|
|
|
Your donations help keep this valuable resource free and growing. Thank you.
|
Brake expectations |
Post Reply 
|
Page 12> |
| Author | |
jfcwilson94 
AMC Fan 
Joined: Jun/05/2018 Location: Chapel Hill, NC Status: Offline Points: 17 |
 Post Options
 Thanks(0)
 Quote Reply
 Topic: Brake expectationsPosted: Jul/19/2018 at 3:56pm |
|
Hey all, my brakes have always been more then a little underwhelming, but I just went through and did new rotors, pads, master cylinder, booster, and got the system bleed professionally. The result is that theres no more squish in the brakes, but it just doesn't stop the car very quick. I have to push the pedal all the way down to get any braking, and the smallest let up from the floor results in brake dragging and car movement. So I guess I'm asking: should I expect better? Or is this as good as it gets for a '73 ambassador?
|
|
 |
|
|
jpnjim
AMC Addicted 
Joined: Nov/25/2007 Location: New England Status: Offline Points: 2752 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/19/2018 at 4:23pm |
|
I'm pretty sure I'm going to go through the same thing when I get my 71 Javelin back on the road. It's too bad, because the Jeeps I daily drove once I stopped D.D.ing AMC's all had much better brakes than my AMC's even though the brakes were the same size as the AMC's and the vehicle weights were similar. My only hope is that somehow the "wooden-ness" of my AMC brakes in the past was because I never bedded the pads in properly. It could also be compound related, or maybe the older AMC boosters just aren't up to snuff. Swapping in a later Jeep booster into earlier Jeeps seems to wake them up so maybe that's what our AMC's need too(?) For what it's worth I've heard many say that the Kelsey Hayes brakes (that I have, and I guess you have too) are some of the best stopping AMC setups, maybe someone with expertise in setting them up will post in this thread.
|
|
|
71 P-code 4spd Javelin/AMX
some Jeeps and some Fords |
|
|
|
|
billd
Moderator Group 
Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/19/2018 at 5:05pm |
|
Depends on the pads you had put in - if you put in HARD pads, which is actually the trend, IMO, then you get more life, but not as STICKY a pad, so it takes more push to stop.
More sticky pads will likely be your preference, but they don't last as long. The newer pads, in my opinion, and that's based on the last several brake jobs I have done, simply aren't as sticky as they want to be able to guarantee them forever. Even those I put on my 73 are underwhelming - but they are the new material, harder pads and not as sticky. On other words, check what the pads are made of and the CoF (coeffecient of friction) is on the edge of the pad. I bet it's a lower CoF than what you may have had originally. We discussed CoF in my thread about converting my 73 Javelin to K-H heavy-duty brakes. Yeah, for the rotor mass and pad and caliper size, I expected tire-squealing performance, but the new pads I put in just won't do that. It stops, but I have to push. On the other hand, I'll likely die before these pads need to be replaced!
I could say that the finish they put on rotors if you have them turned can matter for a while, and if the brakes end up gettiing hot or burnished before broken in - I have seen that over the years, too. We always used to tell people avoid emergency get-em-really-hot sorts of stops for a few miles. That was years ago, previous brake lining materials and rotor finishes. |
|
|
|
|
Red Devil
AMC Addicted
Joined: Jul/10/2007 Location: Canada Status: Offline Points: 1743 |
Post Options
Thanks(1)
Quote Reply
Posted: Jul/19/2018 at 5:11pm |
|
Were rear drum brakes fit with new parts? It's a braking system - front & rear. Both need to be working properly to have good balanced braking.
If you have to push the pedal to the floor to get any braking, then something's not right: - system not bled properly ... how confident are you in the "Professional"? Car shouldn't have left their shop if you have to push the pedal all the way down to stop. - contaminated fluid - when was last time system was flushed? - rear drums not adjusted properly resulting in excessive pedal travel - new booster pushrod not adjusted properly resulting in excessive pedal travel - new pads and shoes not bedded yet to the discs and drums ... old days could get shoes arced to match the drum for proper braking from new rather than having to wear them in. Some places that reline shoes will still arc them if you give dimensions, e.g. Porterfield. High braking effort: - incorrect or malfunctioning booster or engine vacuum too low to provide full boost ... does it have a lumpy cam? - poor pad/shoe compound or mis-matched compound - glazed or contaminated pads or shoes - pads or shoes not bedded - caliper or wheel cylinder seals dragging ... when were calipers and wheel cylinders last rebuilt/replaced? - incorrect bore master cylinder (too big ... but that would typically cause a high pedal) - faulty brake control valve limiting rear pressure too much or restricting flow - pedal or pushrod bushings worn & damaged causing high friction There are also higher CoF/higher temperature range pads and shoes available from a few aftermarket sources that can increase braking force and/or reduce effort and also reduce fade to improve overall braking performance. Parts store replacements aren't always the best. At max braking effort (max pedal push force) you should be able to lock the tires. If you can lock the tires and braking is poor, issue is tire grip not the brakes. May need to take it to another shop. Hope this helps,RD |
|
|
|
|
Trader
AMC Addicted
Joined: May/15/2018 Location: Ontario Status: Offline Points: 6876 |
Post Options
Thanks(1)
Quote Reply
Posted: Jul/19/2018 at 5:43pm |
|
I just went through the dead opposite experience. The brakes grabbed with little petal and little effort.
