Steering, Suspension, & Brakes

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kmcrae
kevin McRae
Dorset, England
(19 posts)

Registered:
08/22/2009 09:33AM

Main British Car:
1978 MGB GT Rover 3.9 V8

V8 axle/ rear suspension
Posted by: kmcrae
Date: November 25, 2009 04:00PM

Just rebuilt a V8 axle that is destined for my rubber bumper v8 conversion. The car still has the original 1800 axle fitted which has the anti roll bar mounted on it. The V8 axle does not have this facility on it at the moment. Should I cut this off and re-weld this on to the V8 axle?
I am looking at lowering the car to chrome bumper height and using gas dampers with poly bushes, would i be better fitting a pan hard rod to improve the rear end or keep /(up-rate) the ARB?

Has any body any advice on which springs to use, could i keep the existing ones and use lowering blocks, is there any benefit from using up-rated or V8 springs.


Moderator
Curtis Jacobson
Portland Oregon
(4411 posts)

Registered:
10/12/2007 02:16AM

Main British Car:
71 MGBGT, Buick 215

authors avatar
Re: V8 axle/ rear suspension
Posted by: Moderator
Date: November 25, 2009 04:18PM

Opinions will vary... but if I were you I probably would transfer the anti-roll bar mounts and reinstall the original bar PLUS I would also add a Panhard rod. The two devices serve two different purposes. Will your new axle have a limited slip differential? Will you be uprating the front anti-roll bar? If you answered yes to either of those two questions, the rear anti-roll bar will be especially helpful. The GT already has slightly more tendency to roll than a roadster, just due to weighing more and to having its center of mass slightly higher, so rear anti-roll bars are more helpful on a GT.

As for springs, I would not uprate to V8 rear springs. In fact, one of these days I plan to replace my GT springs with roadster springs. The only reason you would want a higher spring rate in the rear would be so you can carry more luggage, and my days of carrying heavy luggage are way behind me. Besides spring rate, the original "V8" springs had an extra leaf so perhaps they provide a little better resistance to tramp - but if that's a big concern for you, you'd do better to address it with anti-tramp bars (or one of the alternative linkage arrangements.) Softer springs will help with grip and will help reduce unsprung weight which in turn improves ride quality and handling,


kmcrae
kevin McRae
Dorset, England
(19 posts)

Registered:
08/22/2009 09:33AM

Main British Car:
1978 MGB GT Rover 3.9 V8

Re: V8 axle/ rear suspension
Posted by: kmcrae
Date: November 27, 2009 11:55AM

Thanks for the advise, I should clarify a bit more. The car will be converted to chrome bumper look which will save on the rubber bumpers weight. The front will be up-rated to lower springs, Spax and poly bushes and up-rated ARB. I am not looking at fitting a LSD for the moment as I will be putting a tame Rover V8 in it say up to 230BHP. But will see how it goes as I am a long way off from this.

I thought the reason the late rubber bumper cars had the rear ARB was due to height and weight of the bumpers

Thatís good news on the springs then, just need the lowering blocks now.


castlesid
Kevin Jackson
Sidcup UK
(361 posts)

Registered:
11/18/2007 10:38AM

Main British Car:
1975 MGB GT Rover V8 4.35L

Re: V8 axle/ rear suspension
Posted by: castlesid
Date: December 05, 2009 08:15AM

Kevin,

When I got my 75GT it had the Moss Hopkinson handling kit fitted with the rear anti roll bar and the rear ride height was still 16.1/2" the car was lethal especially in the wet.

As part of the suspension upgrades I REMOVED the rear anti roll bar and fitted the Moss MGS 40721 reverse spring eye rear springs which lower the rear 2" these are much flatter and have a spring rate of 110lb.I retained the original Monroe telescopic dampers, part of the original conversion which have proved to be very compatable with the new springs.

The springs also imrove the axle location by reducing lateral movement and for a road car a panhard rod is unnecessary.

