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Question on power to manual brake conversion

Old 01-10-2019, 07:31 PM
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scottjamison
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Default Question on power to manual brake conversion

Based on the issues I am continuing to have with my power brakes because of my low vacuum, I am planning to switch to manual brakes.
I already have Wilwood calipers and M/C but I don't like having to run a vacuum pump to get enough vacuum and I think my booster is just a pain in the *** overall.

Has anyone done this switch? Any suggestions or learnings?

From what I understand, I need a higher brake pedal ratio for manual brakes. I haven't looked under the dash yet but the assembly manual suggests that there is already a hole higher up on my brake pedal. If not, I may be screwed because there is no way I can get a drill in there to drill a higher one.

I very roughly measured the pedal ratio. 4" to the rod on a 13" pedal. He told me for manual brakes I am going to need the attachment closer to 2.5" from the pivot!.
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Old 01-10-2019, 07:44 PM
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HeadsU.P.
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Its my understanding that you will need to change your MC again, to a manual unit. The difference is how far or how close the piston is to the mounting flange surface. One piston is more shallow than the other when viewing from the back side or booster side or firewall side. This will affect the pedal rod length.

What are the drawbacks of your electric Vac pump? Noisy? Runs all the time? Takes up valuable space?
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Old 01-10-2019, 07:47 PM
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Big2Bird
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Manual m/c has a 1" bore. Use the upper hole on the pedal.

Power m/c has a 1 1/8" bore. Use the lower hole on the pedal.
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Old 01-10-2019, 07:50 PM
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Yes it can be done.

Yes, the pedal already has the holes needed. You値l have to switch your stripper plate for the brake light switch. It値l go in the hole currently occupied by the clevis and visa versa. There is a different striker plate for manual.

You値ll need a manual pushrod. Theyre are not easy to find.

the hole in the firewall will have to be elongated. I値l post the pic if I can find it.

Last, you値l need a new master cylinder with a smaller diameter bore.
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Old 01-10-2019, 08:10 PM
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Originally Posted by HeadsU.P. View Post
Its my understanding that you will need to change your MC again, to a manual unit. The difference is how far or how close the piston is to the mounting flange surface. One piston is more shallow than the other when viewing from the back side or booster side or firewall side. This will affect the pedal rod length.

What are the drawbacks of your electric Vac pump? Noisy? Runs all the time? Takes up valuable space?
Yes. All of the above. It is loud, adds complexity, adds load on the electrical, takes up a lot of room.
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Old 01-10-2019, 08:12 PM
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Originally Posted by CA-Legal-Vette View Post
Yes it can be done.

Yes, the pedal already has the holes needed. You値l have to switch your stripper plate for the brake light switch. It値l go in the hole currently occupied by the clevis and visa versa. There is a different striker plate for manual.

You値ll need a manual pushrod. Theyre are not easy to find.

the hole in the firewall will have to be elongated. I値l post the pic if I can find it.

Last, you値l need a new master cylinder with a smaller diameter bore.
Thanks.
I already have a 1" bore Wilwood M/C and the guy said they can send me the rod for it.
Its VERY good to know that I should already have an upper hole for it on the pedal.
I will take a look at the 68 switch. I think that one will be ok with the change in pushrod location.

Yeah if you can find the pic of the firewall, I would totally appreciate it!
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Old 01-10-2019, 08:30 PM
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Originally Posted by scottjamison View Post
Thanks.
I already have a 1" bore Wilwood M/C and the guy said they can send me the rod for it.
Its VERY good to know that I should already have an upper hole for it on the pedal.
I will take a look at the 68 switch. I think that one will be ok with the change in pushrod location.

Yeah if you can find the pic of the firewall, I would totally appreciate it!
Lets see if this works. The only place I could find it is on Photobucket. If you haven稚 heard, Photobucket sucks putrid donkey *****.

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Old 01-10-2019, 10:03 PM
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I've got all the parts here to swap to manual myself, but I'm going to change to dual masters with a balance bar at the same time to allow me to tune the brake balance front to rear. Actually not overly expensive, probably no more than replacing a factory master and booster, but will require removing and modifying the brake pedal, as well as modifying the firewall and fabricating some brackets and brake lines.
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Old 01-10-2019, 10:47 PM
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Richard454
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Here's a good visual-

Manual on the left- Power on the right-




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Old 01-10-2019, 10:57 PM
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Man up. The power booster in mine failed this Fall. Just have to put one's quads to work. I can lock all four. Just is a bore on an incline when stopped. Some real pressure has to be maintained on the pedal or the car will roll.
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Old 01-11-2019, 06:07 AM
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You dont 100% need a manual rod. You can space out the matter cylinder too. Just an idea, it's what I did after having no luck finding a proper rod.
I also kept the (new) power master I just bought. Seems to work fine. Maybe needs a bit more effort.

