[dmorg1]

I am looking to replace the Master Cylinder on a 68 manual disc setup and I am finding that all of the venders list only the MC for disc with power assist.

When I referenced the MC Usage Chart in the 68 service manual it lists two different cylinders one for Manual Disc and another for the Power Disc.


Does anyone know if the Manual Disc MC is available?

Can the Power Disc MC be used in it's place without jeopardizing the system?



Thanks,

Dave

[Scarebird]

How about more info, like what this is going on?

[marxjunk]

rebuild yours, take it to NAPA, tell them you want yours back, its for a numbers car, they understand..look for theoldest guy in the store..done it many times

you can do it yourself if ya aint scared..as long as theres no pitting in the bore go for it

those kits are all over ebay..buy an A/C delco or Delco/moraine..no jap junk..its real easy, just intimidating..

yes they are diff..i dont know what it is, but manual disc and power disc have a different code on them, id imagine its the bore size...has to do with leverage....

[dmorg1]

Scarebird,

For a 68 GTO

Mark,

The manual says bore is the same but the displacement capacities are different.

Rebuild will be plan B if it's not available.

Dave

[marxjunk]

i see



Ive seen a bunch of Man disc Oldsmobiles in 68-9, but never a Pontiac...strange..join classic oldsmobile and poke around on there....all the w31 and w3os are man because of the cam in them...i bet theres at least some info, when you join you can do a search..lots of info on there and a few life longs that help

[dmorg1]

Mark,

Thanks for the Olds lead, I will check it out.

I guess the Manual Disc was not a very popular option.


PHS is showing RPO 521 (Disc Brakes Front) without 502 (Power Brakes)


Dave

[marxjunk]

NEVER SAW A PONTIAC WITH MANUAL DISC..EVER..SOMETHING RARE THERE...

[Verdoro 68]

FWIW, I had a '68 LeMans parts car with manual discs about 20 years ago. Definitely an odd option.

[corn goat]

paulatfast pointed me toward using the 1977 transam manual disk master a couple of years ago .I have been using one for 3 years with out a problem on my 69 gto w/front discs and rear drums.

[6869GTO]

My 68 is a manual disk car. The master that was in it when I got car back in 1977 or so was not the original and thou it looked correct minus delco markings , actually had the residual valves at both ports and explained why front disc had a heavy drag. Removed front valve and all was good. Fast forward to 2012 and thou car is now in progress resto bought the new master and questioned whether it would work w/manual disc and vender put me in touch w/MBM and rep said no problem. When I got it I immediately checked to make sure there was no residual valve at front port and there wasn't,,,, and wasn't one at rear port either! Another call and none of the masters that MBM manufactures have a residual valve for rear drum and if you have a problem w/rear brakes you can add one. ???? OK will see. So long story short the new Masters that most vendors carry are made by MBM and should work though I still have no seat time to say otherwise. Also hang onto your original hold off valve cause the repop wont seal a 3/16 from master to valve. Seat is about .060 deeper than factory valve and line ferrule nut will bottom out before line is seated.

[dmorg1]

Leo,

Thanks for that information.

Is it the MC309 you have that has no residual valve?


Dave

[6869GTO]

Yes MC309. Again they made it sound as though none of the masters they sell have them.

[dmorg1]

Update,

So it turns out that the MC on the car now is not correct (both reservoirs are the same size) but it does have the 1-1/8" bore and it does have the check valve in the drum port only, so the rebuild plan is out.

I purchased the MBM MC309 and sure enough no check valves were installed so I sent an email to the MBM rep. and you are correct Leo that their MC's are not supplied with check/residual valves.

I asked him if the check valve was needed for the rear drum brakes and was told to use one at my discretion.

So now I am looking to install the check valve.


Does anyone know where I can purchase a check valve, spring and a tube nut seat for a 9/16" tube nut?

or

Do I need to purchase a complete cylinder repair kit?


Dave

[VAB5]

Check with InlineTube.com. They have a lot of unusual stuff, and guys who know what they are doing.