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Old 09-11-2011, 10:26 PM   #1
k1rodeoboater
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For those of you who've done a power disc swap how'd you extend the pushrod???

For those of you who've done a power disc brake swap, how'd you end up extending the booster??? Pics would be much appreciated.

I'm currently stuck at this point with how to extend my pushrod on my booster. I tried to make a linkage that attached to the hole in the booster pushrod from the pedal but it kept flexing/bending at that point.
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Old 09-12-2011, 12:53 AM   #2
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

You will have to cut the 'eye' off of the booster pushrod for starters. Then either cut and weld your original master pushrod to the booster, or find a piece of DOM tube to slide over the two and cross drill and pin them together. Sorry I don't have any pics of either one.
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Old 09-12-2011, 09:10 AM   #3
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Once you go with a power booster, don't you also have to drill a new pushrod hole on the pedal 1" lower? I guess because of the angle change the booster adds.
At least I thought I read that someplace and did that to my truck.
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Old 09-12-2011, 09:10 AM   #4
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

I used a power brake booster and master cyclinder from a 91 burb (donor vehicle) we extended the rod like this.........(I did not have the correct all thread we just used a bolt got these at Loews, I do not thing one has to have grade 8 for this application....JMO Kieth

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Old 09-12-2011, 10:02 AM   #5
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Quote:
Originally Posted by kieth View Post
I used a power brake booster and master cyclinder from a 91 burb (donor vehicle) we extended the rod like this.........(I did not have the correct all thread we just used a bolt got these at Loews, I do not thing one has to have grade 8 for this application....JMO Kieth

http://kieth.smugmug.com/Trucks/66-G...5_tXS55Sq-A-LB
hmmm that method looks pretty simple, I cut and welded mine using the 63 piece and the 87 piece, but the bolt method looks a bit easier!
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Old 09-12-2011, 10:26 AM   #6
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

You could have a machine shop make you a new rod longer than you need, then bolt it up and mark it exactly where you need it, cut it down, grind off the rough edge and ta-da.

-W
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Old 09-12-2011, 09:31 PM   #7
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Sorry I did not take pictures -- I thought it might be boring...
I cut the eye off the pushrod, Then took a 3/8 rod coupling, drilled out the threads (slightly smaller than the rod) for about 1/2 inch, pressed it together and then spot welded it on the stub from the booster (vacuum or hydroboost) .
I used the eye from my 64 , and welded a 3/8 rod coupling on that piece also in the same manner .
I then used some 3/8" all-threaded rod for the adapter piece between the two rod couplings.
The threaded rod ended up about 3 or 4 inches long. I used 3/8 nuts and lock washers for the jam nuts. It is adjustable Kinda like a turnbuckle but all right hand threads. You can spin the booster end to get the proper amount of play in the linkage.
(The hydro boost end did spin freely, I do not remember about the vacuum boost)
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Old 09-13-2011, 12:04 AM   #8
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

...so in theory...if I were to cut the eye off of my booster, then take a 3" 7/16x20 bolt and weld it onto the end of the booster rod (after measuring to make sure where I weld it up will be the correctish spot) I should be golden then. That way I can retain the stock part of the clevis, have it attached to my booster, and also have it adjustable (somewhat, basically 1/2 turn at a time.)


It's gonna be fun pulling the booster out and figuring out how to keep the MC hooked up.
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Old 09-13-2011, 12:40 AM   #9
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Quote:
Originally Posted by tazattitude View Post
Once you go with a power booster, don't you also have to drill a new pushrod hole on the pedal 1" lower? I guess because of the angle change the booster adds.
At least I thought I read that someplace and did that to my truck.
I believe the reason for lowering the pushrod on the brake pedal arm is not due to the angle, rather it is an effort to reduce the pedal ratio.

A boosted system needs less mechanical advantage because, technically, a boosted system that maintains a non-boosted pedal ratio would/could result in a VERY power system that can be touchy - touchy as in a person would have to get used to it a bit more than a booster + boosted pedal ratio setup.

For manual brakes: 6-to-1 ratio
For power brakes: 4-to-1 ratio (i.e. push rod connection point closer to the pedal pad compared to a manual brake setup)

So, if someone were moving the location where the pushrod connects to the pedal "down" relative to the manual brakes mounting location - it would in effect reduce the pedal ratio from ~6 to ~4-5-ish.

Pedal ratio = (distance from brake pedal upper pivot to center of pedal pad) / (distance from brake pedal upper pivot to push rod connection point)

BUT, having said all this - I think MOST folks do not bother to change pedal ratio when swithing from manual to power brakes - primarily because it could screw up the geometry. Bottom line - the pushrod should be in line (approx) with the line of travel of the master cylinder piston. So, for me, I don't monkey with that and I don't try to fix pedal ratio because I don't want to monkey with (screw up) the geometry and I figues that since I'm converting to power anyway, I might as well have BIG power (i.e. boosted + manual mech advantage).



Edit - IF your new master/booster combo has a firewall mount that tilts the mc piston line of motion, then yes - in that case you might need to drill a new hole (in order to maintain correct geometry - not for pedal ratio stuff) - I'd have to rely on kit directions for that!

Edit #2 - so, for example, if installing a booster with Captain Fab's bracket (parallel to the firewall), I would not move the pivot point and I'd accept a slightly higher than desired pedal ratio. but if I were installing one of the kits that tilts the booster so it is not parallel to the firewall, then I'd want to attach the push rod to the pedal at a point that will keep the motion of the push rod in line with the line of motion of the mc piston.

My head hurts.

Last edited by jocko; 09-13-2011 at 12:47 AM.
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Old 01-23-2012, 01:35 AM   #10
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

-bump-
Any more info or experience regarding this topic?
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Old 01-23-2012, 01:47 AM   #11
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

No Jocko has got it...... Mine I cut in half, threaded it and threaded a piece of DOM and made it adjustable, did mount it one inch lower.
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Old 03-18-2017, 01:48 AM   #12
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

I'm having some issues with my brakes and think it may have something to do with the geometry or just length. 1969 Blazer, 10 bolt front with disc, 14 bolt rear that I just switched to disc. Switched to mid 70's MC and have .20'' between MC pushrod and contact point in MC. As far as I know its a stock booster. What dimensions do I need on the rod between the pedal and the booster? The clevis in engine bay from booster is tight up against the firewall, is that normal or should I have a gap? What dimensions should I be looking for? Bench bled MC. Trying to bleed lines and can't seem to pump up any pressure. Tried bleeding with a partner. Also attached a clear tube to each of the 4 bleeders and taped them to side of Blazer so they reached above MC to try and get all air out. Just can't build up pressure. Suggestions?
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Old 03-18-2017, 11:43 PM   #13
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

A couple of things. That .200" gap is too much. I will have to check and see what the acceptable clearance is. next is the master you are using. If you are using a stock truck master for a disc/drum system, that is not correct. You also need a disc/disc prop valve or an adjustable valve in the rear circuit. Depending on just what calipers you are running, you should have at least a '77-'84(?) Corvette master or maybe a different one all together. This thread may be of help.

https://ck5.com/forums/threads/4whee...linder.174038/

Quote:
Originally Posted by Baketown Scotty View Post
I'm having some issues with my brakes and think it may have something to do with the geometry or just length. 1969 Blazer, 10 bolt front with disc, 14 bolt rear that I just switched to disc. Switched to mid 70's MC and have .20'' between MC pushrod and contact point in MC. As far as I know its a stock booster. What dimensions do I need on the rod between the pedal and the booster? The clevis in engine bay from booster is tight up against the firewall, is that normal or should I have a gap? What dimensions should I be looking for? Bench bled MC. Trying to bleed lines and can't seem to pump up any pressure. Tried bleeding with a partner. Also attached a clear tube to each of the 4 bleeders and taped them to side of Blazer so they reached above MC to try and get all air out. Just can't build up pressure. Suggestions?
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Old 03-19-2017, 10:27 AM   #14
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Thanks Captain. The MC is for a mid '70's Corvette (disc/disc). The gap I spoke of is .02'', my bad. Not using prop valve since I have all disc. I do have an adjustable valve to dial in the rears. El Dorado calipers in rear. I thought I had all bases covered (fools mistake) and that is why I was questioning the pushrod dimensions. I'll keep bleeding to see if that could still be my problem. I did read the link you sent but I was thinking my MC was big enough and I have checked the booster and it checked out. Thank you.
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Old 03-20-2017, 07:31 AM   #15
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Wow 2 people across the map having the same problem lol ME. Im using cadillac rear calipers also. I mounted my booster/master directly onto the firewall though. Im about a week in and not been able to get a good brake pedal. Have you adjusted your rear parking brakes? I just ordered a residual pressure valve from summit to try and correct it thanks to abother C10 guy who told me the wilwood valve fixed his 4 wheel brake issue. Mine will get a decent pedal but when i start the truck and booster starts working it goes all the way to the floor?
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Old 03-20-2017, 09:53 AM   #16
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

