High speed brake pull, Grand Marquis

[ford46guy]

This is a brake pull that happens around >70MPH under harder braking. It feels like the car squirms if you brake hard enough. Otherwise normal, rides great.

I went thru the car and replaced(not so much for this issue but over the past year):
1) Rotors, (used old pads from old rotors, they were ok but warped), Wagner TQ.
2) All wearable steering linkage parts(4 Tierod, drag link, pittman arm, idler arm) got alignment
3) Lower BJ, uppers are still ok
4) New Continetal Tires.
5) New KYB shocks.

went over suspension, control arm bushings are original. They pass a prybar test, but I can't say they look pristine.

One shop said it could be tire squirm from new tires.
Another said calipers, and they said if you are in this deep just pop them on yourself.

Both shops said the original bushings are unlikely bad - They said on such a large car you would have tons of other issues.

 

[drolds]

Both Front Brake calipers. Do not delay, this is a real safety issue.

 

[901Memphis]

Yep time for some remanufactured calipers I'd say. That would be the cheapest next option. Try to get a good set, if that's even possible

 

[Rand]

you reused old pads on new rotors??

Which way does it pull?

 

[jr047]

I chased a problem like that for too long before I replaced both front brake hoses, and that resolved it permanently. You either have a bad suspension joint, bad or stuck caliper, contaminated brake lining, or a blockage or leak in a hose or hard line.

 

[JamesBond]

My town car felt squirmy under braking in heavy rain.

In doing some online reading, I came across info suggesting that the rear axle backward/forward caliper arrangement could contribute to braking weirdness.

I never bothered to try to resolve the issue as it wasn't that bad.

 

[ford46guy]

Thanks for the replys. All hoses and brake fluid were changed too, I didn't mention that. Since the calipers didn't show any resistance when I compressed them I kept them. All pins are lubed. Calipers are like $60 with discounts. One tire place said to change them ASAP, they weren't looking to make money telling me to do it. His opinion is that a 150K caliper is a time bomb, even if there is no visible signs of pistons binding. He test drove it and said in his 40 yrs experience it is a caliper issue. He said to do the rears as well, but that isn't that critical.

It pulls to the right. Sometimes the pull feels like it comes from the rear axle.

Tonight I took it for some hard braking, and it seemed to improve when I got the brakes very hot.

Maybe reusing the old pads wasn't such a great idea? The old rotors had a hot spot on them, but I sanded the pads down, they were about 70% of life life. No crazy wear. Maybe one pad got glazed? May spring for new front pads and rotors.

 

[mk378]

Pull to the right of course suggests that something on the left is weak.

When you overheated the right brakes and made them fade, you have a more balanced situation.

Make a few hard stops and pull over and check the temperature of all the wheels. If one is not as hot as its counterpart on the other side, that one isn't braking as hard as it should. Also, drive for a while without using the brakes then check for any wheels heating up, which would mean a dragging brake.

You should not need to replace rotors again right now but it is definitely not a good idea to run old pads on a new rotor so spring for a set of pads.

 

[ford46guy]

Originally Posted By: mk378
Pull to the right of course suggests that something on the left is weak.

When you overheated the right brakes and made them fade, you have a more balanced situation.

Make a few hard stops and pull over and check the temperature of all the wheels. If one is not as hot as its counterpart on the other side, that one isn't braking as hard as it should. Also, drive for a while without using the brakes then check for any wheels heating up, which would mean a dragging brake.

You should not need to replace rotors again right now but it is definitely not a good idea to run old pads on a new rotor so spring for a set of pads.


Yes, going to check this...

You are right! Meant calipers, not rotors! The rotors are almost new!

 

[ford46guy]

Ok, I can get 4 calipers for around $100 with Advance discounts. But before I pulled the trigger I took it out on the thruway when there was no traffic to do a final diagnosis.

I made some very hard stops from 70MPH. This car has very strong brakes. After about 5 stops the pull was almost gone.

Then I put it on the jack and noticed that some grease fittings may have squeezed out grease very close to the rotors. I did pay attention the orientation of the grease boots(the BJ boots actually say point away from the wheels) but none the less I saw grease on the rotor end. Also the Tie Rods could be a culprit too. I recently greased it up for an oil change. Strange though it was a high speed only issue. Maybe it was low speed too but didn't really notice it.

Thing is when I greased there was no excess coming out. I did use two pumps. I think one pump is more than enough. There is very little fillable area between the joint and the socket.

I've measured almost 500 degrees on this car with very aggressive braking. For the most part these calipers have equal temperatures side to side. I guess that cooked off any remaining grease.

I will probably do the calipers though for that price, they are originals. May get some performance friction front pads too, I did reuse Theromquiet pads that were almost new. Grease could contaminate them as well.

 

[Gasbuggy]

I've had some interesting issues with ABS cars after having to replace parts and bleed front brakes.

 

[ford46guy]

Originally Posted By: Shark
I've had some interesting issues with ABS cars after having to replace parts and bleed front brakes.


Bad ABS units could bleed off pressure on a circuit. In rare cases you can completely lose brakes.

 

[Gasbuggy]

Getting air out of the ABS pump can be very difficult. I own a Motive pressure bleeder now.