Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2145783
09/01/16 11:29 PM
09/01/16 11:29 PM
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Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
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Posts: 36,041
Lincoln Nebraska
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Strange though, the pedal goes to the floor when bleeding, but seems to stop part way down with the bleeder screws closed, feels like there is a physical stop. put a block of wood under the pedal to limit its travel to the normal height (anytime, when checking or bleeding). clarify about the pedal stopping halfway down (which it would do if the brakes were functioning normally), more details please
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2146080
09/02/16 12:40 PM
09/02/16 12:40 PM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
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Circle Track
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this is power discs/drums right? (1) recheck the round pushrod nub clearance (2) take the line off of the MC front port (for the rear brakes) & cap the MC with the brass inverted flare male plug fitting & drive it & see how it acts with us isolating the front discs
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2146295
09/02/16 06:07 PM
09/02/16 06:07 PM
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BcudaChris
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Will do.
I also had one of the MC-Prop valve coiled lines with one coil above the MC. Rectified that and will bleed, test and recheck the pushrod clearance before isolating the front.
Might not get the opportunity until Monday though.
Last edited by BcudaChris; 09/02/16 06:09 PM.
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2148861
09/06/16 03:12 PM
09/06/16 03:12 PM
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BcudaChris
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Allright, so here is the latest.
1st, I have NOT yet isolated the front brake channel and tested.
What I have done is re-bleed the brakes (using a 2.4 under the pedal) after re-routing both MC-prop valve lines such that all of the coils are below the level of the MC mounting. I also visually verified brake operation at all four corners.
The result is a HARD pedal that feels as it should, and normal braking is as it should be. That said, no matter how hard I stand on it at any speed, not even the rears lock up and it gently slows to a stop after a much longer distance than it should. The pedal does not pump up, and braking begins immediately upon pushing the pedal.
Could this symptom be caused by an MC mismatch? I replaced the stock replacement (Big A Auto no less!) MC with a KH unit from Rock Auto listed for an 89 Diplomat. It is listed as having the desired bore. Several aftermarket brake manufacturers list "Master cylinder bore size too small for the system volume requirements." in their troubleshooting guide for "Poor Brake Pedal" but the symptom is no more specific than that.
Last edited by BcudaChris; 09/06/16 03:22 PM.
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2149198
09/06/16 10:27 PM
09/06/16 10:27 PM
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Posts: 36,041 Lincoln Nebraska
RapidRobert
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I had that real drawn out stopping distance once & it was a partly crimped front line (before the splitter so both fronts affected) on the stock car but people have reported that too large of MC bore dia will give an inodinately hard pedal to the point of literally having their a$$ up in the air stomping on the pedal to generate any force but that ain't been my exp with the 1&1/8 MC I used on my 65 dart (& I ain't that strong). what Bore is yours? I gotta lean toward a partial blockage of some sort & I would go ahead & isolate the halves again for a start
live every 24 hour block of time like it's your last day on earth
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2149642
09/07/16 03:04 PM
09/07/16 03:04 PM
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Posts: 14,889 up yours
Supercuda
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Rear brake performance can be affected by wheel cylinder size as well.
Larger bore rear wheel cylinders put more force on the shoes than smaller bore.
You all may be focusing on the wrong end of the braking system.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2149697
09/07/16 03:54 PM
09/07/16 03:54 PM
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Stock for what though? Cause you say this Of note, through all of this I've replaced both rear wheel cylinders (one defective, and one because I needed a later style one to go with my AL master cylinder (bran new for an 89 Diplomat) and the RF caliper after I broke the bleeder screw off. And it's confusing.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2149711
09/07/16 04:12 PM
09/07/16 04:12 PM
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So, you have a mostly stock 73 Cuda disc brake car with a late model M/C?
I did that when I converted my 65 Cuda to discs, Mushy pedal no matter what so I just went with a 4 bolt disc M/C.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2150071
09/08/16 12:14 AM
09/08/16 12:14 AM
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BcudaChris
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Lines inspected, no kinks or reduced line diameter anywhere where I monkeyed with them. I did not chase all the lines to the end of their route however. Rear channel isolated, noticeably reduced braking performance, but still unable to lock the fronts. De-isolated the rear channel, bled and back to the former situation. The 3/32" smaller than stock bore diameter is all I can think of that *may* cause this symptom at this point. This will teach me to cheap out. Anyone need a new 1 1/32 MC? I may have one available Any other thoughts on troubleshooting avenues guys, before I part with more cash? PS, I just noticed I failed to cite the Ehrenberg Disk-O-Tech article a couple of posts back. I poached that text right from the MA website.
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2150105
09/08/16 01:03 AM
09/08/16 01:03 AM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
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Circle Track
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Lincoln Nebraska
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I still think not enough psi is reaching the corners. I also dont think the 1&1/32 bore is a problem. a 2000 psi gauge hooked to the corners would ans that (I have one & it was cheap). you know what I would do, just me I would run some parts house prefabbed 3/16 line from the MC port next to the firewall to a brass inverted flare "T" then run both outlets to the front discs (with the other MC port capped). with it bled out if it wont lock em it'd have to be the calipers (one or both) or the MC. those lines are pretty reasonable as are the fittings & you have been comfortable with the fabbing you have done so far in diagnosing this
live every 24 hour block of time like it's your last day on earth
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Re: Drum Brake Troubleshooting
[Re: BcudaChris]
#2150107
09/08/16 01:08 AM
09/08/16 01:08 AM
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rhad
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way back when i had a older (70's) winnabago motorhome come into my shop with back brakes completely burnt up,even cracked one drum,someone had replaced the master cyl about 300 miles back down the road,i replaced everything on the rear brakes,took it for a drive and it wouldnt stop well just slow down no matter how hard you pushed on the petal,after some head scratching i decided it had the wrong (to small) master on it)put the correct master on it for a 400 series truck and that fixed it,however the problem started when the owner left the other shop he forgot to release the parking brake,and drove it that way for around 300 miles without knowing it hope this helps some a true story!!
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