Coulda been worse

[Buzz]

I had an interesting experience today. I've been trying to figure out what my rearend gear ratio is. I only know that its a posi unit and since there are no tags on the diff, I decided to run the car at different speeds,note the rpm's and use the gear speed calculator to give me a ballpark. On my way back home, I slowed almost to a stop at an intersection before making a sharp uphill right turn. When I accelerated mildly through the turn, I heard a sharp snap from the back of the car and the rear seemed to squat a bit. As I slowed to a stop there was a grinding/shaking/bumping action in the rearend. My first thought was that a drive axle or a U-joint had failed. The right rear wheel seemed to be at a noticeable negative camber (leaning in at the top)and I looked under to see what was broken. Everything seemed intact. Joints, axles, control arms, shocks - nothing seemed out of place. I got in and very slowly pulled ahead a few feet. The grinding and bumping continued even at walking speed. Further checks revealed nothing. I was about half a mile from home so I limped it home VERY slowly and jacked up the rear. By now I'm thinking wheel bearing, axle u-joint or the rearend itself is shot. After spinning the wheels, crawling around and checking everything and still finding nothing. I lay under the car and had Pauline spin the wheels by hand. Well at a certain point on the rotation, the entire rear end assembly gave a big shake. 3 of the 4 bolts holding the differential housing to the frame had sheared off leaving one shaky bolt barely holding it on.
What would cause this to happen? I would expect a lot of things in the rear end to let go but not the diff mounting bolts! The car has been driven fast on twisting roads and a small course on an old airbase. I have launched hard on a measured 1/4 mile and spun the tires a few times on the street, but generally it hasn't been abused at all.
A few questions:
What's the basic procedure for dropping the rear suspension?
What are the specs on the four mounting bolts?
Is there anything else I should check as a possible cause for the shearing?

Any help would be appreciated.



Tropical Buzz

[casaleenie]

I'm going to follow this thread very carefully..

I developed a nasty negative camber also but none of the other symptoms..
Seemed to happen very quickly but upon inspection I didn't find anything... Put the car away for the season and will have it looked at again in the Spring...


Haven't heard much from you on the Club Cobra Forum for the past year. Glad to hear you here...


AL
2899386

[Buzz]

Al, always good to hear from you. For the better part of the past year, I've been busy expanding my business regionally which pulled me away temporarily from most of my preferred activities. It seems to be difficult getting technical help here - the last three threads I posted requesting Unique specific assistance (rear sway bar, electrical problems)got plenty of views but no replies. I'm getting some help as before on club cobra but it sure would have been nice to hear from Unique owners who are hands on familiar with our setups. Thinking about what you posted; one day while out driving, on three or four slow turns I was startled by a brief and sudden squirrely rear steer type of sensation. Right afterwards, everything felt fine - the conditon never repeated and I was unable to find anything wrong when I got home. I wonder if that was the beginning of my current problem.

Tropical Buzz

[pgermond]

Buzz,

Don't know about the others, but if I had any experience with your issue I would have chimed in.

Good luck, and keep us posted as to the cause - might come in handy.

Phil

427 Roadster, #4279436
Southern Automotive FE
3:31 and Toploader

Roseville (N.Cal)

[clayfoushee]

Buzz, unfortunately, the more technically inclined here aren't checking in as often or posting. I'm not one of those (technical experts), but I did spend a lot of time thinking about what could have happened including putting my car on the lift this afternoon and looking at the mounting points.

What clued me a bit was 69 Mach 1 that I recently bought. When I first drove it, after nailing it and letting off the power, it would veer suddenly left. When I examined it, the rear end mounting pounts weren't even finger tight! The rear end was wandering all over the place.
There does seem to be a gathering consensus on CC, and you seem to be getting some help. Plus, your latest post over there seems to implicate that the problem was there earlier, and you just didn't notice the symptoms. I probably wouldn't have either.

Thanks for the post here, however! This doesn't seem to be a common problem with Uniques or people would have chimed in, and I think we've all found that regardless of the manufacturer, these cars need to be checked frequently for loose bolts in various places.

Clay

'98 Unique #9299, 427FE side oiler (452.1-stroker), top-loader (close), 3.31 rear

Annapolis, MD

[Buzz]

Thanks guys. Hey Clay, check back to the thread over on CC. Karen sez hi! Ahh what the heck, I'll attach it here too.


Tropical Buzz

[Poorboy]

Buzz,
Dropping the rear end out is very simple. Support the center section(on a floor jack is best), take out the 4 bolts on each upper shock mounting plate, remove the 4 drive shaft bolts, remove the trailing arms at the axles, remove the 2 center section braces, unhook the brake line(put a cap over the end),remove the one remaining center section bolt, lower assembly down.
The bolts are allen head cap screws 1/2 13. I would guess they had worked loose, letting it move around is what sheared them.

[Buzz]

Much appreciated, Poorboy! Exactly what I'm looking for.

Tropical Buzz

[eliminator]

Buzz,

Be sure you use good quality Grade 8 bolts when you replace the broken bolts (not the hardware store grade 8 bolts). I would say those have been loose for a while. A little lock tite on them will make sure they don't loosen up. There are no other issues with your rear-end. These are some of the bolts that should be check at least yearly.

