Strange Brake Question

[lake_harley]

The title is actually a little bit of a play on words. I have a Strange Engineering B3362 (I think that's the number) Fast Fill master cylinder on my FED's brakes. Other than bending a brake pushrod last year the brakes have worked fine. I replaced the whole master cylinder when that happened ($$$$) and the brakes have been fine. A problem developed today so we loaded up and went home.

If the driver steps on the brake pedal rapidly it feels solid and stays in place if you keep pressure on it. But, if he's "feathering" the brake, like during staging and then applies more pressure to footbrake the car the pedal drops slowly. I'm puzzled why it holds under quick application but leaks down with gradually increasing pressure.

Any thoughts before I tear into it early next week? I still have the old MC and have thought of putting it back on, but using the pushrod from the new MC since the old one had been bent slightly.

Now if anyone wants to help with my off-the-line stumble which is messing with our ET big-time, I'd be doubly grateful! Right now I'm more interested in making sure it will stop before I worry about making it go!

Lynn 

[denverflatheader]

Lynn - your 3362 master cylinder is rebuildable.  Strange sells kits, around $50.  Dragster brakes are different than a passenger car.  They are not going to last 75,000 miles plus.  Due to extreme pressure and the resulting heat from high speed stops, you do need to inspect your master cylinder and calipers if you experience brake issues.  The usual fix requires replacing o-rings and seals.

However, with the few number of runs that you and your driver have done the past year, and your description of the bent master cylinder pushrod, you may have a different issue with the master cylinder that is causing your problem.

Below information is from the Strange Brakes Website; maybe check your pushrod linkage alignment to see if your master cylinder has primary piston skirt damage.  Happy Easter!  Alan 


Primary Piston Inspection: The primary piston needs to be inspected. The piston skirts and faces highlighted in red should be carefully inspected. If the push rod linkages are misaligned and the pushrod is being engaged at an angle, the piston is forced to rub against the master cylinder bore surfaces. This will result in shiny spots or in extreme cases deformation of the skirt towards the front of the piston. If there is evident damage of the piston skirts the master cylinder bore should be inspected. Furthermore, the brake linkages should be corrected so they’re in line with the pushrod prior to master cylinder reinstallation.

Master cylinder bore inspection: It’s vital to inspect the master cylinder bores for wear, scoring and deposits. Discoloration or shiny spots in the bores are acceptable. Scoring should be felt by the finger. Generally, if the depth of a score catches the finger as it’s glided across, the master cylinder body is not acceptable. Scotch brite can be used to gently scuff out any minor scores. Scores will cause fluid to seep past the cup seals and inadequate to no brake pressure to develop. If the master cylinder body is found to be unacceptable, please contact Strange Engineering. After inspection the master cylinder bores and body should be cleaned with brake cleaner and dried prior to reassembly.

[lake_harley]

I printed out the 3 page installation and use guide from Strange which included what your post included. The bent pushrod was a rod that was about 8 or 9" long going from the foot brake pedal and threaded onto the MC pushrod. I admit, it was too weak and bowed one night but thankfully the chute slowed the car before the end of the track shut down area. It bent pretty much and also bent the pushrod of the MC itself so I replaced the whole MC. I have since fabricated a stronger pushrod going from the pedal to the MC. It's not 100% a straight line push but I don't think it's more that a few degrees off of straight with the MC bore. I'll get the body panels off of the car tomorrow to investigate more.

Thanks for your reply!

Lynn

[lake_harley]

Upon inspection of the piston and bore there's no sign of wear, scuffing or scoring. I have a rebuild kit on the way. We'll see what happens when I put it all back together.

Lynn

[lake_harley]

I installed the rebuild kit parts and all is well. It baffles me what might have been the problem but the brakes work fine now. Strange charged me $33 to ship a 5.5 Oz. package from the Chicago area to Southeast Missouri though. No overnight or anything just UPS Ground....seemed excessive!

Lynn