[carbonmike]

When I got my '66 wagon a year ago I inspected the brake system and everything looked good, pads/rotors/drums/shoes were in all good order. Previous owner had installed stainless flex lines, pedal always felt good and stopped fine. However the car would pull to the right a little under braking. After replacing bushings/ball joints and an alignment, it still pulled to the right. After a while I noticed that the right front wheel was always dirtier, however the left pads were wearing faster. Suspecting mismatched pad compounds I picked up a set of $11 pads for a 240 that dropped right in. After a quick break in no more pulling. Great problem solved.

Well in the process of doing this I noticed that the pedal would get softer and softer as I drove. But I was no longer driving like a normal person but repeatedly braking hard to test the system. Ordered a new set of pads/shoes from VP with proper 122 parts. System was heavily bled and only saw clean bubble free fluid. After a breaking things in and repeated drum adjustments I get the same thing. When I first start driving the braking engagement point requires little movement, but as I drive more the pedal gets softer and softer. When things first start to get soft I can pump the brakes a little and things stiffen up but after even more driving even that results in a squishy pedal feel.

I freely admit I am now really pushing the braking system so I could very well be just getting things hot and experiencing fade. Is this normal?

As things are super stiff when cold I don't think I have any air in the system. There is 0 fluid loss so I have no reason to think there is a leak somewhere. I am just worried that now I have been really jamming on the breaks that I could be causing my master cylinder to begin failing.

 

[LloydDobler]

If you used the pedal method of bleeding, it's very common on an old car to push the cylinder down into an area that hasn't been used for a while, which has dirt or corrosion in it. That damages the seal and leads to what you're experiencing.

First check is to watch if the fluid level is dropping, and feel the firewall above the pedal for any moisture. If there isn't any, then your cylinder seal is probably okay. On the stock master cylinder, any fluid that leaks around the seal is going to end up on the driver's floorboards.

Other than that, drive it normally for a bit and see if you still notice the soft pedal.

 

[carbonmike]

I used a vacuum bleeder during the initial front pad replacement. Used the pedal method the second time around. However I certainly pushed the master cylinder deeper than it has been in a while when troubleshooting my pull issue. That is when my problems started. I have not found any fluid leaking inside or around the master, but I am thinking this is the problem.

I have a brake servo sitting in the basement. This might be the perfect time to upgrade to the 67-68 non-triangular dual circuit brake setup.

LloydDobler, I remember you asking about this upgrade in another thread that turned into a bit of a s@it show. Did you ever do it?

 

[LloydDobler]

Nah, I never drove my car enough miles to warrant upgrading yet. I mean, I put new calipers on and new hoses and the pedal is so firm it feels like it doesn't even move, I just push harder and the car stops faster. They're really nice. I have to re-route some lines for the motor swap I'm doing so at some point before it's running again I'll probably convert.

 

[Dimitri]

You probably suffer from brake fluid boiling.

I have this occasionally, when I drive very hard. I usually feel the car pulling some too, partly because there may be a pressure drop on the right side (momentarily) as you compress the vapor. But this happens when you drive the car extremely hard on winding roads. Upgrade to a more advanced brake fluid would eliminate the problem.

 

[142 Guy]

You make the comment that things are stiff when cold. If the pedal feel always returns to normal after vehicle cool down, then Dimitri probably has the answer.

You refer to brake fade. Fade can occur without loss of pedal pressure because it is due to overheating of the friction surfaces. Fade can cause loss of pedal pressure if the overheating results in boiling of the brake fluid. If you are going to continue 'testing' your brakes, upgrading the brake fluid may address the fluid boiling issue (stay away from DOT5 fluids). It won't necessarily fix the fade issue. You may have to consider some form of additional brake cooling which would help address the fade and may fix the fluid boiling issue. What kind of wheels do you have, a solid disc steel wheel? A cast / forged alloy wheel with large open areas in the disc might improve cooling. In addition to Dimitri's suggestion, the pulling could occur because you have differential cooling between the right and left front wheels which is affecting the performance of the friction surfaces.

