Problem with power brake swap

[fs64]

Swap utilizing a used 2001 GMC booster with a new 1970 Buick estate wagon master cyl. ( Autozone M-1489) utilizing Captain fab bracket. (Nice piece: need it, get it!!!)
All new lines, shoes, hoses and wheel cyls. new drums on front, turned drums on rear. Initially had trouble bleeding front brakes, found that intermediate rod was putting pressure on the master in the resting position and apparently not allowing fluid from reservoir to refill the cylinder. Adding a spacer between the booster and master allowed us to bleed fronts without further problem. Plan was to cut intermediate rod down to correct length.
Pedal is high and solid, however the truck does not stop well with pedal as far to floor as it will go. It is not soft and booster checks out fine. Removed the spacer from between the booster / master and it seemed to help minimally? The pedal to booster rod is adjusted to about an 1/8 of an inch and booster rod starts in motion with same. Placed clay between booster and master and clearance is about 1/32. Front drums are adjusted up well with appropriate drag. Rears are adjusted a little a little looser and are cut slightly larger than the max spec. but they will lock up when brakes are applied hard.
Current plan is to replace master cyl. with a NAPA # NMC P1971 and try again.
Any help, recommendations or suggestions are greatly appreciated. ( just don't mention discs )
Thank you all,
Todd

[PGSigns]

Have you got the shoes adjusted up close? Sounds a little like the are set to loose and you are running out of stroke before you get good pressure on the shoes.
Jimmy

[luvbowties]

Originally Posted by fs64

Swap utilizing a used 2001 GMC booster with a new 1970 Buick estate wagon master cyl. ( Autozone M-1489) utilizing Captain fab bracket. (Nice piece: need it, get it!!!)
All new lines, shoes, hoses and wheel cyls. new drums on front, turned drums on rear. Initially had trouble bleeding front brakes, found that intermediate rod was putting pressure on the master in the resting position and apparently not allowing fluid from reservoir to refill the cylinder. Adding a spacer between the booster and master allowed us to bleed fronts without further problem. Plan was to cut intermediate rod down to correct length.
Pedal is high and solid, however the truck does not stop well with pedal as far to floor as it will go. It is not soft and booster checks out fine. Removed the spacer from between the booster / master and it seemed to help minimally? The pedal to booster rod is adjusted to about an 1/8 of an inch and booster rod starts in motion with same. Placed clay between booster and master and clearance is about 1/32. Front drums are adjusted up well with appropriate drag. Rears are adjusted a little a little looser and are cut slightly larger than the max spec. but they will lock up when brakes are applied hard.
Current plan is to replace master cyl. with a NAPA # NMC P1971 and try again.
Any help, recommendations or suggestions are greatly appreciated. ( just don't mention discs )
Thank you all,
Todd

First, I'd guess a booster from a 2001 model vehicle would NOT be for a drum/drum system. What kind of MC is that one u mentioned?... Napa# NMC P1971 ?? Looks unrealistically expensive for a remanufactured one at that. Many of us have had good luck with 1971 master cyls. IIRC, there are some 1971's that take the same mc for drum/drum brakes AND for that word you said not to mention; I'll just call it also for an X/drum system..

Also, many have had better service from new MC's than from re-mfg'd. ones.

One more important thing to remember: adjusting up tighter on rear brakes results in greatly increased pedal.
HTH,
Sam

[Captainfab]

The braking system being a drum/drum system has absolutely nothing to do with what booster to use. What master cylinder to use is determined by the braking system (drums/drums). The OP is using the recommended master cylinder for the booster he has, although that part number doesn't look right unless it is a superceded number. The A1 Cardone number I have purchased in the past was a 10-1363.

I agree that the issue could be shoe adjustment and or a bad master cylinder.

Originally Posted by luvbowties

First, I'd guess a booster from a 2001 model vehicle would NOT be for a drum/drum system. What kind of MC is that one u mentioned?... Napa# NMC P1971 ?? Looks unrealistically expensive for a remanufactured one at that. Many of us have had good luck with 1971 master cyls. IIRC, there are some 1971's that take the same mc for drum/drum brakes AND for that word you said not to mention; I'll just call it also for an X/drum system..

Also, many have had better service from new MC's than from re-mfg'd. ones.

One more important thing to remember: adjusting up tighter on rear brakes results in greatly increased pedal.
HTH,
Sam

[fs64]

Thank you all for the response. The problem was a defective master cyl.
The knowledge shared here is greatly appreciated.
Todd