So, my '66 was a power drum brake car with a Powerglide. I have since done a disc brake conversion (no change to booster, no change to anything at the pedal). When I did the disc brake conversion (Wilwood front and rear kits with Wilwood tandem master cylinder), other than setting the booster pushrod length, I really didn't have to mess with anything under the dash at all. I am now in the midst of an LS swap with a 5-speed. That, of course, necessitated disassembling the pedal setup to put in a clutch pedal and a manual trans brake pedal, and I also ended up getting the brake booster rebuilt as well. I've been at this for two years now, and as I'm putting it back together, I find myself in one of those situations where things don't seem right, but it has been so long, you can't quite remember how they were when they came apart...
I appear to have two issues:
1. I believe I have the striker for the brake light switch installed correctly on the new pedal, and the same way that it was on the old pedal. The striker hits the switch perfectly (note, switch removed in the photo below), but it interferes with the rubber bumper. The way I have the striker, the switch, and the bumper mounted matches the assembly manual. What am I doing wrong here?
Here's a video:
https://flic.kr/p/2n6t5vK
2. The pushrod from the booster is not long enough to allow the pedal to touch, or even come close to the bumper. I have no jam nut for the clevis, and based on my memory and the power brake diagram above, there is no adjustment here, and the push rod is intended to be tightened agains the clevis. The manual brakes, by contrast, show a jam nut and an adjustment instruction, but that would be achieved by adjusting the booster to master push rod length for a power brake car, so that kind of makes sense to me. The service manual talks about adjustment in the manual brake section, but not in the power brake section. Either way, even if I was to adjust it, I simply don't have enough pushrod length to reach the bumper. Have I got something configured wrong here? Is it possible when they rebuild my booster it was assembled incorrectly or they used a different pushrod? The end of the pushrod is marked "C6". Is it possible the power brake cars don't use the bumper? Mine had a bumper installed, but I couldn't say for sure if it actually topped out against it. It isn't actually shown on the power brake diagram though. Perhaps I should just check for the 4.12" dimension?
seventy2plus2 said
Mar 3, 2022
RE Question 1: I got looking at your photo of the striker, vs the assembly manual. Your photo shows the striker being mounted on the passenger (right) side of the pedal arm, whereas the assembly manual shows it being installed on the drivers (left) side of the pedal arm.
jduffett said
Mar 3, 2022
Hmm yeah I see that... I'm 90% confident the way I have it is how it was mounted on my old pedal, and if I swapped it to the other side it wouldn't hit the switch, and in fact it would become "adjustable" because the bend wouldn't bear against the pedal arm to prevent rotation.
jduffett said
Mar 3, 2022
So, I'm starting to think... The striker is shown for power brake only, and there's no mention of a change or adjustment to the switch. The bumper is also not shown for power brake, and the description of the power brake system includes "permits the use of a low brake pedal"... All this points towards the pedal not hitting the bumper at all, with the top-out position limited by the booster push rod. If that's right, then it answers both 1 and 2. The confusing part is that my car had a bumper installed, but then I guess the power brakes could have been a retrofit. Would I expect to see J50 on the cowl tag if it was ordered with power brakes? Will have to confirm pedal is the right distance from the firewall and I get full MC stroke with the clevis bottomed on the pushrod I guess!
EDIT: This is Chevelle information, but it supports my theory, and I suspect it is generally applicable: https://www.chevelles.com/threads/4-wheel-disc-power-booster-brakes-conversion-kit-inline-tubes.1061137/
-- Edited by jduffett on Thursday 3rd of March 2022 11:53:00 AM
jduffett said
Mar 5, 2022
Well, the measurement to the floor at the top of stroke is indeed in the ballpark of 4.12 at top of stroke (depending on how you measure), so it seems the no-bumper approach with the clevis tightened all the way down on the pushrod is the correct configuration for power brakes.
cdnpont said
Mar 6, 2022
Hello John. Seems like you have it worked out pretty well. Fwiw, here's a shot of when I mocked up for the 11" booster. on the 65. Done to the to get the right rod length. I had to cut down and thread the pushrod to make it fit as it actually was way too long as supplied. I ended up with with just the right amount of freeplay, and the arm contacts the bumper. One other thing, my setup never had that switch striker. The switch contacts the arm directly, is adjusted mid-way and works fine... so far. I'm using a 1" bore disc/drum master, and the pedal travel and feel is "just right".
