[en] The parameter xi, which characterizes the anisotropy of the emitted electrons relative to the spin direction of the muon, is a sensitive indicator of possible V+A admixtures to the dominant V-A weak interaction responsible for muon decay. We report here new results relating to the measurement of xi based on an experiment performed with a highly polarized surface muon beam at the TRIUMF cyclotron. The muons were stopped in thin metal foils in order to minimize depolarization effects. A spectrometer consisting of magnets and position sensitive detectors was tuned to accept electrons near the end point of the decay spectrum. Two largely independent methods were used to determine xi. In the first we measured the rate of positrons emitted in a direction opposite to the muon's spin as a function of their momentum when the stopping target was immersed in a 1.1 T longitudinal magnetic field. In the second method the stopping muons were subjected to a weak transverse magnetic field and the amplitude of their spin precession oscillation was used to determine xi. Based on the results from both methods lower limits on the mass of an intermediate vector boson which couples to right-handed weak currents are 400 GeV/c² when no constraints are placed on W/sub L/ - W/sub R/ mixing and 470 GeV/c² if mixing is assumed to be absent. These limits represent about an order of magnitude improvement over those obtained from previous measurements of xi. We have used the same apparatus to measure the anisotropic shape parameter delta. Preliminary results are consistent with the expected value of 3/4 with errors that are a factor of two smaller than previous measurements