Grinding noise coming from manual transmission in 3-5 gears?


#1

Hello all, I have a 98 saab 900 se turbo.90000 miles on it.

Just had a new clutch kit/throwout bearing and master cylinder clutch installed, as the clutch was going bad.

When I shift the car (while driving) from 2nd into 3rd/4th/5th gear,and accelerate I suddenly notice what sounds like a “grinding”/raspy noise that stays with the car while in those gears. It does not occur in 1st or 2nd , although it seems that in first gear the rpms go up real fast now (could the gears be slipping again?? this is a brand new clutch…).

The second I shift to 3rd gear and give it gas, the noise shows up instantly. Now when I let my foot off the gas, the noise goes away 100%. The second I give it gas again, it comes back. Also I don’t believe the noise increases or decreases in relation to the speed of the vehicle. It seems to stay constant no matter what speed I’m at, as long as I’m actively giving it gas.

It occurs every time I drive…not sure what to do and what causes this…maybe I just need to check the transmission fluid?

Please help.


#2

Your synchros are probably shot.
A synchro is a set of two matching frictional surfaces that preengage the shaft of the gear going in with that of the gear being engaged just before the actual gear teeth engage. It allows the gear being engaged to be brought up to the same speed as the engaging gear, making the teeth engage smoothly. Synchros are, however, subject to wear. And when they do wear, they don’t properly get the two speeds the same and crunching happens. The synchos themselves can also make a continuous raspy noise even after the gears are engaged.

Man, that’s hard to describe without sketches. I wish I could figure out how to add sketches, but I lack the high-tech sophistication.


#3

It sounds like the clutch is not adjusted correctly. When releasing the clutch pedal to move forward how high is the pedal when the clutch begins to grab and move the car? If correctly adjusted raising the pedal midway of its total sweep should put the car in motion.


#4

I agree; it sounds like the clutch is slipping and is it possible the grinding noise is related to an exhaust heat shield problem?


#5

But the noise continues once they’re in gear, so it’s not (just) the clutch adjustment or the synchros, right?


#6

Worn out synchros will do this. That’s what led me to suspect them rather than a clutch adjustment.

The synchronizer is actually a separate part that rides on the gear shaft. It has engaging cogs that cause it to spin with a gear being engaged and a conical friction surface the mates with an adjacent conical surface to bring the other gear to speed, much as a clutch can be used to engage a flywheel and pressure plate. As a separate part that is no longer in play when the gears are fully engaged, it can buzz from vibration.


#7

When I had bad synchros they would cause grinding going in to gear, but not while in gear.

First thing I’d do is drain the oil into a pan and look for metal bits. If there, uh-oh…


#8

I would have a MECHANIC, maybe the one who replaced the clutch, drive the car and see what he says…I bet they dropped the exhaust pipes to replace the clutch and that’s where you will find the noise…


#9

Some do, some don’t.
Good suggestion about the pan. I like that idea.


#10

I was basically trying to save some money by not taking it to an actual shop but rather I went to a mechanic who just did the job in his backyard. I was there the whole time and it looked (at least) like he knew what he was doing…

Anyway, I guess I’ll just take it to a shop to get it inspected and hear what they have to say, but from what I’m reading here, worn out synchros might be the problem? Possible clutch adjustment?

What about the exhaust heat shield rattle, is that something I can check/sort out myself?

Spent so far between buying parts and paying the guy: $750,so it’s all starting to add up…

Does anybody know how much to replace synchros?

Also, don’t wanna look like a total idiot when I go to the shop…

Thanks.


#11

Also, how come this problem just appears now…? Didn’t have that before. Is it by replacing clutch/dropping exhaust?


#12

The fact that it started with the work makes something like the heat shield or some other installation-related problem more likely. I’d ask the guy who did the work to take a look.

If it is synchros, that’s $$$. Probably better to have a used transmission put in. But you’re far from know what the problem is, go after the exhaust system problem and heat shield first.


#13

Replacing synchros is not something you can do yourself in the back yard. It’ll take a qualified tech. However, you should never go into a shop thinking you already know what’s wrong based on internet forums. Tell the guy what you’ve read on the forum along with your symptoms, even print it if you’d like, but let him do the diagnosis. It’s pretty much impossible for anyone over the internet to do a real diagnosis, just to make an educated (or uneducated) guess.

If Rod and OK4450 are right, and they may be, than it’s a result of the clutch change.
If my guess is right, than it’s simply wear & tear catching up to you.


#14

The only thing keeping me from saying “synchros” is that OP says it’s not RPM-dependant. When the clutch was replaced, the transmission fluid was drained. It’s at least possible mech forgot to refill. It’s worth checking…


#15

Excellent points. And an excellent suggestion.
All we can do from here is suggest ideas and things to check. Hopefully the OP will post back when the cause gets diagnosed. Hopefully one of the ideas will help.


#16

My Corolla’s clutch master cylinder is on the fritz of late, and the first symptom was a sort of “clack” sound when engaging third year from second. I suspect your clutch is not fully disengaging for some reason. Could be something as simple as the hydraulics need to be bled again. Address this problem w/due speed as ignoring it could damage the transmission.


#17

Before you do anything else check, as texases mentioned, to make sure that something, exhaust pipe or whatever, is not touching a heat shield during acceleration when engine torque makes it move on the mounts and the pipe with it. I had that with a VW; thought the trans was gone, brought it to at least two shops who agreed that the trans was failing but it was not. The sound was not consistent; some days it was almost gone.


#18

Ok, so I took it to a shop today, they put the car up on the lift and basically the transmission compartment was shaking up and down when switching into 3rd 4th and 5th…

They couldn’t tell me anything else (not very helpful), other than “the problem is inside and we have to check for it”…for which they’re asking me 700 bucks!!!

Getting a little desperate now and don’t know what to do with the car…got an 800 mile drive (and then back) coming up in 2 weeks and getting worried about the car failing on me…


#19

Got to be the clutch assembly installation.
Might as well let them fix it. Or get a second opinion.


#20

It might be worth your while to get another opinion from a reputable shop. Your description of symptoms in 3d and higher gears is a very strong indication that the clutch is slipping. A good mechanic can determine if that is the problem in a matter of minutes. Often mechanics can turn their incompetance into cash if the customer allows them.