Mazda MX5 rear suspension conversion Idea

[Boost All The Dollys]

Hi Guys, didn't know where to put this but here seemed about right.


my idea is to create a conversion kit for a dolomite to change the rear axle to an independent set up for all the usual improvements. the issue I have is space under the car.

the Mazda MX5 mk1 is the perfect donor car for this due to the double wishbone suspension and its wide availability and a wide after market for LSDs and adjustable suspension components. unfortunately, the axle is just a wee bit too wide.

after using Carfolio, I got the rear track measurement for the MX5 to be 1427mm, and I found the standard wheel size to be 14*5.5 ET45. in comparison, the dolomites rear track is 1290mm and a wheel size of 13*5.5 ET35. when calculated, it gives an axle (wheel mount face to wheel mount face) of 1517mm and 1360, a difference of 157mm, which is 78.5mm wider at either side.

wheel arch flares could cover this, at just over 3 inches, group 4 arches would be filled. the issue is that if you used sprint alloys, you'd probable have to space the front wheels out 78.5mm as well, and that doesn't sound safe.

also, there's an issue of mounting the whole thing. if the standard sub frame fits into the area where the old axle would be, it wouldn't be too difficult to create a intermediate frame to use the existing suspension holes under the sills along with a extra mount that could be welded to the underside of the car to provide a stronger mount.

if it doesn't fit, a better subframe could be constructed using box section and being fabricated in such a way that it would fit which may be hard/ impossible if the wishbones are too wide.

what do you guys think?

[soe8m]

Maybe this is some kind of shock to you but there is no such thing on the forum as motorsport register guy's and dolomite related guy's and wanted guy's.
Most of the guy's do read topics and posts in all the different sections here, not only one. So it is not needed to ask the same question over again in all the different sections because it's all the same guy's who read.

Jeroen

[Boost All The Dollys]

Maybe this is some kind of shock to you but there is no such thing on the forum as motorsport register guy's and dolomite related guy's and wanted guy's.
Most of the guy's do read topics and posts in all the different sections here, not only one. So it is not needed to ask the same question over again in all the different sections because it's all the same guy's who read.

Jeroen

Didn't think I'd posted this question in another part of the forum, don't think I asked it on any forum.

If your referring to my AWD dolly thread where I mentioned using an MX5 diff next to the engine, that's a different story, I was never planning on using an MX5 rear subframe for the rear suspension, just bits of the drive line for the front.

This is an idea that I thought it's best to ask much more experience in any modifications that's been done or thought of before.

[Carledo]

I could be wrong, but I don't think anyone has tried anything like this here. There was a guy selling a Dolomite on ebay a while back with some V6 or other in the front and a half completed Mercedes independent rear setup on it, don't know if it sold or what happened to it. I think our own DF has an independant setup in the works for his carbon fibre Dolly but that's not really a street car and he'll probably fabricate most of it!

But in the real world, it's too much agro to try and make something like that fit a car it wasn't designed for - and after all the hard work, the price of success will be a BIVA cos the shell has been messed about with!
I think it would almost be easier to fabricate something completely that will attach to the original mounts and carry your choice of suspension and diff and possibly fabbed shafts to keep the track inside the stock body.

Personally, I think it's too much work for too little gain - but it's your life.........

Steve

[Boost All The Dollys]

I could be wrong, but I don't think anyone has tried anything like this here. There was a guy selling a Dolomite on ebay a while back with some V6 or other in the front and a half completed Mercedes independent rear setup on it, don't know if it sold or what happened to it. I think our own DF has an independant setup in the works for his carbon fibre Dolly but that's not really a street car and he'll probably fabricate most of it!

But in the real world, it's too much agro to try and make something like that fit a car it wasn't designed for - and after all the hard work, the price of success will be a BIVA cos the shell has been messed about with!
I think it would almost be easier to fabricate something completely that will attach to the original mounts and carry your choice of suspension and diff and possibly fabbed shafts to keep the track inside the stock body.

Personally, I think it's too much work for too little gain - but it's your life.........

Steve

Cheers Carledo, it may be possible to do without lopping bits out of the floor plan, which is what I'm trying to do by recreating the chassis rails in an mx5 with box section and mounting it to the suspension mounts on either side and a welded mount rear of the axle

[sprint95m]

Your 1500TC has the same type of diff as the Spitfire/GT6/Vitesse range.
In the world of GT6s and Spitfires there are conversions to use such things as Subaru differentials,
but that is because folk use more powerful replacement engines resulting in destroyed standard differentials.


Dolomite Sprints all have a much stronger diff than this, one that is shared with the TR6. Your best option is to use one of these
which simply involves an axle change.


Without any modification to the body shell, off the shelf suspension components can be fitted to any Dolomite
to give very good handling and cornering.




Ian.

[Boost All The Dollys]

Your 1500TC has the same type of diff as the Spitfire/GT6/Vitesse range.
In the world of GT6s and Spitfires there are conversions to use such things as Subaru differentials,
but that is because folk use more powerful replacement engines resulting in destroyed standard differentials.


Dolomite Sprints all have a much stronger diff than this, one that is shared with the TR6. Your best option is to use one of these
which simply involves an axle change.


