Hello Team, I recently purchased a used 1990 GMC 1/2ton pickup (SL Sierra) with a 5.0L engine and 2wheel drive and am seeking to determine the proper gear oil to use in the 5 speed manual transmission, what do you recommend and why? Thanks, Alaska GMC
Manual Transmission Oil on 1990 GMC 1500 Pickup
by Alaska GMC in Anchorage, AK on June 26, 2009
ANSWER by Russ , June 26, 2009
The recommended gear oil for your 5spd gear box is something called - GLS; GM part no. 12345349. I have not been able to find an specific information on GLS anywhere. I would suggest to check with your local GM dealer and see what the recommend for your area. The requirements in Alaska may be a bit different.
ANSWER by GMGunner , July 13, 2013
GM Performance 88900333 Synchromesh Transmission Fluid