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BRITISH AUTOMOTIVE |
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www.mgbmga.com MGTD Articles |
Technical Information (MGB 1)
NON-SYNCHRO TO ALL-SYNCHRO TRANS
CONVERSION
Last Modified - 01/09/00
MGB 1965-1967
This article deals with the conversion of your non-synchro to all-synchro trans, with or without overdrive, and is applicable to 1965 through 1967 roadsters and 1966 through 1967 MGBGT models fitted with 18GBUH engines. I believe the following list of required components and recommendations will be of guidance:
Engine
Engine back plate and gaskets 18GF onwards (1968 onwards). Rear main oil seal and retainer, flywheel assembly, 18GF through 18V 801/802 (from 18V883 onwards, flywheels had only one locating dowel hole, should you use this flywheel, it will then be necessary to drill an additional hole), flywheel locktab, new clutch cover & disc, crankshaft bushing, starter motor (1968 onwards), top loading oil filter housing with spin on oil filter (Moss oil filter conversion kit P/N 235-940 will not fit when using this starter motor), oil filter housing center bolt 1/2" x 3" USS and center bolt copper washer. Hardware required as follows: 5-5/16" x 2-3/4" SAE bolts, 2-5/16" x 3" SAE bolts, 6-5/16" lockwashers, 1-5/16" shakeproof washer, 7-5/16" SAE nuts, 1-3/8" x 1" SAE bolt, 1-3/8" x 1 1/2" SAE socket head cap screw, 2-3/8" lockwasher and 2-3/8" SAE nut.
Information to retain your original flywheel and bendix style starter motor is as follows:
Attach the engine backplate to the replacement all synchromesh transmission. Drill and tap the upper starter-mounting hole to 3/8" USS (use 3/8" X 1.3/4" bolt with lockwasher).
To accommodate the OEM starter motor bendix, cut at least a 2.5" OD hole in the transmission housing. A hole saw should be adequate for the job. We prefer to use the MGA starter motor with its' smaller bendix, use a 2.125" hole saw for this.
Using a 3/8" drill bit, drill a lower starter motor mounting bolt relief indent hole in the transmission flange to a depth of 1/4".
Remove the engine backplate and helicoil the original bottom starter mounting bolt hole to 3/8" USS (the existing hole is conveniently sized). Use a 3/8" X 1" USS bolt with lockwasher.
Transmission
All synchro trans with or without overdrive (with top fill 1968 through 1974 or side fill 1974 1/2 onwards), gear lever and components 1968 through 1976 including shift knob, retaining plate, 3 special bolts & washers, anti-rattle bushing, plunger & spring, clutch release bearing with clips, clutch release arm pin & bush.
Overdrive
Overdrive isolation switch with adjustment washers (adjust switch to operate in 3rd & 4th gear only, 1977 onwards overdrive only operated in 4th gear. This was achieved by the installation of a micro-switch attached to the selector mechanism, disregard this switch and rewire accordingly). See Tech information on "Alternate Wiring Diagrams".
Transmission Mounting
The existing transmission crossmember assembly may be used with new mounts. However, your original restraint assembly can not be used. We have manufactured a restraint kit, which can be fitted to your existing crossmember and transmission unit. In the event of a front-end collision, or an emergency stop, the fitting of this kit will prevent the radiator fan from burying itself into the radiator. Instead you may wish to install the left hand and right hand engine restraint brackets as found on 68-74 MGBs.Yet another option would be to fit the 74 MGB onwards crossmember assembly, complete with: all brackets, mounts, bushes, buffer pads, engine restraint rod, spacers and front exhaust strap.
Driveshafts
Use Moss P/N 268-080, 30 1/4" length with BANJO rear axles.Use Moss P/N 268-090, 31 1/8" length with TUBE rear axles.
