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post #1 of (permalink) Old 11-21-2000, 10:03 AM
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Drivetran help! Th-Thunk

Help! I have an 84 S-10 Blazer with a 2.8 Liter and a 5 speed. It recently started making a th-thunk, th-thunk noise that comes from the rear of the truck. The noise gets faster and a little harder with the speed of the truck, and goes away when you let off the gas. The noise also goes away if you put it in 4wd. I don't believe it is the U-Joints because there is no play on either of them. With the rear wheels off the ground, there seems to be to inch of play, when moving the drive shaft back and forth back by the rear end (seems about normal). How hard is it on the truck to keep it in 4WD until I can get it fixed?
I am suspecting it is the rear end. If so, what am I looking at to get this fixed or replacing? Is this repair something to be done with basic tools? How much should this cost? Or if you think there is something else I should look into, please let me know. Thanks!


rexxshelby
84 s10 Blazer 4X4 2.8 5 Speed
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post #2 of (permalink) Old 11-21-2000, 11:20 AM
 
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Re: Drivetran help! Th-Thunk

Mine did that just before the rear diffy let go. My pinion nut got loose. Do NOT drive it until you get this corrected, it results in a very dangerous situation!

When this happened to me, eventually my rear end totally locked up. I was doing 10mph in my driveway when mine let go. It would be a catastrophic failure at any road speed, even in a 30mph zone your forehead would probably have a steering wheel embedded in it, I almost did at 10mph. It's like an instantaneous stopping action. Bam and you're immediately decelerating. So I'd have a gear shop take a look at it ASAP. Or at least pull the diffy cover and check for problems. Here are some pictures of the final results of mine:
http://www.sandman454.homestead.com/.../reardiff.html

Don't drive on dry pavement or hard packed surfaces in 4wd, it's fairly hard on the front end components. The driveshaft end that is hooked onto the rear diff should have no play at all, or at the most maybe 1/8" or 1/16" from what I've been able to tell.

It's definitely not a fun thing to have that go out. The only way to tell for sure if any damage has been done is to pull the differential cover and check for damage. Mine did it on coast though and hitting the gas made it go away a bit.

Tim
ORC Land Use columnist
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post #3 of (permalink) Old 11-21-2000, 02:15 PM
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Re: Drivetran help! Th-Thunk

<font color=red>OUCH</font color=red>, Sandman! I've never really seen one spit teeth out quite like that before. The worst I've ever done to a diff is to shear off screw that holds the retaining pin in that goes through the spider gears (looks like a long roll of quarters), allowing the pin to slide out of the carrier. BTW, the axle is an `82 GM 1/2 ton 10 bolt in a 6 lug pattern set up with a factory limited slip / gov-lok / posi, whatever you want to call it.

My truck did exhibit the same simptoms like you mention, rexx. There's a small black screw (5/16" or 11/32" head) that goes into the carrier and points toward the driver's (?) tire. It holds the pin in that I referred to earlier. The pin in my truck started smacking into the pinion every time the carrier spun around in the differential, making a knocking sound. In a parking lot, going about 8-10 MPH, it finally decided to lock up and I almost had the steering wheel become part of my melon. I HAD JUST EXITED THE HIGHWAY minutes earlier where I had been driving about 70.

Luckily, the ring and pinion were not damaged badly and the set could be reused. I did have to buy another differential as the pin was bent and I couldn't find a replacement. The truck still pushes snow like nothing I've ever run before!

<font color=red>TOO MUCH POWER</font color=red> isn't enough.
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post #4 of (permalink) Old 11-22-2000, 09:03 AM
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Re: Drivetran help! Th-Thunk

Thanks for the Info! I had no Idea that the rear end could lock up like that. I am trying to get this fixed as inexpensively as possible.
Is it difficult to swap a "rear end" if I can locate one in a salvage yard? Or if I have a dealer do it, what range of prices should I expect to pay for best case and worst case? Or, am I better off going to a 4x4/Drive shaft specialist (the one I called said between $500 and 1000!).

What would you do? Thanks in advance for any input or Info!

rexxshelby
84 s-10 Blazer 4x4 5 speed.

rexxshelby
84 s10 Blazer 4X4 2.8 5 Speed
post #5 of (permalink) Old 11-22-2000, 09:42 AM
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Re: Drivetran help! Th-Thunk

Either way, pull the diff cover off and check the condition of what you have before you do anything.

If it's just the pinion nut that's loose like Sandman had, just disconnect the rear driveshaft from the axle and tighten it back down (maybe use some Lok-Tite on it). I don't remember the exact torque spec, but it's somewhere around 150 ft-lb. Hopefully the pinion bearings aren't shot and the gears aren't blown apart (see Sandman's post for a fine example of blown apart gears [img]/wwwthreads_images/icons/wink.gif[/img]).

If the problem lies in the rod that goes through the spider gears like on my `82 Blazer axle, jack up the back of the truck, pull the diff cover off and check to see if the rod is bent. If you pull the little retaining screw out, the pin should slide right out if it's alright, if you have to pound on it, it's bent and you'll need a new one. If you do pull the pin out, push in on the axleshafts (tires, wheels) and check to see if the C-clip retainers are in good condition.

