Brake feel question (Small Car kit)

[baltik]

Installed a new smallcar kit, 288mm slotted rotors, hawk HPS pads, bled all 4 corners, stainless flex lines.

Brakes feel amazing around town, great pedal feel, stop quickly, tiny bit of noise on hard braking but nothing terrible.

today I tried to test them in a worst case scenario - ie heavy braking down a prolonged descent. Started by slowing from 70mph to 10mph off an onramp. then repeated hard braking down a hill. towards the end, the pedal feel got noticeably softer, i lost a lot of braking power and I could smell the brakes. While I didn't do any A:B testing I never recall my OEM brakes losing power that much under hard braking.. What should I investigate next? re-bleed? master cylinder? anything else?

[dkoesyncro]

Did you bleed at the proportion valve, "passenger side frame rail, roughly under seat area"?

Possibly new pads?? They may need to get seated, a sort of brake in procedure!

Have you done the BMW booster? This is supposed to have a harder feel and breaking with less effort, unfortunately I can't say fact. I did my conversion as a whole.

[11BC2]

[baltik]

[baltik]

[MarkWard]

Hawk specifies a "bed in procedure" for all of their pad compounds. You need to transfer material from the pad to the disc for the brakes to work properly. I would go back and find the bed in procedure for your compound on Hawk's website.

Better brake pads don't always equal better stopping. The better compounds often require more heat than you can generate out of one panic stop. I have Hawk pads on my vanagon and it stops ok. I have an older "street compound".
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[Steve Arndt]

I bought Hawk ceramic pads for my G60 calipers haven't tried them yet. Did you pump fresh fluid through and replace the old? You may be putting more heat into the fluid and boiling it if it is really old.
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Steve
Steve's 87 Syncro project

[baltik]

I used about 30oz of fresh Dot4 so I feel like the system is relatively fresh, bed in procedure has been followed, green fade seems to be the most likely culprit, hopefully it dissipates with use.

[IdahoDoug]

I have said this before, and I'll probably still be here on the Samba saying it many years from now. Upgrading brakes is not the "bolt it on and my Van will stop better under all conditions" modification that it is often presented as here on Samba. The factory brakes in good condition are quite capable and were the result of a lot of research and subsequent component selection and design by one of the world's largest automakers.

One of these days, my stock van is going to be at a big Vanagon gathering and around the campfire someone's going to challenge me on that statement. The next day there will be a challenge for pink slips in the nearest parking lot and I'll have my 3rd Vanagon.

Good on you for testing what you put on there, Batik. Most people won't find out their "upgraded" brakes cause the rears to lock on dry pavement, or the fronts to lock on wet pavement after the install. At least, they won't find that out until they're in the ditch from avoiding a deer.

If a brake system cannot perform well with new pads and 50 miles of urban driving under its belt, something's not right. Sure, proper bedding optimizes things, but it's not going to cure mismatched components where the front rotors are getting too much braking heat while the rears are along for the ride. I'm here to tell you that if putting new brake pads on a car caused actual problems from not being perfectly bedded, then we'd all know about it and a lot of brake shoe makers would have been sued out of existence. It's a tiny improvement that only serious enthusiasts properly do and a few shops. Millions of hobbyists put on new pads and just drive the car to work every day without experiencing brake fade, so something's up. I'd be testing that on wet pavement panic stops to see if the fronts lock prematurely. I'm not at all familiar with this system, but upgrading the front brakes only to discover you've now got premature fading would cause me to do a bit more testing of what's going to happen with my family in it on a dark winding road.

Any brake system will stop your car on a sunny day heading uneventfully to the coffee shop. Literally any system - A Porsche 930 brake on the left front, a Citroen 2CV brake on the right front, a pair of Yamaha motorcycle brakes on the rears. That will stop you. What really matters is how the brakes will perform when you NEED them to help you out because you're in serious trouble. A rain slicked road at night with your family and full gear in the Van and around a curve is a stalled car. Or a deer. And that is when you'll find out the stock Vanagon brakes might have been a better choice.

I'm not directing this at Batik, who seems like he's doing the right thing - checking a major alteration he made to his Vanagon's emergency performance. Just another opportunity to help the community make good choices on safely owning and operating their Vanagons. Thanks for the bandwidth.
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[baltik]

Doug - that's an interesting theory about front brakes engaging well before rear brakes, shouldering a disproportionate amount of stopping friction and subsequently boiling over. I will try to do a little skidding next time it rains to see if the fronts lock. Is there a proportioning valve or something along these lines that could work?

