Always check with the manufacturer to find out if your parts are going to play nice before you buy, when it comes to brakes. When possible, get everything as a set, because mixing and matching with stuff that's supposed to stop your car could cost lives.
silver69 likes this.

I smile a lot. It makes people wonder what I'm up to...
Grimbrand is offline  
PONY Member
 
GT'sGT's Avatar
 
Joined: Apr 2018
Posts: 933
 
I would say that the lines and all should be replaced with new ones from the same manufacturer if you are replacing part of a system, replace it all, top to bottom.
GT'sGT is offline  
post #15 of 18 (permalink) Old 09-17-2018 Thread Starter
Apprentice
 
mcc351's Avatar
 
Joined: May 2010
Location: Bridgewater
Posts: 195
 
Update- I spoke with Wilwood rep today. He confirmed that the stock MC should be fine as long as it was meant for front discs which it is. I had concerns that the e-coating might be part of the problem but he noted that it will wear off on its own. He did note that the MC should have a min 1” bore. Not sure what the factory had. I did replace the rubber lines with Wilwood braided stainless lines. Almost impossible to re-use the factory rubber lines with the Wilwood calipers. At the end of the day I think I just need to re-bleed the brakes the old fashioned way.

Grimbrand likes this.
mcc351 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Ford Mustang Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a VALID email address for yourself, otherwise you will not receive the necessary confirmation email needed to confirm, validate and activate your new AFM member account.

Failure to provide a VALID email address, will result in the cancellation of your new AFM member account registration.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome
 


Search Engine Friendly URLs by vBSEO 3.6.1