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MG MGB GT V8 Factory Originals Technical - datsun rear independant suspension

Anyone know about this? I was speaking to someone today who says that there was a 1600 datsun with a independant wishbone style rear suspension held in with four bolts. The utility had a ratio of around 3.5, so he says.
Peter

Peter, sounds like the rear suspension on what was the 510 sedan here in the states. Mounted on a subframe which had 4 large isolated mounts. The differential assembly was about the size of that used on a midget, no more that about a 6.5" ring gear at best. Ok for a small 4 or perhaps V6, but I wouldn't use one behind a V8. The diff from the 240Z was similar but a bit larger. There are lots of IRS assemblies now that look promising, check the SUVs using the V8s such as Lexus and Toyota.
Bill Young

Bill, the Lexus diff is cast iron and weighs as much as a whole live axle (well, almost).

The IRS Datsun 260/280Z would be lighter, although it has an unaturally long 'nose' you need to deal with.

FWIW, the Fiberfab Jamaicans built on Fiberfab chassis for V8s used a Corvette diff mated to Corvair rear suspension and axles......
Bill Spohn

Isn't the Corvette diff a Dana44? The late Corvair suspension was good but avoid the early swing axles. The newer mini SUV's might be worth looking at. I'm converting a T-Bird IRS (Lincoln Mark 8 has posi and aluminum housing) but it is very involved the way I'm doing it. Justin has one that uses the same components but done differently. Neither would be THE choice though. And of course there is the ever popular Jag.

Jim
Jim Blackwood

I still like the looks of the Mazda Miata IRS. It is a bolt in sub assembly in a cage. Sports disc brakes and torsen rears are readily available. The ratios are a bit on the high side though with 4.1 and 4.3 I think some early ones had a 3.9 and there is rumour that a lower gearset can be had from Mazdaspeed in the 3.5 range. Also, in turbo miatas and V8 converted Miatas, folks are using the center from the TurboII RX7 without much trouble. The stock rear can hold 200 to 220 rwhp without too much abuse, the TurboII rear is stronger and good for 250+ hp at the rear wheels. The built V* conversions use a T-Bird center and custom halfshafts.

A lightly worked V6 with a V8 box, 16 inch wheels, and a 4.3 rear isn't the worst idea:

74 MPH at 2600 rpm in 5th gear
47 in 4th
35 in 3rd
24 in 2nd
16 in 1st

Now if only I ever get around to it.

Regards,

Brian C.

world's slowest restoration and V6 conversion guaranteed!
Brian Corrigan

The dif in the 510 was, IIRC, an R160. I've been told by a compadre that races 5q10's that the r180 from a 240-260-280Zm, and the R200 from subbies is a bolt in
greg fast

I had a Datsun 510 at one point and the car handled great. The IRS setup was very compact but the u-joints are small and won't hold up to any torque. I replaced several sets as a result of hard driving with a 1.6L engine.
Jim Miller

Peter, Yes the Datsun 1600 did have IRS and a simple four bolt fixing.
There was a sedan , ute and wagon (rare here) version available but the sedan was the most popular.
It was an alternative to the usual Ford Escorts and did reasonably well in rallies and track motorsport. It even had a class victory at Bathurst way back as I recall and still does well in club level activities.

Fundamentally a sound and reliable vehicle but getting a little old these days especially regarding spares and so on.
Personally I would be looking down the options list mentioned above...the 240 / 260 / 280 Z and C series as well as some of the newer "softroaders" out there now.

The 510 was the US designation.

Cheers , Pete.


Peter Thomas

Yeah, the hot swap for 510's is to put a Subaru IRS setup in place. There really good looking units and can stand up to a fair amount of power (whatever the STI is putting out these days).
I also see a lot of Toyota RAV4's and Honda (whatever there smallest SUV is) that seem to have neet looking rear IRS setups in there 4x4 models. They look pretty lightweight, just about the right scale for an MGB, not over built or under built for what a B chasis could handle.
Bill Mertz

You know, it occurs to me that there is a point in modification, past which you are so far from original that you might as well have started with a different starting point as it might get you a superior end product.

If you want an MGB with a V8 and IRS, who is to say that the easiest and best way to do it wouldn't be to stick a Ford V8 into a Miata (a well known and documented swap) and then spend you time stripping off the outer panels on the Miata and replacing them with MGB panels (might as well go fiberglass where you can).

