Disk Brake issue - looking for ideas

[dkemm]

Looking for some crowdsourcing assistance here. 1988 RHD Ninety
Situation - pulsating while braking - similar to a slight death wobble feel. I can best describe it as if the rotors were warped.
The steering wheel does move left-right like a death wobble - a few degrees
It does not happen all the time, most noticeable on offramps, at around 45mph - but even then not all the time / not every time.
In past - the feeling did lead to some death wobble as I had a loose bolt in my steering.
I also thought that it was possibly caused by chassis flex (lots o rust) - replaced with new Galvy Marsland.

I have checked all of my front end, rotors with straight edge, rebuilt swivels / adjusted, packed bearings, etc.
Steering feel is great, issue only happens during braking. When easing upto a stop sign...the pulsating grab/no grab from the brakes can be felt.

PO had replaced calipers and rotors... but I am not sure of the quality (probably based on best price). Could a faulty caliper (cheap) cause the issue?
anything else I should look for? I have fully bled the brakes twice - engine swap & frame swap, so I dont think its a brake line issue.
I have replaced rear drums and shoes....I dont think the feeling is coming from the rear....but open to ideas / thoughts -- like perhaps. only 1shoe is contacting drum...which causes the steering feel? rear is easy enough to tear down to check.

any ideas that I can test?

 

[erover82]

I'd bet the rotors are warped and/or glazed. Doesn't take much to feel it. Visual inspection for glazing and a dial indicator to check warpage.

 

[dkemm]

I'd bet the rotors are warped and/or glazed. Doesn't take much to feel it. Visual inspection for glazing and a dial indicator to check warpage.

thanks...I will check with dial gauge... I checked with straight edge. question though....if rotor warped...shouldnt I feel it with all braking?
I did just take apart the rear drums...make sure cylinders were moving....all looked good....(but dirty)

 

[jymmiejamz]

You probably have some other worn out component and the slightly warped rotors are amplifying the problem. I would check the panhard bushings.

 

[dkemm]

You probably have some other worn out component and the slightly warped rotors are amplifying the problem. I would check the panhard bushings.

All bushes replaced recently… radius arms, trailing arms, panhard, new genuine drop arm, sumo bars, even rear a-arm bush…
after death wobble created by hairline crack on steering box to frane bracket
Pretty sure all bushes are good.

 

[erover82]

thanks...I will check with dial gauge... I checked with straight edge. question though....if rotor warped...shouldnt I feel it with all braking?
I did just take apart the rear drums...make sure cylinders were moving....all looked good....(but dirty)

At greater speeds the higher frequency could be less noticeable, and with greater braking force the calipers may force the rotor to deflect into alignment.