5 speed manual 91 4x4 gear noise in 1,2,3and 5th gear, 4th gear no noise.

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Sounds like it might be a transmission mount or engine mount faulty

check the drain plug magnet for metal bits . If any the box has to come out 4.th gear is straight shaft connection and 5 gear connects from the cluster shaft up to the out put shaft . On either side is a rear main bearing and from your description if that bearing is failed then the 4th gear syncro will not align properly and the gear for 5th will be out of alignment so the syncro to work will not work

Is it a rumble that gets louder as speed increases? It's probably a wheel bearing going bad. Happens a lot on VW and Audi cars.

this would be an internal bearing inside the gearbox on the input shaft......you have the shft coming in form the engine, and the input shaft houses 1,2, 3rd and 4th gears.....the 5th gear is located on an intermediate shaft.....and then you have the output shaft...now if you had said all gears i would have said output shaft bearing......and if you had said 5th gear only, then this would be the intermedaite gear.....

but you are only saying 1,2 and 3......why its not happening in fourth is that the gear ratios that the shafts turn in correlation to thre gearing changes as you get to 4, like on a 10 speed bicycle but in 4th it is a 1:1 ratio, so no excessive loads on the shafts are noticeable....

This will require a transmission overhaul......

It is a 5 speed manual transmission? If it is noisey in all gears except for 4th, then the problem is countershaft bearings.

not unless fifth seases to the baring's. but then it won't even go in to 4th or 5th. it's probably your sincro's that r bad between 4th and 5th.

IT SOUNDS LIKE YOUR CUTCH PLATE WHICH IS ULTIMATELY RESPONSIBLE FOR PUTTING THE CAR IN THE PROPER GEAR, SORRY NO QUICK FIX.

I'm not sure, but that sounds like the throw-out barings. If thats the case and they went before the clutch did, then their could be some big problems up ahead.

Hi,your car may have a bad tranny mount,if not souds like bad gear , (internal)