On the subject of driveshafts, listed below are the combinations of transmissions and rear axles of all model MGB's, including their flange to flange lengths and their relationship to the driveshafts required.
| Transmission Type | OD | Axle | Length | Moss P/N |
|---|---|---|---|---|
| Non-synchro | No | Banjo | 30" | 268-080 |
| Non-synchro | Yes | Banjo | 31 1/8" | 268-090 |
| Non-synchro | No | Tube | 20 7/8" | 268-090 |
| Non-synchro | Yes | Tube | 32" | 268-100 |
| All-synchro | No | Banjo | 30 1/4" | 268-080 |
| All-synchro | Yes | Banjo | 30 1/4" | 268-080 |
| All-synchro | No | Tube | 31 1/8" | 268-090 |
| All-synchro | Yes | Tube | 31 1/8" | 268-090 |
Alternatively, depending upon which transmission/rear axle combination you use, you could lengthen or shorten the existing driveshaft as required.
Alternate Wiring Diagram
We have found the most convenient way to solve any transmission interference to adjacent body problems i.e. in the area of the starter motor.
Before assembling the engine back plate to the engine, temporarily fit it to the all-synchro transmission and remove the transmission material that would have accommodated the top starter motor securing bolt until the 3/8" x 1 1/2" SAE socket head cap screw can be inserted from the rear directly through and butt up against the back plate. This will mean one less bolt securing the transmission to the engine back plate assembly, but should not present a problem.
NOTE: if you prefer not to use this method of starter motor attachment, then a 4lb hammer will do the trick!
Remove original starter solenoid to starter motor cable, enlarge cable end to fit new starter solenoid terminal, refit and re-route cable.
Alternatively, depending upon which transmission/rear axle combination you use, you could lengthen or shorten the existing driveshaft as required.
Tunnel Cover
Electrical (Overdrive)
See Wiring Diagram.
Starter Motor
We have found the most convenient way to solve the starter motor fitment, and with it the adjacent body to transmission interference problem, is as follows. Before assembling the engine back plate to the engine, temporarily fit it to the all-synchro transmission and remove the transmission material that would have accommodated the top starter motor securing bolt until the 3/8" x 1 1/2" SAE socket head cap screw can be inserted from the rear directly through and butt up against the back plate. This will mean one less bolt securing the transmission to the engine back plate assembly, but should not present a problem. NOTE: if you prefer not to use this method of starter motor attachment, then a 4lb hammer will do the trick!
Remove original starter solenoid to starter motor cable, enlarge cable end to fit new starter solenoid terminal, refit and re-route cable.
Tunnel Cover
See :MGB Tunnel Cover Assembly".
Transmission Oil
The introduction of the first rubber MGB (1974 1/2) also saw the introduction of the side oil filler plug transmission, both standard and overdrive trans. What was most interesting was that these trans were filled with HYPOID OIL. During this period of time, I was involved working with warranty claims at a British Leyland dealership. Numerous claims for trans repair problems were subject to rejection because it was thought, at that time, the trans was inadvertently refilled with the wrong oil. According to our information, the specified oil ranged from 5W/20 to 20W/50, depending upon the climatic temperatures. In actual fact, hypoid oil was the specified lubricant used on the assembly line and was confirmed by British Leyland representatives at that time. Somehow, this information never got beyond the assembly line. Factory MGBGT V8 model transmissions were filled with either SAE 80W or SAE 90W, which was also specified in the owner's manual. These trans were fitted with overdrive and, apart from using different gear ratios, they were identical to 1968 MGB's and later models (the overdrive ratio remained the same). Obviously, someone in their wisdom decided that there were benefits to using hypoid oil. Could this someone have been a person who previously worked for Triumph because SAE 80W or SAE 90W were used on most, if not all, of the TR models through the TR7? My recommendation is to use 80W/90-hypoid oil for all non-synchro and all synchro trans with or without overdrive. On overdrive models, overdrive engagement should be delayed for several miles after start up to reduce oil viscosity. Remember, when refilling your overdrive transmission, never use additives.
