Mysterious knocking noise

[rdamonl3]

Hi all, this is my first post and its not coming from a happy place. So ive got a knocking noise. My bronco has done it since i got it about 2 months ago, it happens when im in gear and slowly start to accelerate, i have a 3 speed manual. Its more prevalent in first gear and less in second and cant hear anything in third, i can hear it in reverse as well. The knock is loudest at low RPM and and gets quieter as RPM increases and is gone by 2K RPM. If i rev it in neutral no knock. The knock hasn't gotten any worse, it doesn't matter if its hot or cold, it does it when i first get in the bronco and drive off and it does it after everything is thoroughly warmed up without any change in intensity. The Knock is very steady and seems to be speed based, not RPM based, but only under load, and by steady i mean its not a Knock that "rattles" inconstantly. When letting out on the clutch the RPMs are higher and then the clutch grabs RPMs drop some and i move forward, the knock doesn't seem to follow the RPMs at that time only once the bronco starts moving. HOWEVER once the motor is up to temp and the electric choke lets the RPMs settle to idle i can hear a rattling knock, but only once the bronco is warmed up. When i first start the bronco in the morning at around 55 degrees outside no knock or rattle in neutral. so please help me out!!! oh its a 289 or 302, not sure of mileage either. just put a new flywheel and clutch in with the hopes that the noise would go away, it needed a new clutch anyways, it didn't change a thing knock related. One last thing in neutral i put my ear on the trans shiftier knob and all i could hear was the spinning of the gears, no rattling knocking at idle.

 

[TwoDalesDad]

Have you checked your.....front door?......i got nothin.....sounds like a bearing from where i sit....

 

[jonpblewis@yaho]

99% Its your Drive shaft. Check your u joints and the CV yoke that bolts to the transfer case. Three U joints and CV Yoke are cheep. Replace all of it ASAP before you break something.
If you want to test it pull the rear drive shaft off and drive it on the front in 4 wheel high and see if the knocking is gone.

 

[rdamonl3]

well i took your advice and started looking at the drive shafts. the rear drive shaft has all new u-joints but i still tried to see if there was any slack in it. turns out the slip joint seemed a little worn, i could wiggle it about 10 degrees. i had a front drive shaft out of a jeep grand cherokee laying around and it so happens the u-joins are the same and it was long enough as well so i threw it and and poof no more knocking. thanks for the help

 

[jamesf7278]

what year front shaft for a jeep grand fits the rear on a bronco? are they around the same length?

 

[Bronco Junkie]

I can ALMOST guarantee it is your throwout bearing...as I had a similar issue when I first installed my new clutch and TO bearing.

It will either just go away after worn in (like mine did) OR it was installed wrong.

 

[Dave]

well i took your advice and started looking at the drive shafts. the rear drive shaft has all new u-joints but i still tried to see if there was any slack in it. turns out the slip joint seemed a little worn, i could wiggle it about 10 degrees. i had a front drive shaft out of a jeep grand cherokee laying around and it so happens the u-joins are the same and it was long enough as well so i threw it and and poof no more knocking. thanks for the help

When I bought my first Bronco way back in 80 the PO had replaces everything possible trying to fix a drivetrain shudder an clunking. Everything but the slip joints that is. I got it for cheap. New splines and yokes and it drove like a new vehicle.

 

[rdamonl3]

what year front shaft for a jeep grand fits the rear on a bronco? are they around the same length?

it came out of a 2004 grand cherokee limited V8 with command track full time 4 wheel drive, CV yoke and all. they are the same length but with my 3.5 suspension lift its almost maxed out. i drove it pretty fast over a few speed bumps in the neighborhood to make sure the drive shaft wasn't going to separate when i go over a bump or so on the highway, deff not the safest way to do it but better in my neighborhood the the highway. this is just a temporary fix until i get my T-19 swaped in and take measurements for a new drive shaft.

 

[jamesf7278]

it came out of a 2004 grand cherokee limited V8 with command track full time 4 wheel drive, CV yoke and all. they are the same length but with my 3.5 suspension lift its almost maxed out. i drove it pretty fast over a few speed bumps in the neighborhood to make sure the drive shaft wasn't going to separate when i go over a bump or so on the highway, deff not the safest way to do it but better in my neighborhood the the highway. this is just a temporary fix until i get my T-19 swaped in and take measurements for a new drive shaft.

sweet, sounds like a cheap pick n pull spare to me

 

[jonpblewis@yaho]

sweet, sounds like a cheap pick n pull spare to me

........... X2

Bet it'll fit the front too.