Clunking sf14b

[dogdaysunrise]

There is a reoccuring problem that I am running into, when you change into gear, or between gears there is a very loud clunk at the pinion. Watching the drive shaft it almost looks like something might be binding. I havent taken it apart yet, but do plan on doing so in the coming week at some point. Just wondering if anyone has seen this before and have any suggestions to look for.

It is a sf 14b. Like I said I havent opened it up as of yet, but it does have the RPO code G80 which from what I understand is the gov-lok. If this is the case, could it be an early warning sign that it is going to gernade?

I changed the u-joints today because my first thought on the clunk was u-joints, and the rear was kinda sloppy, but now that the slop is gone and cant absorb the shock the clunk is worse.

Any ideas is apperciated.

Thanks and sorry for the long post.
Mike

 

[dogdaysunrise]

anyone?

 

[Stoner42]

Probably excess backlash in drivetrain (trans, t- case,or rear end) you already elininated u-joints. this basically causes the drive line to get momentum before it engages. Could also be caused by high line pressure in auto trans. First disconnect the driveshaft and see if rear end appears to have to much play.

 

[Stoner42]

sorry didn't read last line right. It appears your diff doesn't have to much play. Is your truck auto or manual? Year? Make?

 

[dogdaysunrise]

Its a 92 k1500, and it has a rebuilt 700r with the full HD package. It clunked before the trans was rebuilt, I always assumed it was my u-joints making that noise and was surprised when it happend right after the change. I will be pulling the cover off on friday to get a better idea of what is going on, just dont have time till then. If it is just backlash, much to worry about? or should i start the hunt for a new rear end?

 

[HarryH3]

Make sure that the pinion nut isn't backing off. The carnage is ugly if it gets too loose. The rear end can lock up and bust lots of expensive parts.

 

[ratzila]

My brothers 14ff did that until the gov lock exploded

 

[dogdaysunrise]

see thats what im worried about, the gov-bomb already is acting up. I got good and stuck one day (forgot to pull the spare from under the truck and it anchored me to the mud ) and it was spinnin like it was open. the truck has just under 315000 miles on it (new tranny and motor and the such) but i have only had it for about 25000 of those miles, so it is possible that it has been switched out somewhere down the line. I guess I wont know much until I open it up... stupid work.

Mike

 

[wy4tt]

Do you have blocks in the rear? From what I understand, they can cause the distance from rear to front, axle to axle to be different if they're not placed just right. This makes the locker "think" that it's turning since one wheel is spinning faster than the other. When only one side is engaged, there is a lot more excess slop and you get that clunk between gears, or when letting on/off gas. You can measure axle front to rear on each side and see if the measurements are the same. I also noticed that, when turning slightly and hitting the gas on/off it went away, meaning one side was spinning slightly faster when going straight. Different size tires can cause it too.

 

[ratzila]

Also check the ubolts. Mine were loose and it caused the centerbolt to break. The rearend would rock back & forth.

 

[dogdaysunrise]

it mostly only happens when im at a stand still or its down shifting as im deaccelerating (sp?)

it didnt do it much at all today, so im not sure what the heck is going on

 

[Stoner42]

you should only worry if it has a lot of play. If possible use a dial indicator to measure backlash. Normally it should be .008-.012 . Another thing to check is the fit of the spines on the driveshaft yolk going into the t-case. The splines will wear and allow movement there. You might not even be able to feel it by hand. Try filling spines in the yolk with the best ,thick grease you can get-it will cushion the hit. GM makes a special grease for just this purpose but its expensive (like $50 a pint) - that how they fixed the same problem in the late 90's when the trucks were under warranty.

 

[wy4tt]

Is there a lot of play in the rear driveshaft? I'd bet their not locking when your'e driving down the road. You could try measuring your rear tires, from the ground to the bottom of the rim and see if they're even on each side.

 

[Stoner42]

I'll add some more - check the play in the spider gears(especially around the diff pin). Secondly the "gov bomb" has a bad name but most problems are with the smaller diffs. The ones in the 14 bolts really arent bad - most failures are the fault of the driver - not the design. Best ways to kill a gov-lock 1)Spin the wheels as fast as you possibly can- not giving it a chance to lock in at a lower rpm. 2)Follow step number 1 with dirty,sludgy fluid that hasn't been changed since it was new.

 

[dogdaysunrise]

thanks for all the input guys, i have been reading on this site for ever now. This is the first time I have actually had to post, I usually find all my answers in here. Best info on the net.

I will let you know more once I crack the case and see whats going on, like I said we had a huge storm here this weekend and I have been re running lines all over the city so its been real busy.

Mike