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The rear end in my 68 C-20 is fairly noisy on accleration and at steady speeds above 40 mph.The usual cause is a worn gear set or bad bearings.The axle bearings are fine so thats not the noise.I had the rear inspection plate off, the gears look ok but there is excessive backlash.For those of you with actual differential experience, would you try to tighten up the backlash first? Or just spend the money to replace the gears and bearings? Houser's rear end service in Pa has gear sets avaible in 3.90 and 4.10 ratios for $450 plus bearings etc. The truck has 4.57 gears in it now.I have done differential work in the past with good results, so I'm not afraid to do the set up.I don't want to buy a used center section that may be worn as much as the one I have.I want to do the job once, and the truck must be reliable thanks

Hi, No it probally would not be advisable to tighten the backlash out. You should take it apart and look at the bearings that is probally the problem. I have done these a number of times and it isnst to bad with the proper tools. Hope this helps...Chb46

Uh oh! I read your post about not screwing around with the backlash and I did that recently. Once I realized what it was, I tightened it back to where I thought it was originally. However, my truck is in pieces and my drive line is out right now. Any suggestions on what a guy can do to make sure the backlash is where it should be with the truck apart like mine is? I really don't want to take the rear end apart, though I do have a a seal leak on the front end of the differential. I replaced that seal and have already torqued the pinion nut back down. What about the back lash?

Ok, I have been told that the auto trans big block C-20 67-72 trucks had a Dana 60 coil spring axle with 3.54 gears. Maybe its 69-72, anyway this will bolt in my 68 C20.Anybody seen a truck equipped this way?I could probably adapt a 73 C-20 and up leaf spring rear easy enough with some cutting and welding on brackets. Rick, the post above was advice to check the bearings and then do the backlash.The pinion has a preload on it. the nut must be tightened exactly as it was. Generally , you mark the nut and the shaft so you can end up where you started, with the original preload more or less.If you have a rear end with a crush sleeve rather than a shimmed pinion preload,it can't be back off if overtightened.The pre load is lost and the preload procedure should be redone. As in disassembly and reassembly.If you turned the adjusters on the carrier bearings and you're sure its back where it was, then its ok.If you have any doubts, get some one you can trust to check it.

[ 12-27-2001: Message edited by: Tony ]

Tony, I take it you have the corperate rear in your '68. If your really into swapping, I used to drive a '68 C-20 stake truck. It was a factory stake with coils and the factory overloads. It had the Dana 60 rear with 4:11 gears. I may still be able to get my hands on the truck, which went to a local scrap yard after the guy i sold it to parted it out.

Since were talkting about our rear ends, does yours (truck) have excessive play in it, i.e I can turn my driveshaft about a eighth of a turn before the play is taken up. I can also feel the slop in it when driving at slower speeds. I have a spare with 4:11 gears, and it feels a lot tighter. Not sure if this has anything to do with the taller gears, or wear.
The 1973 and up 14 bolt is a fairly easy swap, requires the spring pads to be re-located. I have been told they use the same U-joint.

My 85 Dodge truck has plenty of rear axle noise. Even when it was new, I it took it back to the dealer due to excessive back lash. It really slammed the driveshaft when you put it in gear. Dealer said unless it was a full 1/4 turn of driveshaft it was OK. Well, now with 180,000 miles it still the same way. I have had it apart 2 -3 times, each time tighting and adjusting gear pattern and backlash. I found that the axle shaft splines are wore down about 1/3 of what they were to start with. It seems the spider gears were much harder than the axles.
I couldn't tell the difference in the gear noise. I guess once they are worn in, they are quiet or howl no matter what. From what I have found, gears to tight make more noise. I also found out that a tail shaft bearing in the transmission sound a lot like a pinion bearing. I put $150 worth of bearings in the axle and still had the noise. I only found it when I drove with out the carpet. I was cleaning it and had to go some where. I new as soon as I was up to speed where it was coming from! Joe

Tony, get some prussian blue and determine your 'pattern' like they show in about every shop manual. This pattern will tell you what the problem is and what you need to do to correct it. Make sure there is NO slack in the pinion bearings or the carrier bearings. If the noise is constant (not dependent on load) at road speed, I would look closely at the carrier bearings. If the noise is loud when you are accelerating and goes away when you are floating or lightly decelerating, I think the pinion bearing might be rough. If you can't find a picture of 'patterns' I can email you some.. Let me know if you need them.

Blue 66,I'll email you about what you said.
Racecarl,Yeah its really noisy when accelerating, quiet when coasting or cruising. But over 40 mph the rear end howls while cruising also.No roaring noise as in bad bearings, but a really loud howl that is for sure coming from the differential.The gear oil I drained out was black and not much of it.I'm thinking the gears may be toasted due to a lubrication failure.I got an old manual laying around here somewhere with lots of gear pattern pictures.GM sells a gear pattern paint that's really shows the tooth contact, just like in the books.

Tony et al,

I'd like to know the "findings" on this project; I've got the same symptoms from the rear on my '72 C-10, and rear-end work isn't in the picture before spring.
I just keep an eye on the gear-lube level, and drive the truck only when necessary, in the mean-time.

Tony: Noisy when accelerating usually means that there is heel contact on gears. The sound above 40 plus is heel/flank. I would suspect and check pinion bearings, may have lost preload or cracked cup. Should have even face contact with 6 to 8 thousandths backlash. Correct lube level should be around 6 pints. I think what has happened is that pinion bearings have overheated and are probably toast. Heat kills!! This will cause loss of preload, because of expansion rate of housing and spool is much greater amount than the pinion shaft, and ring gear. This will in effect unset the preload! As the housing grows from heat the rear pinion bearing will unload. Also the rear pinion bearing takes all the torque/thrust (accelerating/decellerating)forces, when overheated. Normally all pinion thrust is taken by the front bearing. Check with gear paint, but I'm sure thats whats happening from the sounds you described. You should also check gear hardness with a fine file as some annealing may have taken place on the pinion. The pinion gear itself is very prone to stress/distortion when it has been overheated. Check carefully, gear pattern and inspect pinion for any cracks on flank of teeth. You may very well just want to swap out the gearset and go with new bearings all the way around. Good Luck!!!

The truck ran so poorly when I got it, a little noise was the least of the problems.The noise is slight for the first few miles ,especially when cold.Drive more miles and it really starts to howl even with fresh 140 gear oil.No noise when coasting which usuallly means loose pinion preload.This rear is headed for the scrap heap.Blue 66 lives about 40 miles west of me.If there is any other rear ends in the area he will flush em out.

Some of you guys out there (old car kook?) have replaced the pumpkin in your older 3/4 ton trucks with one from a later 60's truck. Will the swap work the other way around? Will a center section from lets say a 51 3/4 ton fit in a 68 3/4 ton with the same corporate rear axle? I remember you had to change an internal part to make the swap.

Tony,

The way I read the posts on 3/4 ton "punkin' swaps" is that the complete carrier will swap from '67-'72 into 3/4 & 1 ton back to '47.
When installing the 3-something gears into the pre-'67 carrier is when the extra bits are needed.

I had some similar questions a while back and someone down Virginia way directed me to "Randy's Ring & Pinion".