Without any modification to the body shell, off the shelf suspension components can be fitted to any Dolomite
to give very good handling and cornering.




Ian.

I was considering it more for the ability to tune the suspension to my liking, what ever that is, and it's handling when lowered, my 1500tc has been lowered down 1 inch and even now, can be snappy over bumps, I had it go sideways on me going over a catseye at 20mph in the wet. Plus, it would allow for possibly better rear brakes and then I can upgrade the fronts to suit

[marko]

i did lots of maths and investigation on Spitfire rear suspension and ended up with a Scooby LSD and homemade wishbones. Custom drive shafts and GT6 roto-flex uprights with enlarged bearings. in hindsight I'd use some MGF rear uprights with everything else fabricated around that so that the same wheels fit as well as all the mgf patterns, sports tyres are cheaper in the larger sizes, rear discs as standard and it has a remote family history link to BL/triumph.
I've got contact details for the spline cutting people as well as the cheaper propshaft makers if you need.

Good luck, mark.

[Boost All The Dollys]

i did lots of maths and investigation on Spitfire rear suspension and ended up with a Scooby LSD and homemade wishbones. Custom drive shafts and GT6 roto-flex uprights with enlarged bearings. in hindsight I'd use some MGF rear uprights with everything else fabricated around that so that the same wheels fit as well as all the mgf patterns, sports tyres are cheaper in the larger sizes, rear discs as standard and it has a remote family history link to BL/triumph.
I've got contact details for the spline cutting people as well as the cheaper propshaft makers if you need.

Good luck, mark.

I think I'll be ok, but thank you very much for offering, this is a letter in life project after I get my car sorted out. When I mention that it's too wide, it's only 7cm wider at the back, so still enough to go under group 4 arches. Plus, I just need to see if the area above the axle is wide enough, that's the only issue I have so far with it, I have all the dimensions for the Mx5 subframe.

[cliftyhanger]

This thread on CT may be useful, somebody grafting a MX5 subframe onto a herald chassis. He has narrowed the subframe, and intends changing the diff mounts.

http://club.triumph.org.uk/cgi-bin/foru ... 78026/s-0/

Unless you have similar skill levels to him, forget it! That bloke is a pro bodyshop man and really knows his stuff.

But on a dolly, unless you seriously chop the bodyshell about, you will have no chance of getting it in. Besides, live axles can work really well. Nobody complains about the way escorts handle in motorsport!

[cliftyhanger]

i did lots of maths and investigation on Spitfire rear suspension and ended up with a Scooby LSD and homemade wishbones. Custom drive shafts and GT6 roto-flex uprights with enlarged bearings. in hindsight I'd use some MGF rear uprights with everything else fabricated around that so that the same wheels fit as well as all the mgf patterns, sports tyres are cheaper in the larger sizes, rear discs as standard and it has a remote family history link to BL/triumph.
I've got contact details for the spline cutting people as well as the cheaper propshaft makers if you need.

Good luck, mark.

Marko, if you used the std scooby CV's and the metro/mgf outers (nick jones conversion?) you can use the std metro/rover 100 driveshafts. I have!
However, I am having issues with the new zealand pattern front mounting plate for the diff. Far too flexible, it was lifting 15mm and hitting the handbrake quadrant. (150ish BHP and a gearbox that copes easily may be partly to blame!) Temp bodge is a rubber bumpstop, but a better mount system is required. Later. Probably.

Sorry for thread drift....

[Boost All The Dollys]

[quote="cliftyhanger]
Sorry for thread drift....[/quote]

no bother, more info, the better.

I have my car in the air, next time I get time on it, ill measure up the rear axle mounting area and see if the MX5 subframe would fit

[Neil907]

Id be highly dubious about being able to do this as simply as you imagine.
For starters you would have to mount the diff differently to how it is mounted in the MX5 as the front of it is mounted to the backbone which is mounted to the gearbox.
I suspect you would also have to modify the shock top mountings as on both cars these are bolted to the body and not likely to be in the same place.
As for your rear mount to weld to the body, the shell behind the rear axle is not designed to take these sort of loads so would need reinforcing.
At the end of the day anything can be done but It will take a lot of work and your idea of a bolt on kit is probably not possible.
Neil

[Boost All The Dollys]

Id be highly dubious about being able to do this as simply as you imagine.
For starters you would have to mount the diff differently to how it is mounted in the MX5 as the front of it is mounted to the backbone which is mounted to the gearbox.

Could possibly fabricate a mount to attach it to the subframe structure I takes about mounting the suspension to

I suspect you would also have to modify the shock top mountings as on both cars these are bolted to the body and not likely to be in the same place.

As for your rear mount to weld to the body, the shell behind the rear axle is not designed to take these sort of loads so would need reinforcing.
At the end of the day anything can be done but It will take a lot of work and your idea of a bolt on kit is probably not possible.
Neil[/quote]


Would it be possible to add a strut tower brace and add a piece to create a mount point, like a strengthening base that's used for roll cage

[Toledo Man]

For starters, how about doing a "negative suspension jig thingy" like the Project Binky guys do? It would be the perfect base for such a subframe which would pick up on the existing mounting points on the Dolly and would save having to modify the shell.