Brake pulsation after 3rd gear runout

jpctln

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StL, MO

Dec 10, 2004

#1

• Dec 10, 2004

• #1

I'm not sure how long this has been going on, but I know it hasn't always been like this. Anyway, whenever I run my car Full Throttle from 1st-3rd till about 90+, when trying to slow down, the brakes cause the steering wheel, console, and pretty much the whole car to pulsate and shake violently to a stop. This would not happen if say I was cruising in 4th or 5th at the same speed; only when I run 3rd gear out at high rpm's. It goes back to normal though afterward, and does not seem to affect regular driving. So yeah...I'm definately going to take it easy until I figure this out, but I don't know where to start. Do you think it could be the wheel bearings or warped rotors? I don't know why it's rpm dependant and not speed dependant though...that's what confuses me.

 

88_GT_5_oh

Sportin' a turbo 5.0 in Canadistan

Jul 4, 2004

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WPG/MB/CA

Dec 10, 2004

#2

• Dec 10, 2004

• #2

when your braking like this do you have the clutch pressed and braking or just pushing the brake, if you don't have the clutch pushed it could have nothing to do with your brakes it could be motor/drivetrain related.

what the problem could be.. sorry but i don't know but from reading that post it seemed like it could not be your brakes at all

 

jpctln

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Dec 11, 2004

#3

• Dec 11, 2004

• #3

Hmm, great question. I have no idea whether or not I put it in neutral when braking. I'll have to test that **** out.

 

HISSIN50

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#4

• Dec 11, 2004

• #4

what he is actually getting at: do you have the motor braking as you slow down or do you have the clutch in or the car in neutral.

if it happens with the clutch in or in neutral (the latter is the better test), that suggests brakes.

you say this does not happen in 4th and 5th - how about second gear? unless you are turning the same revs in 4th or 5th (as you do in 3rd) the comparison is not relevant (apples to oranges).

remember the dynamics at work when using engine braking: manifold vac goes through the roof, the injectors are barely working (puter controlled), etc..... the engine might not be running its smoothest under these conditions, which creates 'not the smoothest' running, especially in conjunction with the rapid deceleration (a lot of things going on at once).

now if it happens in neutral on any good long hard stop, i would check the rotors for run out, as suggested.

good luck.

 

88_GT_5_oh

Sportin' a turbo 5.0 in Canadistan

Jul 4, 2004

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WPG/MB/CA

Dec 11, 2004

#5

• Dec 11, 2004

• #5

you typed what i was thinking but i didn't know how to put it........lol...you da man hissin50

 

jpctln

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Dec 11, 2004

#6

• Dec 11, 2004

• #6

Thanks for the replies.

I'm going to have to test it out tomarrow, but which should I be hoping for? Would you consider the vibration normal if it were in gear when braking? If it were in neutral, and that suggests there's something wrong with the brakes, I guess I should hope that I had the car in gear...

 

HISSIN50

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#7

• Dec 11, 2004

• #7

88_GT_5_oh said:

you typed what i was thinking but i didn't know how to put it........lol...you da man hissin50

Click to expand...

LOL thanks. now if i could figure out how to articulate what I'm thinking, we would be in business.

JPC, it will be hard for you to articulate what exactly the feeling is like (we are not there with you). winding down from near redline does cause some turbulence - backfiring of some sort is not uncommon, etc. it seems to me that any lack of near perfection in the tune (a slight miss, etc) is exacerbated during this sort of maneuver.

if it happens with the car in neutral, as said, i would look at the brakes and suspension. first thing i would check is brake rotor run out. fox rotors can warp fairly easily. braking the car from 90 mph can do it . an often missed cause is wheel lug torquing. if the sequencing and increments are not done fairly conscientiously (think shop with air guns and a kid who could care less), the rotors can be warped from that alone. then some hot stops after that can exacerbate the problem.

of course, i would recommend NOT DRIVING AGGRESSIVELY UNTIL THE PROBLEM IS FOUND AND FIXED PROPERLY. the driving you are describing is quite stressful on components - i would not do it with compromised components.

good luck.

 

jpctln

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Dec 11, 2004

#8

• Dec 11, 2004

• #8

Well it's coming from the brakes/rotors, because it vibrates when the clutch is in (neutral). I have since retorqued all the lug nuts, so I'll have to see if that does anything. Now, if the rotors are truely warped, what do you suggest I do? Get them turned? What about the rear drums? Could those have anything to do with the vibration...? Thanks for your help.

 

HISSIN50

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#9

• Dec 11, 2004

• #9

if you have a dial indicator and base, you can check the rotors for true. or have a shop check them. IIRC, rotors can be had dirt cheap (new). i might simply swap on new rotors (new pads would be recommended at the same time so they can bed/burnish together).

i would usually think the fronts are the culprit - they have most of the brake bias. also, though im not sure, i think it would take a lot more to distort the drums with lug nut torque (the distortion is what can cause vibration or shimmy).
my two cents.
good luck.

 

ninety15.0

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#10

• Dec 11, 2004

• #10

Did you ever think of the drive shaft. b/c my car does the same exact thing when i either wind out 3rd or 4th...but it doesnt happen when cruising in 5th at highway speeds. Do you have 3.73's or 4:10's out back? With my stock gears i never noticed any vibration until about 120 mph in 5th...but now i notice it as low at 85-90 in third, fourth, and fifth. The stock driveshafts are notorious for losing that little balancing weight and causing bad vibration at speed. good luck

 

HISSIN50

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#11

• Dec 11, 2004

• #11

ninety15.0 said:

Did you ever think of the drive shaft.

Click to expand...

that is a good point i overlooked. even a bad U-joint can create quite a nice vibe. if you live where it is damp, sometimes the outside of the joint is fine but the needle bearings rust/degrade and can cause issues.

good catch, ninety 1.

 

jpctln

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StL, MO

Dec 11, 2004

#12

• Dec 11, 2004

• #12

I have an frpp aluminum one with new joints...

Don't you think if it were the ds I'd be able to feel it when accelerating as well as braking? I only feel it when braking though.

 

HISSIN50

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#13

• Dec 11, 2004

• #13

jpctln said:

I have an frpp aluminum one with new joints...

Don't you think if it were the ds I'd be able to feel it when accelerating as well as braking? I only feel it when braking though.

Click to expand...

unless it started happening right after the DS was installed, i might move that back on the list.
do remember the dynamics involved on the DS. accelerating loads it and the pumpkin gears differently than when decelerating. then factor in decelerating with the motor engaged to the DS while hitting the brakes - the brakes are slowing the rear while the motor slows the front. lots of forces going on there - and lots of loading going on.

 

Mustang5L5

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Dec 11, 2004

#14

• Dec 11, 2004

• #14

Next time you feel the vibration. Push the clutch in and shift to neutral. See if that does anything.

 

ninety15.0

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#15

• Dec 12, 2004

• #15

Well...just throwing in the clutch may not give you the answer. It could still be both the brakes or the DS....even if you throw the clutch in at the top of 3rd at like 4k rpm...the DS is still spinning extremely fast and it would be unloaded at that point...with no strain on it from the motor (the point at which you would feel the most vibration)...even if its a new DS...i would give it a quick check! good luck