Performance / racing pads will help address the fade issue due to high temperatures on the friction surface. The fact that they tolerate higher temperatures may just exacerbate your brake fluid boiling issue. Also, performance pads, particularly racing pads can be the worst thing for urban stop and go driving. They are like R compound tires. They need to be hot to work and will have little grip when just driving around town.

As a side note, if you are repeatedly getting your discs hot enough to boil the brake fluid, you might want to take a look at the grease in your wheel bearings.

 

[Dimitri]

He does not have fade (or at least he does not describe fade). Fade is when the friction coefficient drops due to heat. The hydraulic force is applied, but the force does not result into enough friction, so you have to apply a higher force on the brake for the same deceleration. This does not happen in Volvos. I have had the brake material smell, but never fade. A friend has raced them hard enough where the (stock) brake pad wears out prematurely, but no fade.

In Europe we had semi-metallic pads and shoes, where you never smell the shoe, but not here in the USA. I have heard that you cannot find these materials in the USA. May be if one bought shoes and drums from a European supplier would get more heat resistant friction surface materials.

By the way, brake fade can happen easily on my big Chrysler. Just go to 100 (which does not take long) and do a panic stop at maximum deceleration. I am talking about a near 1 G deceleration, which is possible thanks to 4 piston caliper disk brakes (stock equipment) The car responds great, until about 60, where you need to apply more force. At 30, it is really getting hard on your foot. You do not want to repeat this procedure until a few minutes later.

 

[142 Guy]

I was just responding to the OP's comments in the third paragraph of the original post that he might be experiencing fade. I agree that what he describes does not sound like fade unless as noted the heating is causing the fluid to boil.

I can't comment about the immunity of Amazon brakes to fading. I also don't know what is common with recent pad materials; but, my North American market 1987 745 turbo definitely had semi metallic pads. They chewed through the OEM front discs in a remarkably short period of time.

 

[dcthompson]

I used to get serious brake fade on my 68 122 wagon, which was equipped with Repco semi-metallic pads. I wouldn't get it during a normal stop, but with a full load on a long steep grade it could get downright scary.

By the way, semi-metallics are still available, just not under the Repco name. As soon as I find an ad for some I'll post the ad for the non-believers.

Dan

 

[carbonmike]

240 brake pads will fit in 122 calipers. The backplate is exactly the same, same thickness. The only difference I saw was that they were shorter in height (larger Inner Diameter). I think the cheapo 240 pads I tried during troubleshooting were semi-metallic. I went with 122 style pads partly to see if they were my problem and partly because I was afraid they would quickly wear the very expensive 122 rotors. They had very little bite when cold, but once they got a little heat they worked well until I really stood on the brakes.

Brake fade generally occurs when the pad material gets so hot that they outgas, generating a thin layer of gaseous fluid between the pad and rotor. Vented rotors are designed not to keep brakes cools as much as they are supposed vent this gas.

Although I think my issue lies with my master cylinder it looks like the brake fluid I have been using has a lower boiling point than a lot of other fluids out there. Valvoline synthetic, supposed to be good at not absorbing water but has a lower boiling point than other available fluids. Flying to Japan tomorrow, will be a few weeks before I get to try anything.

 

[bricksnblocks]

Sounds to me like you've got a piston sticking in the left caliper. That will cause the right side to work harder than the left and cause the pull. After driving a bit it will heat up and cause the spongy pedal.

 

[carbonmike]

Sounds to me like you've got a piston sticking in the left caliper. That will cause the right side to work harder than the left and cause the pull. After driving a bit it will heat up and cause the spongy pedal.

The brakes have not pulled since replacing the pads. The brakes are not dragging.

 

[bricksnblocks]

If you're sure the pistons move easily, here is another thing I ran across. The master cylinder has a tiny hole that bleeds the pressure back into the reservoir after braking. If this hole is clogged there will still be enough pressure to make your brakes drag causing the spongy pedal. I screwed up when reassembling mine and put the cupped washer on upside down. That left the rubber cup never getting past that hole. It acted a lot like you describe.