Clunk in front end of Wife's 98 Blazer when in 4 wheel drive

[Blakers]

Hello Folks, I need some help!



My wife's 98 Blazer has recently developed an occassional clunk in the front end. It does it only in 4 wheel drive and at various speeds. It is not binding as it does it on slippery snowy roads. It is just a "clunk" sound every now and then - not continuous.



I found no worn ball joints, no problem with u-joints or boots on front axles, no bad or tight u-joints on the front driveshaft. No other obvious problems.



I've narrowed it down to two ideas:



Could the front axle disconnect be disconnecting and reconnecting causing the clunk?



Could the chain in the transfer case be worn out and binding or jumping teeth?



The clunk seems to only happen under load or steady, level travel. It does not happen while coasting downhill.



Thank you.

Blake

 

[HoleshotHolset]

GM had some NVH problems with the IFS differential on the S-series trucks...



The dealer had the diff out of Mom's Blazer twice and still couldn't figure out the humm/vibration.



I beat the stuffing out of my '91 Sonoma and never had a problem with the x-fer case or the IFS... until I got it airborne one day @ WOT. Let's just say that the landing ate up some parts. :-laf



Matt

 

[CJ8Rockcrawler]

Something else to check would be the idler arm. Mine always made more noise as it was wearing out when in 4wd due to the additional forces. There are also the control arm bushings that could cause a clunk. I never had any trouble my front differential, but I've heard of problems with the joint in the front driveshaft going as well.

 

[Blakers]

Thanks guys.



Is the idler arm the center section of the tie rod? All the tie rod ends seem ok. This clunk is loud and you can feel it right up through the floor and in the steering wheel, though it is hard to tell where it is originating from.



Blake

 

[tmmy]

clunk

take a look at the torsion bar bushings they are located at the end of the torsion bar towards the rear of the truck the bushings are mounted to the frame in between the the doors if a four and behind the rear of the two door version in the frame channel

 

[HoleshotHolset]

I can't belive I forgot about the infamous torsion bar crossmember isolators... I'm loosing all of my S-10 knowledge! Arrrgh!



I looked at a '98 S-10 with a blown transmission today... does that count for anything?



Matt

 

[I-6DZL]

Idler arm ?

Your idler arm is located on the passenger side of the vehicle, the top is bolted to the frame and the bottom is bolted to the center link just inside of the inner tie rod end.



On your blazer the top problems as far as the front end goes are

1: Ball joints, take a pry bar between the spindle and the upper (or lower) control arm and check for lateral movement. If you have movement they're bad.

2: Idler arm, you need a helper to "chuck" the tire side to side while up on jack stands, while you look at both the joints, on the idler.

3itman arm, these are total pain in the arse, and book time pays like 1. 7 to 2. 5 hrs to replace. Check just like the idler.



The torsion bar frame mounts should last longer than 6 to 7 years. GM in they're infinate wisdom supposedly updated these with units that last longer.



It all depends on the clunk that is happening and the noise and feel. Could just be the alignment is out of wack, check the front tires for cupping, or wearing uneven. If uneven or cupping, have the front end checked by a professional. They'll advise from there. Them blazers and jimmies are expensive.

Have you had to put an idler pulley or tensioner, or alternator on it yet? or do any of the above mentioned items ? or how about that damn intake leak? found that yet ?



Good luck

Curtis

 

[Blakers]

This clunk is really a "thud" that feels like something is going to come apart. You'll be driving along and all of a sudden "thud!" It's not just a little play in the steering.



What do these torsion bar bushings do when they wear out?



I could not find any play in the ball joints or tie rod ends.



Tires (BFG ATs) are wearing beautifully and it tracks perfectly.



I've put an alternator and water pump on it. The transmission clutch sets a code all the time and there's some code from fuel tank pressure. Runs perfectly, but the codes keep coming back. If it were mine, I would fix it with black tape, but my wife does not like that idea.



Thanks to all,



Blake

 

[I-6DZL]

Lol black tape... .



When the bushings wear out, they'll give a clunk just like you're describing. If you know what the torsion bar is, then follow it back towards the middle of the vehicle and look at the crossmember that they hook to. At each side of the crossmember you'll see some rubber bushings between the member and the frame.



curtis

 

[RonaldLarson]

suggestion form experience

If it is automatic hub system, the hub springs are likely broken. My old (thank God, gone) Subhuman had the same problem twice. The springs were toast.