Also one point of clarification, on that initial panic stop the new brakes still feel a lot better. It's a panic stop followed by intentional, repeated hard braking down a steep hill that seems to impact performance significantly

[IdahoDoug]

A proportioning valve (there are several types) functions during a hard stop to put more braking power on the fronts simply due to physics. The amount of downforce on a tire's contact patch determines its maximum traction and in hard braking there is more downforce on the fronts, thus to avoid any tire breaking traction it is wise to temporarily (during the hard braking) split the braking force in favor of the fronts. I've heard his type (a ball and spring) on the Vanagon tend to fail in the position of not providing more braking power to the fronts.

So, though this is a worthy thing to maintain, it does not appear to be your issue, which is the fronts are creating too much braking force and thus not balanced well front to rear. I'd really be curious if on a rainy day you find panic braking easily locks the front tires.

Its likely (and predictable based upon the work I saw and participated in at GM) that putting upgraded brakes on the front of your van has caused the front brakes to shoulder too much of the work of stopping the van, which should be balanced between the front and rear. So the first stop feels fine as does around town. But subsequent stops with the fronts continuing to do all the work may cause the rotors to be unable to transfer heat away fast enough. Or the pads may be a type or compound that does not accept heat fast enough to cool the rotors. Or the swept surface is too small and the caliper/rotor was designed for a different line pressure. Or rotor diameter. Or. Or....or... There are so many variables to creating an effective balanced system that if you were to watch a team of trained professionals struggle with it for a month, you'd never try altering your own brake system. That's me.

And they didn't spend their time measuring rotor temps at coffee shop parking lot speeds. Nope. Any hack job brake system will do that. It was panic stops at full GVW with cold brakes. Sustained and repeated hot brakes with evasive maneuvers to see if the rear tires locked and slid the car sideways. Wet pavement. Two tires on wet, two on dry. Gravel. Low tires on one side. Etc. All the conditions that a hobbyist will NOT test for and therefore NOT discover they've now got a vehicle that is dangerous in an emergency.

Until that one day. Someone cuts you off on the interstate and you stab the brakes and swerve to avoid, thinking "Whew, I've got this..." until the rear tires lock for a second and the car rotates slightly sideways and you correctly let off the brakes and the rear tires grip again with a vengeance and even Mario Andretti can't turn fast enough to keep the Van from spinning.

Anyway, enough doom and gloom. I'd very much appreciate hearing what happens on a rainy urban street with a panic stop.

Doug
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[syncro surf]

What Doug says makes a lot of sense. What about SA brakes on a Vanagon?
Presumably these are part of a factory engineered system. Do they require a different proportioning valve? A quick search did not show a kit with a valve. It would be nice to have a bolt on upgrade that was known to work properly.

[Steve Arndt]

T3 Chris has posted calculations. At best the standard G60 x 288 kit is 11 percent more braking force. Not a lot and probably within the factor or safety and design window. Not a big change.

I'm doing G60s and 312 rotors. But coupling that with VW LT 25mm wheel cylinders and semi metallic high friction shoes. That is known anecdotally to be a good balance.
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Steve
Steve's 87 Syncro project

[Stuartzickefoose]

Has anyone used a aftermarket adjustable proportion valve with their upgrades brakes? I see no reason why a tweaked like myself (in every sense...) couldn’t in theory:

Install new Fronts

Install new adjustable valve

Go to a gravel parking lot, and lock it up a handful of times and see when it’s just the fronts, adjust it to the rear, until at low, medium and Heavy stops, all found wheels lock equally. Lot of time to set it up this way, but in my head it makes sense.


Personally I agree with Doug, and 95% of vans out there have stock brakes that when adjusted properly (key point) and drums worn in right and pads evenly clamping, that it will bark the tires just fine. Just most people upgrade “broken” brakes. Most, not all. A fully loaded camper syncro 16”. Blah blah blah might need a bigger brake setup etc after heavy mods, but most of the time it’s just new parts and adjust and the stock stuff works fantastic.
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Stuart Zickefoose

2011 Jetta Sportwagen TDi 6 speed manual

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