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Volvo Amazon Brakes

Joined
Oct 18, 2017
Location
Portland OR
Hey all. Just finished up rebuilding and bleeding the brakes on my Amazon. I have the single circuit front discs, and drums in the rear. I have rebuilt calipers up front, and new drum cylinders in the rear, as well as a dual output Wilwood master cylinder. Despite all this, the brakes still seem pretty weak. Im not accustomed to driving unassisted brakes, so Im unsure if they should feel so (for lack of a better word) terrible? Anyone have any experience with inline brake boosters? Since my master cylinder has a rear and front output, it looks like I could only make either the front or rear boosted. Seems like the steering shaft would have to be modified to fit a booster behind the master cylinder.
 
Manual brakes were always harder to press down on.

Master cylinder's inner bore diameter, and wheel cylinders'/calipers' inner diameter determines foot pressure required.

If a vehicle had a single piston master cylinder, then front and rear wheel calipers/cylinders could have had different inner diameters, due to weight differences between front and rear axles.

So, if the dual piston MC has different sized bores for front and rear calipers/cylinders, then MC will most likely be exerting more hydraulic force on front wheels than on rear wheels

I don't know if they make a dual chamber MC with equal bore sizes.

Years ago, I installed a MC designed for a heavier vehicle onto a lighter vehicle...talk about touchy brakes.
 
Yeah, what's the bore on your Wilwood MC?

I'm using 122 discs up front on my PV, with drums out back, with the stock PV master cylinder (I really, really should put a dual circuit MC on it).

The brakes take more pressure than normal, but nothing crazy. A *firm* press to get maximum braking (threshold).
 
Can we get a bit more information? Like is the pedal low? Is the pedal firm but requires a bit of effort? When Volvo boosted this braking system. They used a remote Girling booster that mounts to the inner left fender. It was used on wagons and 123GT and was an option for other models. Then Volvo changed the booster to a Lockheed version and that is the only one available. I believe Volvo also installed a dual circuit master on the last couple years of production. You could try to get some more information on that setup.
 
The Wilwood master is a 1inch bore from what I remember. The pedal isn't low and doesn't have a lot of creep. Just requires quite a lot of force to lock up the tires. I was able to make it leave tire marks on the pavement when slamming them. I have a Wilwood proportioning valve for the rear brakes, so Im able to relatively control their pressure. I have brand new pads and shoes all the way around, so maybe I just need to lay down some material on the old rotors and drums. The car hasn't been driven in over 5 years.
 
Stock MC bore size is 7/8". I think your master is too big.

Single circuit cars were boosted on all 4 wheels. Late '67-'68 dual circuit cars were only boosted on the front brakes. In '69 they used a 140 style booster/master but we didn't get those cars here.
 
I was trying to google up the bore and not finding anything definitive. But yeah, larger MC bore than normal - less 'leverage' in the system, more force needed for a given amount of braking.
 
Ahh, makes sense then. Read online that a larger bore will give less pedal travel, but require more force to stop. Anyone have any familiarity with the inline vacuum boosters? Found a model listed as a VH44 that people have used on MGs and Datsuns. Could I just run two of these for the front and rear, or junction my two MC outputs into a single input, and then split them after the booster to go into my proportioning valve? Looks like installing a booster behind the MC like in a modern car is a real PITA with the steering shaft where it is.
 
It can be done. This is how the factory did it on the late cars. This one is plumbed for dual diagonal brakes.

171324206.v14VhMXD.12212.png
 
I'm not accustomed to driving unassisted brakes, so Im unsure if they should feel so (for lack of a better word) terrible?
Manual brakes definitely can work. I've driven a lot of 1960s and 70s American vehicles so equipped, which I found exquisite. Wonderful feel, excellent modulation, not requiring a whole lot of pedal pressure. Have you ever had the pleasure of piloting a late 60s land yacht? (Floating down the highway on your living room sofa, it seats 6 in blissful comfort, 8 in a pinch, holds a half dozen suitcases and a surfboard inside the trunk... no kidding...)

