Does anyone know what size allen head I need to use to remove the fluid fill bolt on the differential?

Rene

 

are you sure it's an allen wrench, all the ones I've done I just used a 3/8 ratchet with an extention on it

 

I was going to replace the fluid but I didn't have the right allen wrench for it. I am sure the bolt is an allen head bolt. The size is smaller than 10mm but bigger than 8mm. I think it may be a standard size allen head. Did you mean that the fill bolt on your differential just takes a regular 3/8" socket? A socket will not work on mine.

Rene
91 RS 305

 

I haven't seen the one on my car, but the one on my truck is just the regular 3/8 ratchet, not a socket, the actual ratchet fit on it w/o a socket

 

sounds like someone replaced it with a recessed hex pipe plug instead of the recessed square, i know i always do when i rebuild a rear. try a 3/8 allen socket