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MG MGB Technical - Need help. MGB w/ Nissan 5 speed

I just bought a '72 GT with a Datsun 280Z gearbox. It has the original Lockheed master and a Z car slave cylinder. Problem is, the clutch fully disengages 2/3rd's of the way down on the pedal stroke and goes over-center after that; not to mention it's stiff as $%#@. Anyone have any idea what the easiest solution is to correct the ratio imbalance; change master or slave?
David

David
An MGB slave cylinder will work, but you will need to fabricate the right length rod from the cylinder to the clutch lever. The ratio of master cylinder diameter to slave cylinder diameter is the problem. The B slave cylinder is larger in diameter so it has less travel and is a lighter push. But, because of the less travel, it has to be adjusted with just the right length of rod. As the clutch wears that optimum length will vary.

If you want to take the trans out you can change the Datsun throwout bearing carrier to an earlier model that is shorter, or cut the bearing plate off the pressure plate or both (the throwout bearing will engage directly on the fingers). This will result in the throw of the master cylinder being less. It works fine that way on my car with mgb '67 clutch master cylinder and 1973 Datsun slave cylinder. The clutch is a little heavy, but works just fine.

Barry
Barry Parkinson

David, I have been selling & doing this 5 sp. & the 280 turbo, t-5 setup for 6,7 years & drive one every day. I tryed to use a B overdrive & after 3 gave up on me, I went to the Z 5sp. I use the std. B master cyl. & STOCK B SLAVE CYL. All I do to the slave is file out the holes that bolt the slave to match to the trans. bolt pattern. You will need to use allen bolts to hold the slave on for you can not use a std. bolts, thay will jam up when you try to tighten them. A real good conv. when done right.
Glenn Towery

David,

Can you tell which conversion you have? There are only two Nissan 5-speed conversions that I know of: Novus and Rivergate. I have a Novus kit on my 1800-five-main-converted Magnette, but on a previous Magnette I made the conversion with a Rivergate kit. With the Novus kit, I practically have to stand on the clutch pedal with both feet. There are other problems too. I'm in the process of redoing this car now, and you can bet the first thing I'm going to do is change out the kit from Novus to Rivergate.

If you believe you have a Rivergate kit (does the car use an MG starter or a Nissan starter?), by all means contact Bill Perry at Rivergate. They offer at least two different lengths of clutch lever rods. Their kit does use the Nissan slave with the original master, so even if this is not their kit, they will have the answer.

FWIW,
Allen
Allen Bacheldr

A side benefit to the 280z trans conversion is that the electronic sender from the late 1980's 300z will screw right on the 280 trans and allow you to use an electronic speedometer. VDO makes matching electronic speedo and tach that are just under 4" in diameter. In my '67 they look real good and work far better than the orig guages.
Barry
Barry Parkinson

Allen
Does the Rivergate backplate use the mgb starter? The backplate I used (I bought it a British car flea market in Dixon CA)uses the MGA starter bolted to the transmission and not to the back plate. I used an after market gear drive starter for the early (pre 68) mgb. I had to grind the (67) B starter flange and the back plate a bit and modify the starter bolt hole spacing to get it to fit the Z bellhousing.
With the modern gear drive starter and after-market rotation adjustment, I was able to rotate the starter motor right down next to the pan.
I used an early small diameter alloy flywheel which had the ring gear chamfer facing the rear. The new starter has no problem engaging the straight cut teeth on the front side of the ring gear.
Barry
Barry Parkinson

Barry,

The Rivergate kit uses the '68-80 MGB starter. Their kit includes a flywheel that is in between the diameter of the late B and the early ones originally mated to the three-synch boxes. Because the backplate is designed to incorporate the 18GB-18V rear mainseal, it will not work with a three-main 1800 or any of the 1500-1600 blocks. Either the late B starter or the gear reduction units designed to replace it will fit without modification, except the rotational adjustment on the gear reduction starter.

I'll know more about the Novus kit once I take mine apart. But it appears that the backplate is cut around the starter such that the Nissan starter bolts directly to the bell housing. The previous owner of this car kept a VERY detailed log and it seems apparent that this starter arrangement has been weak; the bell housing has been unable to withstand the torque of the starter. I believe the transmission case has had to be replaced twice due to this.

