Hey guys: 66 Mustang coupe, 289, automatic. I put in new front and rear u joints. Still getting a noticeable clunking, vibrating when I put it into reverse. I put the car up on jacks and did several tests: I put it in reverse, and also accelerated. Clunking when shifting info reverse, vibrating. Also, I noticed one rear wheel spins when I put into reverse, but both wheels are not spinning at the same time. Is that normal? Are both wheels supposed to spin when shifting in reverse? Clunking is still very noticeable. Thx in advance for help troubleshooting.
66 Mustang clunking sound going into reverse
iwantapony
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- Reaction score
- 15
- Location
- Texas, USA
Hey guys: 66 Mustang coupe, 289, automatic. I put in new front and rear u joints. Still getting a noticeable clunking, vibrating when I put it into reverse. I put the car up on jacks and did several tests: I put it in reverse, and also accelerated. Clunking when shifting info reverse, vibrating. Also, I noticed one rear wheel spins when I put into reverse, but both wheels are not spinning at the same time. Is that normal? Are both wheels supposed to spin when shifting in reverse? Clunking is still very noticeable. Thx in advance for help troubleshooting.
- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
I think I know exactly what this is - and it's not even expensive to fix. =)
The "clunk" is the giveaway. Your u-joints are shot. When you put it in drive, there's slop in one (or more) of your u-joints, so the 'clunk' is the play being taken up. If you gently accelerate, there's no noise, or not much, but there may be vibration because things are out of place and not balanced. When you let off on the gas, CLUNK again as the play in the drivetrain goes the other way - wheels driving engine. Then you step on the gas again, and CLUNK, now the engine's driving the wheels again. Classic. With the car up on jackstands, you can just grab the driveshaft by hand and wiggle it back and forth to see how much play the U-joints have. It should be "none".
As for the 'one wheel spinning' thing, this is the job of your differential! You might expect them to both go equally, but they have to be able to spin at different speeds so you can go around corners. When you turn, the inside wheel must go slower than the outside wheel, or else one will have to scuff and slip. The differential is kind of a neat thing. If the car's in park (driveshaft can't move) and both wheels are off the ground, you can turn one by hand, and the other will spin the opposite direction. If one is held, and the driveshaft turns, the other wheel will spin at double speed.
If you want to see more and understand the dark sorcery behind this nifty gearing trick, here's a video:
Definitely fix this - you don't want your car flinging the driveshaft out on the road while the car's moving! It could cause a wreck, or major body/mechanical damage, or both! But it's not hard to do.
Welcome to AFM!
Edit: DOH - apparently I did miss a very important line here. I see that you did fix the u-joints! >.< PMAZ is right to check the slip yoke next. It should slide in and out easily just a little, but should have zero play in any other direction. If there's any slop at all, something's wrong with the tailshaft or your slip yoke.
The last thing it could be is your rear gears. Does it growl or whine out on the road? Usually you'll hear things going a long time before they're shot, but if there's a problem with the pinion gear, you could test it for play with the rear wheels, and by wiggling the diff end of the driveshaft.
The "clunk" is the giveaway. Your u-joints are shot. When you put it in drive, there's slop in one (or more) of your u-joints, so the 'clunk' is the play being taken up. If you gently accelerate, there's no noise, or not much, but there may be vibration because things are out of place and not balanced. When you let off on the gas, CLUNK again as the play in the drivetrain goes the other way - wheels driving engine. Then you step on the gas again, and CLUNK, now the engine's driving the wheels again. Classic. With the car up on jackstands, you can just grab the driveshaft by hand and wiggle it back and forth to see how much play the U-joints have. It should be "none".
As for the 'one wheel spinning' thing, this is the job of your differential! You might expect them to both go equally, but they have to be able to spin at different speeds so you can go around corners. When you turn, the inside wheel must go slower than the outside wheel, or else one will have to scuff and slip. The differential is kind of a neat thing. If the car's in park (driveshaft can't move) and both wheels are off the ground, you can turn one by hand, and the other will spin the opposite direction. If one is held, and the driveshaft turns, the other wheel will spin at double speed.