Since this article was first written, there has been considerable debate on the Internet regarding the use of hypoid oil. According to the experts, the high sulfur based additives in hypoid oil will eventually corrode the brass synchro rings as fitted to the non-synchromesh transmission. This has been proved scientifically so we must conclude, based upon this information and this information alone, and do not use hypoid oil in these early non-synchromesh transmissions.
Personally, from experience, I can almost guarantee that the layshaft and needle roller bearings on the non-synchromesh transmission, along with possibly the first gear hub and laygear assembly, will need replacement well before any problems surface with the brass synchro rings. Should you have to rebuild a non-synchromesh transmission due to layshaft or needle roller bearing wear, then one would be smart enough to replace the synchro rings at the same time.
I once had a customer with a 1967 MGB who had been coming to my shop for 19 years. In 1978 we overhauled his transmission and added hypoid oil, the mileage at that time was approximately 120,000. The transmission was overhauled due to laygear, layshaft, and needle roller bearing failure. In 1992 (approximately 150,000 miles later), the transmission was rebuilt yet again. Failure, yes you've got it, layshaft and needle roller bearings! Neither of these two rebuilds was due to brass synchro rings failure. I eventually lost contact with the customer whom at that time had approximately 325,000 miles on the speedometer.
If your transmission rebuild was due to brass synchro ring failure, then you should feel comfortable switching to engine oil such as Castrol 20W/50.
See "MGB Tunnel Cover Assembly".
This new tunnel cover is designed to be used with your original gearshift boot and chrome finisher ring. Also recommended is the gearshift lever as fitted to the 1968 thru 1976 models.
Installation Instructions
First, if your new tunnel cover assembly is painted black, remove paint in the area of the flange where the anticipated holes are going to be located. Also, cut out the portion inside the scribed line where the gearshift boot will be fitted.
1. Remove radio speaker console and ashtray (if fitted).
2. Pull back the upper tunnel carpet and remove metal cover.
3. Make two hacksaw cuts at the rear of the tunnel aperture following the original width to a depth of 1 1/2". Proceed and hacksaw across these two cuts, file any sharp edges that may exist after removal of metal.
4. Position new tunnel cover and mark location of the original securing bolt holes; this procedure is best accomplished while the transmission unit is removed (an inspection light shining through from underneath the body will help in locating these existing holes). Rather than drilling these new clearance holes (19/32") all at one time, proceed and drill several at a time positioning and repositioning the tunnel cover and remarking holes as necessary. Secure with 9 of the original SAE 1/4" bolts and new washers.
5. Mark 4 holes located as follows: 2 across the top rear and one either side of the rear tunnel. Using 9/64" drill bit, drill through into the metal tunnel. Remove the new tunnel cover and drill through these 4 holes using 1/4" drill bit (install 4 #10 self-tapping screws upon final assembly).
6. After the trans and gearbox components are fitted, refit tunnel cover and secure. Position and centralize gearshift boot and finishing ring, mark and drill holes using 9/32" drill bit. Install 4 nutserts.
7. It will now be necessary to recarpet a short portion of the body tunnel. My suggestion is to partially glue down this new carpet to the uppermost part of the new tunnel cover so as to leave access to the securing bolts, and then install several snap button assemblies (Moss P/N 226-800 & 266-338) to secure the remaining carpet. Should you ever need to replace the overdrive lockout switch (based upon the presumption that you have installed an overdrive transmission), you will need to remove this new tunnel cover or, alternatively, remove the engine/trans unit. If you have installed a non-overdrive trans, go ahead and glue down the entire new carpet. If your vehicle has reverse lights fitted, the backup light switch can be replaced from underneath the vehicle; this applies to both non-overdrive and overdrive transmissions.
8. Finally, once the carpet is installed, refit gearshift boot and chrome finishing ring, install 4 screws provided in kit.
Components
| Qty | Description |
|---|---|
| 1 | Tunnel Cover |
| 9 | Washer |
| 4 | #10 Self tapping screws |
| 1 | Nutsert kit |
| 4 | Phillips head screw |