Diff Mount Problem. Having A Bad Day. Help Needed

[GregTas]

My car when bought didn't have a diff fitted or a front diff mount. I decided to make the front mount. Race car only so I went solid aluminium. From pics on the web I'd looked at I wrongly thought the front mount bolts were all in a line.

 

So I machined up my mount and was quite pleased with it. I went to fit it and It was only then I realised that I had a problem.       

 

Could someone please help me out and tell me how far the front diff mount holes are ahead of the centre crossmember hole.

 

Now it's also possible I have the rear hanger in back to front. I have the flat plate forward so the diff sits further forward. Is this correct?

 

 

Problem

 

 

 

 

 

Edited April 21, 2018 by GregTas

[Riceburner]

This was the style I previously ran Greg. Not sure on dimensions or scales though. To me your diff position looks correct.

[dat2kman]

Your moustache bar ( rear hanger) is correct.

You,ll need to remake your ally front mount, with more ffset.

Shame you have'nt got a cruddy old mount you can coppy.

[GregTas]

This was the style I previously ran Greg. Not sure on dimensions or scales though. To me your diff position looks correct.

 

Yeah that looks nice. A bit more elegant than mine.

 

Your moustache bar ( rear hanger) is correct.

You,ll need to remake your ally front mount, with more ffset.

Shame you have'nt got a cruddy old mount you can coppy.

 

Thanks on the moustache bar.

 

It is a pity I didn't have an old mount. I could now measure how far the diff sits forward from my holes but the rear bar flexes a bit which is why I thought the actual dimensions would be better.

Edited April 21, 2018 by GregTas

[600Z]

Just remember both uni’s have to run through the same angle but opposite so they cancel each other out or you will get vibrations.

[GregTas]

Yep. I'm running RB25. I've tried to get gearbox inclination and driff flange on same angle as best I can. I worked out 25mm diff mount was a good height. So used 25mm thick block for it. I'll see how it goes.

Edited April 21, 2018 by GregTas

[260DET]

Just to be difficult there is no way in the world that I would use solid mounts, that parts like the diff a stressed member which they were never designed to be. There is at least one soft mounted design around that you could fabricate, even use the stock mount with a steel hoop around the diff with adjustable bumper rubbers works.

[smugley]

Hi Greg

My Tarmac car uses a piece of solid plastic/rubber block bolted between the diff and cross member .

It's dimensions are 23mm thick 140mm wide and 90mm deep .

Worth a try as it works on my car .

Cheers Doug

[dat2kman]

Sold mount diffs are fine.

The rubber mounts that factory fit are purely to reduce NVH

The stupid rubber band was an afterthought, as the front rubber mount will tear, due to torque reaction

Rear bar, being spring steel, will fatigue, sually at the stud holes in centre.

AZC se a CNC item, as a replacement for the crack prone rear mount bar.

Prior to AZC many rally prepped cars ftted fabricated bracing between diff studs and body hangers.

[GregTas]

Hi Greg

My Tarmac car uses a piece of solid plastic/rubber block bolted between the diff and cross member .

It's dimensions are 23mm thick 140mm wide and 90mm deep .

Worth a try as it works on my car .

Cheers Doug

 

Doug, that's interesting. I could do that but I would have to chase some material if I was to go that way. What held the diff down to the crossmember? I'm thinking the long bolts go through the crossmember to hold it down.

Edited April 22, 2018 by GregTas

[smugley]

Hi Greg

Yes correct the bolts hold it to the cross member through the frt two holes in the diff housing . I can take a picture of it in position if you need one .

Cheers Doug

[GregTas]

Thanks on the photo Doug, but no need. Looking at my photo I can see they would go through that front seam that extends forward.

 

I could  even be crude and do one like yours with a block of wood. I could get shot down for saying that, but I'm sure would work fine. Just need to make sure the grain runs across the car.

[260DET]

The R200 diff on the project Z31 is solid mounted but all four bolts on the front are used plus there is a torque stay. If a diff is solid mounted it should have extra support because it is not designed to be a structural member, cracking around bolt holes can result too because of the extra shock and lack of some give. The more power the more support required. But I'm a fussy bugger who likes to build well and forget.

[GregTas]

Don't you worry I'm very fussy too, but all I need for now is that bolt offset dimension I was chasing.

[Riceburner]

Keep an eye on the front cross member hole with the solid mount, mine had mushroomed quite a bit with a few small fatigue cracks. I only had a stock rear bar with used rubbers allowing it to torque left to right on the central retaining bolt.

 

The Stuart Wilkins Motorsport captive mount is awesome and 100% fail safe. 

 

Steer clear of the ron tyler mount, The Siddons team 240z snapped one in a corner! Pic attached from there facebook feed.

[GregTas]

I had seen those mounts and wondered about them.

 

With it bolted down from below the way I was doing it the only week point is the load around the single bolt. I'm sure it would crack there after a while.

 

I could do my mount the way Doug did with the two bolts through the diff going all the way through the bottom crossmember and also beef up the crossmember. It would never break then, but  the R180 is really just to get me going. I'll probably go R200 SN with locker, but that will take quiet a bit of fabrication on my part and the car still need quite a few other things done on it so my focus for now is to get the car going.

Edited April 22, 2018 by GregTas

[smugley]

Hi Greg

Here's the pick anyway

Edited April 22, 2018 by smugley

[GregTas]

Hi Greg

Here's the pick anyway

 

Thanks. That picture is interesting because your two diff bolts go right through the middle of the cross member, like I thought mien would, Yet with my diff the diff bolt holes are hanging out the front. Is you diff siting further back?

[smugley]

Mine is a R200 in a 12/71 complied shell

Yours is a early Vin # car that might have the forward mounted diff from the factory ??

[GregTas]

My car is 741. I don't know if that is early enough for a fwd diff or not. Perhaps I can use my ally mount and a different mustache bar?

 

Does anyone have any personal experience on the original mounts and know what one looked like for a car about the same age as mine?