If you want to see more and understand the dark sorcery behind this nifty gearing trick, here's a video:
Definitely fix this - you don't want your car flinging the driveshaft out on the road while the car's moving! It could cause a wreck, or major body/mechanical damage, or both! But it's not hard to do.
Welcome to AFM!
Edit: DOH - apparently I did miss a very important line here. I see that you did fix the u-joints! >.< PMAZ is right to check the slip yoke next. It should slide in and out easily just a little, but should have zero play in any other direction. If there's any slop at all, something's wrong with the tailshaft or your slip yoke.
The last thing it could be is your rear gears. Does it growl or whine out on the road? Usually you'll hear things going a long time before they're shot, but if there's a problem with the pinion gear, you could test it for play with the rear wheels, and by wiggling the diff end of the driveshaft.
- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
Another useful thing you could test is to disconnect the driveshaft and turn the rear wheels by hand. Try one on the ground and turn the other by hand. If it's not perfectly smooth, and there's any clunking, bumping, grinding, etc, you could determine if it's a problem with your differential. If it's not the diff, then it's something with your transmission.
Yeah if greasing the yoke doesn’t do anything, then grab the half u-bolt on the pinion with both hands and quickly rotate it back and forth. Don’t worry about breaking anything. Shake it in all directions and see if you notice any play, rotating, side to side, up down, in and out.
My Mustangs needed yoke lube with 5,000 miles on them. I can’t imagine an old Mustang that is having u-bolts replaced not needing it. My 4Runner is supposed to have six grease fittings lubed in the driveline parts every 15,000 miles. Driveshafts need care and most noise comes from dry or worn fittings.
- Reaction score
- 15
- Location
- Texas, USA
Hey guys, thanks so much for these responses. Let me pour through them in more detail. As noted, I had put in new front and rear ujoints because I had been told that is typically the problem when there is a clunking sound when shifting into reverse. After putting in these new ujoints, I am still getting the clunking sound. My door plate tag says I should have a 2.80 rear axle, 7 3/4 inch. I have a 66 Mustang, coupe, 289, 2bl, C4 trans. I got underneath, and I believe the previous owner put in a different rear axle (see picture of rear axle tag in my car). I think now there is a 3.00, 8 inch rear axle on there. Slip yoke looks fine, and slides in fairly easily. Did I put the driveshaft back in wrong?
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- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
Looking at those pics has me wondering! How are the caps being retained in that yoke? They would normally be "in' farther, and there's a clip that holds the cap in place?
If those caps are sticking out farther than they are supposed to, then there would be a ton of play in there, and the U-joint would be slopping around.
This is what it should look like:
I think we may have a culprit!
- Reaction score
- 15
- Location
- Texas, USA
Thx for the feedback.
What year, engine, and trans is your mustang? [mine is 66, coupe, 289 2bl, c4 auto trans.]
My ujoints do not have end caps. My front and rear ujoints use c clips.
But, to your point, I'll put the driveshaft back in, and really check the fit and/or looseness of those ujoints especially in the rear. Thx.
- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
My current "Mustang" is a '67 Cougar. But I've worked on quite a few years of actual Mustang too. =) Our cars share the same drivetrain, plus a few extra inches in the driveshaft, and an interesting little weight on the tailshaft of the C4 transmissions they used in '67 to damp harmonics. There should be virtually no 'wiggle' to the driveshaft with the U-joints properly installed. I'm not sure if the inside faces of the yokes are machined to any kind of spec, so I really wonder if those C-clip retainers are a problem or not! I will admit, the smooth, flush faces of the caps do look pretty cool though. =)
- Reaction score
- 15
- Location
- Texas, USA
67 Cougar, very nice! Do you happen to know the toque spec to the ujoint bolts? I put the drive shaft back in. Checked for loosness/movement, etc. Still clunking, but maybe not as bad. Maybe I need to torque those ujoint bolts to the correct setting?
