carbdoc Posted November 27, 2006 Share Posted November 27, 2006 This problem, which I originally posted about six months ago, still persists. My 1970 Chrysler 300 with power drum brakes stops as though is has "anti-lock brakes", or as though only the brakes on one axle are working. The pedal has only about 1" of travel before it encounters what feels to be a "mechanical stop", but when a bleeder is cracked (or a brake line is removed from the master cylinder) the pedal goes all the way to the floor as one would expect. Under normal stopping circumstances, the problem is not evident. But under sudden-stop conditions when all four wheels should be locked-up and slidin', the brake pedal hits that 1" "false bottom", stops moving and, instead of the wheels locking up, the car slows and eventually rolls to a stop. There is nothing I can do to force it past the 1"-travel point short of opening the system. This is pretty unnerving since I know that this is not as it should be.Here is what I have done thus far. Five years ago: rebuilt the system completely -- lines, hoses, wheel cylinders, you name it.This year (after this problem surfaced): again replaced the master cylinder (new), replaced the booster (rebuilt by Booster Dewey), bled the system, pulled my hair out.Nothing changes the symptoms described above. Could the little valve inside the junction block be stuck or otherwise fubar? I don't wish to replace it gratuitously just to find that I have wasted time, money and effort and failed to solve the problem -- again.Please let me know if you have encountered this problem and how you solved it -- even if it was on some other brand of vehicle!Thanks!Jeff Link to comment Share on other sites More sharing options...
ted sweet Posted November 27, 2006 Share Posted November 27, 2006 disc on front or drums all around? Link to comment Share on other sites More sharing options...
carbdoc Posted November 27, 2006 Author Share Posted November 27, 2006 Ted,Drums all around. No proportioning valve, just a junction block. I don't wish to install discs; this is a certified HPOF car.Jeff Link to comment Share on other sites More sharing options...
ted sweet Posted November 28, 2006 Share Posted November 28, 2006 i think its a bad master cylinder. Link to comment Share on other sites More sharing options...
carbdoc Posted November 28, 2006 Author Share Posted November 28, 2006 Ted,Do you really suppose that two successive master cylinders would exhibit exactly the same symptoms? The Laws of Probability seem to suggest otherwise to me . . .This problem became evident this past spring when I first took the car out of winter storage. When I put it away last year, it stopped fine; when I roused it from hibernation, it acted as described. My first assumption was, indeed, the master cylinder. But replacing it produced no change whatsoever.Jeff Link to comment Share on other sites More sharing options...
Guest carlnut50 Posted November 28, 2006 Share Posted November 28, 2006 Jeff, If you had a frozen wheel cylinder(s) the fluid would still come to the cylinder and squirt out if you opened a bleed valve, or cracked a line. The master cylinder does not know the difference between a properly functioning cyl. or one that is completely frozen. The hydraulic pressure eventually deadheads either way. Link to comment Share on other sites More sharing options...
Guest carlnut50 Posted November 28, 2006 Share Posted November 28, 2006 Jeff, Jack up all 4 wheels and with a helper,make sure all 4 are actually applying brakes when the pedal is depressed. Link to comment Share on other sites More sharing options...
carbdoc Posted November 28, 2006 Author Share Posted November 28, 2006 Carlnut,Good suggestion. It seems surprising that a wheel cylinder (or two) would seize so completely over the winter in a system which was totally overhauled (including new wheel cylinders) less than five years previous, but it is certainly worth investigating.BTW, I always disassemble new wheel cylinders and lube them generously, particularly the metal pistons which are supposed to stay "dry", with compatible lubricant before installation. Doing so seems to prevent problems later on, but this may prove to be the exception. Thanks.Jeff Link to comment Share on other sites More sharing options...