Napa lost my original booster and sold me a "booster" that they stated would work. Well it did bolt up and did work, but too well. At AMO I bought an original rebuilt unit and the difference is night and day. I now have pedal travel and very good braking. This is with new ceramic pads - no fade and can lock it up at any speed. I would be looking at the booster for pin adjustment and holding vacuum from your description. Try plugging the booster vacuum off and see if there is a large difference. If there is not much then that booster is not adjusted, leaking vacuum or just plain wrong booster for the car.
|
|
|
|
|
jfcwilson94
AMC Fan
Joined: Jun/05/2018 Location: Chapel Hill, NC Status: Offline Points: 17 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/26/2018 at 3:24pm |
|
It seems like the problem must be the booster. I plugged the vaccum and the pedal got a lot harder. I'm not sure what's wrong though--the pedal is easy to push down when the booster is hooked to vaccum, but it just doesn't lock up the brakes. By the time I hit bottom on the pedal the car is just barely stopped.
|
|
|
|
|
73Gremlin401
Supporter of TheAMCForum 
Joined: Mar/02/2013 Location: Stmbt Sprgs CO Status: Offline Points: 946 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/26/2018 at 3:35pm |
This sounds exactly like what I'm dealing with on my Concord now - pedal is definitely 'assisted' but doesn't seem to accomplish much in terms of actually stopping the car. I'm 99% sure I've got a slowly leaking diaphragm. I tried driving with the vacuum line disconnected and plugged, and the motor ran slightly better, and the brake pedal got super hard, which seems to confirm my suspicion. so I'll be pulling the booster shortly to get it rebuilt, and see what happens then... |
|
|
73 Gremlin 401/5-spd.
77 Matador Wagon 360/727. 81 Jeep J10 LWB 360/4-spd 83 Concord DL 4-dr 258/auto  |
|
|
|
|
FSJunkie
AMC Addicted
Joined: Jan/09/2011 Location: Flagstaff, AZ Status: Offline Points: 4742 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/26/2018 at 4:25pm |
|
You should be able to stand that Ambassador on its nose with not much pedal effort when the brakes are operating as they were designed. Engines that are not running well won't produce much vacuum nor do engines with big cams. Low vacuum won't give you much brake boost. A faulty booster won't give much boost either. All result in a pedal that is extremely hard to push but the pedal won't be low to the floor. A low pedal is often an indicator of total hydraulic failure in either the front or rear brakes so you are running on front or rear brakes only. The pedal will be extremely low, just off the floor in that case. It's a limp home mode.
|
|
|
1955 Packard
1966 Marlin 1972 Wagoneer 1973 Ambassador 1977 Hornet 1982 Concord D/L 1984 Eagle Limited |
|
|
|
|
jfcwilson94
AMC Fan
Joined: Jun/05/2018 Location: Chapel Hill, NC Status: Offline Points: 17 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/26/2018 at 4:40pm |
|
Neither of the above scenarios are the case here-- the pedal is easy to push, it just doesn't stop the car well. and it returns all the way up, does not hang near the floor
|
|
|
|
|
tomj
AMC Addicted
Joined: Jan/27/2010 Location: earth Status: Offline Points: 7539 |
Post Options
Thanks(0)
Quote Reply
Posted: Jul/27/2018 at 12:43am |
|
pro work or not, it sounds like you have multiple problems. bleed the brakes again, furthest wheel to closest. if that doesn't do it, pull the master and bench bleed it. i find it takes a lot longer to bench bleed than ever seems reasonable. every single tiny barely perceptible bubble must be gone, if even one microscopic bubble appears, keep bleeding. there's no shortcut. it's gotta be bench bled. then reinstall and bleed the system. i would think a dud booster would make the pedal be extremely, too-firm, not soft. something's wrong. i haven't had power brakes for so long i can't comment further. but a solidly air-free manual brake system will have a short stroke and rock-solid stop well before the pedal bottoms. wheel cylinders or calipers waaaay out of adjustment will also make brakes have huge travel. |
|
|
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
|
|
|
|
Post Reply
|
Page 12> |
Tweet
|
| Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |
Click for TheAMCForum Rules
Topic Options
jfcwilson94 wrote: