One last quick master cylinder question/pushrod

I installed the corvette master cylinder. I also lengthened the stock pushrod by about 5/8" of an inch, because a few said that with the new master swap, you have about 2"-3" of pedal travel before the brakes come on and it is a good idea to lengthen the pushrod between a half inch and and inch.

When I installed everything, I noticed the newly lengthened pushrod pushes the master cylinder piston in about a 1/2" into the bore. I am assuming this is allowable and this will result in the brakes being activated quicker since the piston is already pushed into the bore a little.

Any thoughts or comments? I think I am ok but juts want to check before I start bleeding!

.... I used the stock push rod w/ no mods. Work fantastic for me. i was wondering what everyone was talking about having to lengthen it. I didn't need to.

Oh and BTW ... I checked my line hook ups yesterday. The firewall line does go to the FRONT brakes and the other to the REAR.

I am sure it did work fine as is after doing the mod the other day. Lengthening the rod will obviously make the brakes engage almost as soon as you depress the pedal, giving you instant stopping capability.
I just hope the piston being in the bore about 1/2" won't be too much etc.
Thanks for the brake routing help as well...I am all good to go and should have her on the road by next Sunday....

I also used the stock push rod. I do have a couple inches of travel but think I'm still fighting adjstment issues. Went for another drive today and again back drums are warm, front drums are cool. Weathers been so nice I'd rather drive around than crawl under and adjust brakes.

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Originally Posted by teking

.... I used the stock push rod w/ no mods. Work fantastic for me. i was wondering what everyone was talking about having to lengthen it. I didn't need to.

Oh and BTW ... I checked my line hook ups yesterday. The firewall line does go to the FRONT brakes and the other to the REAR.

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Would you happen to have the part number for the master you installed teking?

Just go to any auto parts store and ask for a 1976 Corvette master cylinder with manual brakes. Easy...and it was like $26.00....

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Originally Posted by Fastfrankie

I installed the corvette master cylinder. I also lengthened the stock pushrod by about 5/8" of an inch, because a few said that with the new master swap, you have about 2"-3" of pedal travel before the brakes come on and it is a good idea to lengthen the pushrod between a half inch and and inch.

When I installed everything, I noticed the newly lengthened pushrod pushes the master cylinder piston in about a 1/2" into the bore. I am assuming this is allowable and this will result in the brakes being activated quicker since the piston is already pushed into the bore a little.

Any thoughts or comments? I think I am ok but juts want to check before I start bleeding!

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You need to change the pushrod so the piston is back against the snap ring when the brakes are not applied. If left this way the pressure in the brake line won't be able to release properly causing your brakes to drag and maybe lock up. You should really have a very slight amount of pushrod movement before it starts moving the piston, probably talking about thousanths of an inch but just enough so you know that piston can come all the way back.

I don't know if I agree with you or not. As long as the piston returns behind the tiny holes where it forces brake fluid out of the master and into the lines should be all that is needed.
Even though the piston is this case is a half inch into the bore, you are still starting and ending with the same amount of fluid being pushed out and then being sucked back in.
I'd really like to hear from someone who has lengthened their pushrod and can peek under their dashboard and see if in fact their piston in the master is pushed into the bore a little and how well their brakes function.
Basically, whoever has lengthened their pushrods has to be in the same situation as me as far as the piston being pushed in a little....maybe I am wrong....
Anyone here who has lengthened their stock rod and can check on this under your dashboard?

wouldnt it be nice to just have a proven truck master cylinder kit all engineered out with a 1 hour install and know for sure its correct ?

For some yes, and others no. I know guys who stay in the garage to get away from everyone else.

What type of brake fluid are you using with the vette master?

I buy whatever is cheapest....Autozone Brake Fluid, Advanced Auto Brake fluid etc.....as long as it is new, it works for me.

Well who here has the lengthened pushrod??? Apparently there were a few who have done it, yet no one has come forth yet? C'mon fellas....if you have the lengthened pushrod, is your piston pushed into the bore or not? At this point, I am going to use a spare rod I have.

gimpy, W H O could 'everyone else' be???????????????. LOL.

DOT 3, 4, 5,? The only references I've seen in the manual just say no petroleum based fluids.

XJ Chief...it doesn't matter....just think way back in the 1960's, do you think they even had DOT anything regarding brake fluids? LOL

Walk into your local auto store and buy whatever makes your heart go pitter patter! DOT 5 is more money than DOT 3. I am real cheap....so I buy whatever has the lowest price tag...I wouldn't put DOT 5 in anything unless it required it like in a Lamborghini or something. I bet you could you use hydraulic jack fluid in theses trucks and it would work. Keep it simple please...

Just wanted to makes sure that the truck didn't require silicon fluid. I keep seeing these little placard stickers which made me wonder.

http://http://www.flmv.net/images/DECALS/DECAL28A.JPG

http://www.flmv.net/images/DECALS/DECAL28A.JPG

The M715 did not come with silicone brake fluid. DOT 5 is mineral based but rated for a higher temperature. You really don't have a need for DOT 5 in the M715. Just get DOT 3 if it had mineral based fluid in it before.

Non petroleum base is the spec...remember that brake fluid absorbs water...so it cant be petrol based...oil and water dont mix... none of the common brake fluids from the past 40 years or more would be petrol based...

You are right. I was thinking British there for a moment instead of military.