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MG MGB GT V8 Factory Originals Technical - Steering Rack Swap Questions

Q. Apart from the gearing ratio, what is the difference between the chrome & rubber bumper "B" steering racks, ie. if a put a rubber rack on the chrome bumper xmember, where will the new column be in relation to the original chrome bumper one (lower/higher, shorter/longer etc.

Q. Are the internals swappable? to give a chrome bumper rack the easier gearing of the later type.

Q. Better still, has anyone come up with an after-market powered steering unit, that keeps the original geometry and does not involve cutting your mounts.

Q. Are the powered steering units off Grey Import Japanese MGRV8ís the same mounts and geometry. Obviously these MGR racks were originally sourced from the UK, does anyone know who supplied or manufactured them for Rover.


Nick Smallwood

At the very least, the RB rack's column is longer.
Apparently, that was done to put the U-joint nearly inside the footwell. That allows more room for the V8s exhaust.
But not for the room gained, I would've never gone through the effort to convert my '71 GT when I put in the Buick V6.
I believe that there is a difference at the XMBR mounts as well. Or so I've read here.
But if you're innovative enough, you can accomplish anything!
Randy Forbes

I just looked up the part number for the housing in the dealer catalogue that covers the early MGBs including the V8 and found only one number for both. Therefore, it appears, only the rack and pinion are different in the complete units. It certainly looks as if you mounted the later rack and pinion unit on the early cross member, the shaft would follow the same path as before, but would continue another five or six inches. The pinion shaft is much longer to reach farther back to the u-joint which is mounted on a column that is two inches shorter, to also reach farther forward to clear the longer V8 and lower an inch to account for the built-in spacers on the cross member.

I was surprised how much easier the rubber bumper MGBs are to steer than the chrome bumper MGBs. Still, if you are planning this conversion on a four cylinder MGB just to ease the steering effort, you should test drive one first. Itís not as effortless as power steering, but I feel it more than half way there.
George Champion

Thanks George & Randy
looks like I can use the rubber rack to lighten my steering if I have the column shortened and re-splined.

I have 235mm tyres on the front and I consider my present car chrome bumber GT with 165mm tyres too much like hard work.

Nick Smallwood

Nick, I think you'll find it a lot cheaper to have the shaft shortened by chopping out a section of the shaft.About 2.25" from memory, then having the two remaining pieces dowel jointed together with an interference fit of about 1.5 thou. then finally weld them.I don't know about Solihull, but in Sydney splining means big bickies. Barrie E


Q1: Isupoose that the internals are swappable but by the time that you have changed both the rack and pinion assembly you arent left with much.apart from the body tube and diecastings. Remeber that not only the pinion shaft is longer but that the r/bumper X member rack mounts are different-longer and higher to compensate for the X member being spaced down from the chassis rails. Putting a r-bumber rack on the c/b mounts results in the shaft pointing upward and it is way too long.You will have to change the angle of the mounts-I didmine by cutting them off and rewelding them-others on this bbs have used tapered shims andslotted rack mounting holes-dodgy in my opinion but you have to see for yourself-go throught the archive on this BBS.

Jap Rv8s did not have PAS -I believe that Roger Parker was investigating this for a project-imy opinion the 2.9 rack is perfectly light with propoerly set up suspension but it's your choice.


John Bourke

(Must go -I'm iin God's Country borrowing BobPs machine.............)
Thomas Hardy

I agree having the shaft shortened may be an easier route, I have an excellent engineer locally.

I will get hold of a RB rack and do a direct comparison. I assumed the alloy cast mountings were the same, so only a shaft shortening was required.

Thanks for your input.

Nick Smallwood

I believe Barrie has the right idea re dowel shortening the pinion shaft. Just assure your engineer has a lathe and dosn't just chop and eyeball it. I had my shaft dowel shortened and it is within 3 thou" of dead straight. Good deep chamfering for a stout weld and a carefull clean up and it's even hard to see the join. About 15 min labour as I recall. I used a cb x-member and frigged with changing the rack mounts on it to accomplish similar geometry of the cb set up with the recessed uj at the column end per rb cars. Very time consuming, but I've been led to believe that nothing handles like the cb car. The interesting thing is that I used the pinion shaft from a supposed '76 and the rack from my '71 and ended up with the '71 high gearing (a bit twitchy at speed perhaps, but it'll keep me awake on the highway). The gear splines of all parts were identicle regardless of rb/cb. When exactly did the ratios change? It obviously was after the intro of the rb car at least on n/a models.

You must have aquired a later shaft with early gearing, maybe an early/changeover model. The teeth numbers have to be different, to effect the ratio.

Anyone have the answer to this puzzle?

Nick Smallwood

I'm not quite sure what the question is but I think that the answer might be like this:

62-74 CB rack 2.9 turns short pinion continuous round groove around joint splines

74-76 RB rack 2.9 turns long pinion single flat on joint splines-interchangeable with OE V8 rack

73-76 OE V8 rack 2.9 turns long pinion continuous groove around joint splines

76-80 RB rack-3.5 turns long pinion single flat on joint splines

Also to be found are:

Supra manufactured racks from the early 90's on with are 3.5 turns in both long and short shaft configurations-Moss cheapening things up again.Recog nise these by the simplified castings and no 'CAM Gears' script.

I don't know about the new Argentinian made racks.....


John Bourke
John Bourke

Thanks John,

Just the info I was looking for.

Nick Smallwood

Nick...BL used a standoff on the rubber cross member to get it farther away from frame rail & achieve higher ride...thus the longer pinion shaft..take that standoff away & you have a chrome cross member...rubber rack will fit on a chrome cross member but because cross member is closer to frame rail the pinion shaft is higher in the car than where the firewall hole is...can make shaft align with the opening in the firewall by tilting it a little (believe you shave .003 off rack mounting flanges to tilt pinion shaft downward to align w/hole in firewall)..if the rack's ratio is the same, short or long shaft will fit either rack...
Anthony Barnhill

to put the rubber rack on the cb xmember you must mount the rack higher and further forward to 1) accomadate the longer steering shaft; and 2) line the tie rods up to parallel with the lower A arms so you don't get "bump steer". 5/8" od box channel tubing on top of the cb mounts works just fine. the channel extensions tilt down so the height comes out at just about stock.
Barry Parkinson

This thread was discussed between 01/07/2000 and 15/07/2000

MG MGB GT V8 Factory Originals Technical index

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