Side-to-Side Movement under Hard Braking

[idahorally]

I've got a 94 4.0 2WD that has some pretty terrible braking power. Pads and rotors are in good shape, however under hard braking the truck will dance pretty aggressively from side to side. When I first bought the pickup the previous owner had a jumper wire in the Brake Fluid Reservoir Sensor to prevent the ABS light from staying on, I went ahead and replaced the sensor. The ABS light stays off, unless you guessed it, I mash the brake pedal all the way to the floor. Whether or not I am parked or driving, this is the case.

I am considering potentially just replacing the entire front setup, calipers and all. Any guidance on where else to potentially look for a culprit?

 

[Uncle Gump]

That truck has RABS... just the rear wheels are anti lock. The RABS system doesn't even come on unless both rear wheels stop turning while the vehicle is still moving. It has zero to do with the front brakes.

Secondly if the pedal goes all the way to the floor... you have some sort of problem in the hydraulic system or rear brakes are really out of adjustment. So does the pedal really travel all the way to the floor?

 

[idahorally]

No, sorry, the pedal doesn’t literally go to the floor I was just referencing when I have to mash it down in a sudden traffic stop situation.

 

[MikeG]

Side to side movement means one side of the truck is engaging the brakes a LOT harder than the other.

Start with basics, bleed the system out, and especially make SURE the rear drums are adjusted out enough where they are actually doing something.

Those steps are cheap, after that, maybe just replace the calipers and wheel cylinders. Cheaper than being in a wreck.

 

[idahorally]

Easy enough, I’ll get that done on my next day off. Based on both of your responses can I assume the rear brakes are more than likely the culprit in this? I’ve been primarily focusing on it being caused by the fronts.

 

[MikeG]

Poor braking can be caused by the drums being severely out of alignment (just recently went through that so it's fresh on my mind). However, pulling to one side may also be the front brakes, that one is harder to diagnose from afar.

 

[idahorally]

Understood. I’ll start with the flush and rear adjustment and go from there.

 

[franklin2]

While you are working on it, if you mess with the front and have it off the ground, before you take the tire off each side, grab the tire at 12 noon and 6 o clock and try to wiggle it to check for play. Then grab the tire at the 3 o clock and 9 o clock positions and try to wiggle. There should be no play at all. Loose parts in the frontend will cause wandering during braking as well.

 

[Uncle Gump]

The strange part of the OP's symptoms is that the ABS light turns on while depressing the brake pedal while the vehicle is stationary. I think there is some overlap in functionality in the warning indicator between the fluid level in the master and the actual functioning of the hydraulic system. Similar to the way a proportioning valve use to trip the indicator pre RABS. Or maybe it's the park brake and fluid level tied together... I just can't remember and I don't have a schematic to look at. Maybe @RonD can shed some light on this. But if the ABS light turns on while vehicle is stationary... I would think you have severely out of adjustment rear brakes or there is a hydraulic leak in the system.

As for the "dance pretty aggressively from side to side"... @franklin2 pretty much covered my thoughts. Any play in the steering or front suspension will get amplified during hard braking.

Maybe you can answer a couple more questions...

Is the brake pedal firm and at the top?

Is the brake pedal low and mushy?

Does the brake system lose any fluid?

 

[idahorally]

Just finished doing a run through on the pickup..

@franklin2 there does seem to be a bit of play on the front wheels primarily from the 3-9 holding position. Steering has always been very loose in the vehicle, but the alignment stays true. I was considering just the steering box but maybe it is more suspension related.

@Uncle Gump The brake pedal seems fairly normal, and responsive, it's definitely not firm at the very top but certainly mid push and it never bottoms out. The emergency brake fully engages around the 7th-8th click, out of about ten. I have not witnessed any fluid loss no.

In assessing the drum brake adjustments... before I started the tires could freely spin about 2/3 a rotation with a hard turn, based on the videos I watched that was seemingly in line with what I should expect. I gave the adjustment cog a number of spins, that should have resulted in the shoes being adjusted out, but I never noticed any more grab on the wheel spin test. I continued to adjust to an excess, and still, did not notice an increase in grab. I think I will probably be buying a new rear shoe/drum/spring set and swapping it all out.

While I was under the pickup I did find that the rear differential needs oil, I am not sure how low it is yet, I am going to go run and grab some 80w90 and see.

 

[alwaysFlOoReD]

There is another potential area on the steering column that can be worn, that is the rag joint.

 

[idahorally]

After addressing the differential fluid issue (it was only about 400ml from full) I went ahead and flushed the brake system.

I am pretty sure the driver side rear assembly was the potential primary culprit in my braking issue. Once it was bled through that side the pedal firmed way up, about to take it out around the neighborhood to see how it feels overall.

 

[Uncle Gump]

With the description of your rear brake adjustment experience... It sounds to me like you were either turning the adjuster the wrong way... or you thought it was adjusting when it really wasn't.

I'm going to recommend you pull the rear drums off and just give the rear brakes a complete inspection. Something certainly isn't right in there.

 

[Bgunner]

As long as your adjusters are working properly all you need to do to adjust the rears is hold out the e-brake release handle and pump the e-brake pedal to adjust the rear brakes. They will not over adjust so just pump it all you want.

Just a quick tip for your gen truck once to u know the rear brakes are working properly.

 

[idahorally]

Well the firmness of the pedal dissipated after about two hours of being parked. I am out of daylight so I can’t go rebleed.. but there’s definitely something amiss with the drivers side rear assembly. Now that I’m aware of that I can definitely tell it pulls to the right under hard braking.