Jbws86928

I fire the 86 928s up. I get a high pitched hum or whirling sound. Is this normal?? This is a California car. C03 on the option chart. Does this mean some type of emmision control or electrical air pump? Or What?? I am shooting in the dark !!! Comes from underneath

the flyin' scotsman

Is it an automatic transmission? If so the 'drive shaft' still spins in park or neutral.

dr bob

Automatic trans? If so, grab a mechanic's stethoscope and listen to the torque tube for bearing noises.

If it's a manual trans car, push the clutch in and put it in any gear; if the noise stops, it's likely those torque tube bearings.

WallyP

One possibility is that the bearings in the torque tube (contains the driveshaft) are going bad. If so, the hum should change with engine RPM.

If it is a manual transmission, push the clutch in, put the transmission in gear and see if the hum stops.

If it is an automatic, the driveshaft turns with the engine all of the time, so the hum will never change.

Mrmerlin

Warning dont run the engine till you have inspected the crank freeplay.

pull the dipstick out and with a piece of lamp cord, sample the oil, drip the oil onto a black piece of cardboard see if it looks like metallic particles.

The whine could be the thrust bearing due to forward pressure on the flex plate.
If the flex plate check has not been performed now is the time to do it if you have an automatic car.
The correct way is to remove the exhaust from the manifolds ( disconnect the O2 sensor at the CE panel first then feed it through the chassis hole) ,
then drop the exhaust.
Then remove the lower bell housing then inspect the flex plate , if its bowed forward then you need to loosen the front pinch bolt on the drive shaft coupler, after this is done check the crank freeplay, then remove the rear heat shields then check the rear pinch bolt by the transmission. install the bolt with some blue loctite on the threads then torque to 66ft/lbs.
pry the crank to the rear of the car then fit the front clamp bolt.
The freeplay for the crank is .004 in. new and a max of .016in. if its more than this then your thrust bearing is close to failure and this will take out the block

M. Requin

Fuel pump?

Jbws86928

It's an automatic, do all 928's hum? I am hearing the hum when I drive. Normal? I got Wally P's reply about humming all the time, but, do you always hear the hum when driving???

dr bob

No, they do not all hum. Please reread the posts above about torque tube bearings and diagnosis. Bad bearings make a rumbly hum that can be easily heard with a stethoscope, or even with a screwdriver handle at your era and the blade on the tube.

The 'new visitors' thread at the top includes a pile of great info. Read through that, and pay particular attention to the discussions on "thrust bearing failure" and the methods for relieving driveshaft preload on the thrust bearing, and measuring the end play on the crankshaft while the coupling clamp is loose. Your description of the hum is more typical to the torque tube bearings but both need to be checked. Thrust bearing problems are almost always fatal to the engine, so action on that should be higher on your list than driving it. There is no forgiveness on this.

Let us know what you find, please.

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Housekeeping:

Welcome to Rennlist! You've landed on what is likely the best support network ever for these cars. You've managed to share the year of your car in your screen name. Better though is to put a little more info in a signature line or two. At the top of the page, select 'User CP'. You'll have options to build a signature are that will be placed at the bottom of every post. Put the car in it, "Purple '86 Auto" or whatever color it is, and your location city/state, and country if you are outsdie the US. If the VIN is over 1000 for your '86, it's referred to as an '86.5. The 86.5 has the brakes and suspension upgrade to the S4 stuff, a pretty significant improvement. There are many users here who will make themselves available to listen to funny noises, answer the "what's that?" questions, help you with DIY tasks or pinpoint local mechanical talent to keep your car in good shape. Just for typing in a little info.

Erik N

If your tires have a pronounced "V" pattern to them that could be the problem. My car howls with a lot of "super directional" type treads. Try flipping the tires side-to-side (reversing their rotation) and see if that changes the humming noise.

WallyP

If you hear the hum while you are sitting still with the engine running, and while you are driving, it could be the torque tube bearings - and no, it is not normal.

With the engine running and the car in park, get out and kneel by the rear bumper and listen for the fuel pump - it should be a hum or singing noise, not too loud.

Try to determine whether the noise is from the fuel pump under the metal cover just inside the rear bumper, or from the round metal tube running down the middle of the car.

If it is the torque tube bearings, they rarely fail suddenly and catastrophically - they just gradually get louder and louder and finally fail.

Repair can be:
- Replace the torque tube with a (hopefully) good used one.
- Replace the torque tube with a rebuilt one.
- Replace the bearings with stock ones.
- Replace the bearings with the improved ones that Constantine developed.
- Replace the torque tube with a Constantine-rebuilt one, with the improved
bearings.

It is a very good idea to replace the torque converter bearings and the transmission seal at the same time.

And, BTW - the HVAC vacuum system can also hum or sing, but that is usually from inside the dash or under the hood at the brake booster.

James Bailey

Good to see you posting Wally !

soontobered84

+1 This is what I'm thinking also. He really doesn't tell us what part of the car he's hearing it except from underneath.

Jbws86928

Thanks Wally and all, I will do this and report back and hopefully it is the fuel pump. Thanks

Mrmerlin

If this is a new car to you,
you still need to check the crank flex plate, I was working on an 86 with a similar whining noise and the flex plate was pushed forward, lucky that the owner stopped driving it when he heard the noise, in my case the crank end play was .007in. after relieving the flex plate clamp

Jbws86928

MrMerlin, The 928 is new to me, my issue is finding someone who understands 928's. I can do some repairs, but what I have read from yours and other posts, that the flex plate and thrust bearing issue is not for the faint of heart or nonexperienced 928 wrench turners. I live in Decatur Illinois ( Central Illinois ) and got screwed by the import car mechanic here. ( BMW 740IL ) So I now do my own repairs. The 928 seems very complicated. I have looked at other posts about mechanics and Illinois was not listed. If you have any inside info about mechanics in Central Illinois , the help would be greatly appreciated. Thanks to you and all for all the info.