My thought is you need a longer pushrod. The arm should certainly contact the bumper with a little freeplay. If not, then all the springback stop is carried somewhere in the booster.
Interesting! I confirmed tonight with the pedal where it is, I easily get full stroke on the master before I hit the floor. So, what I have will work, I guess it is just a question of preference about pedal height at this point. I have a few threads protruding through the clevis, so I could pretty comfortably make the pedal a little higher with some washers without having to worry about thread engagement. Your setup looks like the clutch and brake are almost even. Was your car originally a power brake car? I notice your clevis is a slightly different design from mine.
So, my '66 was a power drum brake car with a Powerglide. I have since done a disc brake conversion (no change to booster, no change to anything at the pedal). When I did the disc brake conversion (Wilwood front and rear kits with Wilwood tandem master cylinder), other than setting the booster pushrod length, I really didn't have to mess with anything under the dash at all. I am now in the midst of an LS swap with a 5-speed. That, of course, necessitated disassembling the pedal setup to put in a clutch pedal and a manual trans brake pedal, and I also ended up getting the brake booster rebuilt as well. I've been at this for two years now, and as I'm putting it back together, I find myself in one of those situations where things don't seem right, but it has been so long, you can't quite remember how they were when they came apart...
I appear to have two issues:
1. I believe I have the striker for the brake light switch installed correctly on the new pedal, and the same way that it was on the old pedal. The striker hits the switch perfectly (note, switch removed in the photo below), but it interferes with the rubber bumper. The way I have the striker, the switch, and the bumper mounted matches the assembly manual. What am I doing wrong here?
Here's a video:
https://flic.kr/p/2n6t5vK
2. The pushrod from the booster is not long enough to allow the pedal to touch, or even come close to the bumper. I have no jam nut for the clevis, and based on my memory and the power brake diagram above, there is no adjustment here, and the push rod is intended to be tightened agains the clevis. The manual brakes, by contrast, show a jam nut and an adjustment instruction, but that would be achieved by adjusting the booster to master push rod length for a power brake car, so that kind of makes sense to me. The service manual talks about adjustment in the manual brake section, but not in the power brake section. Either way, even if I was to adjust it, I simply don't have enough pushrod length to reach the bumper. Have I got something configured wrong here? Is it possible when they rebuild my booster it was assembled incorrectly or they used a different pushrod? The end of the pushrod is marked "C6". Is it possible the power brake cars don't use the bumper? Mine had a bumper installed, but I couldn't say for sure if it actually topped out against it. It isn't actually shown on the power brake diagram though. Perhaps I should just check for the 4.12" dimension?
So, I'm starting to think... The striker is shown for power brake only, and there's no mention of a change or adjustment to the switch. The bumper is also not shown for power brake, and the description of the power brake system includes "permits the use of a low brake pedal"... All this points towards the pedal not hitting the bumper at all, with the top-out position limited by the booster push rod. If that's right, then it answers both 1 and 2. The confusing part is that my car had a bumper installed, but then I guess the power brakes could have been a retrofit. Would I expect to see J50 on the cowl tag if it was ordered with power brakes? Will have to confirm pedal is the right distance from the firewall and I get full MC stroke with the clevis bottomed on the pushrod I guess!
EDIT: This is Chevelle information, but it supports my theory, and I suspect it is generally applicable: https://www.chevelles.com/threads/4-wheel-disc-power-booster-brakes-conversion-kit-inline-tubes.1061137/
-- Edited by jduffett on Thursday 3rd of March 2022 11:53:00 AM
Hello John. Seems like you have it worked out pretty well. Fwiw, here's a shot of when I mocked up for the 11" booster. on the 65. Done to the to get the right rod length. I had to cut down and thread the pushrod to make it fit as it actually was way too long as supplied. I ended up with with just the right amount of freeplay, and the arm contacts the bumper. One other thing, my setup never had that switch striker. The switch contacts the arm directly, is adjusted mid-way and works fine... so far. I'm using a 1" bore disc/drum master, and the pedal travel and feel is "just right".
My thought is you need a longer pushrod. The arm should certainly contact the bumper with a little freeplay. If not, then all the springback stop is carried somewhere in the booster.