I have a friend working on a 1968 Shelby GT350 that was supposedly recently restored. Among other problems, he's having a problem with the brakes. When stopping the car, the rear wheels will lock up when trying to stop the car. He has installed rebuilt calipers that were matched to the set taken off, new pads, and all hardware. New master cylinder and the car has what appears to be a newly rebuilt banded brake booster. We have checked the booster to cylinder rod and verified it is of the correct adjusted length, and it moves freely. The proportioning valve/distribution block that came on the car was replaced with a rebuilt assembly. The system has been bled several times with no issues. Unfortunately, we still have the same fairly weak front wheel braking, and the rear wheels locking up easily issue.It sounds like proportioning problem. Too much in the back and not enough in the front. Where any metal lines changed when the different proportioning valve was changed because it reads like the lines from front and back have been reversed. There are a lot of variables and without seeing how things were done it is just a guessing game IMO. I would change out the proportioning valve out for a new one or someone who knows what they are doing rebuild it . At least that way you can rule the proportioning valve out.
Any suggestions on what we might be missing? It's a power disc brake car. Are there different power boosters for this car, might it have the wrong one, or maybe the wrong calipers?
Thanks Bob. To the best of my knowledge, the hard lines were not replaced. As to being improperly connected, I thought the lines different sizes, or at least the fittings were so you could not mix them up. If the rear line did get attached to one of the 2 fronts, then only 1 of the fronts, would be attached to the rear and one of the fronts would stop as normal?Like I said without seeing what someone else has done it is just a guessing game. In this case if tracing the lines down they should be routed the same as on your 69 coming off of the master and proportioning valve. The most logical explanation for what you describe is an ill preforming proportioning valve. Regardless of where the problem lies the best of luck finding it.
Unfortunately, I do not know what was done on the previous "restoration". I might have to go and verify the position of each hard line.
Thank you all for the comments. Now that my guests have headed back up to Tampa, I'm going to take my 69 GT350 over to my friends so we can look at things side by side. Mine has the KK big spindles. What differences would we be looking at with the 68 and 69 GT350's?KK spindles do not have anything to do with the braking system relative to this discussion.
KK spindles do not have anything to do with the braking system relative to this discussion.
The calipers bolt to the spindles, so that means there is nothing in that area that would be different. Thank you.Yes it bolts on the same.
Check the proportioning valve for proper function and adjust/replace if needed.
Ensure rear drum brakes (if present) are correctly adjusted, not too tight.
Inspect for contaminated brake fluid; flush and bleed the system thoroughly.
Verify rear brake lines for damage or collapse, especially rubber sections.
Confirm the master cylinder matches the braking system?s specifications.
Test the brake booster for proper operation and ensure even vacuum distribution.
Do you have the calipers on the correct sides?+1 . They are right and left specific.
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Many of us have had to replace the wheel cylinders. Yours may be wrong. Can someone tell him the diameter of the piston in the correct rear wheel cylinder?
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