1963 ford thunderbird brake booster3/24/2024 In such a case, when you bolt the M/C to the booster, the pushrod engages the master cylinder and pushes on the piston and absolutely can cause an issue similar to that described here. It?s not pushrod travel that can cause an issue like this, its push rod length, being too long specifically. If the pushrod travels 1" (say) down the m/c then it will come back exactly the same amount and the same amount of fluid will be pumped back and forth and I don't see how more fluid could get in to prevent the brakes releasing. I doubt if the length of pushrod has anything to do with it. The heat may also have damaged something in the caliper too - but I'd look at air in the system and low fluid first I also suspect the heat may have boiled some of your brake fluid, essentially vaporizing it, which is compressible, just like air, which would reduce brake performance significantly. I wouldn?t have thought to check this myself though since I?m assuming you replaced the Master Cylinder with an appropriate stock version - best thing to do might be to compare the two and see if the new one has a shorter recess in the bore - if it does, the pushrod will be too long.Īs for why it barely brakes at all now, assuming the above is correct - You released all the residual pressure when you opened the bleeder, so that would reset the brakes back to a rest position, BUT, you also likely introduced some air into the system and may have dropped the level of fluid in the master down far enough to reduce pressure. That residual pressure builds on itself every time the brake is applied. If the booster pushrod does not allow the Master Cylinder to fully retract, some of the pressure used in braking will remain as residual pressure in the line, and consequently, apply a small residual pressure to the calipers and drums. Depending on how much preload, the brakes can work fine for a while, but every time you use them, they get a bit tighter, until eventually they really start to drag (won?t take much for a caliper) and ultimately lock. If the booster pushrod is too long it "pre-loads" the Master Cylinder. This is my guess also, providing everything else operated normally before and the only change was the M/C and then a bleed. I had a similar problem when I replaced mine and found that the rod was set too long on the rebuilt unit. When you replaced the master cylinder did you adjust the push rod length? It's very important that the length of the new rod is adjusted properly or the brakes may not fully disengage which could lead to the symptoms you described.
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