Hmmm...wheelbase MGB = 91"
Wheelbase (late) Miata = 91.7"
Bill Spohn

PS - but if you were going to all that trouble, it would make sense to use the much more attractive MGA body instead...;-)
Bill Spohn

I agree with Bill on that one, although if people want to do the engineering just for the sake of it, why not.
I was never big on an IRS MGB (already have a lotus elan) but I thought about converting to coil springs with trailing arms and a panhard rod or a triangle like Alfas use.
-Bill
Bill Mertz

"If you want an MGB with a V8 and IRS, who is to say that the easiest and best way to do it wouldn't be to stick a Ford V8 into a Miata (a well known and documented swap) and then spend you time stripping off the outer panels on the Miata and replacing them with MGB panels"

Way ahead of you, Bill. I have already mentioned here that I like the handling of my dad's Miata SE so much that I might have to bond MGB panels to side of a Miata & install a Rover V8. Btw, the Miata SE is parked in the garage right next to his original owner 1963 MGB. Mom's Honda is in the driveway.

Carl Floyd

The Jag uses the Dana 44, as well.

These guys can custom build an IRS any way you want it, including using the 9" Ford third member:

http://www.cwiinc.com/index.html
Carl Floyd

Bill,

Not a bad idea, but Miata doesn't have a hard top cousin, so re-work the GT just because I can (or at least I think I can). Really just for the fun of doing it, and making it work right!


BTW, Isn't there a company out there making a composite chasis for the MGA that uses supra suspension bits... damn beautiful car the MGA is.

Cheers,

Brian C.
72 BGT
90 Miata
00 A8
Brian Corrigan


Hey guys... have a look at this: http://www.britishv8.org/MG/ToddBudde.htm

You'll have to scroll down for IRS pictures and notes. A more detailed write-up has been promised and is expected soon! (This preliminary write-up was just put online tonight.)
Curtis

Now THAT is what I'm looking for. A pair of wishbones can be got, adapted or built easily enough and a diff' cage made up to locate the arms. It's the half shafts etc that is the expensive/hard bit. This implies that the 280Zx either has the same track width as MGB's, or those arms are trailing. Is this a limited slip diff?, what is the ratio?
Does anyone else know anything about this?
Peter

Rear track on a Datsun 280 ZX is given as 54.3 inches and the usspension is a "Chapman Strut" according to the info I managed to find on Google.
No idea of the ratio though.

HTH , Pete.
Peter Thomas

Thanks Pete.
MGB is 50.25.
Incidentally how is track measured?, from the centre of the tyre?
Displacing the diff' forward 2.8 inches would pull the wheels infar enough, but would this work or wear out in no time? I'm inclined (no pun intended) to believe that it would make no difference. Upward or forward displacement should all be the same. Any engineers reading? Might be good for weight distribution. (There's a 3.7 limited slip version of the diff' which sounds a bit RV8'ish). Price is good (low) and they appear unbreakable.
You couldn't use the existing suspension set up but the datsun wishbones (or similiar) could be adapted to a custom centre cage. Or rather the cage made/adaped to the premanufactured other parts. It is after all just a steel square with some strategically located boltholes. Use shimming for alighnment, arduous, but a one of. Struts to the forward spring hangers to feed force into the car. Bolt up the the back of the boot.
Peter

Peter,
Track should be measured from tyre centre to tyre centre.

Cheers , Pete.


Peter Thomas

Guys, if you REALLY want to spend money and end up with an IRS car (that goes about as well as a non-IRS car) look at the whole Miata assembly.

A friend is about to use the whole assembly bolted into a kit car and it lends itself to that sort of thing.

Look up Lo-Cost and you'll see lots of stuff on these - usually hooked to either the Miata engine or a 3.4 GM V6

You must of course fabricate suitable rigid mounting for the diff and suspension.
Bill Spohn

I don't like the loss of the battery boxes nor modifications to the fuel tank and feel quite certain the job can be done without it. Also offsetting the diff to the front or rear to compensate for too long halfshafts is really not a good idea. For a small offset the angles might work but to get 2" would require an extreme angle and life and behavior are sure to suffer. Shortening the halfshafts is a better solution even if the strength suffers a little.

Jim
Jim Blackwood

I still like my Ford based IRS, just wish I could get it welded in! Yes, I had to lose the fuel tank, and yes I've had to move the battery box (while figuring out how to weld this thing in) but when I'm done it should be sweet!

