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MG MGB Technical - Lots of questions all in one post

Hi All

Got the engine and transmission out of the B GT this weekend. Also got the rear suspension referbished with all new rubber, new hubs for the new chrome wires and front end out for a full rebuild this week.

Question one.

How have the tubless dayton chrome wire rims been holding up? One of my club members running tubless wires on his 38 Hot Rod has had a lot of leakage and is now back to running tubes. Prior to fitting the tires, I would like to know how others have been finding the Dayton tubless?

Question two

I have a driveshaft I purchased off ebay that was sold as out of a 75 MGB. When comparing it to the shaft I took out, they are identical in length and have the same part number. Can anyone tell me what number is on the later MGB driveshaft? Mine is AHH7487 This is on both the one out of my 67 B GT (regular 4 speed 3 syncro transmission -- we are adding an OD transmission) and the one I bought on e-bay.

Question Three

Any good recommendations on fitting the rebuilt front end? Any tricks to get it aligned correctly. I don;t have that pointed aligning tool that the shop manual shows.

Question Four


I noted that my heater drain bulb (Tims Knob?) Is hard and not allowing but a drip of water out. Any reason not to cut it?
Bruce Cunha

Bruce,

I have been running a set of 72 spoke Dayton tubeless chrome wires on a '71 roadster for at least five years without even a hint of problems.

Mack
A Sneed

Hey Mack, thanks for the tip, that is an excellent road thru the valley there from the picnic today. Got thru there in no time to Pigeon forge.


Bruce,
As long as those nipples are sealed in the rims there should be no leakage.

The early trannies up to 68 had a different length driveshaft for the od verses the non od. Are you installing an original early 3 synchro od transmission? Or the later 4 synchro with od?

You should be able to check fit the steering column to the steering rack column without the pointers. However, for accuracy, a machinist with a lathe and a drill can make these for a minimal cost.

Cut off the end of the bulb.

Mark
MWhitt

' Think I remember reading somewhere that while there are two driveshaft lengths, the difference was about 3/8" and in fact, any driveshaft will work with any combination of 3-sync, or 4-sync with or without either of the overdrives.

Can somebody confirm? Deny?

Allen
Allen Bachelder

Bruce,

The reason that the bulb has hardened is that over a period of time debris has built up inside the buld as dust and dirt and small animals etc. have gotten wet and accumulated there and dried out and simply hardened. Try squeezing the bulb several times from different sides to break up the hardened accumulation (Bassically a hardened mud ball) and it will start falling out and eventually be all cleaned out again. I had to do this to mine.

Cheers - Dennis
Dennis & Pat Rainey

Allen,

The early 3 syncro conversion requires a new, longer driveshaft. Original, non-o/d driveshaft is waaay too short for comfort when converting.

Other combos of conversion may in fact not need a different driveshaft, but earliest conversions do for certain.

Paul
Paul Hanley

I just cut the knob off my drain tube, no problems with it anymore.
LuvMyMG.

I have a 3 syncro non-od in the car now and will be adding the nonsync D Type OD. From what I have read, there were two different driveshafts for the non-od and the od D type. But the later MGB used a single lenght which is the same as the D type OD drive shaft.

Must e some other difference, I would think you could get 3/8 inch expansion from the front yoke.

Those of you that have done the D type conversion, what did you do?

Thanks Mack

Ok, will run them tubless and see how it goes.
Bruce Cunha

Always thought the the battery position was partly to do with weight distribution. Low down, behind the driver but infront of the rear wheels with two batteries the placement couldn't be much better in terms of that.

Chris.
Chris Currah

Bruce: I did the conversion to a D type OD this summer on my '64 and indeed, I needed to change the driveshaft. The shorter (30") driveshaft was used for the early banjo axle cars, which I had, and the longer (31.125") used for the early tube axle cars, up to #138400, according to Moss. From #138400 a 32" driveshaft was used. I suspect what you have are the later versions. I used one of the 31.125" versions and it worked perfectly. Also, just a note - on my car the crossmember supporting the gearbox used a different combination of holes in the side rails (further forward), although the holes were there. I would suggest at least chasing the threads of all the holes before you start to bolt up the crossmember. It is much easier to do with everything out of your way.

Good luck,

Don
don scott

Bruce,

BGT's only used 2 different props (driveshafts). The BGT only ever had the tube axle that was used until the end, so don't worry about the early banjo axle issues. The 3 sync NON OD box uses the same prop as all the 4sync boxes, whether OD or non OD. The odd one out is the 3 sync OD, which is 2.4cm longer. So you will need to get hold of this prop.

