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Weird pull on braking...

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farna View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2021 at 5:56am
Pulls to driver's side. That eliminates the distribution block.

"Pull is only on braking, gets worse the harder you brake and is to the driver side front."

It could be the caliper is stiffer on the driver's side. Wouldn't hurt to pull the driver's side caliper and disassemble it. Just pop the piston out (with air pressure) then pull the seal out of the body. Clean the caliper body, especially in the seal groove. Any corrosion under the seal will cause the seal to be tighter. I've had that happen mostly with aluminum bodied calipers, but it can happen to a cast iron caliper also. Check the seal for any damage as well. If the square cut seal isn't in properly that could cause the caliper to be tighter. Of course you will have to thoroughly bleed once done, which brings me to another thought, maybe there is some air in the lines, probably on the passenger side. That would cause the driver's side to grip quicker. Won't hurt to bleed the passenger side again, as air will work it's way through the lines down to the caliper as the brakes are used. If there is a slight leak at a connection or bleeder it could suck air in without letting fluid out.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote troutwilly Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2021 at 9:41pm
Frank, I know you are way more knowledgeable than me, but here's my logic:
The passenger side front brake is fed from the pressure differential switch (or distribution block as I have referred to it).  The driver side front brake is fed directly from the MC.  If there is a problem with the PDS, such as a blockage, then wouldn't the passenger side not operate as efficiently as the driver side, and cause a pull to the driver side?  By the way, my apologies to all, especially dpimm, for not seeing the pull direction earlier.

This also triggered another thought, referring back to Trader's comment about incorrect plumbing. 
On the PDS, the lines to the top fittings come from the MC, one for the front, one for the rear.  The bottom fittings have the lines running to the brakes, again, front and rear.  The flow should be straight through the PDS, not cris-crossed, meaning if the top left is for the fronts, the bottom left should go to the front passenger, the right goes to the rears.

This all caused me to run out and check the TSM.  It has a list of things to check for different problems.  Under the "pulls to one or the other sides" it lists:
A - observe for smooth pedal operation when bleeding system, one wheel at a time.
D - wheel bearings loose.
E - wheel alignment.
G - worn or contaminated pads.
L - support plate/bracket loose, worn, or distorted.
N - caliper not aligned with disc.
V - caliper piston stiff, frozen, or seized.
X - caliper cylinders mis-matched.
R - hoses/lines kinked, cracked, dented, or clogged.
W - caliper cylinder cups swollen, worn or damaged seals, bores rough or corroded.

Many of these things have been suggested in one way or another.  Would be good to step through each one and check them off.
Bill O.
70 AMX
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2021 at 9:51pm
I think all y'all are making this far more complicated than it needs to be. 

Dpimm: did this ever work right? Or is this the first use after you swapped all the parts? More background helps. Are the parts new? 

If these are used, 1978 donor parts, I'd suggest that the donor parts are likely bad. If you have knowledge to the contrary, let us know.

Shocks, sway bars, etc, will have no effect on straight-line smooth-road braking. Alignment would have to be REALLY bad to have a one-side-only terrible pull. If you have toe crazy outwards, it'll pull badly to the side you're turning towards even slightly. Heavy toe-in, usually pretty even. 

Do you have enough miles on it to know if tires are wearing OK?

If it always pulls to one (drivers) side no matter what, while testing on a straight and level road however minorly imperfect, I'd concentrate on brakes, without testable reason otherwise.

Does the car pass basic sniff tests? Jack each/both wheels up, do they spin free?

Press the brakes hard, all the way, let go. Does each wheel spin free?

Press the pedal just a little, does one lock up first? (Car jacked up, ordinary friction and minor side to side differences are exaggerated, don't try to read tea leaves too closely.)

Edited by tomj - May/06/2021 at 9:57pm
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