What's different about this Cosworth diff mount?

Post by **anglin** » Fri Mar 17, 2006 9:54 am

vcallaway wrote:replacing the diff mount with a solid one and not doing the other bushings is asking for trouble. The beam bushings and trailing arm bushings all have give in them. If they are old and the diff mount is solid you have placed a tremendous amount of stress on those mount points. Busting a diff case is not high on my things I want to do list.

Personally, I would only use a solid diff mount combined with a solid beam bushing. And only for racing.

Vince, you are spot on. This is why there is a set of solid beam mounts to go with the mcÂ²racing solid differential mount. The solid beam mounts are incredibly labor intensive to create and I think Grayson has gone through 3 prototypes of the design and still isn't happy with it. He has the fit into the beam and the chassis correct, but the assembly of the components in a manner that is both perfect for the application and not too complex is difficult to come by. There are poorer ways to accomplish the task, but remember that we race with these components, so putting a crappy setup together just isn't going to fly with us.

Here's a link to the solid diff mount. The solid beam mount page hasn't been posted yet.

http://www.mc2racing.com/products/xr4ti ... index.html

Post by **Grayson** » Fri Mar 17, 2006 12:38 pm

Just to alleviate any confusion that may exist, here are my thoughts.

1.) Using a polyurethane diff mount:

This mount duplicates the functionality of the Ford Group N differential mount, which was intended for rally use. To make this mount, Ford simply poured stiffer rubber into the EXACT same molds they used to make the stock diff mount. Why? Because it saves them money. We don't have bean counters at mcÂ²racing, so we designed the mount with perfection in mind. That is why the polyurethane mount is lighter, cheaper, better-looking, and has replaceable bushings. Of course, our mount costs us MUCH more to make.

I never recommend using the polyurethane diff mount with stock rubber beam mount bushings. At the very least polyurethane should be used there. As for the STA bushings, the softer those are, the smaller the forces are on the diff mount. Therefore, it is just fine to use stock STA bushings with a polyurethane diff mount.

2.) Using a solid aluminum diff mount:

This mount duplicates the functionality of the Ford Group A differential COVER, which integrates the "diff mount" with the diff cover in one solid piece. Thou shalt not install this mount without solid aluminum beam mount bushings. Again, the STA bushings that are used have nothing to do with anything.

3.) Recommended rear bushing setups:

Street and light race cars
Polyurethane diff mount
Polyurethane beam mount bushings
Nylon STA bushings
Polyurethane sway bar bushings

Dedicated race cars
Solid diff mount
Solid aluminum beam mount bushings
Nylon STA bushings
Solid sway bar bushings (which do not exist)

By the way, for the record, I have two solid aluminum beam mount bushing designs that I am ecstatic about. They're perfect designs, but they are excrutiating to make. I'm happy with the bushings when they are finished, but I don't like the price tag I have to stick on them.

Grayson
http://www.mc2racing.com

[email protected] · Post by **[email protected]** » Fri Mar 17, 2006 6:34 pm

I don't want to take away from the awesome service MC2Racing is providing so thanks a ton! Great products. I bought a fare amount of their hardware to complete my rear end overhaul.

That said I wanted to share that I made my own solid diff mount out of the stock unit. It seems like a rather solid design. I won't be posting a picture as my welding is horrendous.

To do this I made a template and cut up the backing plate from two diff mounts. This is a decent gauge steel that you could get anywhere. Cleaning the excess rubber away to get a good weld and cutting the steel plates to fit was all that was entailed. If I had to do it again I'd buy MC2Racing's! But it's done and seems to be holding up well.

The diff is even closer than stock to the floor pan now causing more rubbing so I had to clearance the drive shaft and haulsee adapter even more with a big pry bar. Using a jack stand on the floor board was not effective.

The car now vibrates on decel at 70mph instead of 60 so at least I can cruise at a decent speed until I swap in the world class t-5 and align the tranny properly.

