volare disc brake dragging

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May 13, 2011 | 02:58 PM

cookieman69

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volare disc brake dragging

I have 1955 f100 with volare front end I will list what I have and what I have done to see if anyone has ran into this before , volare clip GM duel master cylinder, 8 inch power booster ,3/16 lines( steel ) rebuilt calipers ,new rubber brake lines residual valve I have checked clearance on rod between m/c and booster 1/8 inch there is play in peddle to m/c when sitting still front wheels turn fine after driving 2 miles front brakes start to lock up further you go hotter they get let cool off ok again same thing again when I go down the road. tryed experamint yesterday when they cooled off I went down road never touching brake and they started dragging again any ideas Thanks Michael

May 13, 2011 | 03:30 PM

sdetweil

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From: Pflugerville, tx

so, it sounds like the booster is pushing on the master rod. just for grins, unplug the booster vacuum, plug the manifold or hose depending on which end you disconnect, leaving the booster with no vacuum.. practice stopping without boost.. make sure you know what you're getting yourself into. test drive

also, maybe the pedal is bouncing against the booster (unlikely)

the booster is probably heating up from the drive. is this under the floor?

Sam

May 13, 2011 | 03:32 PM

GreatNorthWoods

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From: Littleton, New Hampshire

Make sure a 2 lb residual valve is plumbed into the front and not a 10 lb. I think you could also increase the clearance on the MC push rod to 1/4 inch. That would help some...

May 13, 2011 | 03:59 PM

sdetweil

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From: Pflugerville, tx

Quote:

Originally Posted by GreatNorthWoods

Make sure a 2 lb residual valve is plumbed into the front and not a 10 lb. I think you could also increase the clearance on the MC push rod to 1/4 inch. That would help some...

good points.. I missed the residual comment, so this must be under floor..
and you could back off the clearance, finding that clearance balance in city traffic is pain.

Sam

May 13, 2011 | 05:34 PM

cookieman69

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Quote:

Originally Posted by sdetweil

I am having trouble getting a full pedal so i don't want to have anymore play than needed on booster rod I understand as little as 1/16 is ok when this happens I have gotten out and checked for heat in the lines, booster/master cylinder and the only thing that is hot are the calipers ??

May 13, 2011 | 06:13 PM

sdetweil

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From: Pflugerville, tx

Quote:

Originally Posted by cookieman69

well, the fluid is designed NOT to expand or contract. so that ain't it.
you've replaced all the wheel end parts, so THAT ain't it..
we're down to the booster, master or residual valve. never heard of a residual doing this..

sam

May 13, 2011 | 07:06 PM

BBKtech2

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I thinking the residual check like mentioned. Are you sure its a 2lb in the front? Are you sure its plumbed in line in the proper direction? This sounds just like when we used to use the single resivoir fruit jar master cylinders with discs and you had not removed the check valve, the front brakes would apply and heat up.
Making sure the back brakes (if drum) are adjusted up all the way will bring up a low pedal. The huge Volare caliper puck requires quite a bit of fluid to move, hence more pedal travel when applying.

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May 14, 2011 | 12:43 PM

sdetweil

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From: Pflugerville, tx

Quote:

Originally Posted by cookieman69

Well, that means its the residuals probably. Are u sure they are 2lb for disk?

All 4 hung up sounds odd tho
Sam

May 14, 2011 | 12:51 PM

#10

GreatNorthWoods

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From: Littleton, New Hampshire

Are you using a combination valve with the GM master cylinder? Is is possible you have the combination valve plumbed incorrectly? Do you have a high heat source close to a front brake line (like exhaust headers)? I have had a similar problem on two ocassions. On one the front brake lines were clogged and on the second the MC push rod was too long. I have run out of ideas as to what it could be.

May 14, 2011 | 05:45 PM

#11

cookieman69

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I removed residual valve same thing without it I suspect m/c might be to blame but why dosen't it build pressure when I pump it garage

May 14, 2011 | 05:58 PM

#12

sdetweil

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From: Pflugerville, tx

Quote:

Originally Posted by GreatNorthWoods

and he said all 4 were hung up..

Sam

May 14, 2011 | 06:32 PM

#13

GreatNorthWoods

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From: Littleton, New Hampshire

If you figure out what it is I'd surely like to know. Somehow the fluid is expanding in the lines causing pressure that is not being relieved or once the fluid leaves the MC, something is not allowing it to drain back...