MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - gear box rebuild how hard is it?I h

I have done just about evrything on my 1960 MGA One thing I havent tried is its gearbox.No one localy seems to want anything to do with it.Now that second gear syncro has taken a hike. I must deal with the problem at hand. Any sugestions? Terry and his A
T.P. Bernhardt

Fairly easy, actually. Take it apart, replace any broken or worn parts, and put it back together. Nothing like rebuilding an engine, as nothing needs machining for the gearbox.

For about everything you need to know about the MGA gearbox, check here: http://mgaguru.com/mgtech/gearbox/gt1.htm -- and if you still have any questions, do aks.
Barney Gaylord

Hi Terry. I have overhauled my tranny twice in 25 years. The last time I rebuilt it, I made some notes to assist me when the tranny needs to be rebuilt again. Here are my notes. I hope you find them useful.

MGA Transmission Rebuild
1956 Transmission NO. NGN 2262

It is late November 2003. I have just finished rebuilding the transmission from my MGA 1500 roadster. Here are a few notes and pointers that will assist in the next transmission overhaul.

Degrease the outside of the transmission before disassembly. When removing the rear extension, re bolt the remote shifter assembly back in place, so you can use the shift lever to move the shift forks. Remove the speedometer drive unit, and the shifter interlock unit. The shift forks must then be moved and manouvered so that the rear extension can be removed from the main gearbox housing. This is best accomplished by putting the transmission in neutral. The three shift lever channels are then aligned, and the shift mechanism can be easily moved to one side, and the rear extension removed. The rear extension may be a tight fit and might have to be gently tapped off from the main case.

Once the rear extension is gone, the 3 steel shift rods need to be removed. To do this, remove the 3 setscrews holding the shift forks to the shift rods. Unbolt the steel block at the back of the main aluminum housing (2 bolts) using a socket wrench. The shift rods will have to be partially moved rearward to allow clearance for a socket wrench! After the shift rod block is free, then pull all 3 shift rods toward the rear, but DO NOT remove them from the steel block, or detent springs and ball bearings will fly out and get lost. Once all 3 shift rods are pulled back, the shift forks, inside the main housing can be removed. Remove the forks in the order they appear from the large opening in the main case. The reverse fork is removed first, then the other 2 forks are sequentially taken out.





Once the forks are out, the reverse gear can be removed, by loosening the single lockbolt (with lock tab) and removing the bolt. The reverse gear shaft taps out toward the rear.

When reverse gear is removed, the layshaft can be tapped out, and the laygear can be set in the bottom of the gearbox. The 3rd motion shaft is then removed by tapping it out from inside the gearbox. Use a long narrow brass punch or piece of hardwood. Be sure to check the laygear end play which should be around .002 to .006 inches. Oversize laygear thrust washers are available from Moss and elsewhere.

To remove the gearbox front cover, the clutch throwout arm must be removed first. When the front cover is off, carefully mark the front cover mating area in regard to location of the layshaft. The front of the layshaft is notched, and a semi circular section fits into a corresponding notch in the front cover. Failure to mark the orientation of the layshaft to the gearbox casing makes re fitting the front cover a guessing game. If marking IS forgotten it is JUST possible to put the front cover in place and then rotate the layshaft from the rear of the gearbox with small needle nose vice grips, until the layshaft is felt to engage the notch in the front cover. The layshaft can then be tapped forward where it will seat in the front cover.

When the mainshaft is out, the input shaft can be tapped out from inside the gearbox, using a long (brass) drift punch or piece of hardwood. Be careful not to pound too hard on the bearing, since it would be damaged.





Degrease the inside of the main and rear extension housings. Degrease all nuts bolts and washers. Wash out the case components with solvent. Replace front and rear main seals if required. Check the clutch lever pivot bolt and bushing for wear and replace as required.

In regard to disassembly of the mainshaft: Remove from the mainshaft, the first sliding hub that houses the 3rd and 4th synchro rings. DO NOT separate the parts of the sliding hub, as springs and balls will fly out. Reassembling the hub is difficult to impossible without special factory tools. Check 3rd and 4th gear synchro rings for wear, and replace as required. Then remove the next helical gear and bronze bushing that is fitted on the mainshaft.

This exposes a splined steel washer. Look for a spring loaded pin poking out from the mainshaft, that holds the splined washer in place. Using 2 jeweler’s screwdrivers, compress the pin, and rotate the washer in either direction. This lines up the splines on the washer, with the splines on the mainshaft, so the washer can then be removed. This washer can be difficult to remove.

Use one screwdriver to compress the pin, then wedge the other screwdriver between the pin and the splined washer. You should then be able to rotate the splined washer, and remove it. Once the splined washer is off, you can remove the next helical gear, and replace the second gear synchro ring if required. More disassembly of the mainshaft is not normally required unless wear further down in the mainshaft components is suspected. Reassemble everything in reverse order.

When putting the bronze bushing back on the mainshaft, be sure that the oil hole in the mainshaft lines up with the oil hole in the bronze bushing. This is important for lubrication of moving parts!