You will also need to get a different speedo, or have your non OD speedo converted.

I have just bought a 3 sync OD box to do this converson on my 67 BGT, but I was lucky and have been able to get the prop and speedo at the same time. I have not been able to get the vacuum cut out switch, and these seem ridiculously expensive second hand and are NA new. I am planning to run without this. What are you doing regarding this? Have you managed to get a switch, or a new substitue?

Cheers
Iain

67 BGT
I D Cameron

Bruce,
Here is a link to an article I wrote several years ago about adding an OD to various year B's.

http://www.custompistols.com/cars/articles/ts_od_gearbox.htm

HTH - Tom
Tom Sotomayor

Ok, Thanks Tom and Iain.

So looks like the OD D type is the only box with a different drive shaft. Ok, so I need to find one of those. Anyone have one?

Iain.

I was able to get the vacuum switch on e-bay. Did not pay as much as others, but it was not inexpensive. From what I understand, you can run without it. Others that are running without it may be able to add some tips.

Bruce Cunha

I am interested in Don's comment that he used the 31.125" shaft instead of the 32" Given the shaft can expand, what are the risks of using the slightly shorter drive shaft and expanding it?

I know MOSS lists the longer as available, but I would rather not spend extra money if I can.
Bruce Cunha

Bruce,
The only time you may have a problem is with the rear suspension fully extended. After installing the trans jack up the car and let the rear suspension drop until the rebound straps are tight. Offer up the drive shaft and see how much "extra" extension you have available in the driveshaft.

If there isn't enough you've got three choices:
1. Buy the correct driveshaft.
2. Have a driveshaft shop lengthen and rebalance your existing one.
3. Make up a spacer plate and use longer bolts to connect.

Good luck.
Tom

BTW - You won't need a different speedo since you are putting a D type OD in a Mark I car. The OD speedo and the non/od used the same TPM (turns per mile). The OD speedos did carry a different part/serial number but functionally they are the same.
Tom Sotomayor

"The OD speedo and the non/od used the same TPM (turns per mile)."

Not according to information from a repairer in the UK. For Mk1 cars the Jaeger non-OD was 1060 tpm and OD was 1040 tpm. For the Smiths non-OD was 1040 tpm and the OD 1020 tpm. It was after that on Mk11 cars that the non-OD and OD tpms became the same at 1280, until rubber bumper cars when they were the same at 1000 tpm.
Paul Hunt 2

I was told the same as Paul. Hence why I have got hold of the speedo from the same car as the OD unit. Don't know if that is correct. I am picking them up on Sat so should be able to tell you after that!

Iain
67 BGT
I D Cameron

Oops - my bad. You guys are right, I was thinking of post 67 cars.

Even if you don't swap speedos, the induced error is only about 2%. That's something you could easily live with.

Tom
Tom Sotomayor

Found the correct drive shaft. One of our club members had a spare.

I have been looking for the MK1 OD speedo. Last one on E-bay went for around $100. Change is not that great. If I note it is off significantly, it is simple enough to make a decal for the glass face that will give me a corected speed.

With the new computer programs out, most graphics shops can do a decal up in a matter of minutes.
Bruce Cunha

Bruce,

' Sorry I was wrong about the driveshaft lengths. But in this thread, I learned something that I will need to know soon as I'm about to convert my 3-synch '65 B to D type O/D. However, I had a similar problem on a 5-speed conversion on my Magnette. I took a spare rear drive flange to a machine shop and had them make up a one-inch spacer. I suspect one could be made even thicker than that. This spacer works great. But since you have the correct length, that's even better yet.

Putting a decal on your speedo face is a nice way to correct your speed readings, but it won't fix your odometer. During the winter uneMGeeable months send your speedo to Nissongers and tell them which transmission you're using. They'll calibrate it correctly for you.

FWIW,
Allen
Allen Bachelder

Hi Allen. Great idea. Since I am not running stock tires (slightly smaller than original) this will also increase the error. I noted on my trip to Gattlinberg that I am off one tenth of a mile for every 5 miles.

Will give Nissongers a try.
Bruce Cunha

Picked up my box for the swap. Also got 2 propshafts and the correct speedo for an extra £20 ($35), so happy with that. Will take the box up to a friends that has a lot of experience with 4 sync boxes and have hime look it over for wear. I suspect there is some. If I pull the input shaft up and down I can feel some movement. Is this normal?

Cheers
Iain
I D Cameron

This thread was discussed between 02/10/2006 and 10/10/2006

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