Brake question for the collective:

E

Erickz

Well-known member
Have a Bugeye H Prod car that moves almost violently left to right under braking. The harder the braking the more violent the movement left to right. It was unsafe at Grattan. Toe is set at zero, uses the common big brake kit (MGB calipers, Spitfire rotors etc); uses Tilton 0.625 bore front M/C and same rear M/C; also has the brake balance/bias kit from Tilton (red knob).
Tried moving the bias all to the front with no change and then all to the rear with no change. Brakes were all bled and the pedal was firm…unlike my resolve to continue driving the car.
Any suggestions before I get into it would be welcome.
Thanks
EZ
 
First guess would be something loose in the steering portion of the chassis. all tie rods, ball joints, steering linkages, etc intact and in good shape? no play in anything?

What type of brake lines? are all of the flexible hoses in good shape? I had an issue with a street car (pickup truck) many years ago with a brake that started dragging on one side during a trip. The factory rubber lines are comprised of several layers of rubber. the inner tube/ jacket/layer had developed a crack and then collapsed internally. It was acting as a restrictor on application of the brakes and a check valve when I released.
resulted in the steering pulling one way, then the other as the brake pressure on the good side went up & down with the pedal action. the other side was more gradual because of the restriction in the line. When I released, it pulled hard to the bad side since the hose was keeping the fluid from flowing backward and the caliper from releasing.

I got stuck in heavy houston traffic on the way home and it was a nightmare. When I eventually got home, the wheel bearing on that side had boiled all of the grease out and was smoking what was left.
The wheel was so hot, I was afraid the tire bead was going to melt and explode- water sizzled on the rim when I flicked some on it for a temp check. yeesh!

I let the whole assembly cool off over night, then replaced everything on that corner of the truck- caliper, rotor/hub/bearings, pads, lines, etc. I wish digital cameras were ubiquitous back then since those pics would have been great for a brake shop's wall of shame.

Anyway, those are the two things I'd look at--- all joints/ steering parts tight and in good shape, and all hydraulic brake parts working freely.
 
Thank you. Should have added braided lines all the way around as well as disc brakes in the rear.
 
Matt brings up a lot of good points. As David Kizer reminded me last night, difference of caster can cause the car to pull to a side under braking. Also, if a one of you shocks is not working as well as the other, it can change the dynamics under braking. Good luck.
 
Depending on how everything is plumbed, I cannot perceive any of the problems coming from the pedal assembly itself, but it's always worth a look to check for loose stuff.

what condition are all of the flexible lines? at ~$25/each, they are cheap to replace and rule out. If you need custom lines assembled, I have used Techna-fit ( https://www.techna-fit.com/ ) with great success for years. I used to buy them by the dozen and never had a quality issue.

Any chance you have fluid (bearing grease, gear oil, brake fluid, etc) leaking on a rotor and causing brakes not to work until it burns off? how are the pads and rotor surfaces? I would think one front rotor would look different. No chance you installed a brake pad backwards? (not that any of us would ever admit to making that mistake before....)
 
Definitely seems likely that a binding caliper, or sloppy suspension pivot are the most likely candidates, but I have seen odd, darty behavior when running worn out tires as well.
 
In addition to all the great advice above, be sure to check the rear suspension/bushings/brakes and axle assembly as well. Does it feel like the steering wheel is being pulled hard under braking? If so, most likely a problem in front. If the car is darting hard and the steering wheel doesn't feel like it's being yanked, it could be coming from the rear.
 
I always start with checking both front hub bearings . More slop in one side will kick back the pads further.
Next would be fluid drop. Open both front bleeders and watch the fluid dropp inot a pair of cups. The shorter side will drop faster , but both should flow a good bit if the MC is above the calipers. If it is not, pump the pedal gently. A pinched hard line or crappy soft line will hinder flow .
Next. would swap rotors side to side.
Swap pads side to side.
Remove pads on one side and apply pedal pressure. How hard do you have to push to move the pistons?
same on the other side.
If the calipers are mounted on fabbed brackets , if one is cocked a wee bit , it may bind up a little. Breaking in the pads with usually cover a slight misalignment .
 
Great comments/suggestions - thank you.
Yes the steering wheel feels as though its being pulled.
Yes the calipers are mounted on fabbed brackets.
All the brake lines are new as of Nov 2020.
Thanks
ez
 
Sooo... more thoughts.. has this been happening for some time, or a recent thing that started? did it start small and gradually worsen, or just *bam* there it is?

Any clunky noises while driving to indicate a loose or worn component?
When was the last time the calipers were rebuilt?
 
New calipers this season over the winter. Thought it was happening at Gingerman but others complained of similar issues so I chocked it up to the track getting grooves from heavier cars. Did not notice at PittRace in May, so came on at Gman then really showed itself at Grattan.
 
I'd start at the front wheels and disassemble and check part by part until you find it.
If the lines and calipers are all new and the problem started after that, I'd first look for a poorly assembled/ defective line or maybe a stuck piston in a caliper. As said earlier, brake lines are cheap to replace and if there's nothing wrong with the old ones, flush with water, blow dry, then pack in the spares bin next to the caliper rebuild kit, spare pads, and rotors.
 
I would start with finding a concrete pad get the car moving at least 20 mph on it. Slam on the brakes to lock them up. Get out and see if they are all locking up and if they are all locking up at the same time. This should give you an idea of where to look next. It is a good idea to get the brakes warmed up before doing this because they perform differently when hot.

You can do this on asphalt also but it is more difficult to lock up and is harder on the tires.
 
Have you tried 4 brake pressure gauges yet. You can video gauges with a verbal countdown to compare readings. Will help identify which wheel is locking and if it holds pressure. Video slow braking, hard jab/release and hard held braking test.
 
And the winner is……the steering arm was pulling out of the kingpin, threaded holes had stripped. Looked okay under load but would deflect when steering was engaged. So thank you all.
You’ll all get two seconds off of your qualifying time at Indy.
EZ
 
This thread is what production car racing is all about. Lot's of great suggestions and a solution. Reminds me of time once at the Runoffs when Toni's car would develop a miss after one lap on track. We rewired, changed everything in the fuel system and the motor. Finally, after losing all four days of qualifying, we were getting ready to take the car across the street to Lanier, someone asked if we had changed the battery. Of course not since it was brand new for the Runoffs. But, we took the battery out the tow truck and installed in the car and headed for Lanier. There we found no miss running both race and counter race on the oval. Sent a crew guy back and got the new battery. And there was our miss again. Friends helping friends.
 
Erickz":3lkt2fb8 said:
And the winner is……the steering arm was pulling out of the kingpin, threaded holes had stripped. Looked okay under load but would deflect when steering was engaged. So thank you all.
You’ll all get two seconds off of your qualifying time at Indy.
EZ
Click to expand...
Glad you found it! that coulda been ugly going into T1!
 
Glad you found it. I was going to suggest steering too. I had a similar issue when I was running an older formula Mazda. I would hit the brakes and I could see the front left start to toe out. The harder the braking the more it pulled.
 
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