Guest edalfa Posted December 16, 2006 Share Posted December 16, 2006 My memory has been jogged a bit. I had a 72 Newport in the late 70's and it seems to me there was some kind of rudimentary "antilock" system discussed in the sales literature that came with the car. It was undoubtedly optional and my car did not have since the only options were a rear window defroster(!) and a vinyl roof.Ed Link to comment Share on other sites More sharing options...
carbdoc Posted December 16, 2006 Author Share Posted December 16, 2006 Ed,You are right. I may be mistaken, but I think that this option was available on Imperial starting in '71 or '72 -- or perhaps it was standard on Imperial and optional on everything else. I had forgotten all about this feature, too, until you jogged MY memory. I wonder how many of the surviving cars still have operating ABS . . . I have owned my '70 for nearly 14 years, driven it tens of thousands of miles and been over every square inch of the braking system; beleive me, it does not have nor did it ever have anti-lock brakes. It never stopped that way either, until this year!Jeff Link to comment Share on other sites More sharing options...
Guest edalfa Posted December 17, 2006 Share Posted December 17, 2006 Jeff,I wouldn't be surprised if it were an Imperial only option. The cutting edge stuff always started at the top.I'm curious about your booster rebuild. Was there a problem with the booster? I can't recall what the early 70's Mopar configuration was but it seems like an unusual step for your symptoms. GM booster failures that I've experienced tend to go to the floor. But come to think of it, when I left the vaccuum hose and check valve off of my Nova, the symptoms were pretty similar to yours. The pedal went pretty far down but then it was like stepping on a brick with minimal response. (lucky thing my neighbor had a long, uphill driveway!)Ed Link to comment Share on other sites More sharing options...
carbdoc Posted December 18, 2006 Author Share Posted December 18, 2006 Ed,Exactly. Here is the shortest version of the long story which I can muster.I took the car out of winter "mothballs" in April or May of '06. It stopped as if it had anti-lock brakes. I observed that the master cylinder (rebuilt five years prior) was leaking from the rear, so I replaced it with a brand-new one. No change. I called Booster Dewey who had rebuilt the booster five years prior, and he opined that the booster had been damaged by the leaking master; made sense so, after checking my booster's vacuum hose for clogging/collapsing, I sent it off to be rebuilt by him again. No change.I called Dewey again, and he suggested trying an alternate style of booster which was offered in '70, so I had him send me yet another rebuilt unit of that type. No change.I have bled and re-bled the new master, bled the brake system at each wheel cylinder and torn most of my remaining hair out: no change. The car is now put away for the winter; this problem will now wait until next spring to be re-addressed.Thanks for the input!Jeff Link to comment Share on other sites More sharing options...
Guest edalfa Posted December 18, 2006 Share Posted December 18, 2006 One last question. Did Mother Mopar list different master cylinders to correspond with the different boosters? Enjoy your holiday.Ed Link to comment Share on other sites More sharing options...
ted sweet Posted December 18, 2006 Share Posted December 18, 2006 u need to pull the wheels are check everything. Link to comment Share on other sites More sharing options...
carbdoc Posted December 19, 2006 Author Share Posted December 19, 2006 Ed,If so, I am not aware of it. The disc brake option, of course, used a different master with unequal size reservoirs.Ted,That is exactly what I intend to do before the 2007 touring and show season begins.And to all of my fellow AACAers, I hope everyone has a Merry Christmas and a Happy New Year!Jeff Link to comment Share on other sites More sharing options...
rocketraider Posted December 22, 2006 Share Posted December 22, 2006 I think you have one or more frozen wheel cylinders. My Toronado w/ drums did the same thing several years ago- 2 days before we were leaving for the Olds Nationals! I can about guarantee the Chrysler w/c is easier to remove than a Toronado front. Have to take the dadblamed knuckle loose to get the brake hose off... Link to comment Share on other sites More sharing options...
Guest Randy Berger Posted December 22, 2006 Share Posted December 22, 2006 I think rocketraider is right. If not completely frozen, the pistons are not moving smoothly in one or more WCs. Link to comment Share on other sites More sharing options...
carbdoc Posted December 23, 2006 Author Share Posted December 23, 2006 Thanks, Glenn and Randy. I will definitely check out those wheel cylinders. Have a Merry Christmas!Jeff Link to comment Share on other sites More sharing options...
