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No Front Brakes!

C

cbucket

Member
No, I'm not stupid enough to build a car with no brakes, the ones I have aren't working properly.

This set up is all new parts - everything. The M/C and pedal assembly is Speedways under floor kit, Dodge rear end with standard drum brakes (everything replaced) and new Disc/rotor on the front. 2lb (front) & 10lb (rear) valves installed in the lines, All new lines, no leaks.

The problem is the front disc brakes are very weak. There is some stopping power there but very little. The rears I can lock up if I really step on the pedal. The front not a chance they'll lock up. Nothing is seized in the caliper - pads move like they should.

So that's where I am. Any ideas on where to look?
 
Have you thought about adding a adjustable proportioning valve? Are you sure that the master cylinder is plumbed to the proper brakes, ie, front resevour on mc to rear brakes and rear resevour to front (application specific)? Are all of the lines free and bled, no sharp bends, kinks, or air? Are the residual valves installed in the correct orientation? Is the pedal stroke correct, ie, releasing and applying proper stroke for the mc? Does the mc supply the correct fluid flow for your calipers and wheel cylinder selection? Just some initial thought.
 
The front brakes should be plumbed to the larger reservoir end of the master cylinder, which might also have a larger piston.
If it has a stepped piston, the larger piston will be on the pushrod end of the master cylinder.
Summit sells a brake pressure gauge with adapters that fit into the bleeder valve hole. If you have everything plumbed correctly and your residual pressure valves are good, the gauge will be next. What is your pedal to master cyl ratio? I think 5 to 1 is minimal on manual brakes. Metallic or racing brake pads are not the best for street stops. The double letters on the side of the pad material relates to the coefficient of friction of that pad. The higher the letter, CC compared to FF, CC will be a harder pad, FF will have a higher friction at a lower clamp pressure. Hope some of this helps.
 
The kit I used is a 6:1 ratio with a 1" bore M/C designed for disc/drum combo. I'm pretty sure it's plumb right but certainly double checking at this point isn't going to hurt. I did check the lines to make sure there was pinch or crush line. The rest I'll check shortly.

This is a new build and this is the only thing left to get it on the road.

Thanks for the tips.
 
cbucket said:
The kit I used is a 6:1 ratio with a 1" bore M/C designed for disc/drum combo. I'm pretty sure it's plumb right but certainly double checking at this point isn't going to hurt. I did check the lines to make sure there was pinch or crush line. The rest I'll check shortly.

This is a new build and this is the only thing left to get it on the road.

Thanks for the tips.
Click to expand...
It’s just part of the process to work the kinks out... good luck and post your results for the next guy in line.
 
The verdict is in - Faulty Master Cylinder. While it was new the larger section generated little to pressure. Hopefully I can pick one up early this week.
 
I narrowed it done several ways - first I removed the cover and pumped the pedal, I saw movement in the one reservoir but not the other. I put a vacuum bleed on the front caliper farthest away from the MC, no matter how much fluid I drew, air was in the line, indicating a leak somewhere, since there was no visible leaks I assumed the MC. Final test I would have done first if I had the gauge then. A friend had a pressure gauge I put on the line, barely registered on the gauge.
 
Thanks cbucket, I can sleep now that I know! :)
 
Could somebody be kind enough to provide a little more education for me. I picked up someones project and it will soon be on the road. It had the original mid-30's Dodge drum brakes up front and from what I can tell a late 60's mustang MC. I replaced the front drums with discs and everything seems fine...it stops just fine. Now, keep in mind all my brake experience has been with systems that had boost so I am kind of new to this. I just finished reading this thread and realize that I am pretty sure the PO plumbed the front brakes to the front reservoir of the MC. Should I re-plumb?
 
MichBucket said:
Could somebody be kind enough to provide a little more education for me. I picked up someones project and it will soon be on the road. It had the original mid-30's Dodge drum brakes up front and from what I can tell a late 60's mustang MC. I replaced the front drums with discs and everything seems fine...it stops just fine. Now, keep in mind all my brake experience has been with systems that had boost so I am kind of new to this. I just finished reading this thread and realize that I am pretty sure the PO plumbed the front brakes to the front reservoir of the MC. Should I re-plumb?
Click to expand...
Is one reservoir bigger than the other? Disc brakes "use" more fluid than drums.
 
I won't tell you what to do, but keep an eye on the fluid level as the front brakes wear, you don't want the reservoir to run dry.
 
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