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Old 07-31-2019, 05:15 PM
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Default Master Cylinder std depth measurment

Can anyone tell me how deep a short pocket master cylinder should be & where you measure it from?

I am going to guess that the pin sticking out of the booster should just touch the center of the cylinder, but not depress it at all until the pedal is pushed?

I need a spacer pin as I just realized I have a deep pocket master & a short brake booster in my GTO.

I thought I had an old master somewhere to compare, but I can't find it

Thanks, 68RT

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68 GTO 4-spd Convertible
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Old 07-31-2019, 07:14 PM
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I found a mid 70's GM original. Not sure what its from, but it looks like I can measure from it. I would imagine there are only two types from a pin depth perspective?

Thanks!

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68 GTO 4-spd Convertible
78 S/E Trans am L78, WS6 Auto
78 S/E Trans am W72, WS6 Auto
79 10th aniv W72 Trans am
80 Indy pace car Trans am
89 Trans am GTA
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Old 07-31-2019, 08:04 PM
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2 pin sizes are available, one for power brakes and 1 for manual. From what I can remember the longer of the two is for power, could be wrong on that though, been a few year since I was playing with this. Sold off my booster stuff to go to Hydraboost. Will try and find measurements. Not tonight though.
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Old 07-31-2019, 08:11 PM
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More info,
>
>
> On the left is the long 4 inch pushrod, On the right is the 2 5/8" short
> pushrod, a difference of 1 3/8". Note the O ring to seal vaccum.
>
> The matching master cylinders are below. Deep hole 1 5/8" on left is for
> manual brakes, OR is used on power brakes with the long pushrod.
>
> The cyl on the right is POWER BRAKES ONLY, 3/8" depth hole, the pushrod
> attached to the brake pedal arm will fall out if used on a manual system.
>
> Measuring depth with my dial calipers, the deep master cyl is 1.350"
deeper
> than the shallow.
>
> A manual brake pushrod is aprox 7" from tip to clevis pin.

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Old 07-31-2019, 09:03 PM
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Thanks, that helps. I believe the master I have is from a 1970 ish corvette,
It does have the 1-1/8" cylinder so should be correct, just has the deeper pin hole.
After some searching I see there are some spacers made for this.

Thanks for your efforts!

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68 GTO 4-spd Convertible
78 S/E Trans am L78, WS6 Auto
78 S/E Trans am W72, WS6 Auto
79 10th aniv W72 Trans am
80 Indy pace car Trans am
89 Trans am GTA
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Old 07-31-2019, 09:09 PM
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I just measured the depth between the two cylinders I have here. The one is 1.332" deeper. Just about 1-3/8" like you mentioned.

Thanks again

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68 GTO 4-spd Convertible
78 S/E Trans am L78, WS6 Auto
78 S/E Trans am W72, WS6 Auto
79 10th aniv W72 Trans am
80 Indy pace car Trans am
89 Trans am GTA
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Old 07-31-2019, 09:15 PM
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Interesting that the spacers that I am finding are called 1-1/2" I am guessing thats overall length, not subtracting the dished end that contacts the rod from the Booster.

https://www.ebay.com/itm/Deep-Bore-M...5/132374630834

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68 GTO 4-spd Convertible
78 S/E Trans am L78, WS6 Auto
78 S/E Trans am W72, WS6 Auto
79 10th aniv W72 Trans am
80 Indy pace car Trans am
89 Trans am GTA
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Old 08-01-2019, 01:31 AM
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Would suspect you are correct about measurement. I was able to buy a correct length pushrod from MBM Brakes, but appears they don't sell it any more.
http://mbmbrakes.com, but you can ask.

Glad to help out. Just passing on info that was passed onto me. Changed out mine to Hydraboost.

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