Sixer
Well-Known Member
67 R/T, power drum brakes. Pedal travel seems normal. As applied-1" nothing, 1 1/2" nothing, 2" instant stop-fells as though lockup is imminent. On dry street one thing, in wet could be a killer. Ideas?
Grabby brakes
- Thread starter Sixer
- Start date
See if the rear brakes are actually working.
If there's lots of room between the shoes and the drums, this could be a symptom of that. I've seen people who know the shoes and drums are shot, run the adjusters in until the grinding stops.
If there's lots of room between the shoes and the drums, this could be a symptom of that. I've seen people who know the shoes and drums are shot, run the adjusters in until the grinding stops.
Sixer
Well-Known Member
MoparMikey
Well-Known Member
As stated earlier, the shoes are probably out of adjustment (too much space between shoe and drum)
check brake shoe lining......if grease or some other lubricant gets on them... they will grab.....not slip like you think it would. think about all new springs and adjusters also...not all that expensive !
Sixer
Well-Known Member
All good ideas. According to the seller, the brakes are pretty new, and the booster and master cylinder are definitely new, so hopefully it's just an adjustment. Does seem to have quite a bit of pedal travel before the hit comes. As weather here precludes my driving it to work (full shop) it will have to wait for better weather. I'm too damn old to crawling around on a garage floor anymore!
67 coronet
Well-Known Member
first shots would be adjustment,or poss axle seal leak contamination.sounds like you need to pull them to check for sure.
Sixer
Well-Known Member
They hit way too hard to be a rear problem-and they hit hard enough to lock the rear were that the case. I suspect poor adjustment 1st case-pedal travel is fairly long, then WHAM they hit, and hit hard. Modulation is near impossible. been a long time since I had a car with drum fronts (and these are fairly hefty ones at that) so the delayed contact/heavy self energizing combined with a power booster idea works for me. No evidence of rear seal leakage.
Sixer
Well-Known Member
Another thought I've had is that due to the PO putting in a new booster AND master he may have inadvertently (or stupidly) installed a unit meant for disc brakes. That would certainly give the front a severe bias and over-boost. We shall see.:icon_sad:
Sixer
Well-Known Member
Guess what? Got home from work-popped the hood-sure as ****-split master cyl, 1 large (DB) chamber, one small. Large chamber at rear of MC, assuming that's the Mopar disc brake style. Would explain why these brakes come on like I'm tryin' to stop a 747. Thanks for the replies guys, there WILL be more, I'm sure. Funny though as the PO told me a shop bled the system and could not explain why the brakes were so touchy-keep in mind that few are schooled in oldskool. Try and explain polarizing a generator........
MoparMikey
Well-Known Member
That makes no difference. Hydraulic function is based on the bore size, bowl capacity has nothing to do with it. 1" disc master = 1" drum master. The extra bowl capacity is only for the increase in piston volume so you don't run out of fluid as the pads wear (move) out. Now you could have too large of a bore (1 1/8") coupled with a good size booster will overpower the smaller drum cylinders which may very well be your case. Check the master, if it's 1 1/8" bore change to a 1" bore. Power drum/drum cars came with 1" bore normally.
Sixer
Well-Known Member
Makes sense. Thought it might be the answer, as the larger fluid demands of the caliper would require more fluid delivery capacity. They do both use a 1" bore as per the manual, once I saw that I kinda deflated a bit. Oh well, back to the drawing board. I may just shitcan the fronts and get Summits disc conversion.
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Sixer
Well-Known Member
Has anyone here used a disc conversion kit from Matts Classic Bowties? How about Master Power Brakes? Or can you recommend one. Thanks
Sixer
Well-Known Member
Thanks for the response concerning disc conversion-of which there were none. Good posts on the issue, then suddenly nothing. Why? As I acclimate myself to the move here, I expect some reluctance to deal with the new guy, but I would surely hope that any and all requests for relevant info would be offered. I have been in forums for years, 90% of which were technically oriented. I have much to offer, can you not share?
scotts74birds
Well-Known Member
I have no experience with the aftermarket conversions. But here is a link to very popular, [and in-expensive!] factory disc conversion. http://www.moparaction.com/tech/archive/disc-main.html
If you have a disc master on an all drum car you need to fix that first. The drum brake master has a residual pressure valve but the disc brakes don't require that. What will happen is the small reservoir (rear brakes) will contact before the fronts so the whole system is out of balance. Also, as mentioned, if you have grease on the shoes that will cause your brakes to be an on / off switch. You may have two problems here. Get the drum brake MC and check the rear brakes. If you have rear end oil on the shoes that means both axle seals are bad. There is the seal in the housing and a seal in the axle retainer plate because the rear axle bearings are not lubed with rear end oil like other cars and must be packed with grease.
Sixer
Well-Known Member
Leaning more and more to just kitting the fronts, still don't know if I have seal leaks for sure but there is no evidence visible so far. The action of theme sez otherwise, so I'll have to wait until I can get him up on the hoist and disassemble. By the way, when did Mopar quit the lefty/righty on wheel nuts? The kit I'm looking at is only $450 and uses the same components more or less as listed at the moparaction site.
Sixer
Well-Known Member
Well, after pulling the brakes apart this weekend, I made a call to Right Stuff today and ordered up a disc conversion setup, complete with master and booster. The drums are out of round, turned to near limit, shoes thin and needing replacement, so the hell with it, I'm gonna do it once and do it right. It still appears to be a booster/master issue-loosen up the shoe adjustment and it just takes longer for the grab to occur-tighten them up and it moves to the top of the pedal, but still it happens. Can be modulated, but only with very careful application-and slow speed is spooky. Could be a damaged booster-just don't know. But the car drives terribly this way, yet goes down the road nicely. Enough. Thanks for the help.
I had the exact same problem with my 68 GTX. I put a dial indicator on the drum where the brakes touch and they were totally OUT OF ROUND ( WARPED ). When I would slowly apply the brakes the drums would get close to the inner diameter of the drum. Then grab hard because of this out of round When I came to a stop sign or intersection. I had the drums turned and it fixed the grabbing. Does not take much to warp 11" drums.
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