Does anybody know how long the brake booster rod is supposed to be for a disc brake conversion?I bought a kit off of e-bay and installed everything,bled master multiple times,brakes bled good,but when driving the pedal has to go all the way to the floor for the brakes to even start grabbing.We've tried different masters and proportioning valves we've even plumbed in residual valves with no improvements.Any suggestions?Were at a loss!
This may be a silly idea.....does your brake pedal have two holes in it...I know the 68-72 versions do....the upper hole is for manual brakes and the lower for power brakes. The back of your master cylinder.....does it have a counter bore or just a shallow depression? The new boosters come with 2 pin lengths...the longer pin goes into the master cylinders with the counter bore....the shorter pin goes with the shallow depression master.
Sorry to hi-jack the thread but I need the same info for a '68 power drum brake rod length. On the '68 I bought last year, I thought it had an issue as the brake pedal was right at the top with no free play and it didn't feel like much stopping power. I have since replaced the booster and the master cylinder and it was the same. Then I thought I had and issue somewhere else in the system. Just recently, I have repalced everything except the steel lines. New hoses, wheel cylinders, etc - same thing. Also it seems to get worse the longer I drive the car. The more I use the brakes each trip - the higher and harder the pedal gets. This goes to the point of locking up the brakes eventually. I now am thinking that the push rod at the front of the booster is too long or the indent in the master cylinder piston is not deep enough. I don't think the pressure is being allowed to bleed off once the foot pressure is released. So I need the length of the front pushrod and the depth of the M.C. piston indentation. Thanks :idea2: Thanks
On my master,the depression in the back of the piston is shallow,just has enough of a indentation to hold the tip of the rod.The longer rod wouldn't even allow us to bolt up the master to the booster.Im pretty sure we didn't move it up because the booster rod wouldn't shorten up enough to line up with the upper hole.
The shallow depression is correct for the short rod. When you said you tried different master cylinders....were they new? I had several problems with rebuilt master units and no longer use them.....TRW/Moog make new masters.....I use them, cost about $45 and never had a problem since. Dukec, Did you replace the rear brake hose? If so, sounds like another bad master cylinder.
George Yes, I did replace the rear brake hose. I originally thought that my problem was there. But no change. Also the master I changed was to a new NAPA. Maybe I need to figure out a way to put a pressure gauge in the system to see what is happening.o No:
the master cylinder that came with the kit originally was new,then we tried a rebuilt and a used one.Same problem.After we bleed the brakes the pedal feel like should until you pump it 5-10 times then you get almost no pressure until you get to the last inch of travel and then its hard as a rock.The pedal has to be all the way down to the floor for the car to even slow down.
to me, i am no mechanic, it sounds like the rod is short. try a longer one. if it is too long then the brakes would be dragging. get a couple of rods longer. try a longer one then another longer one till the brakes drag. then cut a small amount off. i hope this works. jim
Ok,I've checked and we have the proper rod in there,the booster to pedal rod is in the lower hole,still bleeds great but there is no stopping power and I can only press the pedal down about an inch.I have a 1 1/8" master so could it be that the booster is bad?There is no change in the pedal if the engine is running or not.
To check the booster, pump the brake pedal a few times with the engine off. Then apply pressure to the brake pedal and start the engine. If the booster is functioning properly, the pedal will sink down as the engine starts.
Be sure your bleeder screws on the new calipers are facing UP. I'm reaching here, but I have heard of people getting them backwards.
I had a similar problem. What I found it to be was I didn't have the brakes adjusted out enough and also found a leak at the joint over the rear axle. My brakes would seem to work at first that eventually feel like I had no brake again. Only found leak when was on a lift so could look at all bleeders and connections to see if was leaking. I too thought it was the rod being to short on the booster to master cylinder, but was wrong.
as some of you might now i had the same problem except a bit different, front wheels locking up after a short drive, changed pads, calipers, for the front, then disc brake master cylinder, still the same..then cut the push rod down about a quarter of an inch, and then it stoped locking up, then noticed you had to push the pedal inn all the way to stop it, them i said...ok rear shoes are worn out lets replace them along with cylinders, bled the entire system and still nothing, still did not stop...then i changed the master cylinder and booster both matched from the manufacturer just as i bought it from autozone.. slaped it on and bam..tried it today and works great now, brakes good, and does not lock up anymoreou: the good side of this is i have all of the brake system brand spankin new:bglasses: went throught lots of headaches and time...but i never thought about the booster, the thing i did not notice is that the original one from the car did not have a removable shaft (the one that pushes the master cylinder) and the new one from autozone had the 3 inch or so removable shaft, which was the different thing from both, try checking out your booster, might be the problem.. hope this helps.
Yea I think its got to be the booster,I'm going to buy one from O'reilly since my friend works there and I can return it if its not the problem.
yea, i wouldnt go that route with oreilys or kragen. their booster alone was 130 something bucks, their booster and master cylinder combo was 200+ bucks, i bought the booster from autozone with master cylinder for 130 bucks minus the 30 core.. seemed like a heck of a good deal...and great quality. i dont know how much discount youll get but its good to find out:TU:
Be careful when buying boosters from the local parts stores....most are made by Cardone and they are made in China....they do not look anything like the originals. The "Partsladi" on Ebay sells new ones with the Delco Morraine stamp for $99.
The booster line is getting about 15-16lb of vacuum.I'm going to try the booster from a local store because I can return it either way and get a nice one.
