Broken Driveshaft

XR7 Dave

Registered User
I think I know why the driveshaft broke on the XR7... Went to replace the driveshaft and discovered a trashed out poly diff bushing. Now that I think about it I heard a clunk back there during my burnout but didn't worry about it.

Well, I guess I should have.....
sterb148.gif
 
Yeah, shock loading... The diff bushing on my 90 is shot but I haven't found a good replacement yet. I just make sure I preload the driveline at the track. Of course with an auto its less likely to shock the driveline.
 
That's a shame Dave, and makes me wonder if the poly diff bushings are really a good idea in the 5-spds. In fact, I'm still debating whether poly bushings (in general) are a good idea. So far the only constant positive is longevity, because increased stiffness (like in your case) can be a bad, bad thing.
 
Paul ya read it wrong...His Poly bushings were shot..Thus adding more movement to the Pumpkin, throwing his pinion angle way off and binding the univerasal joints to the point where something snapped (just my theory)

Now I have also torn up a set of poly diff bushings whereas the stock rubber ones tend to deform but last forever..

What did I learn...I should have checked my rear diff mount

Theory...

The difference in the durometer of the bushing (and overall condition of my rear mount) was enough to cause the poly bushings to deform past thier tolerences thus ripping.

Soo...Make sure at the very least your rear mount is in GREAT condition if you want to use poly front bushings on your diff. Rubber woudl have lasted MUCH longer in my case
 
I split mine (auto trans) after one track outing. I went back to OEM and didn’t have any issues. I think poly is brittle and will split under a hard impact load.

Stan W
 
I split mine (auto trans) after one track outing. I went back to OEM and didn’t have any issues. I think poly is brittle and will split under a hard impact load.

May want to check your rear diff bushing..A bad rear mount would cause excess forced to be applied to those
 
I am getting ready to install a new iron pumpkin 4:10 gear
and T-Bird 88 rear poly bracket. Would it be best to just
use new rubber stock front bushings, or go the poly bushings
on the front? This rear will only be used for the 06 shootout.
If that make a differents.

Then I will switch back a 3:73 gear & MK VIII aluminum rear
I am going to have built for daily use.. And will use T-bird 88
poly rear bracket .So would the rubber bushing or poly be the
best for street use?

Thanks Randy
 
Randy I think that so long as you dont have excessive movement from that rear mount go for poly front bushings. The cobra guys are running solid aluminum in both front and rear with no ill effects
 
I think I am going to solidify mine. If it does not move, it will not flex right? This makes it more of a stable platform. See the other discussion on swapping over to the Mustang Slobra setup. They were using metal in their replacement parts as well.

Chris
 
Chriss..If you solidify the rear mount Maximum motorsports sells aluminum front diff bushings that are adjustable to set pinion angle..I may go that way soon on my 5 speed
 
My rear mount is very tight, no problems there (it's modified). I've been thinking of going solid too, just a little concerned the design should have some give. I believe it was Jerry who recommended someone against solid mounting some time back. Don't remember the details anymore.

I will not be using poly mounts anymore. I agree that the poly is too hard in comparison to it's strength. Most likley this car will just get stock mounts.
 
I trashed a poly bushing on my 92 and when I called Bill E. to get a replacement under warranty, he told me that he has NEVER heard of these going bad. Mine tore and came out in two small chunks. I have the new ones for my car but haven't installed them because the car is down and needs some work. My auto car has a messed up stock one but I never feel it while driving, just noticed I can push up on the diff when I was under the car and the one bushing looks smashed. I will replace them all soon on both cars.
 
Well, the way I see it, for cars making more HP with less weight but hooking tons better...I think if there was going to be failure, they would see it. I think those mustang guys may finally have something right.

Chris
 
Ya poly front diff mounts dont work I have seen 3 sets brake.
One of them blow everthing out all that was left was the washers.:eek:
 
had it happen also

I had one of my poly diff mounts grenade on me also. Heard a clunk as I was going down the track after shifts. When I got it home checked it out and one had disappeared on me...
 
My poly mounts are scrap too. Although, they are about 6-7 years old, they're probably been bad for quiet sometime. The pass. side upper was deteriorated worse than the stocker when I took it out in '99. All of them look like they'd been deteriorating badly. And I've driven the car less than 10k miles in the last 4 years or so. But have put about 70k on since the bushings went in.

Of course this comes just days before the shootout.... Not looking good right now. The Blackbird's in the garage with no rear end (putting in another set of gears) and no intake (putting on a Randy Baker piece)... and I'm sick. Gonna be a long week of late nights. Might have to call in sick on Monday to make sure it's ready by Friday for the shootout. :D ;)
 
Back
Top