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MG MGB GT V8 Factory Originals Technical - Lowering a RB MGB

I have a '77 MGB which I have tried to lower using rear aluminum spacing blocks and early GT front springs. It does sit lower but the back end seems to flex more than it should without the lowering blocks. How are the rear springs in a RB car different from those in a CB car? I seem to remember it was something to do with the rear shackles but can't quite recall. Also, I am thinking about lowering the front by using a CB front crossmember and modifying the rack mounts to accept the RB steering rack. Any suggestions/comments on how I should go about it?
thanks
Jake

Jake

I have a 74 1/2 RB MGB. I rolled this car in 1990 and while replacing the broken front end parts, I inadvertently replaced the front coil springs with CB coils. This gave the car a raked look. Eventually I had the rear springs re-arched to suite, this only cost $90cdn.
I now sit between 14” and 14-1/8”on all 4 corners. The big difference I notice is a lot less body roll in the corners.
Here are a couple links regarding lowering suspensions and the ride height
http://www.mgcars.org.uk/cgi-bin/gen5?runprog=mgoc&p=emg/may97b.html
http://www.mgbmga.com./tech/mgb14b.htm

Bruce
Bruce Mills

Jake,

The rear spring shackles in the CB car mount direct through the crossmember (through which is welded a stiffening tube). This takes care of around an inch an a half. The front spring attachment location is also higher by around an inch and a half. (I have just compared and measured the difference between the two).

Any remaining difference would be in the spring shape.

Let me know if you want a photo and I will take one and email it to you.

Sounds like I will be doing the same or similar as I am tranferring CB gear into a replacement RB shell.

Regards,

Dom
Dom

I have lowered 3 cars using lowering blocks in the rear & have not experienced what you describe. If anything, the rear is a bit stiff using RB springs. If you have too much flex, check the U bolts to see if they are tight. I suggest replacing the rubber bushings & spring pads with poly parts from the mail order sources.

Using the early crossmember is the correct way to lower the front & still maintain suspension travel.
Jim Stuart

Jake,

I lowered my RB V8 conversion by using 480 lb. springs (part #AHT21) in the front and "reverse-loop" springs in the rear. I can try to find a part number for these if you're interested. Haven't seen them advertised much but my local supplier can get them.

I've got the car down to 26" front and back measured at the top of the body strip where the chrome strip attaches to. I can't give you the measurements at the wheel arch as I've attached Sebring fenders.

I tried the lowering blocks at first but they didn't lower enough and just didn't seem right having them in there.

The AHT21's will (supposedly) lower a RB car to 35cm or about 13 3/4" measured at the front wheel arch. Based on Bruce's measurement, looks like he's got the standard (up to 1972) CB springs (348 lbs.) which the graph says should be 36.5cm (14.3"). The post-73 springs are rated at 372 lbs at 37cm (14.5"). Part numbers are: AHH6451 & BHH1225 respectively.

There is three more lowered springs but they're listed as: Road/Lowered, Road/Sprint and Race. Might be a bit much for daily driving.

HTH
Simon
Simon Austin

Thanks for the info on the front springs, I currently have AHH 5789 (pre-'72 BGT's) for the front springs, they offer the smallest lengths both free and compressed, but cause the A arms to have a negative camber which in turn pulls the bottom of the wheel in when they pivot upward, plus the tie rods are not horizontal. I personally don't like that and have thought about some neg camber A arms but that still leaves the travel of the suspension alot shorter than I would like and the tie rod situation. I think I will pursue the CB crossmember modification with the 2 u joint approach in the rack and as for the rear, Ill check the U bolts and the rubber pieces to make sure all is in order there and if that doesn't fix it, Ill see about reprofiling the rear springs or fitting some CB rear springs.
Dom,
Thanks for the picture offer, if you wouldnt mind sending them, Id be happy to get them.

Thanks again everyone for the help.
Jake

Jake - one can get very bored by continually grounding - have you thought of the cost of mufflers ?
Of course one can lower successfully but looking back most of us were so pleased to have a little more clearance.

There are passable alternatives.

Bruce - you must be one of the unlucky ones. While folk were rolling TRs like cigarettes before breakfast, the MG got a reputation for sticking to the road. Glad you survived. Many of the TR folk didn't !

RMW

FWIW - I lowered a RB car the 'long' way by going back to CB specs.

See "Lowering a RB MGB" in the MGB General board.

I did not realise that Jake had double posted at the time :(


Cheers
Ian F
Ian Fraser

Jake,

I'll send some photos tomorrow (I never got around to taking them today sorry).

Ian,
Having just read your other reply, I am impressed! Due to the access difficulty to the rear spring hanger drilling location I had all but given up this idea. How did you drill the hole? WRT the front end did you ever consider modifying CB steering shaft etc to avoid the need to modify the xmember?

Regards,

Dom
Dom

Hi Dom

Shackle Mounts

I was able to cut the gusset and remove the spacer tube in one piece using a 10mm cut off wheel in an angle grinder, Plus hammer and cold chisels etc.

I put a small pilot hole in the centre of the dimples in the chassis frame using an angle drive on the end of an electric drill, and then went to about 12mm (the largest drill that would fit in the angle drive chuck)

I then used a tungsten carbide cutter (as normally used in a die grinder) clamped in the end of an extension section (the type that is normally used as an extension when drilling through wood with a flat bit)

I slid a length of aluminium tube over the extension, and then clamped the end of the extension in my drill.

Then by threading the cutter and shaft through the bumber mounting hole at the back of the rear guard, and holding the aluminium tube in one hand and the electric drill in the other, I was able to guide the cutter and enlarge the hole to fit the spacer tube.

Since then, I have got a die grinder, and after spending a couple of days going round second hand tool places to get the angle drive, discovered that the local hire tool place has a Makita right angle drive drill for hire that would have made drilling these holes a cinch. But that is always the way.

Access for welding is difficult, even with the car on a spit. I would not recommend that this conversion be attempted from underneath the car.


Steering

You may be aware of this - , but I'll go through it anyway.
The RB cars have a shorter steering column and a longer pinion shaft than the CB cars, and also a smaller universal. This is a 'one size fits most' measure, in that it works ok on the B series engine, and clears the rear of the exhaust manifold on the V8's. The steering ratio on a RB car is also lower.

Things that did not change was the angle the pinion shaft makes with the rack, and the centre line position of the steering column.

So in order for a RB pinion shaft to meet a RB steering column, the steering box has to be mounted on a slight skew. (passengers side forward) Although odd, this skew does not affect the suspension bump/droop steering geometery to a great extent, although Ackerman angles are not correct at full lock. (at full lock you are in a carpark anyway, or verging on being out of control at high speed anyway, so a degree or 2 don't matter.)

To use a CB rack in a RB car, either the RB steering column needs to be lengthened, or the CB pinion shaft needs to be lengthened. Not an impossible task, however in NZ this sort of work needs to have a design certificate from a registered mechanical engineer, and if welding work is needed, then a certified welder and appropriate heat treatment is required. The whole process needs to be certified by a 'certifier' who is approved by the Land Transport Safter Authority.

Its far easier to shorten the RB pinion shaft, and adapt the mounts. (Certification is still required, but the requirements for this sort of work are not as onerous as work in steering components themselves)

Cheers
ian F
Ian Fraser

Hi Jake- There is a gent in UK offering a 1 inch vertically lowered Swivel soas to keep the full range turning geometry correct. As we all know, it is partially compromised using the shorter spring. Sorry, can't remember the URL, think it was in a tech article by the "Autoist". My suspicion is they be expensive! Vic
vem myers

This thread was discussed between 17/01/2005 and 27/01/2005

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