Point is, if that thing can stop so well with 4 big drums and no power assist, then doing so is clearly not an insurmountable engineering challenge. :lol:

By comparison, I found power brakes feel mushy, take getting used to. But decades later, in today's world, no one is used to anything else.

The pedal isn't low and doesn't have a lot of creep. Just requires quite a lot of force to lock up the tires. I was able to make it leave tire marks on the pavement when slamming them.
Yes, it's possible to lock up all 4 wheels -- if you're in an "oh sh!t" panic mode it's actually pretty easy -- but you don't reach that limit anywhere near as soon as with power brakes, obviously. There's a lot more "room" to play with modulating the pedal. So, if lockup is how you're judging the efficacy of the system, it's going to fall short of your expectations. In my opinion, how it feels prior to lockup is vastly more important. A high, firm pedal as you describe, without creep, sounds positively delightful. You may have to tweak something so that a "normal" pedal pressure provides a "normal" stopping response, before you can judge how well you enjoy daily driving.
 
Manual brakes definitely can work. I've driven a lot of 1960s and 70s American vehicles so equipped, which I found exquisite. Wonderful feel, excellent modulation, not requiring a whole lot of pedal pressure. Have you ever had the pleasure of piloting a late 60s land yacht? (Floating down the highway on your living room sofa, it seats 6 in blissful comfort, 8 in a pinch, holds a half dozen suitcases and a surfboard inside the trunk... no kidding...)

Point is, if that thing can stop so well with 4 big drums and no power assist, then doing so is clearly not an insurmountable engineering challenge. :lol:

By comparison, I found power brakes feel mushy, take getting used to. But decades later, in today's world, no one is used to anything else.


Yes, it's possible to lock up all 4 wheels -- if you're in an "oh sh!t" panic mode it's actually pretty easy -- but you don't reach that limit anywhere near as soon as with power brakes, obviously. There's a lot more "room" to play with modulating the pedal. So, if lockup is how you're judging the efficacy of the system, it's going to fall short of your expectations. In my opinion, how it feels prior to lockup is vastly more important. A high, firm pedal as you describe, without creep, sounds positively delightful. You may have to tweak something so that a "normal" pedal pressure provides a "normal" stopping response, before you can judge how well you enjoy daily driving.

I actually have had the pleasure of driving a '63 Plymouth Fury that I was detailing for a customer, and even though it had unassisted brakes, and had been fairly neglected mechanically, it still stopped somehow easier than my Amazon with brand new hardware. Which leads me to believe that something must be wrong with the brakes. Ive bled the system multiple times, so Im pretty sure all the air is gone, but I will try again and test all 4 corners are actually engaging.
 
I've had the same issue on my single circuit system since I've owned my 122. I've just gotten used to them sucking.
http://forums.turbobricks.com/showthread.php?t=325555

I've decided to just overhaul the entire system and switch to boosted dual circuit. I also plan on doing all new hard and soft lines too. Not just because of the lack of pedal, but dual circuit is just safer in general.

Why is the dual circuit better? Isn't the pressure from the manifold the same regardless of how many lines are going to the wheels? I have the braided stainless IPD lines in all the flexible hose positions.
 
It's just a safety thing. Any single failure anywhere in the system of a single circuit system and you have no brakes at all. Generally speaking, if one circuit fails in a dual circuit system, it's pretty unlikely that the other would fail at the same time, so you'd have 'half' the brakes.

In traditional dual circuit systems, that could mean the fronts (good) or the rears (not so great, very unstable to say the least). But Volvo went way above and beyond with their dual-diagonal system. Each circuit operates half of each front caliper, and one rear brake. So regardless of which circuit fails, you've got braking on both front wheels and one rear. Which works so well you probably wouldn't notice much of a problem if it weren't for the warning light.
 
^ +1 to Volvo going far above and beyond. :nod:

I don't even know of any other car that has a brake failure light. Or would need one.
 
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