Topic: Braking problem - 68 GT350

[69GT350H]

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.

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?

[Bob Gaines]

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.

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?

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.

[69GT350H]

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?

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.

[Bob Gaines]

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?

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.

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.

[Bob Gaines]

Certainly not the cause of the overall problem but because of a possible contributing factor I should mention given the weak front brake symptom that if someone install the front caliper wrong  (side to side)the bleeder will not be positioned correctly and you will not be able to bleed all of the air out of them. It can be easy to get them mixed up and installed wrong . Don?t ask me how I know.

[Coralsnake]

More pictures please

Front and rear brakes.

Just to be clear the rear brakes are drums?

[69GT350H]

I need a little break (not brake ) here till Milton passes. I'm in Miami but will be hosting some friends that have evacuated Tampa.

[70cj428]

Just a couple more ideas, make sure the car has the correct rear wheel cylinders. There are several visually identical wheel cylinders with different internal bore diameters and the wrong ones can change the factory proportioning. Also, make sure the front calipers are not swapped side to side. If they are swapped, they won't bleed completely, and you'll have weak front brakes. If nothing else works, try swapping out the master cylinder ...

[69GT350H]

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?

[Bob Gaines]

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.

[69GT350H]

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.

[Bob Gaines]

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.