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Are there any mechanics here?


Steve47
10-30-2008, 08:48 AM
I have what I believe is to be a rod knock. If it is a rod knock, How difficult of a job is it to repair on a Astro?

I've been told this:

If the oil pump fails the bearings will shortly follow since you have to have oil pressure to protect the bearings.

Cut the oil filter open before you do anything else. If you have bad bearings it will be full of metal. If the oil filter is clean then you've dodged a bullet and there's some other problem, like possibly a stuck oil pump relief ball.

brcidd
10-30-2008, 02:40 PM
When I hear an Astro rod knock- I opt for a good used low mileage replacement engine- done it 4 times on 3 different vehicles- a salvage yard unit can be as low as $500. Repairing one rod knock is usually an indicator of more to come-- to me it is just easier to change engines- less money anyway. And just think of all the spare parts I get-- those intake parts alone are worth $500- like the spider assembly and a few of the others...

A loose flywheel can sometimes sound like a rod knock- seen that once on an Astro....

Did you loose oil pressure? Those oil pressure sending units go bad a lot....

Scrapper
10-30-2008, 03:19 PM
you have to tear moter down or get a used one.

Steve47
10-31-2008, 09:20 AM
"Did you loose oil pressure? Those oil pressure sending units go bad a lot...."

Yes, Initially the oil pressure read zero according to my son. This is what took place.

Earlier in the day my son called me and told me the engine had a ticking sound. I told him to come to the house. (he was about a mile from home) I checked the oil and it was down two quarts. He went and got the oil and we added to the proper level. Two hours later I got a call saying he was broke down on the highway. I went to get him and asked what the van symptoms were. He said, he was getting on the highway and the van felt like it was loosing power. he said the oil pressure gauge read zero and the engine was getting loud like a banging sound so he pulled over, shut it off and called me. When I got there, I checked the oil level and it was fine. I started the engine and there was a squealing sound from under the van, the oil pressure would only rise if I gave it some gas, the squealing sound went away and I drove it down the breakdown lane at about 40 mph, (it drove well at that speed) , while getting off the highway as I decreased speed the oil pressure was dropping fast, I would put it in neutral and keep on the gas a bit while coasting and the oil pressure would come back up, each time the oil pressure would drop the check gauges light would come on. So, I got as far as my mechanic and left it there overnight. Went back the next day and he says, it could be rod bearing. I drove it home, about 3 miles and it ran fine with a slight knocking sound. The oil pressure stayed where it should be but the engine idle seemed a little high (probably due to not letting it warm up) ,, The mechanic says the van runs fine when the oil is cold but once it warms up I will lose the oil pressure again as the oil thins out? So, the mechanic says it could be a rod bearing, not sure - I'm trying to find out what else may be the problem and what I should be looking for.

AND, thanks for responding to this post because my back is up against the wall on this one and I really need to know where I stand with this van - and to boot- I just had the crankcase fluids, rear end fluids changed last week as well as 4 new tires put on it 4 days ago - I do have the van maintained very well and I'm still a little confused as to why I was down 2 quarts of oil to begin with. It shows no signs of leaking.

Blue Bowtie
11-01-2008, 08:01 PM
I'm still a little confused as to why I was down 2 quarts of oil to begin with. It shows no signs of leaking.

Obviously, without a leak, it was either being burned or was never filled.

I just had the crankcase fluids, rear end fluids changed last week..

Perhaps, would that answer your question? Was this at some 30-minute oil change specialty service? If so, your story would not be unique.

Fortunately, in the case of an AWD Astro, removing the oil pan for inspection of the crank is relatively easy. There is almost nothing there for interference.

http://mysite.verizon.net/strey/files/4WDOilPan.jpg

Two of the transmission bolts will need to be removed, and the pan bolts. If the problem is a damaged bearing shell and the journal is serviceable with polishing in place (which is sometimes the case) you might be very lucky. If there is any crank/journal damage, either the engine would have to be removed, or at least the torque converter would have to be unbolted and slid back to allow the crank to come out with the engine installed.

Of course, if the engine has been operated with inadequate lubrication, there are likely other problems, and patching it up with a reground crank is only the beginning. Once you drop the crank, the heads would need to be removed so the pistons can be pushed up and out. A quick look at the skirts and rings will tell the rest of the story.

In any event, I would strongly advise replacing the oil pump if you do anything to repair the engine. DO NOT use a factory oil pump and relief on this engine - EVER! An aftermarket pump with higher volume is an absolute necessity. The OEM oil pump has barely adequate gear displacement to maintain barely adequate pressure at idle on a new engine in very good condition. It's a fuel mileage game the manufacturers are ALL playing, and a dangerous one, at that. Install a pump with more than adequate volume and a 45 PSIG relief at a minimum, and never look back. Replacement pumps are only about $50.

