TJefferson2020

Well, I took it out on the freeway today for the first time since replacing the tires and general post paint assembly. (64 - power brakes, discs in front, adjustable proportioning valve for rear 215/70/15's rear, 215/60/15 fronts)

Granted the road was wet today from heavy fog but hard braking is a pants shitting affair. Skids easy and pulls hard to the left.

I dialed in additional rear braking - slight improvement but still not right.

Also, weird chattering from the rear when I let my foot off gas at 50-70 mph.

Could it need an alignment from new tires?

I'm going to get under it and check EVERYTHING. could be Ujoints too.

Jebus H. Sometimes - bang, zoom to the moon with these cars....

A-Snake

Are you sure you have fresh rubber brake hoses? If old, the right front may be collapsing.

TJefferson2020

Not fresh but installed 10 years ago. Braided stainless.

TJefferson2020

Going to take a nap, then get the car in the air. Might run a GoPro of rear suspension.

Sniper168gr

Check your right front caliper. It is probably leaking. Went through this with all three of my mid-years this year.

65GGvert

What's skidding? Left front? Rear also?

TJefferson2020

Left front.


I discovered the chattering. Rear lug nuts not torqued to spec.

I'm going to find a parking lot and do some testing.

TJefferson2020

Did more testing today. Increasing rear pressure seems to have made a huge difference. Much better on dry pavement too.

It's getting there. I still might pull the left caliper and check the seals, hose, etc.

kellsdad

When they pull left, its the right side that's not working.

Sniper168gr

if the car pulls to the left it will be the right caliper which may be leaking. This is because of the fluid on the right side lubricates the disk and it slips during braking. As a result, The left caliper does the breaking and pull the car to the left. After you drive the car for awhile ithe ability to stop may improve as the right side disc cleans up from use. You’ll know right away when you pull the right wheel.

68hemi

I assume you are running two different profile heights for front fender clearance but that is not generally a good idea and may be contributing to your problem.

TJefferson2020

Aha! That makes sense.

Yes. I wonder about that too. Once I get the brakes balanced and checked, I'll skid pad a little and see.

I figured out that 215/70/15s will fit if you have the right backspacing on the rims. Mine are vintage Torque Thrusts designed for drums. I have to use a 1/4" spacer to clear the calipers on the front. That pushes the tire out just far enough to be a problem.

I will likely start saving for new TTs with at least a 3.5" back spacing.

I still have the Mickeys that match the rears. The look and feel of those tires is amazing. I was bummed that it rubbed (just barely).

Sniper168gr

Any news?

TJefferson2020

It's been raining here non stop so I haven't been able to test anything or remove the wheels.

TJefferson2020

RESOLVED.

I just needed to dial in more rear pressure. Checked front calipers - all good. I have an adjustible proportioning valve. I have it at full pressure now and the braking is much better. It will skid normally like a non ABS car and in a straight line.

I took it out and did hard braking at freeway speeds, locking them up. Pedal is a little hard but otherwise see,s to be performing normally.

kellsdad

Glad to hear its getting better. ... Keep in mind that the optimum is to have the fronts lock slightly before the backs. That assures you are getting maximum braking from the tires that have the most downward force on them during hard braking. It also reduces the likelihood of losing directional control if the back tires lock up first and cause the rear end to step out.

65tripleblack

If you can get right and left evenly balanced on the front tires, then optimal braking is achieved by slowly transferring transferring bias to the rear wheels until the rears just begin to lock ahead of the fronts.

The fronts should carry the lion's share of the bias, but if they lock before the rears then steering control is lost which is why pre-ABS cars were rear biased. In other words: tweak bias to maximize front bias, although not to the point where F lock before R.

kellsdad

I will respectfully disagree. If the fronts lock first, you've gotten maximum braking from the fronts up to the point where they locked and all you have to do is back off a bit to regain maximum front braking and steering. In the mean time the rear tires are not trying to steer the car. ... If the rear brakes lock first, you have to get off the brakes immediately to keep the back end from trying to pass the front (spin out) which means you never reach maximum braking from the front two tires that have the most traction. At least that's the way I learned to do it for road racing tracks.

65tripleblack

That is true, assuming the driver is a trained and seasoned road racer.

TJefferson2020

I'm no expert on this topic. I'm dialing seat of the pants. Right now it feels like the rears locks right before the fronts. I'm close to the right ratio. I did notice the right rear will lock up first for some reason. All components check out (hoses, calipers, etc).

Tomorrow I'm going to adjust the brake shoes a bit to balance the rear. I thing the left side needs a couple turns on the adjuster.

I will also give the valve a half turn and test again. I've got a great abandoned road nearby. All the houses are gone. I filmed there when all the deserted houses were still there. An entire subdivision abandoned. Very weird. Now just foundations.

That's why I decided to use an adjustible bias valve. It makes a huge difference. Since I drive on I-35 a lot, I need predictable braking. It's still terrifying. People are nuts.