Judging by your description, I wonder if you have a Novus backplate. Since this backplate is designed to fit a Nissan starter, that would explain the modifications you had to make to fit your aftermarket MGB starter. This is another reason I'm going to redo mine with a Rivergate kit.

FWIW,
Allen
Allen Bachelder

I have used both set ups & rivergate is the way to go. I have used the Z slave & the clutch is a bit to hard to push, the B slave is real nice, like a stock O/E B cluch push. The flywheel you need is the 65-67 5 main bearing flywheel & it works with the 68-8- starter. The trans to use is a 79 to 82 280 & you can get a 90 deg. speedo cable drive, with the right count for your speedo. You will need to change the speedo cable end that threads onto the drive, for thay are different threads. Rivergate makes the best backing plate & there flyweel set up is much better & safer than the novis redrilled Z flywheel. Allen, we have a novis backing plats Z stater on a HIGH COMP. B with 50.K on it & the starter bolts have been no problem. You could Heicoil the case were the starter bolts go, this is what rivergate does with there starter bolt holes.
Glenn Towery

I think my backing plate was a copy as the bolt holes were slightly shifted.

I aligned the oil seal hole with the orig backing plate and elongated some of the holes to get the right fit. It then took a little jiggling on the installation to get the trans properly aligned, but once it was done it works well. The starter has about 5500 miles on it with lots of short runs and starts. So far there is no sign of any loosening or failure of the starter bolts.

An alternative would be to drill the bell housing starter bolt threads out completely and have a nut and bolt securing the starter, rather than a bolt into threads in the alloy trans housing.

The ratios are different on different year Z transmissions. The 81 -83 have a higher first gear (lower numeral, closer ratio) and more step up on the 5th gear. My tires are 195 55 15 which are about 5% under stock diameter. 3000 rpm is 70 mph in 5th. It is about 10% more overdrive than the mgb overdrive or the Sierra trans.

The MGB o'drive is nice but the 5sp has evenly spaced closer ratio gears (except 5th), is more reliable than the MGB trans, and about 50 lbs less than the overdrive. I've had both trans in my car and can speak from experience.
Barry Parkinson

Hi Glenn, Barry, and others,

Glenn, I definitely agree with you, having experience with both the Rivergate and the Novus. I have no experience with the Ford Sierra kits, but the Nissan transmissions are probably a better, more common, choice for North American owners. Regarding starter mounting, I'm just more secure with the starter bolts going through the backplate, rather than bolting directly to the bell. This way, the backplate absorbs the lateral starter stresses. I'm not sure the direct bell mounting can really hold the starter parallel to the ring gear.

Glenn, I have a high respect for your knowledge of such things, but my recollection is that Rivergate's flywheel diameter is a hybrid. I used an 18GB ('65-67) engine, and Rivergate still exchanged it rather than use it. Am I wrong about the size? Regarding angle drive and speedo cable, Bill Perry at Rivergate takes care of all the brain-work for you. I just told him my speedo cable thought it was looking at a 4.3 rear end, and it's actually looking at a 3.9. He did the rest. All I had to do is screw one end on the tranny and the other on the speedo.

I don't know the year of the Nissan box in my Novus Magnette. But the one I bought (rebuilt and guaranteed by Rivergate) is a '79. I think I remember that Rivergate uses a Nissan slave, but the hydraulic hose provided matches threads on the Magnette MC. Mine was the first Rivergate Magnette conversion done. The finished product was oh so smooth. On the Magnette there is no tach, so I don't know what kind of revs I was doing but it couldn't have been more than 3000 at 70 mph. I know from my Bs that I get edgy and nervous listening to a B block revving at more than 3500, yet I could cruise the 18GB/Rivergate/Nissan Magnette with a 3.9 rear end at 75+ (emphasis on the "+") for whole days without feeling any stress at all. In fact, the problem was keeping this car under 80 mph. (The Navigator, you know...)

Happy New Year!

Allen
Allen Bachelder

I meant that Rivergate exchanged the flywheel - not the engine!
Allen

I have 20-25 280Z conv. that I have done & I have used the 65-67 5 main fly. onn them all! As far as the Ford set up, it cost too much hear in the U.S.A., with all the Z trans. sitting around.
Glenn Towery

For my conversion I used an alloy flywheel for the 5 main bearing pre '68 engine. It fits the bell housing and the starter (after market gear drive for a '67) mounts,(with some mods) fits, and engages nicely.