I retained the metalistic front bushes and used blue poly bushes for the rear shackles.

I was also considering fitting modified anti tramp bars but at the moment this has not proved necessary even though I have approx 265+BHP and 300 lb/ft of torque.

The difference in ride,handling and grip is almost unbelieveable, it rides like a modern car and the traction is extremely good even in the wet as proved when I took Pete Mantell for a drive a couple of weeks ago in pouring rain, Pete was amazed that there was no wheel spin even with a bootful of throttle.

If you fit these springs you will not need lowering blocks which are a bad idea with a V8 as this increases the torque reaction on the axle and causes axle tramp.

Do not be tempted to use any of the other standard cheaper leaf springs or the parabolics which are on offer, they are nowhere near as good.

Re the front end, if you are talking about the Spax telecopic conversion that fit to the rear of the wishbone I would again not recommend it, all the reports that come back say that the spax are too stiff and the comprimised mounting method is not a good idea either.

Much better to get a pair of properly rebuilt lever arm dampers, 500lb lowering springs and a 7/8" antiroll bar, a MGB handles better with a relatively stiff front end and a compliant rear.

Appereciate Curtis has a different opinion but can only speak from personal experience.

Regards,

Kevin Jackson.


Bruce Mills
Bruce Mills
Vancouver Canada
(71 posts)

Registered:
11/28/2007 09:31PM

Main British Car:
1974.5 MGB Roadster 3.5 Rover

authors avatar
Re: V8 axle/ rear suspension
Posted by: Bruce Mills
Date: December 05, 2009 09:48AM

Kevin

I went a slightly different route with my 74.5 X RB. Polyurethane bushings through out, CB spring up front with sway bar.
On the rear I have stayed with the stock rear end no sway bar and had the rear springs re-arched. This lowered the car to pretty well CB height. (I don't know why more people don't do this rather than buy the new 'too high' rear springs)
This winter I am converting over to Monroe shocks as advised by some of the guys on this BBS [forum.britishv8.org]
My engine is a Rover 3.5 with perhaps 200 or so HP. I have never had a problem with axle tramp.
Hope it helps

Bruce


kmcrae
kevin McRae
Dorset, England
(19 posts)

Registered:
08/22/2009 09:33AM

Main British Car:
1978 MGB GT Rover 3.9 V8

Re: V8 axle/ rear suspension
Posted by: kmcrae
Date: January 07, 2010 03:21PM

Gents,

Thanks for the advice, I think I will go for the new springs Kevin mentioned. Did the 2" springs do the job Kevin? I do not want to cause problems for the exhaust, but the drop appeals to me. I was a bit sceptical about the blocks so this does sound the best option.

The consensus seems to remove the ARB, I have been looking at the Panhard options on the forum, Curtis you have done a good job on yours even with the mention of the boot strengthening! Think I will start a new thread on this shortly.

I have bought a full set of ploy bushes as I destroyed the original metalastic ones with a blow torch, dam rusted bolts! I had to resort to the angle grinder to get the bolts off, the same for the rear ARB.

Its good news to know that I do not need the tramp bars.

I have seen that the Front Spax option is not that good now looking at the other threads, may look at the Moss coil over option or the up-rated dampers but need to get the rear done first.

Regards,

Kevin


Bill Young
Bill Young
Kansas City, MO
(1337 posts)

Registered:
10/23/2007 09:23AM

Main British Car:
'73 MG Midget V6 , '59 MGA I6 2.8 GM, 4.0 Jeep

authors avatar
Re: V8 axle/ rear suspension
Posted by: Bill Young
Date: January 07, 2010 04:02PM

Kevin, while I doubt it you'd want to use a rear anti roll bar I think I'd go ahead and transfer the mounts anyway, at least that gives you an option for the future if you decide to take in some track days and find that you need to increase the oversteer a bit to balance out a large front bar. I think you'll find the original bar too heavy in the rear, but the mounts will serve for smaller bars as well with different bushings.



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