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#1 |
Tot Roddin'
Join Date: Apr 2005
Location: Mid-MO
Posts: 24,461
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Brake Pressure Loss
My FIL has a '69 SWB C/10 with a fairly well built 350 running a 292 cam, and it's running power drum brakes. Now for the problem...
When driving the truck it seems like the brake pedal and brakes don't have the grip they should give it's a power drum setup. Now I know drum brakes (even with a booster) are not like disc brakes but when I first purchased my '69 it would lock'em up without a booster. Things we've tried: Vac Canister - No effect Replaced Power Booster - No effect He recently added a 700r4 and had the shop check everything to ensure it was properly hooked up by the PO; everything looks right it just won't stop like it should. We would like to determine the culprit without the need to upgrade to disc brakes. Does anyone have any ideas? Thanks in advance guys! (Pics of the truck to come)
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-Nate ![]() 1969 CST SWB - Project Blank Slate (4.5/6" ECE Static Drop, 6-lug disc brake upgrade (manual), Billet Specialties Vintec 20x8.5 255/40 (F) 20x10 295/40 (R), 250 I-6) 1960 AMF Skylark - Tot Roddin' (Lowered with custom frame; soon to include custom push bar and interior) 2008 Silverado CrewCab 1LT (5.3L, 3:73, 4x4, LT1, Z-71, Towing Package) |
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#2 |
Registered User
Join Date: Jun 2010
Location: Upland Ca
Posts: 4,143
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Re: Brake Pressure Loss
Will it lock up if pressed hard? Are the shoes and or drums glazed over? How much vacuum is the motor making at idle? I'll assume the shoes are properly adjusted.
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1972 C10 SWB, Air, PS, PB, 350/350THM. Second owner. 1965 Corvette roadster, 44K miles, 327/365 SHP, 4 speed, side exhaust, knockoffs, teak, second owner (bought in 1970), Have ALL numbers matching components. My frame off restoration thread: http://67-72chevytrucks.com/vboard/s...d.php?t=556703 |
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#3 |
~Rest In Peace~
Join Date: May 2005
Location: CALIFORNIA NOR CAL
Posts: 9,707
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Re: Brake Pressure Loss
pictures of shoes and hardware please
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is it fast ? it has a lighting bolt donut? B___H please, I can remove 90% of your so called "beauty" with a kleenex |
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#4 |
Eat, Sleep, Drive a Chevy
Join Date: Apr 2010
Location: the town of the cow, Texas
Posts: 1,152
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Re: Brake Pressure Loss
The title of the post says "pressure loss" yet you changed out the vac canister and booster are you feeling like its a hydraulic issue now?
when you changed the booster did you notice any brake fluid inside the old booster where the push rod is? have you looked at the wheel cylinders? have you tried bleeding the brake fluid? also as asked above be sure the shoes are not "glazed" good luck
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Trey Silence may be Golden, but Duct Tape is Silver! 72 Short Step 57 "big window" short step |
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#5 |
Active Member
![]() Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
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Re: Brake Pressure Loss
Usually when you have a sudden loss of hydraulic pressure you check the brake lines, brake cylinders and master cylinder for leaks first. If there's no leaks and it's something that just happened all of a sudden, the master cylinder should be the next suspect. There are some seals inside that leak and allow fluid to be bypassed and not go to the brake cylinders.
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#6 |
Registered User
Join Date: Apr 2000
Location: Bonne Terre, Mo
Posts: 3,005
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Re: Brake Pressure Loss
I personally would want to pull both rear drums and visually check some things. The glazing, evidence of the wheel cyl are not leaking and the axle seals are not leaking grease on the shoes. ( when a truck sits a while those axle seals glaze the shoes in a hurry) Insure the adjustment on the shoes is right upon reinstallation. Then check the front wheel cylinders for signs of leakage on the shoes and readjust the front shoes. Re bleed the system. If you find no evidence of leakage and braking doesn't improve to what your expecting, I would be looking more closely at the master cylinder provided you have good vac pressure into the booster.
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'69 Chevy Long Fleet & '71 GMC Short Step & Project "ODD BALL" "You can wash a pig, soak it in most expensive perfume. In the end it is still just a pig." ODD BALL build thread http://67-72chevytrucks.com/vboard/s...d.php?t=478629" |
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#7 |
Registered User
Join Date: May 2008
Location: Mesa, AZ
Posts: 281
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Re: Brake Pressure Loss
I've never worked on a brake booster, however I have experienced hydraulic pressure loss in a different vehicle. The master cylinder was bad and the fluid would bypass the rings. But this didn't make the vehicle hard to stop, it stopped well, but when sitting at a light or something, with my foot firmly on the pedal, the pedal would slowly sink to the floor. Pressure loss would do that.
But, when I first got my truck, the first vehicle I owned with an automatic transmission, I didn't realize the idle was set too high. This made it a bear to stop. I checked everything in the brakes until I checked the idle speed. The torque converter is designed to transmit very little torque at low RPM (like idle). But as RPM increases, torque does so too, but at an exponential rate. Once I set the idle speed correctly, the brakes worked like a dream. So basically, I was fighting the engine every time I wanted to stop. What's worse for me, not having power brakes, I had to put a lot of effort into the brake pedal to keep the engine from moving the truck. I almost rear ended someone in a drive thru because I didn't realized I relaxed my leg a bit! |
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#8 |
Tot Roddin'
Join Date: Apr 2005
Location: Mid-MO
Posts: 24,461
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Re: Brake Pressure Loss
Sorry guys... been away for a few days. I will print out your recommendations and we'll start looking at the truck. It's been crazy hot here the last few weeks so it might be a bit before I can get my FIL out.
![]() Thanks for all your recommendations!
__________________
-Nate ![]() 1969 CST SWB - Project Blank Slate (4.5/6" ECE Static Drop, 6-lug disc brake upgrade (manual), Billet Specialties Vintec 20x8.5 255/40 (F) 20x10 295/40 (R), 250 I-6) 1960 AMF Skylark - Tot Roddin' (Lowered with custom frame; soon to include custom push bar and interior) 2008 Silverado CrewCab 1LT (5.3L, 3:73, 4x4, LT1, Z-71, Towing Package) |
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