I think I've said that for 2 years now... LOL
Justin

Yes, I don't want to lose the batterybox area either and don't see why you would need to. I've still got dreams of putting twin petrol tanks there and living the dream of generations of MGB owners. Having an empty boot (trunk).
Now wouldn't that be an attractive package. A bolt in limited slip IRS rear that includes twin petrol tanks, plus a swing down thing on the back of the diff cage for holding your spare to the bottom of the boot.
.. dream on.. dream on...
Peter

IIRC Nissan used two positions on the 240-280Z, not ZX cars. There was an offset of two inches for-aft- don't remember much more about it
greg fast

?
peter

Peter-

I'm assuming the question mark was in response to my comment, which was directed to Blackwoods comment on offseting the diff front to rear to accomodate axle length.
greg fast

No, thanks anyway Greg. There was a new thread concerning datsun IRS which was raising much the same questions and ? was to stop it dropping off into the archives before the "new thread" orrigionator could read Jim's and Peters remarks about CV strength and track width. And of course your own, and every one elses invaluable contributions!
Peter

Greg,

Are you the Greg Fast originally from California. If you are I'd like to ask you some questions about your V8 conversion as there are similarities to mine. You may reply offline. Thanks,

David
David Cousins

You guys check out the "hot rod" catalogues too..like "Speedy's" or such. There are several fresh made IRS systems out there for different applications even some small light T bucket cars, and most are similar to the Jag XKE types, and made to bolt up or weld on easily. Yes the Datsun 510 sedan IRS was held on by 4 BIG bolts only...I doubt that there would be anything under a B to which to bolt it though. Also it had the same "tuck under" nature as the Corvair earlys and old VW bugs, and the racers are severely limited in travel and run negative camber, to keep things in place...like the rear of the car.
The Miata type with double A arms is the best now.
Wayne Hardy

IRS, is not a bad thing when well engineered.
The Nissan type was design to have lots of squat during accelaration, this would prevent the wheel hop during braking, this system is a comprimise and not the best solution.
An IRS was mainly use for better quality ride. The Miata or the C4 (late C4's) Corvettes perhaps have the best design for all around purpose. When use for racing it only has about 1/2" travel or less, it's almost like a straigh axle. The Miata offers a nice combination of A arms and has a great control on anti squat and wheel hop during braking, to make this suspension work it needs high rate springs plus other things. I had a E prepare Miata and own a Lt4 Corvette
with some pieces from Gulstrand.
A straight axle with a well engineer multi link works great for all type of use. The roll steer can be adjusted. The solid axle can have negative caster and the toe can also be adjusted. This is a common operation in Trans Am and other cars such as NASCAR.

IRS rrequires a multituded of adjustments to work properly and is not an easy job to get it correctly set up, specially when tranfering an IRS from another car to the B.

The track is measured from the face of the mounting face, from the face of the drum to drum, the B with steel wheels is 52" the wire wheel is 50"

If I was going to do an IRS I would copy the Miata and keep it light.
Weight is an important factor in the suspension.

One of the best solid axle suspension is the one on the new Ford Mustangs.

Next is the multi link (4 bar) with the right geometry roll steer can be control, anti squat, anti dive etc.

I ma not saying that the IRS woiulkd not work on the B, what I am saying is that it would take lots of work and someone with experience to do it correcltly.
Bill Guzman

It would indeed be a lot of work, and the pay-off isn't worth it.

I raced a TVR which is basically a sports racing car with uneven length A arms front and rear. On a smooth track the advantage over my MGA race car was negligible. On a rough track it was better.

If you are going to be driving 10/10ths on the street, it might be worth it, but if you do that, you'll be in jail pretty quick any way......
Bill Spohn

Bill,

You been under Steve Carrick's car? This is what I was scheming on several years ago. Didn't build it, Steve did. Three link, live axle, perfect for MGB.
Carl Floyd


The track measurement is always measured tyre centre to tyre centre at ground level according to the SAE.

This is to take into account wheel offsets which are left out of the equation when drum face to drum face measurements are quoted.

Cheers , Pete.
Peter Thomas

Peter, We in the USA use drum to drum and then add the offset for type of brake, such as disc offset etc that is what the machine shop ask me everytime I take a rear axle to be cut to fit the MGB

They ask for drum to drum, stock brakes or disck brakes and if disc brakes are going to be use, whos kit etc. I am sure you are correct.

Carl, yes a 3 link (4link counting the panhard bar)is good that is what the Ford Mustang has. A bit tricky to build, but GOOD!
Yes Carl I saw it last year, nice.