Last edited by Dusky; 01-11-2019 at 06:08 AM.
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Old 01-11-2019, 07:35 AM
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I just went the other way. Manual to PB. I swapped out the whole pedal box to a PB pedal box. I have the manual pedal box if you want to go that way.
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Old 01-11-2019, 11:39 AM
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If you look at the pic that I posted closely, you’ll see some of the differences for the pedal box that Gordon is talking about. The manual box has studs coming out towards the master cylinder, just below the top two holes on the power brake box. It can certainly be done without it and the hole locations aren’t hugely different, but if you want to do it as closely to original as possible...
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Old 01-11-2019, 02:58 PM
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Scott, here are two pics of the bracket I got from Master Power Brakes which allow you to use manual brakes with the power brake pedal box which I am doing. As you can see on the bracket, the master cylinder mounting holes are right in the middle of the power box/brake booster holes with some adjustment available as seen in pics. Now everything I have seen and read says manual master mounting studs were only a half inch below the top holes, so I may make a new adapter bracket to these dimensions. Third and fourth pic show difference between power and manual firewall where you can see how close to the top holes the manual master mounts. Matching up Richard’s pic above, with my bottom pics you can see the difference in manual and power pedal box. Easiest may be to get the manual box from Gordon and just drill the new holes. The metal reinforcement is there in the firewall to accommodate both set ups.

Outside of this bracket, I did everything people have said up above. Top hole in pedal, manual brake pushrod (Ebay), different brake light switch bracket, and 1” bore master cylinder. They worked great, although while my car is apart I may remake this bracket to match factory dimensions of manual master cylinder mount. Hope this helps!










Last edited by 69ttop502; 01-11-2019 at 03:10 PM.
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Old 01-11-2019, 05:00 PM
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Bought a 75 at the auction. halfway home I got out to pull the cap and see what's wrong with the brake fluid level. I realized there was no power booster. I can't understand anybody removing power brakes.
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Old 01-11-2019, 05:09 PM
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Originally Posted by scottjamison View Post
Based on the issues I am continuing to have with my power brakes because of my low vacuum, I am planning to switch to manual brakes.
I already have Wilwood calipers and M/C but I don't like having to run a vacuum pump to get enough vacuum and I think my booster is just a pain in the *** overall.

Has anyone done this switch? Any suggestions or learnings?

From what I understand, I need a higher brake pedal ratio for manual brakes. I haven't looked under the dash yet but the assembly manual suggests that there is already a hole higher up on my brake pedal. If not, I may be screwed because there is no way I can get a drill in there to drill a higher one.

I very roughly measured the pedal ratio. 4" to the rod on a 13" pedal. He told me for manual brakes I am going to need the attachment closer to 2.5" from the pivot!.

I have been thinking about doing the same thing as I was not happy with how far down my brake pedal goes. I want to say Wilwood suggest using a 1" for power brakes and 3/4" bore for manual, you should check with the manufacturer of your Master cylinder.

Last edited by Kacyc3; 01-11-2019 at 05:11 PM.
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Old 01-11-2019, 05:25 PM
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Guys removed PB or found manual disc cars back in the day so they could save weight and not have hassles with rowdy cams. They stop just fine
Using a vacuum canister and PB,right on the line of "ok" and having to eliminate them....Im spoiled though they are stayin
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Old 01-12-2019, 11:17 PM
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Hydraboost?
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Old 01-13-2019, 03:22 PM
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Originally Posted by Kacyc3 View Post
I have been thinking about doing the same thing as I was not happy with how far down my brake pedal goes. I want to say Wilwood suggest using a 1" for power brakes and 3/4" bore for manual, you should check with the manufacturer of your Master cylinder.
Iam using the 7/8" master cylinder from wilwood, Iam sure they dont do a 3/4?

i did a power to manual conversion, the manual brakes work great, the 7/8 gives more line pressure, so easier on your leg

Last edited by corvettedave383; 01-13-2019 at 04:39 PM.
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Old 01-13-2019, 03:59 PM
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Originally Posted by corvettedave383 View Post
Iam using the 7/8" master cylinder from wilwood, Iam sure there dont do a 3/4?

i did a power to manual conversion, the manual brakes work great, the 7/8 gives more line pressure, so easier on your leg
I've got the 7/8" as well- they don't make anything smaller in the tandem style.

It was recommended as I'm running 14" 6 pistons calipers
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