Guest Posted December 23, 2006 Share Posted December 23, 2006 Post deleted by psatchwill Link to comment Share on other sites More sharing options...
carbdoc Posted December 24, 2006 Author Share Posted December 24, 2006 Satch,Thanks for the tip! I replaced all of the hoses five years ago (along with everything else), but that doesn't mean that one of them hasn't failed prematurely. However, if this is so, why am I getting fluid to squirt out of the rear wheel cylinders under pressure when I bleed 'em? Jeff Link to comment Share on other sites More sharing options...
LARRYCAROL Posted December 27, 2006 Share Posted December 27, 2006 Jeff I just read about your problem & every time i have seen this it was caused by too little vacuum at the booster. The port on the manifold could be clogged, the check valve stuck, or as i had on my ford the rubber hose was bad. That hose is special & if you us fuel line hose it can colapse inside.I hope this helps. Larry Link to comment Share on other sites More sharing options...
carbdoc Posted December 29, 2006 Author Share Posted December 29, 2006 Larry,Thanks, Ill be sure to check it out. In the past, I have recieved only funny looks when requesting "brake booster hose" at the auto parts store so I have learned to request transmission cooler hose instead. It is much stiffer and resistant to kinking and, as you point out, internal collapse. Link to comment Share on other sites More sharing options...
Jim Cannon Posted December 30, 2006 Share Posted December 30, 2006 Any chance of any oil or grease contamination on the brake lining of just one wheel? I had a '41 Chrysler that would occasionally bleed a little wheel bearing grease on one front wheel and that wheel would really chatter when braking. Locked up sometimes. New grease seal on the front wheels fixed it. A little oil could have run down on one brake shoe over the winter on your car... Link to comment Share on other sites More sharing options...
carbdoc Posted December 31, 2006 Author Share Posted December 31, 2006 Jim,I have had difficulty keeping the Chrysler's rear axle seals from leaking since I've owned it, so I am very familiar with the sensation which that causes. Leaking seals create a completely different feel; this problem feels as though the car has a "steel block" bolted to the toe board which is preventing adequate brake pedal movement. You get the impression that with just a bit more pedal travel the car would stop just fine. Open a bleeder or a line, the "steel block" goes away and the pedal goes straight to the floor. The problem, however, returns as soon as the hydraulic system is closed again. I can't describe it any more accurately than that.JeffJeff Link to comment Share on other sites More sharing options...
Guest aussie610 Posted January 1, 2007 Share Posted January 1, 2007 Dumb thought, when the master cylinder was replaced, did you replace the bar that pushes on the master cylinder (Sorry not good with this modern stuff) We had a similar problem with the Graham, and the rod that activates the master cylinder was bent slightly. Link to comment Share on other sites More sharing options...
carbdoc Posted January 2, 2007 Author Share Posted January 2, 2007 Neil,Thirty-seven years old and HPOF-certified is "modern stuff" . . . ?Both pushrods (pedal-to-booster and booster-to-master) are in good shape. Believe me, I know: I've taken them off and reinstalled them enough! But thanks for the input.Jeff Link to comment Share on other sites More sharing options...
Guest windjamer Posted January 4, 2007 Share Posted January 4, 2007 Jeff, please pull the vacume hose at the booster. Should have min. 17-18 in. vacume.Check for build up of carbon at vavume sourse and hose and the valve between hose and booster. Dick. Link to comment Share on other sites More sharing options...
Rusty_OToole Posted January 4, 2007 Share Posted January 4, 2007 This may sound strange but a flex hose can fail in such a way that a flap of rubber blocks the hose. The harder you push the brake pedal the harder it shuts off the fluid. When you release the pedal it relaxes and allows fluid to flow thru slowly.Try slamming on the brakes on a dirt road. When no other traffic is coming of course. Check the skid marks and see which brakes are locking up and which aren't. This will at least give you a clue where to start looking. Link to comment Share on other sites More sharing options...
carbdoc Posted January 6, 2007 Author Share Posted January 6, 2007 windjamer,I seem to recall having checked the hose already, but I'll certainly do it again.Rusty,Good suggestion; I'll try it!Jeff Link to comment Share on other sites More sharing options...
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