Ford Mustang Forums banner

1 - 20 of 25 Posts

·
Registered
Joined
·
92 Posts
Discussion Starter #1
I'll start off by saying this is my first time on forums so bare with me lol.

I bought my 3rd mustang, a 89' notchback 5.0 (carb) :salute: a couple months ago. I've spent a bunch of time since I bought it correcting some engine issues. But I'm needing some opinions before I just start throwing money at the drivetrain. I'm pretty new to working on cars so I bought this one for the learning experience and boy I got what I paid for. Here are some specs on the drivetrain.

t5 trans
8.8 rear end
4.10 gears
welded spider gears (limited slip going in soon)
stock driveshaft

Here are the issues.
When going down the road in say 4th or 5th gear. When barely on the throttle (like seriously barely touching it) the car feels like its clunking really bad but if I give it more throttle it stops the clunk. You can feel it in the shifter handle. It's really only noticeable when in 4th or 5th but its really bad in 5th. It also has a bad vibration at highway speeds and only gets worse the faster I go. 60 mph in this car is crazy sketchy. One thing I cant understand is that when I'm going around 55 mph and throw it in neutral the vibration is even more apparent and kinda goes away a little when I'm acting like I'm putting it back into gear, but once back in gear the vibration starts again. I will say that I'm not sure who welded the spider gears and I do not know if they had a clue what they were doing. All rear end mods were done by the previous owner. I don't know if these problems are coming from the rear. Only thing I've touched is the engine.

Anyone ever have these problems? I would really appreciate all advice!!
 

·
Registered
Joined
·
35,861 Posts
I'd get a new and properly set up diff in the car first before you do too much more trouble shooting. Much of what you're experiencing could be due to problems with that rearend. Be sure to check the condition of the u-joints when you pull the shaft out to do the rearend work. With the proper diff in the car and confirmation that u-joints are ok - then see what you have. Wouldn't hurt to have a local driveshaft shop (a lot of truck repair places can do this for you) check out the runout on the driveshaft to be sure it's straight.
 

·
Registered
Joined
·
92 Posts
Discussion Starter #3
I'd get a new and properly set up diff in the car first before you do too much more trouble shooting. Much of what you're experiencing could be due to problems with that rearend. Be sure to check the condition of the u-joints when you pull the shaft out to do the rearend work. With the proper diff in the car and confirmation that u-joints are ok - then see what you have. Wouldn't hurt to have a local driveshaft shop (a lot of truck repair places can do this for you) check out the runout on the driveshaft to be sure it's straight.
Thanks for the reply Michael Yount! That sounds like a plan to me. I definitely need to get this fixed soon before something goes kaboom while i'm going down the road. I'd say I'll go ahead and rebuild the rear end because its apparent that the previous owner just threw parts in and hoped it worked. That's pretty much how this build has been going since day 1. I'll probably go ahead and upgrade to a 31 spine axle and limited slip while i'm at it and upgrade to an aluminum driveshaft since from what I've read the stock driveshaft doesn't fare well with 4.10 gears. But anyways, thanks again for the reply!
 

·
Premium Member
Joined
·
1,485 Posts
Make sure your driveshaft flange to pinion flange bolts are tight as well.
 

·
Super Moderator
Joined
·
27,655 Posts
Does this only happen at very low RPMs or does it happen at higher RPM's too?
 

·
Registered
Joined
·
92 Posts
Discussion Starter #6
Does this only happen at very low RPMs or does it happen at higher RPM's too?
The clunking only happens when i'm coasting in 4th or 5th and I'll barely touch the throttle to maintain speed. But once I give it a good amount of gas the clunking stops. I believe it also clunks a little when I'm coasting in 5th gear. As for the vibration its completely speed dependent. I do think the clunk would happen at pretty much any rpm as long as I'm barely touching the throttle.
 

·
Registered
Joined
·
35,861 Posts
The clunking only happens when i'm coasting in 4th or 5th and I'll barely touch the throttle to maintain speed. But once I give it a good amount of gas the clunking stops. I believe it also clunks a little when I'm coasting in 5th gear. As for the vibration its completely speed dependent. I do think the clunk would happen at pretty much any rpm as long as I'm barely touching the throttle.
Sounds like it could be that the backlash has opened up significantly. You won't hear it under heavy throttle or deceleration because that keeps the gears completely engaged. But you hear it big time when you're under light/no load because that allows the pinion/ring to slam back/forth into each other.
 

·
Registered
Joined
·
92 Posts
Discussion Starter #9
Sounds like it could be that the backlash has opened up significantly. You won't hear it under heavy throttle or deceleration because that keeps the gears completely engaged. But you hear it big time when you're under light/no load because that allows the pinion/ring to slam back/forth into each other.
Do you think I will need to replace the pinion when I tear into it? Who knows how long it has been like this. Also, do you think the car is okay to drive or should I park it until I can fix it? I don't want to be going down the road and the rear lock up.
 