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- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
Should be between 20-24 lbs. More importantly is to do both sides gently all the way down first, and sort of work from one side to the other, back and forth so they get even torque instead of being put on "whopperjawed" as my grandpa would say. =)
- Reaction score
- 15
- Location
- Texas, USA
Thx so much for the advice. I'll go back down there and torque them based on your recommendation. Thx!
- Reaction score
- 15
- Location
- Texas, USA
OK, torqued ujoint bolts to 20 lbs. Still clunking pretty good when shifting into reverse. With the car up on jacks, when I attempt to wiggle/move the rear of the driveshaft that connects to the axle, there is not any give up or down, or sideways. Nice and firm. BUT, when I rotate the driveshaft (when in park) there is definitely give (kind of a thunk) where the rear of the driveshaft connects to the pinion/gear -- is that source of the clunking? Or, is that normal? Thx again!
- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
100% not normal. Check your gears by putting one on the ground, and leaving transmission in Neutral. Chock the front tires for safety. Rotate the raised tire, and wiggle it back and forth. If there are any tooth problems on the ring or pinion, you will find them, if you go around a few times. Any clunks, or non-smooth operation (forward and backward!) will let you know. it should be smooth as silk, with very minimal play.
It sounds like you might need to rebuild your rear end!
It sounds like you might need to rebuild your rear end!
- Reaction score
- 15
- Location
- Texas, USA
thank you again. I am a total novice at this. I will do as you suggest here, get on it tomorrow and over the weekend. Thx!
- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
Everyone's a novice until they've done it a few times. =)
- Reaction score
- 15
- Location
- Texas, USA
OK. Took turns putting each rear tire up on jacks individually, while the other one was on the ground. while in neutral. when moving wheels forward, generally smooth. BUT, when moving wheels in reverse, a lot of clunking and movement/give. That is the case with each rear wheel (moving wheels in reverse). I gather that is not normal. Strange that moving wheels forward generally smooth/ok. Reverse has the major clunking sound and give. The sound is definitely in the rear. I do not hear the clunk/sound from the front by the transmission. So, problem with each of the rear axles and with the gear/pinion? Thx again.
- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
Ouch! It's possible for teeth to be worn on one side but not the other - or to have a crack (or wear) in a pinion support so that it has more problems turning one direction than the other. Sounds like some disassembly/repair and possibly replacement is in order!
- Reaction score
- 15
- Location
- Texas, USA
Thx so much for all your help. Which supplier would you recommend to buy a new pinion, and/or gear, and/or rear axles? I checked the tag on the differential - WDY-AA, 3.00, 8. I have a 3.00 gear ratio, 8 inch rear end. {Appears the previous owner put in a differential from a 76-78 Mustang, based on the WDY code. WDY was not a 1966 rear axle code.] Are the rear axles different lengths for the driver's side and passenger side? 1966 Mustang coupe, 289 2bl, C4 auto trans. Thx again!
- Reaction score
- 3,411
- Location
- Sedgwick, KS, USA
Hopefully your rear axles are fine, and should not need replaced. You may need a new chunk (the removable center section of your differential that holds the gears). While you have it all apart, since you need to remove the axles anyway, you may as well do the brakes and axle bearings too. Without trying to 'advertise' anyone here, I used a guy out in Arizona who sold me a new chunk for my Cougar with Torsen type limited slip and 3.55 gears (for my new overdrive transmission). I would not say that I'm particularly knowledgeable about pricing on rear ends, but I did a lot of shopping, and felt like $755 was a good deal for what I got, fully ready to go and shipped to me. You may be able to get away with just new bearings, gears, and a local shop putting 'em in, for a lot less. Until you disassemble it and look to see what the damage is, you won't know what you need for sure.
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