Updated link to oil pan photo.

Steve47
11-02-2008, 10:57 AM
Perhaps, would that answer your question? Was this at some 30-minute oil change specialty service? If so, your story would not be unique.

Nope, I had the mechanic replace the crankcase fluid in accordance with the Technical bulletin, he did it correctly, ,, drained, replaced with autotrak 2 ,,, driven,, drained and refilled ,,, replaced the rear end fluid at the same time ,, had the tranny fluids serviced on time as well ,,, I use this van for work and it is maintained very well, 4 new tires on it two days before this bearing problem ,,, my mechanic said the vans are notorious for developing this problem without warning ,,,

Blue Bowtie
11-16-2008, 10:57 AM
It seems that I missed that bulletin. There are quite literally millions of these engines around, many with 200,000 miles or more, and I don't see/hear about bearing failure on them without some reason, such as contaminated or inadequate lubricant. This is the SAME crankshaft/rod/piston design that has been in use in Chevrolet V-8s and V-6s since 1955. If you ask around, you would probably get just the opposite feedback. Even those who prefer other engines will grudgingly admit that the SBC rotating unit is among the most reliable and robust designs ever used.

I would submit to you that your mechanic is perhaps misinformed.

Steve47
11-16-2008, 05:39 PM
I'm not so sure I've spun a bearing. After all the reading I've been doing it could be something else. I haven't started the van for a bit now. I'm going to have it towed to have a different mechanic check it out. I'm hearing different things,, like maybe a cracked flexplate even.

Below is the Technical Bulletin I was talking about. I was also informed this bulletin was for Older model vehicles as well. What do you think?


Bulletin No.: 99-04-21-005B

Date: September, 2002

TECHNICAL

Subject:
Transfer Case Shudder
(Flush and Replace Transfer Case Fluid)

Models:
1999-2003 Chevrolet Astro (AWD)
1999-2003 GMC Safari (AWD)
1999-2001 Oldsmobile Bravada
with All-Wheel Drive (http://www.automotivehelper.com/topic218484.htm#) (NV136) Transfer Case (RPO NP4)

This bulletin is being revised to add model years. Please discard Corporate Bulletin Number 99-04-21-005A (Section 04 - Driveline Axle).

Condition

Some customers may comment about a vibration (shudder) during tight turning maneuvers on dry pavement at vehicle speeds less than 8 km/h (5 mph).

Cause

This condition may be caused by a slip-stick of the clutch plates in the transfer case clutch pack. On 1999 and newer models, the preload that is designed into the clutch pack may contribute to the condition. In addition, contamination of the fluid may interfere with the friction modifiers.

Correction

Flush and replace the transfer case fluid on affected vehicles using the following procedure and the part number listed below.

Perform the following diagnosis prior to flushing and replacing the transfer case fluid in order to properly identify the shudder.

Diagnosis

1. Verify the shudder in the vehicle. The vehicle needs to be at operating temperature (driven at least 5 miles) for proper diagnosis. After the vehicle is at operating temperature, drive in a tight circle just short of steering wheel lock, at a speed less than 8 km/h (5 mph) in order to identify the shudder.

2. Identify what rear axle type the vehicle has.

^ If the vehicle has a standard rear axle, then proceed to step 3.

^ If the vehicle has a locking rear axle, remove the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual. Drive the vehicle as outlined in step 1.

^ If the shudder goes away, install the front propeller shaft and proceed to step 3. Refer to the Propeller Shaft subsection in the Service Manual.

^ If the shudder does not go away, the locking rear axle may be the cause. Review the owner's records and determine if the rear axle was serviced at the first scheduled oil change. If records indicate that the axle service was done, then revaluate the condition using diagnostic information in the appropriate Service Manual. If the rear axle was not serviced, service the rear axle.
INFORM THE CUSTOMER THAT THE AXLE SERVICE IS AN OWNER'S MAINTENANCE ITEM NOT COVERED UNDER THE VEHICLE'S WARRANTY.

^ Install the front propeller shaft. Refer to the Propeller Shaft subsection in the Service Manual.


3. Flush the transfer case with the blue colored fluid (AUTO-TRAK II) using the procedure and part number listed below. Perform the flush procedure even if the transfer case contains the blue colored AUTO-TRAK II fluid in order to remove any possible contaminants. The AUTO-TRAK II fluid contains an improved friction modifier that should correct the slip-stick condition. Refer to the Transfer Case subsection in the Service Manual for information on draining and filling the transfer case.


Flush Procedure

Important :Refer to Corporate Bulletin Number 99-04-21-001, dated April 1999, for important information on removing the transfer case drain and fill plugs.