·
Registered
Joined
·
981 Posts
I looked a long time at mine before I found that Ford in their infinite wisdom puts a bolt on the rear upper control arm that is one size at the head and another where the threads are and when I replaced this bolt the clunk I heard on tip in and out at 40 or 50 mph was gone Of course check the U-joints and driveline backlash
 

·
Registered
Joined
·
92 Posts
Discussion Starter #12
I got under the car and everything is very tight, no play. I haven't been able to check backlash yet. It's driving me nuts. Can you check backlash without tearing into the rear end? Sorry if that's a dumb question but might as well ask lol.
 

·
Registered
Joined
·
1,741 Posts
«1992 Mustang Service Manual Table of Contents»
«Group 00: GENERAL SERVICE INFORMATION»
«Section 00-04: Noise, Vibration and Harshness»
«DIAGNOSIS AND TESTING»



Clunk Diagnosis

Clunk is due to backlash in the driveline, but not necessarily in the axle. To determine whether driveline clunk is caused by the axle, make a check of the total axle backlash as follows:

1. Raise vehicle on a frame or twin hoist so that rear wheels are free.

2. Clamp a bar between axle companion flange and a part of the frame or body so that flange cannot move.

3. Lock left rear wheel to keep it from turning.

4. Using a torque wrench located on a wheel nut, rotate the right wheel slowly until reaching a torque of 6-8 N-m (5-6 lb-ft). Hold a chalk marker against one side of tire 304.8mm (12 inches) from center of wheel.

5. Rotate wheel slowly in the opposite direction until reaching a torque of 6-8 N-m (5-6 lb-ft).

6. Measure length of the chalk mark, which is the total axle backlash. It should be 25.4mm (1 inch) or less. If the backlash is within this limit, check the following items:

l Engine mounts

l Transmission mounts

l Universal joints

l Slip yoke

l Loose companion flange bolts



Check for the following conditions if backlash is excessive:

7. Elongation of the differential pinion shaft holes in the differential case.

8. Missing differential or side gear washer.

9. Galling of the differential pinion shaft and bore.

If none of the above conditions show up, there may be a loose fit of the axle shafts to the side gear splines. Continue as follows until the correction is made.

10. Install new side gears and check the backlash.

11. Install two new axle shafts.

12. Replace the axle assembly.
 

·
Registered
Joined
·
92 Posts
Discussion Starter #14
Thanks for all the replies everyone! Can anyone give my some input for the vibration? Could this possibly be the rear end too? Its terrible when I put it in neutral and cleans up a little when I put it back in gear when going 50+mph.
 

·
Registered
Joined
·
4,669 Posts
Thanks for all the replies everyone! Can anyone give my some input for the vibration? Could this possibly be the rear end too? Its terrible when I put it in neutral and cleans up a little when I put it back in gear when going 50+mph.
You can try to minimize it by clocking your driveshaft and seeing if there is an improvement and then re-clocking if needed. Kind of a pain in the ass but its free, doesn't require any serious disassembly, and won't cause any trans fluid loss as long as you don't pull it out of the tailshaft... so don't pull out! :lol:
 

·
Registered
Joined
·
92 Posts
Discussion Starter #17
Okay guys update here. I finally got the money to do the rear end swap. While I was there I got all new suspension parts. Springs, shocks/struts, rear upper and lower tubular control arms. new brakes all the way around. I changed the rear end and all suspension parts in the rear and was so stoked that before starting on the front I took it for a drive. I was expecting a nice vibration free ride for the first time and NOPE. Vibration was still there. Driveshaft ujoints were fine. Is this coming from my transmission/clutch?????? Please help me this is getting ridiculous!
 

·
Registered
Joined
·
261 Posts
I had a very similar problem on a completely stock mustang that took me forever to find. It turned out that the tranny mount was a little loose. It would do that same thing your describing (clunking, vibration through the shifter, etc). It could be loose or maybe torn. Its a shot in the dark...
 

·
Premium Member
Joined
·
3,333 Posts
If you still have a stock steel driveshaft, that is probably the source of the vibration. Since you installed tubular aftermarket control arms, in particular uppers, this is going to make the vibration conducted into the chassis much worse since they have stiffer bushings in them than stock.
 

·
Registered
Joined
·
92 Posts
Discussion Starter #20
If you still have a stock steel driveshaft, that is probably the source of the vibration. Since you installed tubular aftermarket control arms, in particular uppers, this is going to make the vibration conducted into the chassis much worse since they have stiffer bushings in them than stock.
Would the stock driveshaft cause clunking too?
 
1 - 20 of 25 Posts
Top