Anyone know a part number for a 4-wheel disc mc with around 1-1/8" bore that has a short pushrod hole? I've ordered a couple of different ones for early 70's corvette, but they had deep pushrod holes. I have a short pushrod and need a shallow hole. No parts store has been able to tell me before ordering whether the hole will be shallow or deep. '79 Trans Am , maybe? Thanks for the help.

Sure, you have to get a power brake M/C b/c they have shallow holes whereas the non-power M/C's all have deep holes to keep the rod from falling out if the piston sticks in!!

I made a rod "centering cap" locator for my 1.25" piston M/C for my "pdqCBB" setup to keep that from happening.

GM has made such a locator stock, but you would have to hunt one up in the Salvage Yards b/c it isn't a service item anymore..

pdq67

PS., the easiest way to do this is to ask a friendly Partsperson to bring out some of their inventory of M/C's and measure them.. That's how I found my M/C..

dont know if the '79T/A has a deep or shallow, but it is definitely 1.125". You could use a spacer in the hole if you have power brakes.

78-81 corvette is a shallow 1.125"

manual vs power is not always the definitive answer on deep vs shallow. Either could come either way, but if it was manual/shallow, it required a retainer for the rod.

I ordered a power MC and it came with the deep hole. I suppose I'll try the the 78-81 MC, but this will be the last shot in the dark, as I'm sure the parts man will be getting sick of special ordering parts that I keep returning. If that doesn't do it then I'll make a pushrod extension, although I wanted to avoid that. Thanks for the prompt help.

I made my pushrod locator out of a, solder on, copper water pipe cap that just fit almost perfect over the boot end of my M/C!!!!

I then cut it to length so that it was long enough to fit past the rubber cap's dog-knot groove.

Then I drilled a center hole in it and very gently peined it in a couple of spots with a sharp centerpunch into the "dog-knot" groove. This locked it in place perfectly to me....

Make the hole slightly bigger b/c the pushrod pivots oh so slightly as it goes in and out.

AND the hardest part to me was that it took me four try's to adjust my pushrod so that it just kissed the M/C's piston the needed/wanted, about .030" free play to give about an inch travel on the top of the brake pedal.......

I had to remove my M/C four times and adjust my pushrod before I got it spot-on as I also crawled under the dash head first to eye-ball the .030"/1.00" pedal travel each time I adjusted it!!!

What a pain, but I wouldn't trust any other way to do this right!!!!!!!!!!

pdq67

So you're actually able to adjust the pushrod within the booster by changing its attachment to the pedal? For some reason I thought the amount it protruded from the booster was fixed. I'm sort of an idiot so this might take a few explanations. graemlins/clonk.gif

My manual p/r has a what is like a long "coupling-nut" on it that I can adjust it with since it is two piece.

I think it even had a small lock-nut too?? But it's been a while...

pdq67

I think pdq67 is talking about the pedal rod not the rod coming from booster to master cyl.
The second rod pulls right out of the master cyl and can be replaced with a longer one, or you can cut a piece of rod and insert it into the master cyl for a spacer.

you could have a machine shop make up a new longer rod in stainless for you, or maybe you can buy one from one of the booster vendors.

I think the easiest solution is to just insert a rod into the hole as a spacer and be done with it. Thanks to all for your help.

My bad!!

David is right! I'm ignorant on power brake boosters!

Sorry..

pdq67