Ron

 

[Blakers]

This has an axle disconnect system like the 94-02 Rams. My feeling the problem is in that disnconnect system. She took it to a local mechanic as I don't have the time to fool with it right now. So far he can't find the problem.

 

[Blakers]

I have heard these Blazers are very prone to vacuum leaks around the intake. Does anyone know the exact place they leak and what gasket needs to be replaced?



I am getting 20" Hg of vacuum at idle. That sounds ok to me.



What is the idle speed supposed to be once warmed up? It is idling at about 900 - I know fast idle is a sign of vacuum leak.



The clunk problem still has not been solved. It was at a local garage for 4 days and they can't find it. I will look at it tomorrow.



Thanks.

 

[RonaldLarson]

Idle speed

Sounds high, but what does the tune up data sticker say? It should be on the fan shroud area, or under the hood. 650-750 sounds reasonable. I'm sure you have looked for the sticker, but just a heads up.

Yes, these engines had vacuum problems. It involved the main vacuum pick off point at the rear of the engine. A bulletin instructed the tech to move it, but I don't recall where. Maybe a GM tech can help you with some free info.

My '87 had NO power brakes when leaving from a stop!! They moved the pick off and it improved. Cost me a serious rear-ender. Good old GM !

Ron

 

[HoleshotHolset]

what does the tune up data sticker say? It should be on the fan shroud area, or under the hood.

It probably says: No adjustments necessary.



Matt

 

[Blakers]

Update

Update:



Yesterday I pulled the battery tray and looked at the servo unit for the front axle disconnect. It seems to work fine, except there is vacuum at the servo ALL THE TIME - even when in 2 wheel drive. Should not the vacuum cease when in 2 wheel drive?



What controls when there is vacuum at the servo or not? Is there a valve? This thing has the push button 4x4 switch.



I think this could be the root of the problem.



Thanks,

Blake

 

[HoleshotHolset]

It has been a long time since I've had to wrench on an S10, but the 4x4's had a little vacuum switch that screwed into the transfer case.



The GM parts counter will know exactly what you're talking about. Easy, cheap fix.



Alternatively, you can buy a cable operated deal if you get sick of the whole vacuum actuated stuff. Check it out here.



Matt

 

[Hummin Cummins]

I've been fightin with my wife's 98 also. She just called the other day sayin she had a clunk/vibration in the front end. It turned out to be it seemed it was trying to go into 4wd when she was goin down the road. I put it in 4x4, then back out and all seemed fine. Not sure what was goin on.



Chris

 

[justinp20012500]

Your idler arm is located on the passenger side of the vehicle, the top is bolted to the frame and the bottom is bolted to the center link just inside of the inner tie rod end.



On your blazer the top problems as far as the front end goes are

1: Ball joints, take a pry bar between the spindle and the upper (or lower) control arm and check for lateral movement. If you have movement they're bad.

2: Idler arm, you need a helper to "chuck" the tire side to side while up on jack stands, while you look at both the joints, on the idler.

3itman arm, these are total pain in the arse, and book time pays like 1. 7 to 2. 5 hrs to replace. Check just like the idler.



The torsion bar frame mounts should last longer than 6 to 7 years. GM in they're infinate wisdom supposedly updated these with units that last longer.



It all depends on the clunk that is happening and the noise and feel. Could just be the alignment is out of wack, check the front tires for cupping, or wearing uneven. If uneven or cupping, have the front end checked by a professional. They'll advise from there. Them blazers and jimmies are expensive.

Have you had to put an idler pulley or tensioner, or alternator on it yet? or do any of the above mentioned items ? or how about that damn intake leak? found that yet ?



Good luck

Curtis

All good advise...



Done the alternator, but nothing else except a fuel pump. (Sender unit bad)



Over 100,000 K on the wifes 2000 blazer and not many problems. It still gets 18 MPG even with my wife driving!!



I am having a similar clunk. My first suspicions was the idler arm. I guess I just have to stop being lazy and get under there and check it out...





Justin