I haven't seen the backing plate which uses the back plate for starter support, but the version I'm using seems fine to me.

Barry
Barry Parkinson

Glenn and Barry,

I'm not about to argue anything to do with MG mechanics with Glenn Towery! Clearly, I'll take your word for it. I suspect the reason why Bill Perry exchanged my flywheel is because he probably resurfaces them and puts new ring gears on them. ' Sorry, I was confused about that. And Barry, the backplate in question is the one sold in the Rivergate kit. I have a picture of mine assembled to the engine with the starter mounted; all ready for the transmission to be bolted up. In the big picture, I have no idea whether this is a better arrangement or not. I just thought it looked more rugged to me, given the problems that my Novus car has been through. I hope yours lasts forever, and Happy New Year to all!

FWIW,
Allen
Allen

Allen
It's my understanding Rivergate machines the late flywheel down to the diameter of the early flywheel and then mounts the early ring gear.

If you are planning to go alloy - just buy the pre 68 alloy flywheel. If you have access to a pre-68 five main bearing flywheel, just use that flywheel. The clutch disk is the same diameter with either flywheel.

Barry
Barry Parkinson

Allen
Looking at photos you emailed me, your backplate is 1/ thicker and 2/ mounts the starter on the backplate, rather than the bell housing. The gap between the flywheel ring gear teeth and the starter cog appears to be about 1/2" in your photo. I had to put a a 1/16" shim in to keep the starter cog from dragging on the ring gear.

The greater distance will also affect the travel of the throwout bearing. I used the short early model throw out bearing AND cut off the bearing face on the pressure plate. In hindsight I think I didn't need to cut off the pressure plate bearing face. However it works very well the way I did it. (The pressure plate bearing face is needed for the carbon throwout bearing-the Datsun throwout bearing is a roller bearing) Either the short throwout bearing carrier, or cutting off the face on the pressure plate is adequate. With the thicker backplate there is more room for the clutch to release and either approach would certainly work. with the MGB slave cylinder there is less travel and the clearances would be more critical than with the Datsun slave cylinder.
The Datsun slave cylinder hose fitting is slightly smaller than the MGB slave hose fitting. It is easy to drill out and tap the Datsun slave cylinder to fit the MGB hose fitting.
Barry
Barry Parkinson

Thanks, Barry. The Rivergate kit uses a Nissan clutch disc inside an MG clutch cover. Their instructions call for cutting off the plate bearing face. It uses the Nissan throw-out bearing and SC, with an adaptor hose running all the way to the MGB MC. I think Bill Perry offers either the long or short throw-out bearing, suggesting that the pedal effort will be less with the longer.

I guess the conclusion to be drawn from all this is that if one can find a suitable backplate, the rest can be quite easily fabricated without any kit. Although we haven't discussed tranny mounts and crossmembers yet. For my Magnette, I took the old transmission, mount, and crossmember to Rivergate's shop and they fabricated a new crossmember while I waited. I walked out of the shop with it and it fit perfectly. But having watched them do it, I'd have to say it didn't look like rocket science. Oh but then, there's the pivot bearing... To me, it's still worth quite a bit to get a box of parts guaranteed to work. Especially when they do.

Allen
Allen

Thanks for all the replies. I have an early Novus conversion with Nissan starter. Rich Wasman built the car about 12 years ago (it was a very fast turbo back then) and he had a hard time with the poorly made backing plate. Several holes were misaligned as was the seal opening. I believe he went through a couple of plates before he received one that could be made to work.

Guess I'll take Glenn's and Barry's advice and go with the 'B slave.
David

David
Maybe I got one of Rich Wasman's rejected back plates. It took a little doing but it works fine now.
Barry
Barry Parkinson

The previous owner of my GT just dropped off a load of spares (he went Corvette after 25 years of MGB; he still has other Brit cars.) In the collection is a spare Datsun 5 speed. How dow I determine what car it came from?
David

The last Datsun 2000 in the early 70's had a 5 speed available. It is more likely a 260z - 280z trans. There is a lot of stuff on those trans, ratios etc. If you google search the web you can probably figure it out.

You could also take it down to a shop or dismantling yard that has a trans out and compare.

Barry
Barry Parkinson

Thanks Barry.
David

This thread was discussed between 29/12/2005 and 09/01/2006

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