Replace the layshaft if it is worn. If the layshaft is worn, the layshaft bearings should likely be replaced at the same time unless in excellent condition with minimal slop.

When installing the laygear, use a “dummy” layshaft. I made one from a piece of standard 5/8” OD PVC plumbing water supply pipe cut to 6 and 13/16 inches long. This is long enough to hold both the layshaft thrust washers in place when the laygear is sitting in the bottom of the gearbox.

To re assemble the gearbox. Fit the dummy layshaft inside of the laygear. Grease the ends of the laygear, and put the thrust washers in place. The small washer goes on small end of laygear, the big washer on big end of laygear.

Install the input shaft. Tap the input shaft into the case, and make sure it bottoms. Heavily grease the inside of the input shaft, and install the 18 needle bearings.

Blow air through the mainshaft oil restrictor to confirm it is clear, then install the mainshaft through the rear of the gearbox, making sure the mainshaft spigot goes into the input shaft straight, and does not dislodge any of the 18 needle bearings.

Do not drive the mainshaft home, but rather, use the rear extension housing gasket to align the rear bearing housing pin in the proper orientation with the case. Then tap the mainshaft all the way home.

Fit the reverse gear, tapping the shaft in from the rear. Make sure the reverse shaft locking bolt lines up with the hole in the reverse shaft, and use a new locking tab.




With reverse gear installed, bring the laygear with thrust washers into mesh with the mainshaft gears. Slide the layshaft into the gearbox from the rear. The layshaft will push the previously installed dummy layshaft out the front of the case.

Install the 3 shift forks and shift rods in the reverse order they were removed. Before the 3 shaft are all the way into the gearbox, bolt the metal shaft block with 2 alignment pins back onto the rear of the gearbox, using a socket wrench. An ordinary box end wrench will not work! Slide all 3 shafts into the box, making sure that the shift levers for each rod are placed on their respective gears in the proper position. The shift rods are then pushed through their respective forks, and all three forks are locked to their shafts using the lockbolts. Make sure that the lockbolts are aligned with the holes in their respective shafts.

Place a new gasket on the rear of the main gearbox housing, and install the tailshaft housing. Make sure that the transmission is in neutral. Then lower the tailshaft housing onto the main case, amnouvering the linkage, so that the main shift lever engages the three shift shaft components, which should be in line, if the transmission is in neutral. Manouver the shifter parts so that the tailshaft housing seats on the main gearbox housing. Make sure that the single stud in the main case receives a locknot and washer before the tailshaft casting is seated on the main case. Bolt the rear housing to the gearbox.

Install the front cover, and clutch lever, with boot.
Making sure that reverse gear is engaged, install the Interlock unit under the small stamped steel cover, and bolt the cover into place using a new gasket. Screw in the speedometer drive sending unit, and bolt the main cover in place using a new gasket.


Install the shifter linkage on the tailshaft casting, (If not already installed) and check that the gearbox engages all gears properly. This can be done by manually spinning the input shaft and watching that the output shaft turns freely. Don’t forget to check reverse gear, and note that the output shaft should turn in the opposite direction to the turning of the input shaft.

Be sure to put oil back in the gearbox BEFORE starting the engine. 30 wt motor oil is specified in the manual, but 20 w 50 synthetic motor oil, or redline synthetic transmission oil is a better choice.

Be sure to check and install a new clutch release bearing, with the carbon portion facing forward, away from the transmission. The carbon block rides on the back of the clutch pressure plate.

Note that the remote shift linkage needs to be removed before the transmission can be reinstalled in the vehicle. Use 2 new gaskets when installing the remote shift linkage.
Glenn

Terry,
It is a very simple transmission and simple to overhaul. Pay particular attention to the brass syncro rings (replace if there is any question of condition)and the layshaft bearings. There is a modification to the layshaft bearing on the A tranny that is simple to do and solves the problem nicely. Let me know if you are interested off line. Have a good day!

John
John Progess

Hi John. I would be intereting in finding out about your layshaft bearing modification, if you don't mind. Thanks! glennsmga@operamail.com
Glenn

I would be interested too. Actually, I think anyone reading this thread would be interested. Why not tell us all?
Steven Trovato

There is a mod that uses a B laygear, which involves some milling of the casing.

My one tip is to use threadlock on all the nuts and bolts inside the box. It's an easy job to rebuild if you are neat, tidy, methodical and clean.

All the bearings are standard ones (apart from the laygear ones) so they should be available from the local bearing suppliers at MUCH lower cost than from Moss etc. Just take them along and they will be able to match them.

dominic clancy

I just spent way too much time reviewing and updating my gearbox overhaul web pages, more pictures and more detail. I also included a few of Glenn's reminder notes (and corrected a few of his oversites like sequence of mainshaft parts). Check here: http://mgaguru.com/mgtech/gearbox/gt203a.htm
and a few pages to follow.

This also includes cross reference links to layshaft improvements here: http://mgaguru.com/mgtech/gearbox/gt204.htm

This does not show another possible modifcation. If you ream out the main case to accept the larger layshaft, you can install the 1967 vintage layshaft with 4 bearings. But this also requires use of the 1967 vintage laygear.

