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View Full Version : TR4/4A TR4A Differential Mounting Bushings



cjimj
07-03-2014, 03:04 PM
Does anyone know how much of a difference there is between the no-name polyurethane bushings offered by Moss and BPNW that cost about $50 for the set versus the SuperPro bushings costing about $130? I've got a set of rear bushings I think I got from BPNW and they're very hard, which may be great for racing, but seems less desirable for a road car. SuperPro offers both road and racing bushings which makes me think the road bushings are a little softer and the racing bushings are more like what I got from BPNW.

I'll spend the extra $100 if the SuperPro bushings are that much better, but I'd rather not if the difference is minor.

Thanks,
Jim

KVH
07-04-2014, 04:09 PM
I would trust Moss on the bushings, and spend time (money) being certain your mounts are secure, not cracked, and not in need of shoring up. It always troubles me when to start and stop once something is apart. When I had my diff out, everything looked great. A friend came over with an air grinder, ground the paint and surface abrasions off the mounts and showed me two hairline cracks. We welded little plates on one Saturday morning. I think I've saved my 4a another 40 years of life, 'cause I doubt the next guy would've caught the issue before something bad happened. I hate seeing these cars parted out. Short answer: I'd go with Moss if all else is fine.

glemon
07-04-2014, 07:36 PM
I don't know the difference in the bushings, personally I would go with Rubber, as I recall the mount on the differential on the 4A IRS can crack as KVH has pointed out, the mounting points in the frame crack as well, even with the rubber it does not move around too much, but I would think rubber would cushion and help prevent cracks in either part better than polyurethane.

Poly is great for the rear trailing arm bushes, I would go there first if you haven't already, and get new rubber for the diff mounts if what you have is old or suspect.

Just my two cents, and I am sure others have their opinions as well.

cjimj
07-04-2014, 07:37 PM
Thanks, I posed the question to Moss on Thursday, however my contact had already left for the holiday.

And yes, the forward diff mounts were cracked, so they've been completely replaced with added gussets, plus I added reinforcement across the top, between the spring mounts. I'm doing a full frame off restoration, which included dipping the frame, so when I'm all done I should have a brand new, and improved, TR4A with most of the weaknesses addressed. My problem is not so much where to start or stop, but how not to throw money at it needlessly.

Jim

cjimj
07-04-2014, 07:53 PM
I don't know the difference in the bushings, personally I would go with Rubber, as I recall the mount on the differential on the 4A IRS can crack as KVH has pointed out, the mounting points in the frame crack as well, even with the rubber it does not move around too much, but I would think rubber would cushion and help prevent cracks in either part better than polyurethane.

Poly is great for the rear trailing arm bushes, I would go there first if you haven't already, and get new rubber for the diff mounts if what you have is old or suspect.

Just my two cents, and I am sure others have their opinions as well.

Interesting point about staying with rubber. After some thought, I think you may well be right. I do have new rubber I bought years ago (that's hopefully still good), but I was semi-blindly heading down the 'poly is new, poly must be better' path.

Thanks for the reality check,

Jim

JerryVV
07-04-2014, 10:55 PM
We all have opinions. I come from the rubber industry and had a little experience with dynamic applications. In my opinion you want some compliance in the diff mounts that rubber will give much better than the harder poly mounts. Poly mounts are good for suspension use if you want the best handling, rubber if you want a better ride. So that's my opinion based on selling the stuff for damping vibration and shock to components. I use rubber on my diff mounts and poly on my suspension mounts on my 4A.

cjimj
07-06-2014, 02:42 AM
After poking around some more, here's what I concluded about TR4A differential bushings for normal road use,

Stock rubber is appropriately compliant and costs 8 x $2.40 = $19.20.

No-name polyurethane has no perceptible compliance and costs just under $70. Given the weakness of the mounting structure this strikes me as a 'will fit' part that costs too much and carries too great a risk of future problems.

SuperPro looks to be the best, combining the rubber's compliance and the poly's durability, but for an overall cost of $172.80.

At under $20, rubber seems like the best choice to me.

Jim