Got the same problem with wifey's Alto (800cc). When the car's cold, absolutely no problems whatsoever. She starts great, idles smooth & pulls away like a cat on cocaine.
Once she heats up she gets cranky. In serious heat with the air-conditioning on, I get clutch judder like you can't believe.
The clutch was allegedly replaced under warranty at about 5k by Maruti Udyog. No problem for some time, issue resurfaced again after about a thousand odd kilometers. Their response: "Alto aisa hi banta hai". @%^%#$#^$#
Am not going back to those A.S.S.es again.
Me got a theory, albeit unproven yet. Maybe it's because of some oil which drips onto the clutch (
a/c or engine), causing it to judder like it's got epileptic fits. This only happens with the air-conditioning on. Switch it off, & she picks again like the aforementioned narcotic cat.
Experts, any input?