1988 GMC Sierra SLT 1500 4X4 front end shake between 35 and 45 MPH

[Brandon Todd]

So I just got my 88 Sierra for a steal because the PO thought the engine was toast. The oil pressure gauge barely marks when the truck is running and sometimes it will go up just enough to shut the check gauges light off. But if you turn the lights or AC on the check gauges light comes on. And if you hit the turn signal the check gauges light blinks along with the signals. This is what brought me to the conclusion that the engine is fine but to make sure I manually tested the oil pressure and it is good. So now I have this truck and I am trying to figure out why it shakes between 35 and 45 MPH I've inspected the front end but I don't see anything that could be causing this. What should I be checking. Also the 4x4 only worked the first time I tried it. now it won't engage. 

[Brian Lindsey]

check tire balance , and alignment

[2reckless2drive]

I would check the wheel bearings possibly the ball joints and while your at it check the C/V Axles. But that wouldn’t be the main problem dealing with the engine.. Could be the drive shaft or universal joint going out. Could be a bent or cracked wheel (which is a very good possibility) As for gauges, is the cluster backlit by LED Lights??? Cuz the PO could have went with aftermarket lights and in order to power them prolly tapped into the wire to the parking lights.. And as I just had the same issue with mine and it’s fairly common I can give you a definite  answer for you 4x4: How the front axle engages is with a thermal actuator and it’s crap..... if it gets cold, the rig gets shut off while engaged, it gets submerged, etc....  whatever the case may be the thing will leave you stranded at the worst time and cause a hell of a headache... I got this deal called a Posi-Lok (nothin to do with lockers) it’s a cable with a handle so instead of having an electric piece of crap, you can manually engage your front wheel drive. It’s damn near like locking in the hubs but for rigs built with an on the fly style of t-case. I highly recommend it man do some research on it it’s pretty slick deal and definitely won’t leave you stranded. Search where that actuator is and see if it engages Or if you can reach under and fiddle with it by hand right now tho just to make sure it’s not the transfer case but even if it’s not the problem with the actuator I’d recommend still getting the posilok.. I’ll post some pics tomorrow. Hope this helps!!!!