i have an 89 mustang GT Hatch 5speed that has a horrible knock in the rear end. it happens about every revolution of the tires it seems. faster and a lil more dull at speed slower and a little more harsh and singular at slower speeds. I have the car jacked up now and thought it was a bad wheel bearing. pulled It and it had some pitting on it. sanded it smooth and put it back in no change. pulled axle and left it out and no change. I currently have both axles out. have pushed and pulled on drive shaft and she is tight. there is some play in the carrier. I just changed the drivers side wheel bearing and put new fluid with the friction additive for the LSD. I have no idea what to do next.
Rear End Knock
- Thread starter rbreith
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Based on what you say, Id pull the driveshaft and check the ujoints, especially the front one. When you take the front yoke off of the driveshaft, put it in the end of the trans and check for play without the driveshaft. Replace the ujoints if needed
Shakerhood
Dirt-Old 20+Year Member
Definitely, Definitely Check the Control Arm Bolts, I have seen an upper one back off before with a not so good end result.
A loose control arm will not make the noise he's describing, especially if it's making the noise while the car is stationary, on jack stands.
- Dec 19, 2010
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Sounds like U joints to me too. It may be carrier or pinion bearings, but U joints typically go bad first.
When you say you have play in the pinion, are we talking gear lash (rotational) or bearing play? (Radial- up down/left, right) or thrust( axial- front/back) a little gear lash is normal. Bearing play you shouldn't feel with your hand unless you know how to feel .002" or less.
I don't remember the lash number off hand. Seems like it's around .012 but that can seem like quite a bit by hand.
Again, most likely U joints, but if you have or can borrow a mag base indicator, it's not hard to do a lift check on your pinion bearings.
When you say you have play in the pinion, are we talking gear lash (rotational) or bearing play? (Radial- up down/left, right) or thrust( axial- front/back) a little gear lash is normal. Bearing play you shouldn't feel with your hand unless you know how to feel .002" or less.
I don't remember the lash number off hand. Seems like it's around .012 but that can seem like quite a bit by hand.
Again, most likely U joints, but if you have or can borrow a mag base indicator, it's not hard to do a lift check on your pinion bearings.
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I'm going to pull the drive shaft this weekend and do new U joints to see if that helps. I have checked control arms and there is no play in them. we will see how it goes. I hope its U joints and not something more labor intensive.
pulled drive shaft and put the end back in the transmission and it had no play it was nice no noise. so I got some U joints replaced them even though they did not seem like they were bad. Was a real pain in the ass getting them back in. Will replace drive shaft tomorrow and hope that solves the issue. if not I will do a check on the pinion bearings.
puled carrier to see if I could make the noise with just the pinion I couldn't so I put carrier back in. going to go get some oil new outer bearing since one was installed backwards. and put the thing back on the ground since I have no idea what to do. going to see if auto parts store has a lash indicator so I can test that but if not. might end up brining it to a mechanic.
checked lash and it is about .011. so that should be good. and not an issue. so I'm changing out the passenger wheel bearing since it wasn't in correct or in all the way ( not causing the noise since it make the noise without axles in). then I'm putting her back on the ground since I do not know what to do.
- Dec 19, 2010
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Man, based on what you are describing it sounds like you either have damaged gears, or a bad carrier bearing. I would recommend changing those bearings and inspecting the gears before reassembling that thing. If you have a goofy axle bearing there's no telling what was done to the carrier.
Pry the carrier side to side while checking the lash. When I was learning to setup my rearend, I found out that doing this actually showed me that my lash was much more than what I had originally thought.
Joe
Joe
thanks gents for the help. I checked the carrier bearings when I had it out hey looked great. changed the right rear axle bearing must be an easier way than what I am doing because that is a pain in the ass. put the car generally back together and it makes the noise. I'm guessing it is with the pinion since I was under the car pushing on the driveshaft pretty hard and I did get some movement. I'm off to Bragg for a few weeks. so it will be next month by the time I get back to the car.
so I checked the sound in 1-5 gear. idling with no load on tires (since there are none on) its un noticeable in 1st terrible in 5th. to me that means its related to wheel speed no to engine speed. which should take drive shaft out of the issue. pinion out of the issue and leave it to the carrier. however I had the carrier out and it looked fine as did the carrier bearings and races. lash was good checked a lot of times. does everyone agree that it should be related to carrier (wheel speed) and not engine speed. or am I wrong since the gearing in the trany makes the drive shaft spin at different speeds in dif gears
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