1. Drain the transfer case fluid.

2. Refill the transfer case with 2 L (2 qts) of new fluid, P/N 12378508 (Canadian P/N 10953626).

3. After refilling the transfer case, drive the vehicle a minimum of 8 km (5 mi).

4. With the transfer case at operating temperature, drain the transfer case fluid again.

5. Refill the transfer case with new fluid.

Important :The vehicle may require approximately 160 km (100 miles) of driving before the condition is completely corrected.

BillTR
12-15-2008, 07:51 PM
Hey BlueBowTie,

Regarding this:

>>In any event, I would strongly advise replacing the oil pump if you do anything to repair the engine. DO NOT use a factory oil pump and relief on this engine - EVER! An aftermarket pump with higher volume is an absolute necessity. The OEM oil pump has barely adequate gear displacement to maintain barely adequate pressure at idle on a new engine in very good condition. It's a fuel mileage game the manufacturers are ALL playing, and a dangerous one, at that. Install a pump with more than adequate volume and a 45 PSIG relief at a minimum, and never look back. Replacement pumps are only about $50.<<

Could you suggest a brand/model of oil pump (or a part number) that would provide decent oil pressure in an older engine? I am helping a friend with some work on a 2002 Astro (he has about 180,000 Mi. on it) and we have to drop the pan to replace a leaking gasket, so I thought this would be an excellent time to replace the oil pump before it fails!!

I am relatively new to the Calgary area, and I do not know who to go to locally for solid advice. I have read many of your answers in these forums and you obviously "know your stuff", so I was hoping you could make a recommendation for us. That way, I do not have to trust the whims of someone behind the parts counter who may not know what he is talking about.

I own a 2001 GMC SAFARI myself and know what you mean about the oil pressure because it seems to me that on ANY of the three Safari's that I have owned (1997; 1999 & 2001), the oil pressure always seems low when the motor is at an idle, even though I am using an excellent quality synthetic oil.
These engines are otherwise so reliable that it would be a crying shame to risk damaging one through low oil pressure when we are going to have the pan off anyway. Besides, $50.00 (or so) is awfully cheap insurance to correct a known weakness!

Thanks,
BillTR

__________________

Blue Bowtie
12-17-2008, 10:38 PM
Use an old style stock replacement SBC oil pump with the full length pump gears, a standard pickup screen welded in place, and a 30 or 45 PSI relief spring.

The OEM pumps are engineered to deliver JUST ENOUGH oil volume at idle to maintain about 10 PSIG. That is supposedly adequate, and saves some pumping energy (and therefore, fuel). The CAFE numbers look better when every one of a million cars saves two ounces of fuel, which is the primary reason it is done.

However, for my comfort, the little extra fuel I might burn is not worth the marginal oil delivery at lower RPMs. I'd rather burn an extra two ounces of fuel an hour to make sure the engine has plenty of lubricant flow.

Steve47
01-03-2009, 08:34 AM
Fortunately, in the case of an AWD Astro, removing the oil pan for inspection of the crank is relatively easy. There is almost nothing there for interference.

I spoke to my mechanic this morning. He quoted me $250.00 to take down the oil pan and have a look. That's not a problem. He said from listening to it after I dropped it off he didn't think it sounded all that bad. He did say this morning that taking the pan down is not as easy as people think it is. He said something along the lines of axle removal? What do you guys think? It's a 97 AWD, make a difference?

Blue Bowtie
01-04-2009, 10:39 AM
The axle doesn't have to be removed, only rolled forward slightly. From the manual:

Oil Pan - 4wd Models
To Remove:
1. Before servicing the vehicle, refer to the precautions in the beginning of this section.
2. Disconnect the negative battery cable.
3. Drain the engine crankcase oil.
4. Remove or disconnect the following: Dipstick Drivebelt splash shield, the front axle shield and the transfer case shield Front skid plate and the flywheel cover Left and right engine mount through-bolts
5. Raise the engine using a lifting device and block in position between the mounts and brackets.

NOTE: Use extreme caution when blocking the engine in position. Get out from under the vehicle and rock the engine slightly once the blocks are in place to be sure the engine is properly supported.

6. Remove or disconnect the following: Oil cooler line Pitman arm bolt and pitman arm Idler arm bolts and idler arm Front differential through-bolts Front driveshaft, if necessary Differential assembly by rolling it forward for clearance Starter motor Oil pan bolts, nuts and reinforcements Oil pan and discard the gasket

On 2WD models, the engine has to be removed to remove the oil pan. The AWD is a lot easier.

Please keep us informed. A crank kit or new set of bearing shells and a good oil pump might solve your problem. That's a lot more reasonable than a replacement engine, and a fresh bottom end should be worth a lot of trouble-free miles.

Steve47
01-05-2009, 09:13 PM
Thanks! I've printed this off and will be dropping at his shop in the morning. I'll keep you updated for sure.

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