Brakes and frame flex

Brian in Wheeling

Brian in Wheeling

Senior Member
What would cause the brakes to self apply when the car moves over a turnoff berm or going over any rough surface like a bad railroad crossing? Usually one of the fronts but occasionally a rear also briefly locks up. Does frame flex contribute to this? Brakes adjusted too tight? Loose wheel bearings?

Thanks,
Brian Warmuth
 
I have never heard of this problem. It will take a lot more than frame flex.

I supposed it could be loose wheel bearings, but they normally chatter.

Check the spring U-bolt clamps to the frame are tight.

Check for a broken frame crossmember.

Check the end bushings on the service brake cross-shaft, where it mounts to the frame. They may need to be replaced.

Check where the wishbone mounts to the underside of the flywheel housing, make sure it is tight.

HTH.

Strange one.
 
i suppose the brakes could be adjusted too tight or what others have said something causing severe frame flex...

what i would do is lay on a creeper and start inspecting the brake system (all pins in place, cotters, no bent rods etc)starting from the pedal to the cross shaft then each brake rod.

make sure the brake rod bushings are in/on the cross shaft and nothings loose.

i thought i remember someone mentioning that certian tires when the car is flexed can catch on the brake rods and bend them up or temporarily pull on them so it brakes that wheel.

with the brake pedal not applied and both front wheels off the ground with the axle ON JACKSTANDS they should turn freely. i would try taking one of the jackstands out and try to simulate going around and over these bumps, maybe then you can see somehting. bunding up. try spinning the wheels both directions and listening for anythign shifting around. turn the steering wheel a bit and see if anythign binds then.

if nothing obvious id pull the drums and see what ya got, could be a broken spring (remember just because a part is new doesnt guarantee it wont break tommorow)
 
As mentioned, broken springs. Do you have the floater kit on the fronts? This would give you the missing springs. Check the 4 bolts that hold the backing plate tight.
 
Yes, as Tom suggests, weak brake shoe return springs or loose front backing plates.
 
The brake system has been completely gone thru by me. New parts where needed, everything tight and adjusted. No bent rods. It does have Snyders or Brattons repro floater kit on the fronts. I've been over the entire frame and it is painted and good -just put the Tudor body back on the frame all bolts are tight. There are no float-A-Motor mounts- original only.
Brian W.
 
Any more ideas on this? Just wondering. Only happens infrequently and only over rough spots seems worse when turning over the rough spots left or right.
 
Was it doing this prior to the brake work or did it show up after? Do you have shocks? If it is more prominent when turning it must lie up front. How's the front spring fitment in the crossmember? Some incorrect shock/ link combo may cause a bind if the brake rod rubs.
 
make sure the front brake shafts are not sloppy
 

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Hi Bryan,

In response to your call for assistance: "Any more ideas on this?"

Jim's keen suggestion in reply no. 2 is worth looking into -- for example:

If the ball on the end of the wishbone is not positioned correctly, and/or, if it is worn & can move slightly up & down or sideways, it can move enough to create rhythmic forces to cause slight frame stress & distortion.

Just imagine what would happen to the front end of your brake rods if one grabbed the radius rod ball & moved it slightly up & down like a pry bar -- then imagine the rear of the brake rods are not moving -- then imagine the very tight small space between the brake bands & the brake drum.

1. If previously disassembled, what did the ball on the end of the radius rod (wish bone) look like?

2. Does the ball possibly fit in a repo worn rubber ball?

3. At the two (2) side springs & sleeves, what is the distance between the bottom cap & top cap? (Should be about 1/8" to 1/4" or there about after the (2) nuts are tight.)

Sometimes even with the best, it does not hurt to look again & re-check possibilities.

Just trying to help.
 
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Given the conditions of when it happens, I would suspect that brake rods might be hanging as they cross over the shock absorber adjusting screws, look for rub marks on the screws & brake rods. Bill W.
 
If the brake rods are adjusted too tight and the front end has any sort of alignment issue (that may cause steering wobble), could that be a cause of some of the front brake lockups?
(I'm throwing this out as a guess, guys??)

I don't think that would address the rear lockups though.
 
I've seen the situation you describe affecting the rear brakes when the levers were installed on the wrong sides and as the suspension moves the axle up, as in crossing a R/R crossing, the brake rods come into contact with the shocks and it bends the rods making them shorter.
 
I have had it happen on front brakes never rear. The action of the front axle going farther from the frame makes the rods tighter. Just like if you have the brake rods properly adjusted then lifted the car by the frame, the front brakes engage. I had it happen when hitting the bump coming into my shop at lets say a high speed.
 
jkeesey said:
I have had it happen on front brakes never rear. The action of the front axle going farther from the frame makes the rods tighter. Just like if you have the brake rods properly adjusted then lifted the car by the frame, the front brakes engage. I had it happen when hitting the bump coming into my shop at lets say a high speed.
Click to expand...
So, J-Bird, ur you sum "speed nut" ur sumtin'? Dog:cool: here, to lecture you:D Ol' Dick Paris took the front wall out uf his garage with his pickup & drove into the den, so's he wuldn't be late fur the NEWS!!:eek: His spoose wuz REALLY ticked off & he had to make his own TOAST, the next morning, after sleeping in the pickup BED!!! SO, J, be KEERFUL!! Buster T.:cool:
 
I have a 25 degree grade going up into my shop, a lift to act as a speed bump, and a 4ft thick brick/concrete wall to stop me. As long as it is my car that gets messed up all is good. I'm never that stupid with customer cars.
 
I've never had a problem like that. My guess is that the service brake cross shaft is binding at the bushings. I would disconnect the service brake rods at the cross shaft and check for binds. Tne service brake cross shaft needs to be a little loose so as to allow for frame flex.
 
If you check the service brake shaft, make sure that there is no interferance between the torque tube and the cross shaft in the full movement of its travel. If the torque tube is rubbing the shaft, this usually means that the frame is sagged at the rear motor mounts. A quick band-aid fix that will solve the problem is to use only the rear part of a float A motor kit. The rear of the float A motor bolts to the universal joint cover and suspends the rear of the transmission and drive shaft from the center crossmember, on top of a rubber block.
 
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