Quote:
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Originally Posted by k2rm
I have a Performance Online MC running 4 wheel discs on my 1970 C20 and the truck stops really well. This is even running the 77 el dorado rear calipers with parking brake which are known to require a lot of volume to engage.
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I am actually strangely familiar with these calipers. 63.5mm pistons if memory serves me right. Every car that used them used a 1-1/8" MC Sevilles/DeVilles/Eldo/Toro/TA/etc.
What bugs me in the Perf Online tech told me that all their MCs use a 1" bore. Now on a non boosted system that's OK with me, but they are using it with their boosted systems as well. I know they use some AL MC, but unless it has a longer than stock stroke, I feel you lose modulation.
Quote:
Originally Posted by MADMIKE
So far this is the hydraulic parts list.
'84 GMC 2500 1-1/4" MC which shares the same fitting sizes.
'72 GMC 2500 Booster, appears to mount the same as the '70 but takes newer MC with a dimple on the piston, rather than the earlier 1.64" recess.
'84 GMC 2500 front hoses. A tad long but we'll see.
'84 GMC 2500 80mm front calipers.
'84 GMC 2500 1-1/16" wheel cylinders.
2- 7/16-24 Female to 3/8"-24 Male adapters(rear drum WCs)
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After a bit of review and back and forth the list was shortened quite a bit.
We had double checked the parts but not everything was adding up. Triple checking showed further differences from the other two sources. I'm thinking the first two had make/model confused.
Comparing parts from GMC to Chevy trucks shows differences. I was a bit surprised that there would be any changes, but there are. Boosters, MC and rebuild kit part numbers are different between the same years. This probably accounts for all the weird discrepancies I was getting while looking up part numbers.
So the
NEW list... hah
'70 Chevy Caprice/Impala/Kingswood/etc MC 1-1/8" MC for Disc/Drum cars with 1.63" pushrod depth.*
'70 Cadillac Fleetwood rear WCs 1" with correct angled 7/16-24 ports.
'84 GMC 2500 75mm front calipers.
'84 GMC 2500 front brake hoses.
This will allow bolt in installation with no adapters or changes to the booster.
Although, I will have to check the pushrod depth. '70 2500 calls for 1.64", not sure if the booster push rod is adjustable, or if I will have to shave .01" off the end of the pushrod.
I tried looking up some dimensional differences between the C10 Disc booster(Rod Code CT3/CT5) versus the C20 booster(Rod Code CT4) but only found depth changes by looking at the C20 drum MC vs the C10 disc MC.
*FWIW the Chevy C10 disc brake trucks appear to use the same MC as the Caprice. However, depending on where you look up parts, the GMC and Chevy truck parts get lumped together often with the Chevy specific part being dropped.
And to just add a bit more to this quagmire of parts.
The MC we are planing on using is this unit.
This is apparently is what the Original PB MC should look like.
But this is what the MC that is on the truck looks like.
I suspect that the original owner had the MC replaced at one time but was given the wrong part for whatever reason. I won't know what the bore is until I pull it and report on it. If it is a 1" bore that would explain the long pedal on the truck.