Freejack · Post by **Freejack** » Fri Mar 17, 2006 7:16 pm

Why is the diff closer to the floor pan than before? I would think it should be the other way around?

Jake

Black94 5.0 · Post by **Black94 5.0** » Fri Mar 17, 2006 10:11 pm

demonfire wrote:just to bump this back up --

i just finally installed the rear diff mount from MC2Racing since i put my merkur back on the road yesterday.

it was quite possibly the easiest mod i've done to my car. i've never done one, and it took me less than 45 minutes total. the fitment is perfect, the quality is amazing. anyone considering this piece -- you wont be disappointed. my car is awaiting a full suspension transplant soon, and even with the OEM completely worn bushings, soft springs, and dampers that are cushy, it feels better.

Yeah, I'm completely satified with my MC2 diff mount...I have the the stock soft rubber bushings and the car is completely different after the install(for the better)...I highly recommend the MC2 diff mount, not to kiss ass or boost their sales

, but as an essential part that the XR4 is missing....Hopefully I'll be buying some MC2 nylon rack bushings soon, as I'm replacing the rack and I might as well do them while I'm in there...I installed aluminum rack bushings in my Stang and I hope to get the same kind of advatage with these....

[email protected] · Post by **[email protected]** » Sun Mar 19, 2006 3:15 pm

My guess is the stock one let's the diff sag since the weight of the entire rear subframe is hanging by this?

Does MC2racing account for sag? In other words how does it locate the dif compared to stock?

Post by **Grayson** » Mon Mar 20, 2006 12:30 pm

Does MC2racing account for sag?

Yes. We based our design off of a 100% brand new Group N differential mount. After installing the mcÂ²racing mount the space between the diff and the chassis will increase, curing any sag issues that previously existed.

Grayson
http://www.mc2racing.com

Post by **John Brennan** » Mon Mar 20, 2006 3:47 pm

So if one has a two-piece D/S, then an alignment check of the CSB would be advised, yes?

MerkXRTurbo · Post by **MerkXRTurbo** » Mon Mar 20, 2006 4:01 pm

Yes, that is a frequent cause of early guibo failure, and the sole cause of poly guibo failure.

Post by **Grayson** » Mon Mar 20, 2006 4:41 pm

So if one has a two-piece D/S, then an alignment check of the CSB would be advised, yes?

Actually, no. If you envision a line passing through the crankshaft, through the input shaft, and through the output shaft, and then extend that line to the CSB, the line should pass EXACTLY through the center of the CSB. If the gearbox mount sags, for example, then the line would not pass through the center of the CSB, it would pass below it. The one thing that the CSB has nothing to do with if the differential.

Theoretically, as long as you have your drivetrain aligned properly, then replacing the diff mount with a new one can only cure problems, not cause them.

If you have a one-piece driveshaft, and you angled your engine+gearbox to match the pinion angle of the diff while a sagging diff mount was in use, THEN you will have to realign your drivetrain. If this is the case, shame on you for aligning your drivetrain while your car was equipped with a sagging diff mount.

Post by **John Brennan** » Mon Mar 20, 2006 4:50 pm

Thanks for clearing that up. I thought it would be worth discussing.

Post by **DPDISXR4Ti** » Mon Mar 20, 2006 5:20 pm

Grayson wrote:If you have a one-piece driveshaft, and you angled your engine+gearbox to match the pinion angle of the diff while a sagging diff mount was in use, THEN you will have to realign your drivetrain. If this is the case, shame on you for aligning your drivetrain while your car was equipped with a sagging diff mount.

What if you tried to align your driveshaft with a tired mount, but found that something other than "book optimal" produced better results?

I ask this question somewhat tongue-in-cheek, but it is what I went through several years ago. Eventually, I just gave up and went with trial & error until I got the least vibration.

Later on, when I upgraded to an AL shaft, I really found that it didn't matter much where things were. When I put the new motor in two years ago with new motor mounts, I never even bothered to check angles - just slapped it in and called it done.

BTW, just to be clear, I don't at all mean to suggest that a new diff mount is not a good idea.