Rick
#4279405

[Buzz]

Will do Rick. Unfortunately hardware store stuff is all that's available down here so I'll have to order them. Good time to place an order anyway as I need a few other small items.

Tropical Buzz

[will butterworth]

While ole winter holds us in the garage it is a good time to go over bolts in structure, steering, as you say rick, stuff does work loose and goes unnoticed until whop.Found tierod end nut almost off once, fellas, put in new msd ignition distr., wires, and plugs, amazing diff. in eng. ,runs like a scalded dog , went to sev. x-mas parades stole the show everywhere we went.Will-Alabama no coyotes this wk.end Rick.

[brfutbrian]

buzz, check the holes on the frame and make sure the 3 bolts didnt open up the holes before each one snapped. later, brian.

[K.Wilson]

Buzz,
I just read your post. It sounds to me like the bolts were not torqued correctly when installed so they vibrated out over time. Unique used to use socket/allen head cap screws for this application that are slightly better than a Grade 5 bolt.

When I built mine I used Grade 8 hex head bolts and torqued them to 85 lb.ft. I would recommend Grade 8 or an NAS (aerospace high strength fastener)hex head bolt as the replacement.

If the threads in the differential are not in bad shape and the holes in the frame are okay you can probably do the repair without removing the rear end. I would use Loctite Red for this application.

If the threads in the differential are damaged it will have to come out. I believe there is enough material there to drill and tap them to 9/16; then you will have to drill the frame holes to 9/16 and get 9/16 fasteners.........Just a thought on the "worst case" situation, but if the bolts were loose for some time before they fell out, the threads could be damaged.

In any case, you will need to square up the rear axle with the frame before you torque it back down or the car will not track properly. I believe I posted detailed instructions on this topic in another post, you may want to do a search.

Hope this helps.


Keith

[casaleenie]

Buzz,

Apparently, all you had to do was post a picture of Karen and the technical info comes flying out of the air...
If I need help down the road I'm going to borrow the picture...

AL
2899386

[spd4me]

Buzz
The easiest way to check your rear end gear ratio is to jack up the rear end, put in neutral, rotate the tire one turn and see how may time the drive shaft turns. If drive shaft turns 3 and a half times, then it's a 3:54. If 3 and a third it's a 3:31. You can go to www.smokemup.com and get some good info.

[rdorman]

Al, rear camber can be a problem with the spiders in the diff.

Safety wire the bolts once you have replaced them. Any airport with a repair center can hook you up with the bolt you need and predrilled at that. Aircraft Spruce is another good resource that you can order from.

Rick

[Buzz]

Just finished dropping the rear suspension. Easier than expected, particularly the driveshaft flange bolts - 3 OUT OF 4 I COULD LOOSEN BY HAND!!! Interesting findings:
- None of the bolts sheared flush with the deck of
the housing; all broke below the tops of the
holes.
- No markings on the bolt head
_ No apparent damage to anything else including the
holes in the frame bracket.
- Bolt looks kinda stretched to me; see what you
think.

Tropical Buzz

[Buzz]

Here's a view of the top of the diff casing. Getting these suckers out is sure to be fun. What size drill and extractor should I use? I'll take the opportunity to order new brake pads and replace the parking brake calipers. Good time as well to inspect, clean and detail the whole assembly .



Tropical Buzz

[K.Wilson]

Buzz,
It looks to me like who ever installed the rear end used the original Jag bolts that have a 60 degree shoulder that matches up to the 60 degree countersink on the Jag subframe. If your Unique frame was not modified with the same countersink it is no wonder they came loose and broke. The tapered shoulder on the bolt was mateing with the sharp edge of the hole so there was almost no mateing surface area between the bolt and the frame hole. Can you see how damaged the holes in the frame are? Do they look like you can clean them up with a die grinder and get a good flat surface for the bolt head?

If it were mine I would try to remove the broken bolts by a low tech method first. I would try to grind a screw driver slot in the top of the bolt with a die grinder and a cut-off wheel or a Dremmel tool with a cut-off wheel, then take a large screw driver and try to back it out. If that did not work you will most likley need a carbide drill bit to drill the bolt for an EZOUT extractor. I think those bolts will be so hard that a regular drill bit will not cut them.
Don't get too concerned if you cut into the differential case some in the process of cutting a slot for a screw driver, there is plenty of material there for surface contact and you will have to run a tap down the hole to clean-up the threads any way. You may want to start soaking the bolts with penetrating oil now to help in the process. Actually, the threads do not appear to be damaged in the photo. This could be an inexpensive fix.
Hope this helps, if you need to discuss this by phone PM me and we can set up a time.

Keith

[Buzz]

Hi Keith. I went out and picked up a #4 extractor and the recommended bit size is 5/16". I've got some Screwloose penetrant soaking in as I type. I have to admit I was not looking forward to the drilling so as soon as I type this I will head down to the garage and give your idea a try. So that's where those bolts came from! Alan Weaver confirmed a while back that the original buyer did not order the suspension from Unique so you're right on the money. Thank heavens for the upgrade to the rear trailing arms and brace. Things would not have gone quite so nicely without them.

Tropical Buzz