Thumping Noise

[Boxologist]

Now a new problem has surfaced. Snake Bit was immediately flatbedded to the shop fllowing yesterday's autoX.

 

Right before lunch, w/ my co-driver at the lightly lauching the car, a loud banging started. The engine was shut down immediately and it was pushed back to paddock.

 

No out of the ordinary noise w/ the engine running, out of gear.

Going into gear, engine running, or as later found out, engine off, loud cyclic banging sound. Not a small thump. a good loud thumping meaning "oh no".

 

With the 7 jacked up, there is some play vertically in teh rear diff when pushing on the pro shaft. the u joints appear fine. I did see a piece of what I assume is the lower diff mounting bolt. It appears to have sheared off. Its a 1/2" x 10" bolt just under the front of the diff. all that i found was a 2' section in one of teh mounting holes.

 

Now reading some stuff on alcester-racing-sevens regarding pulling the prop shaft, it looks like i actually broke the lower mounts as they need 2 seperate bolts and the diff is molded for these bolts to pass thru. these bolt hole carriers appeared to have broken. And they have to be shimmed as well. so may be the diff has too much room to play?

http://alcester-racing-sevens.com/PropChange_DifOut.JPG

the lower half of "D" is missig on both sides.

 

 

So at first i though u joints, but they were fine.

then diff mount, but a replacement bolt, which was incorrect, did not stop teh sound.

Then i though the LSD had siezed.

now i'm thinking broken diff case mounts are allowing play in teh driveline.

 

any other possibilties?

[scannon]

Box,

 

The 10" through bolt goes through the "A" hole (no pun intended) and the two short ones go into the "D" holes which are internally threaded. If the bottom of the "D" holes are broken off then the counter-torque of the halfshafts is causing the diff to rotate around the long bolt in the "A" hole forcing the nose of the pinion shaft to go up until it or something else hits something to stop it. You are going to need a new diff case or a really good welder if you can find the missing pieces.

 

Is there any damage to the frame bosses where the "D" bolts hold the diff to the frame. Check the prop shaft carefully for dents and dings, it may have been what was hitting and causing the thumping noises. Any dings in the propshaft are cause to replace the shaft as well.

 

The shims are there to center the diff in the frame.

 

Those three bolts are on my torque checklist I use before every track event or any time I think things need checking. I have found them slightly loose several times.

Edited August 23, 2010 by scannon

[Boxologist]

Thanks for teh input Skip. Your thoughts are inline with my thoughts with what i've read tonight. You're right to take a peek at the driveshaft as well. When i was under the car Saturday, It appeared that the diff was set in lace to rest on a long lower bolt as there was some scoring on the diff case between where the 2 short bottom bolts are supossed to be. No signs of teh lower half of teh cast holes. Its seems as if one goes, the torque will easily snaps its opposite one.

 

I don't expect any welding. time for a new case. I was expecting the diff to be shot and a Quaife to need to be ordered, but Blatchat seems pretty happy w/ the ZF units if they are properly set and I haven't had any issue w/ mine.

[scannon]

I think there is a good chance that the diff internals will be undamaged and can be transferred over to the new case. Make sure whoever does that task really knows what he is doing. There aren't many mechanics around anymore who are skilled in differential set up. Its as much an art as a science.

[scannon]

Box,

 

I was under my car this AM and find that I have misspoke in my first reply to this thread. My differential mounts to the "A" and "C" holes. The "D" holes are unused. Assuming that your differential mounts the same (both cars are Caterham SVs, mine is an '04 model) then the missing halves of the "D" holes are inconsequential unless there is cracking around where they broke and the lubricant is leaking out.

 

Can you post a picture or two of the damage?

[Boxologist]

just woke up. i'll be heading to the shop in another hour or so?

gotta unearth the build books as well. I have a sinking feeling i'm going to call it a season w/ the 7. I started Miata hunting at 6am so i have a stock car for the local autoX lot and can keep the 7 in condition for smoother lots.

[Boxologist]

mod car blues.

http://psccandnyrphotos.shutterfly.com/2701

[yellowss7]

Jon, the title on the first slide says "for Sale"? are you trying to tell us something?

 

Hope it's not that serious.

 

Tom

[Boxologist]

every photo in the sequence is label w/ the FS prefix. guess it wasn't altered from a previous batch upload.

 

No appears it just needs a helicoil to be put in to frame side lower diff mounts. I should be driving again in time for saturday's nnjr event at teh meadowlands if its at one of the slippery lots.

[MHKflyer52]

Jon,

Have you figured out what is wrong with your 7?

[Boxologist]

bolt probably became loose and then sheared out the threads on teh frame from all the launches.

[MHKflyer52]

Jon,

Hope you can fix it with out a lot of trouble.