Performance Q&A Tech Section

Our Resident tech guru, Big Mac, tells all.

Kevin McClelland Apr 1, 2009 0 Comment(s)

A Boy, we feel your pain. We wish we had the silver bullet, but you've covered the bases. We have a few ideas-and a few questions. Maybe these will trigger some ideas on your end to find your problem. We really want to help!

First, let's talk about DOT brake fluid. DOT 3 brake fluid has been around for decades. It is a glycol-based fluid that works very well but has the nasty habit of attracting moisture into your braking system. Back in the early '80s, DOT 4 (also glycol-based) came along, basically obsolescing DOT 3 fluid. They both have a boiling point of around 500 degrees Fahrenheit until moisture attacks the fluid, then it drops quickly. Issues of moisture and paint corrosion from glycol-based fluids led to DOT 5 silicone-based fluid. This was touted as the best thing since sliced bread, and people began to switch over. But silicone fluid has its own set of problems with aeration and lack of lubricity. The biggest problem with silicone- and glycol-based fluids is their lack of compatibility with each other. Mixing even small amounts will create a sludge that looks amazingly like Italian salad dressing and is about as effective as brake fluid. In some cases, the hardware designed for one fluid will not accept the other. Brake caliper and master cylinder seals, hoses, and other parts won't always work correctly when the type of fluid is changed.

So here's a question for you: Since this is a street rod and you probably have a "clean firewall," have you mounted the master cylinder and booster under the driver-side floor along the framerail? We assume so, because you're using residual check valves to prevent the bleed-down of fluid from the calipers back to the master. Since glycol and silicone fluids really don't like each other, and you said that you flushed the system when you switched from DOT 5 back to DOT 4, maybe you have some salad dressing left in your residual checks. It wouldn't take much to allow them not to seal, bleeding fluid back to the master. This would cause the pedal travel to refill the calipers on the initial application of the brake pedal. If the stuff is floating around in the check-valve chamber, that would explain why the problem is intermittent.

You really have covered most of the bases. Hopefully, the residual checks are the problem. They are easy enough to swap out and won't break the bank. Good luck, and make sure to tap those brakes before movement!

Businessman's Hot Rod
First I just want to thank you guys for the great magazine. I got my second issue just a few days ago. I am 15 years old and just bought my first car, a '72 Buick Skylark with a 455. I need some advice on building the engine. I know it's not a Chevy, but it applies to all big-blocks. Which intake manifold makes more power, an Edelbrock Performer or a B-4B? I heard it was the B-4B, but it is the same design they used 40 years ago so it may be outdated. I am going to use a cam from TA Performance that specs out at 0.460 inch max lift, 223/230 degrees duration at 0.050 inch lift, and 284/288 degrees advertised duration. I will also be using a Q-jet carburetor and stock exhaust manifolds with iron heads, but I plan to swap to aluminum heads later. Will I be able to get away with cast pistons or will I have to upgrade to forged ones? I am going for a compression ratio around 10:1. I would also like to know what kind of power this combo would make. Any advice would be greatly appreciated and will help a young gearhead have the meanest car in the high school parking lot!
Nick Larson
Maple Valley, WA

A We know it's not a Chevy, but you're a new member to the performance fold, and we must not let you go astray! At least you're in a GM vehicle, and I have a soft spot in my heart for big-block Buicks. I owned a '70 Buick GS 455 four-speed convertible that I sold to my dad about 10 years ago. He has gone on to finish the restoration I started, and it's an award-winning original car that he loves to show.


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