Brakes like a brick

[MassViper]

Jumped into my Viper the other night and when I stepped on the brakes there was absolutely no play at all. The peddle didn't budge. I checked the fluid level and it seems to be fine. Any thoughts? Hung up caliper, master cylinder (god I hope not!)? Thanks in advance. Mike

 

[01bee]

I had it happen in an old Porsche 928, sorry to say it turned out to be a bad master cylinder. Good luck.

 

[Steve Miehe]

Sounds like the master cylinder as well. When is the last time you changed the brake fluid?

 

[Bugeater]

Master Cylinders are cheap. I just replaced mine. 187.00 from dealership. I upgraded to a 2001+ (ABS car) master since they have a larger bore/stroke than pre-abs cars. The lines need to be routed to the other side of the cylinder though, as on 01+ cars, the lines go down to the ABS controller first.
Not a big deal.

 

[Tom F&L GoR]

Couldn't it also be a bad power brake booster? Without the assist, the pedal will feel hard.

Bugeater, with the larger MC bore, hydraulically speaking, you displace the same amount of fluid for less pedal travel. So your pedal feels harder sooner? Can you describe what the change was? Thanks.

 

[Bugeater]

Tom,
Thats exactly what I was trying to fix: an overly soft pedal and overly long pedal travel. I changed the master cylinder as well as reduced my front caliper piston sizes to better match the rears (rears are brembo 28mm/30mm).
I replaced front stoptech 44mm/44mm with stoptech 38mm/42mm. I had a serious bias issue and pedal issue in may...

I am not sure if one change or the other played the larger role in reducing the soft travel from about 3 inches to 1 before getting a nice firm pedal. I took the car to VIR for testing and the changes helped dramatically. No flatspotted tires!

 

[Tom F&L GoR]

Bugeater,
If I did the math right, your 44/44 & 28/30 system has about 60% greater fluid volume demand than OEM. Going to the 38/42 fronts made it only 42% greater than OEM. The pre ABS MC is 27mm diameter, so if it went up to 32mm or 33mm with the ABS MC, you'd be back to near-original match of MC supply and brake system demand. Do you know the ABS MC diameter?

Anyway, love those cool fixes with alternate OEM parts.

 

[MassViper]

Its probably been about 3 years since the fluid was last changed. I'm glad to hear that the master cylinder isn't as big a deal as I thought. Thanks to those who responded.

Mike