Buzzing when under a load???

[Code Red]

I have a 95 mustang GT that was converted (by a previous owner) from an automatic to a manual. The tranny, a Tremec 3550, was rebuilt last year. Also installed was a new transmission mount, the clutch and short-throw shifter.

The problem is that under load (above 2800 rpm), there is a buzzing/grind noise that seems to be coming for the Bellhousing area. Sort of like something is binding or rubbing under torque. The noise stops when I release the throttle. Could this be caused by worn pilot or throw out bearings? Or is could it be a flywheel that needs resurfacing or maybe the misalignment of the drivetrain? What could be causing this problem?

 

[NO_RICE]

I have the exact same problem with the same transmission, but mainly in 5th gear at 40+ mph, it gets real loud toward 75-80mph. I just replaced the clutch, pressure plate, pilot bearing and throwout bearing, and also had the flywheel resurfaced. The TO bearing was thrashed it had an elliptical rotation to it. None of these helped and I really didn't expect them to, but I have noticed another thing about the noise, When you get it up to about 2500 rpm in 4th and let it wind down by itself, the chatter is present.

I don't have the money to take it to someone to get it fixed and I can't afford to have my car down for more than a couple days so I have not been able to investigate the internals, but I am hoping someone else could shed some light on our problem.

On a positive note I have been driving it with the vibration/hum/chatter for ~20,000 miles and it hasn't really been a serious mechanical issue yet.

I bought the car from a friend and he told me that the vibration/hum/chatter started instantly one day. He also replaced the dampener bushing where the ball on the shifter handle seats into the socket, with no luck.

I am glad to hear that someone else has a similar situation. Hopefully we can solve this mistery together.

side note:
trans has ~60k miles noise started ~40k

 

[Code Red]

Wow! It's good to know that I'm not alone with this problem.

Honestly, I'm at my wits end on this one. I taken to couple of drivetrain guys. Both says it's the transmission's design and nothing can be done to fix it. I'll have to live with it or replace it. However, neither is sure what is actual problem is. Maybe I should poll other 3550 owners and see if they are having similar issues.

For the last year, I have driven mine about 150 miles daily of mostly highway travel. Like yours, it does not appear to be a serious mechanical issue. It just sounds horrible.

I don't have the money or desire to 'kill a flea with a cannon". So, before I buy a new tranny, I'll do more research.

Let's keep each other posted it we make any new discoveries. Good luck!

 

[88Stangboy]

The tremecs are just naturally loud tranny's. I've driven a couple of cars with them, they all make some type of noise or vibration from my experience, no one i know with one has ever had anything wrong with them, just the noise.

 

[Code Red]

Thanks 88Stangboy for the info. At least I can worry less about it breaking.

I did get an email today that told me that I should pull the tranny and check the shims. Now, the guy who rebuilt it last year told me that he packed it as tight as possible.

Is it possible to pack it 'too tight'? Would that cause that 'buzzing sound'

No_Rice,
do you think that your shims could be packed tight?

 

[NO_RICE]

I doubt it has to do with my shims, but it is certainly possible. I did more research last night, actually several hours here is what I gathered:

1. The noise is most likely normal

2. The tail on the 3550 is lower than a T5 so a lot of people shim them vertically by putting washer between the crossmember and the trans

3. Some people put nylon washers between the shift handle and the shifter

4. It is very important to use the GM synchromesh trans fluid

5. It might need a 3/8" driveshaft spacer to keep the pinon angle correct and eliminate any vibrate that you might get at high speeds due to the standard driveshaft being shorter

6. There is an additive for the trans fluid that will quiet it a little bit but I don't know what or where to get it at the moment.

7. There is a rubber gasket you can buy to put between the shifter base and the top of the tansmission that supposedly helps

8. New, the 3550 came with a sheet that warned the owner, that noise would occur upon acceleration, deceleration, part throttle, WO throttle, etc...

When I unscrew the shift knob The niose is reduced drastically, the resonation is dampened. This makes me believe that with the right combination I could dampen the noise to an acceptable level. Several people said the trans was almost annoying loud.

This weekend I will be trying a few of the things above mainly the nylon washers and the GM fluid and trying to locate an additive. I will let you know if I find anymore info.

 

[Code Red]

Thanks for the all the info. I going to try the 3/8 space on the driveshaft and the washer under the tail of tranny. I think I already have a nylon washer in shifter but I'll check that also.

I made a few more calls and one guy thought that it could be the input shaft. Sounds pricey and I'm sure that it would really solve the problem.

Also, did a few experiments during my morning commute and I noticed a few things.

1. There is a change in resonance if I hold the shifter.

2. If I run 70 mph and shift to neutral, the noise is totally eliminated. (which was expected)

3. Just like it happens with yours, my tranny at 2800 rpm in 4th and let it wind down by itself, the chatter is present.

4. If I run 70 mph in 5th, horrible noise, shift down to 4th gear, the noise virtually goes away.

I am not clear on what this is telling me but I it leads me to believe that something is mis-balanced.

 

[Code Red]

The spacer did the trick! No more problems at 70 & above. Still having the noises as I slow down from 50 mph in 4th. But I really think that this is a design issue.