Swapping a REAR axle is not hard at all. If you go this route, <font color=red>be absolutely sure you get a replacement axle with the same gear ratio!</font color=red> All an axle swap requires is cutting 4 u-bolts (torch), disconnecting rear driveshaft and brakes. Another s-truck axle should be a direct bolt-in (this might be your chance to drop in that 4-wheel disk rear you've always wanted [img]/wwwthreads_images/icons/laugh.gif[/img]). Install and tighten u-bolts, reconnect the brake lines, driveshaft, bleed the brakes, change diff fluid and you're done. I've swapped out a rear axle in a half ton truck in under 2 hours before without help, but I had all the tools needed to do the job.

You should be able to use a 2-wheel or 4-wheel drive rear axle - the wheel bolt patterns are the same. $200 would be a decent price from a junk yard depending on the gear ratio (could be 4.11's with a 2.8L), any less would be a screamin' deal. A posi will run you more. If the junkers want more than $300 for an axle, I'd start looking for a donor truck - buy a truck for the axle, part the rest out and sell the parts; maybe make a little bit of money on top, too.

<font color=red>TOO MUCH POWER</font color=red> isn't enough.
post #6 of (permalink) Old 11-22-2000, 10:31 AM
 
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Re: Drivetran help! Th-Thunk

The hardest part about swapping that axle is: <ul>[*] Getting those stupid bolts that go through the spring eyes out (It can be a major PITA and I had to use a hacksaw to remove one of them)[*] Bleeding the rear brakes when you finish. [*] Possibly going to a brake shop to get the brakes replaced and/or checked, since you don't know what shape those are in. If the brakes on your axle are good and the ones on the other axle are bad, that could possibly get expensive enough if you don't do the brakes yourself, to maybe want to keep your axle and get the shop to do it. Might be cheaper than getting the brakes fixed on the swapped axle plus the cost of that axle.
[*] Of course these items only come into play after you've pulled that differential cover (pull the fill plug first just to make sure you will be able to, if you cannot get the fill plug out, soak it with PB Blaster for a day or so and try again, it should come right out. The reason you want to pull the fill plug is so that you are sure that you can refill the differential with gear lube when you go to put the cover back on. Also, ask the shop if they want the axle housing pulled out of the truck when they do it. Sometimes carry-ins are cheaper for them to do than if they take it off the truck themselves. I imagine there are some shops that do it on the truck but also I'd guess there are some shops that do the work on a bench. [/list]Just some random thoughts...


Tim
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My November article on ORC

http://www.off-road.com/land
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post #7 of (permalink) Old 11-24-2000, 12:36 PM
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Re: Drivetran help! Th-Thunk

UPDATE: I opened up the rear and found that the Ring Gear has 4 severely damaged teeth (in a row) and the Differential Unit has several hairline cracks. New parts from Chevy are over $700 for what I need. I can get a used rear end from the Salvage yard for $200 but I have a few questions. This truck is a winter beater but I may do a 350 swap in the future, but I need to do this repair as cheaply as possible.
What is the gear ratio on this truck, or how can I find out what the Gear ratio is.
Should I swap the whole Axel, or can I just transplant the parts I need out of the Rear end that I get from the yard?
I have been considering putting a 350 swap. With that in mind, what kind of year and make of axel (from the donor vehicle) should I look for that have the same ratio? A posi with rear disk maybe? In other words, if I am going through the trouble and the rear ends are similar in price what kind of things should I look for?
What would you do?
Thanks again for all of the help and comments.


rexxshelby
84 s10 Blazer 4X4 2.8 5 Speed
post #8 of (permalink) Old 11-24-2000, 05:15 PM
 
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Re: Drivetran help! Th-Thunk

<font face="Comic Sans MS">Call Randy's Ring and Pinion http://www.ring-pinion.com (their phone number is on the website). They seem to sell only the best quality components that can be had for any amount of cash and seem to give really reasonable deals. See what they can do for you.

You can find the gear ratio stamped into the ring gear. It'll be a number such as: 41:10 (divide the big number by the little number) and that's your ratio.

Definitely swap the entire axle instead of swapping the ring and pinion and carrier out of the the rear end from a yard. If you just swap the parts from one rear end into another they will have to be set up properly with a dial indicator and shims to get them to ride just right. In otherwords you'd farther ahead to swap the entire axle if you go the swap route rather than the rebuilt route.

The GM "locking differential" offered is the Gov lock, which in my humble opinion (and the humble opinions of others) isn't great. If you go the rebuild route, I would personally go with a Detroit locker (not quite as smooth on the street as the posi type rear differential, although much stronger). You can get it out of virtually any S series vehicle you want to but be sure that you make sure you can bring it back to the parts yard for refund or exchange if there's a problem with it (example would be you get it home, pull the cover and find that it has the wrong gear ratio in it after all). You could go with rear discs but you'd have to get a different proportioning valve than the one you have.

As to the stronger ones, if you get one out of a 4.3L equipped vehicle it should have a 7.625" ring gear rather than a 7.5" ring gear. With that 350 in the plans, however, the weakest link in the system is the front setup with a puny 7.2" ring gear. Either way you'd have to probably take it pretty easy on the go pedal.

All of these are just my $0.02 however.
</font>

Tim
ORC Land Use columnist
My November article on ORC

http://www.off-road.com/land
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