Topic: 66 GT Coupe - "Clunk" when I brake.

[66RavenGTCoupe]

Hi All,

I'm calling out for ideas on where to look for this annoying clunking noise that I have when braking.

The noise happens as I am applying pressure to the brakes and the car is slowing down but the funny thing is that the clunk only happens just before I stop and then there's the single clunk! the harder I brake the louder the clunk. If I brake gently enough - no clunk.

I've checked the rear drums and front KH discs and they are clean, pads have plenty of meat on them and discs/drums are smooth and do not need machining. Made sure everything was tight.

Checked tail shaft for play - seems to be ok. Actually changed it out with the one from my wife's 65. No improvement.

All bushes and bearings are new. Lower control arm bushes have been tacked as one came loose at one stage.

Any ideas at all would be great.

Possibly some of you out there have had the same/similar problem?

Thanks in Advance,

Dan.

[WT8095]

I assume you have the trans in Drive when this is happening. Try putting it in Neutral before stopping - leave it out of gear until you come to a full stop. Let us know what happens.

[66RavenGTCoupe]

Ok I'll try that tonight. Thanks.

[67gtasanjose]

Do not rule out ball joints, in particular the rivets or bolts to the control arms. If they have been rivetted in again, this could be a source. If bolts, they often are soft steel and stretch and loosen up.

Richard

[midlife]

I had that problem with Midlife, but only when I braked hard.  Midlife was a 66 GT FB.  I thought the problem was found when I tore the car down and found a A pillar hinge backing plate sliding on top of the passenger seat pan under the carpet, but the noise was still there after a complete restoration.  I took it to an excellent front-end guy for diagnosis, and he was stumped as well.  I suspect there was something inside the passenger front rail left over from a previous repair.

[drummingrocks]

I know you said all of the bushings are new.  Does that include the strut rod bushings?  One of those being worn out would cause the clunk you're describing.

[J_Speegle]

Front or back?

If front and the good deep clunk check the strut rod bushings, mounting points as well as upper and lower A arm mounting points. Slop in any of these areas will allow the unit to rotate when brakes applied with a good clunk especially once it gets to metal  to metal 

[jwc66k]

Check the universal joints. They "clunk" sometimes.
Jim

[66RavenGTCoupe]

I assume you have the trans in Drive when this is happening. Try putting it in Neutral before stopping - leave it out of gear until you come to a full stop. Let us know what happens.

Oh thank you so much!!!!!

It does not clunk in neutral!!!!

What does that mean now?

[WT8095]

Oh thank you so much!!!!!

It does not clunk in neutral!!!!

What does that mean now?

A couple of possibilities:

1) The splines on the front yoke/tailshaft are not sufficiently greased and thus are not sliding properly. The scenario would be: as you step on the brakes, the rear axle turns from the braking torque. The leaf springs allow it to turn a bit (the opposite of hard acceleration). This pulls the driveshaft backward just a bit. As you are coming to a stop, the leaf springs start returning the axle to its normal position. The splines are binding so they resist, until they *pop* and slide forward. Putting the trans in neutral takes some of the rotational load off the splines so they don't bind as much.

2) Worn/damaged/improperly fitting splines. Same scenario.

3) Insufficient spline engagement (driveshaft or yoke too short). Splines are not enagaged enough to slide properly, causing them to "cock" a little to the side and bind. Seems less likely that this would be alleviated by braking in neutral.

4) U-joints, as Jim mentioned.

There are certainly more possibilities, including a problem inside the transmission or the transmission mounting (including the crossmember). "Clunking" is a classic symptom of a driveshaft problem so I like to start looking there. All of the other causes people listed will cause clunking, too. The trick is to find a way to eliminate some of those possibilities without spending a fortune replacing everything, and you've got a good clue with the neutral test.

[Bob Gaines]

My money is on U joints.

[trucktricksdon]

I had a clunk when braking on my 65 coupe and found that the shims for the upper control arm on the right side had fallen out at some point. They probably rusted away over the years and fell out. I put 2 new shims in and tightened the nuts on the shock tower and fixed the problem. My problem however, was evindent in all braking situations, including when the trans was in neutral.

[66RavenGTCoupe]

My money is on U joints.

Hey Bob,
U joints were changed when I got the tail shaft ballanced a year ago. Seeing that I only drive the car on weekends during the drier period they are still fairly new. Did check for slop and they are snug.

Thanks for chiming in though. Love your 67.

[66RavenGTCoupe]

Do not rule out ball joints, in particular the rivets or bolts to the control arms. If they have been rivetted in again, this could be a source. If bolts, they often are soft steel and stretch and loosen up.

Richard

Control arms are new until I restore the originals. Thanks.

[66RavenGTCoupe]

Front or back?

If front and the good deep clunk check the strut rod bushings, mounting points as well as upper and lower A arm mounting points. Slop in any of these areas will allow the unit to rotate when brakes applied with a good clunk especially once it gets to metal  to metal 

Hard to tell where the noise is coming from but if I had to take a stab I'd say from the back. Strut rod bushings are new and tight. Mount is good.  Will check control arm mounting points though.
Thanks Jeff.