I prefer the 4 link no panhard bar. Even as simple as the multi link is, it requires a bit of engineering to get it right, you can get to much oversteer or not enough anti dive etc. The nice part is that the multi link bars can act as axle locator and roll center can be built in to it.

You are correct Bill. not to long ago on a TV show call Dream car Garage, they build a C3 Corvette for vintage racing, the suspension guy said "To bad we can't install a solid axle in this car" or "The best next thing it would be a solid axle" something like that.
That statement is valid.
Bill Guzman

Carl - I run a 3 link and Panhard on my MGA race car as well.

Could go to 4 link and convert to coil-overs but they don't like that sort of thing in vintage racing......
Bill Spohn

I have an IRS in the works, but for only one reason, comfort. When it comes to ride quality the single largest factor to consider is unsprung weight and this is dictated by simple physics. So far as I am aware nobody has yet found a way around that. So all other things being equal, which they very seldom are, the lightest wheel assembly is going to give the best ride. I do not feel it is necessary to sacrifice handling in the process, but it certainly *is* necessary to to have proper suspension geometry. I have taken a rather basic approach to that problem by deciding initially to retain the geometry of the donor car, but more on that in a bit.

In reducing unsprung weight, everything that can be moved inboard will make a difference. And while it seems pointless to me to use old technology such as the Jag IRS, still it was a design ahead of it's time and a very good one. It can be improved on however, in several ways. I understand the brakes were difficult to service. Modern rear disc designs allow you to remove one bolt, pivot the caliper free, back the piston off with an allen wrench, and you're practically done. But my biggest concern is their use of the axle shaft as a suspension component. Sure it works well, but if the universal joint lets go the wheel collapses under the car, immobilizing it and more importantly making it uncontrollable. A top link eliminates that problem but has to fit under the bodywork. Finally, although I speak from ignorance here, never having actually weighed one, the hub carrier looks rather massive and could probably be lighter, and dual shocks and springs should not be necessary, adding complexity and expense. Aside from that I think it is an excellent unit.

But automotive development has not stood still for the last 40 years and more, and some of the current IRS designs function exceptionally well, exhibiting very refined handling characteristics and good control during accelleration. Please remember that if we are retaining the qualities of the MGB that we liked in the first place, accelleration did not have that much to do with it so maybe we can tolerate slightly less than stellar performance there if handling and ride are exceptional. But we may not have to make too much of a compromise there either, sometimes you just get lucky. For instance, up to now I have run a stock MGB rear axle with stock gears and an open differential. Yet my car has always performed as if it had a limited slip axle, at least on dry pavement. On hard accelleration it lays down two patches, pretty much identical to each other and it always has, both before and after replacing the axle that I finally wore out after 17 years of abuse behind high performance V8's. Why I don't know, other than just the characteristics of the overall package but I suspect it could be duplicated. And I also suspect that more than is expected could be had from the current crop of IRS setups available on production cars. Modern sedans have quite good accelleration characteristics and handle very well. In trading weight for horsepower we are stressing them no more and possibly quite a bit less than their designed application so their performance should not change very much. We can't expect quite the same ride qualities as we have less spring weight, but what we can do in some cases is reduce the unsprung weight even further by moving the brakes inboard and sometimes by using lighter components.

In my specific example I chose a T-Bird IRS. This system is the same as a Lincoln Mark 8 but the Mark has posi and an aluminum diff housing and so would be a better choice. It may have better gears as well. This is a very beefy system for the MG but can be lightened significantly, and one very useful feature is the stamped steel top link arm which can be made to fit under the MGB bodywork with about the same clearance as the Jag IRS. By making new hub carriers I expect to be able to not only move the brakes inboard but retain the original suspension geometry as well, simply moving the inner mounting points inboard enough to narrow the track the needed amount. In this process the lower suspension arm which is cast iron will also be replaced with a lighter tubing unit having the same attachment points, reducing unsprung weight even further. It will be a couple more years before I am able to complete this system, but I expect good performance from it and an exceptional ride. To me, that is enough to make it worthwhile, and I will be taking notes this time in case it becomes popular.

In the meantime I plan to learn a bit more about rear suspension geometry so if any of you could direct me to some good links that would be most helpful. I'd like to know the effects of moving the mount points inward primarily, but also need to bone up on how to control the roll center and a few other things mostly having to do with accelleration and braking.

Jim
Jim Blackwood

As far as top/bottom wishbone length ratio goes I'd go as close to the front ratio as possible.
Peter

This thread was discussed between 19/05/2006 and 23/06/2006

MG MGB GT V8 Factory Originals Technical index

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