There is a rod in the booster, it pushes on the master cylinder. Not the rod attached to your pedal. Make sure that adjustment is correct also.
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Old 03-20-2017, 11:36 AM   #17
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

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Old 03-20-2017, 12:01 PM   #18
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Zach, I have not connected my e-brake cables yet. I need to bleed some more I guess, but can't even get some pressure built up to start. I'll keep fooling with it. Let me know how you do.

Robber, How did you know how long to make your pushrod? What dimensions are you trying to get? Are you trying to get like 1/4'' of play before you're actuating the booster? My pushrod goes from pedal through firewall and connects to the linkage for the booster. The rod coming out of my booster still has the eye on it and it appears the eye part is up against the firewall. Maybe possible the booster is not releasing enough? I'm working out of town but will try and get a picture to tell the story.

Thanks all.
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Old 03-20-2017, 11:47 PM   #19
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Are you sure that you have the correct intermediate pushrod for the style of master cylinder you have? The '67-'76 Corvette master has the deep bore in the back of the piston. The '77+ has the shallow bore (dimple).

Quote:
Originally Posted by Baketown Scotty View Post
Thanks Captain. The MC is for a mid '70's Corvette (disc/disc). The gap I spoke of is .02'', my bad. Not using prop valve since I have all disc. I do have an adjustable valve to dial in the rears. El Dorado calipers in rear. I thought I had all bases covered (fools mistake) and that is why I was questioning the pushrod dimensions. I'll keep bleeding to see if that could still be my problem. I did read the link you sent but I was thinking my MC was big enough and I have checked the booster and it checked out. Thank you.
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Old 03-21-2017, 07:48 AM   #20
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

I have a shallow booster and I added the adapter piece to my master to connect the 2. I am getting brake fluid at all 4 wheels but not as much at the rear. Im swapping my rear calipers tonight since I haven't hooked up my parking brake I've read some say the caddy calipers can give fits if the parking brake is not used frequently. Im going to swap some S10 calipers on and see if it has any affect. Ive blocked off my master cylinder and it holds good pressure hard as a rock. So it should be good. Ive never had this much problems putting on brakes... A week before first cruise inn go figure
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Old 03-21-2017, 10:39 AM   #21
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Are you sure that you have the correct intermediate pushrod for the style of master cylinder you have? The '67-'76 Corvette master has the deep bore in the back of the piston. The '77+ has the shallow bore (dimple).

I did take great care in measuring the existing rod to MC dimensions versus the new MC and got the gap down to .02''. Like Zach, I also have plenty of fluid at all four. This weekend I'll get back to it and see if I can get some pressure.

Zach - From what I have read once the e-brake is connected it needs to be used regularly to keep it adjusted.
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Old 03-21-2017, 12:00 PM   #22
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Re: For those of you who've done a power disc swap how'd you extend the pushrod???

Quote:
Originally Posted by Baketown Scotty View Post
Are you sure that you have the correct intermediate pushrod for the style of master cylinder you have? The '67-'76 Corvette master has the deep bore in the back of the piston. The '77+ has the shallow bore (dimple).

I did take great care in measuring the existing rod to MC dimensions versus the new MC and got the gap down to .02''. Like Zach, I also have plenty of fluid at all four. This weekend I'll get back to it and see if I can get some pressure.

Zach - From what I have read once the e-brake is connected it needs to be used regularly to keep it adjusted.
Yea I have a aftermarket wilwood style master cylinder. I had to add the brass adapter included with master cylinder. But Ive mounted mine directly to firewall so I cant measure my original master and booster. Mine came with a short universal pedal rod with 5 different attachments for the brake pedal.
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