You can also install the MGA 1600 or MK-II tail housing on the 1967 MGB gearbox to get the same final configuration, effectively a 1967 type gearbox with the MGA rear mount.
Barney Gaylord

The modification I used was one I found on this site and it uses first motion (input)shaft needles (20 needed) in place of the rear caged needle bearing. One advantage is that you don't have to drill the layshaft as the origional oil hole will lubricate the needles. You have to shorten the spacer by about 3/8". You use the old cage ends and grind off the ridge and this means that you do not have a "caged" needle bearing in the rear of the layshaft. You use a piced of old layshaft to contain the needles while you install the laygear in the box and then push this piece out when you install the new layshaft. A very simple modification. I have done this on both my cars. Have a good day!

John
John Progess

I have just finished rebuilding my late 1500 gearbox but I didnt find it to be all that easy. I will list a few problems i ran into during my experience. The first problem i ran into was getting the rear extension separated from the main gearbox. The two would separate about 1/2" and then it wouldnt budge. This was because of the rear bearing (the one in the very end of the rear extension) which is pressed onto the mainshaft at that end. Somehow you have to pry the two pieces apart without damaging the two mating surfaces. It took a lot of force.
After getting them apart the rest of the disassembly as mention above was easy.
If you plan on replacing the input bearings and the mainshaft bearing be sure you have access to a press. The old bearings must be pressed off the input and main shafts. Then the new ones must be pressed on. When pressing the bearings on be sure that you only press on the outer races of the bearings otherwise they will get ruined. Pressing the input bearing onto the input shaft was easy, simply press it down to the gear teeth. However when you press the mainshaft bearing on be sure that you dont press it down too far otherwise your 2nd and 3rd gears won't align properly with the laygear upon reassembly. I found this out when i had it back together, i fixed the problem by pushing the mainshaft into alignment while it was in the gearbox case with a press. The laygear was in place to match the alignment. If this doesnt make sense now it will when things aren't aligning.
Replacing the rear extension oil seal and bearing was easy except for the removal of the rear oil seal which i pretty much destroyed upon removal when i had to chisel it inwards to break it.
Removing the circlips from the laygear pretty much bends them so i would save youself the hassel and just get new ones. I removed mine by hitting them opposite the gap with a small chisel to snap them in half. If you plan on reusing the bearing races below the circlips be careful you dont slip and hit them because thy will crack or bend and be useless. I just bought the replacement caged type bearings to avoid the inevitable.
Reassembly required me to press the rear extension back towards the main gearbox housing, due to the rear bearing in the rear extension housing needing to be pressed onto the mainshaft. This was another problem area for me. When i pressed the rear extension down, it caused the mainshaft to slip forwards through the mainshaft bearing which misaligned everything inside the gearbox because it also pushed the input shaft with its bearing out about 1/4". so i finished bolting the two halves of the gearbox together and flipped it around an very carefully pressed on the input shaft. This causes the mainshaft to slide back into place through the mainshaft bearing and the rear extension bearing.

If i didn't have access to a press nothing would have been possible for me. All that is left for me now is to put the front, side and extension covers back on. Others have said this job is easy, and for the most part it is, for instance removing the gears and replacing the syncro rings is super easy as is the reassembly of the mainshaft. Replacing the laygear bearings is also easy.Pressing the new bearings on the input and mainshafts is easy but reassembling the whole thing and getting the alignments correct was where i had the most trouble.

I am an amature and this was my first gearbox rebuild and now that i have seen and experienced all the problems with doing this kind of work it will definitly be easier next time. Especially since i know what to look out for. Let us know how yours goes and post any questions you have. Oh yeah and take tons of pictures of everything every step of the way. I cant tell you how important those pictures will be to you when you go to put it back together. Best of luck.

Ryan Kew

Terry,

Did mine last winter. First gearbox I have had apart.

All I replaced were the synchros, layshaft and layshaft bearings. It transformed the box, I had great difficulty up till then changing from 3rd to 2nd.

I took a chance and didn't replace any of the other bearings or seals and everything seems fine.

Only thing I had a problem with was getting the middle bearing out of the laygear. Eventually left it and just replaced the other two. My excuse, I was in a hurry.

Overall an enjoyable job.

Chris.
Chris C

Terry, one option to consider is to bring your gearbox to University Motors for their gearbox rebuild seminar in February. A long way for you to go I realize, but you will do the work yourself under the watchful eyes of experts.
G Goeppner

Ryan,

You wrote: "When pressing the bearings on be sure that you only press on the outer races of the bearings otherwise they will get ruined."

Oops, wrong. Normally you should push only on the bearing race which is press fit. For removing an old bearing you will throw out, it doesn't matter, just rip it off any way you can, even if you have to cut the bearing to pieces to do it. When pressing a new bearing onto a shaft, push only on the inner race to avoid laarge force on teh rolling elements.

You wrote: "I just bought the replacement caged type bearings to avoid the inevitable."

Where did you get the cage bearings? Very recently someone told me the Victoria British supplied cage bearings (made in UK) will fit on the shaft, or will fit in the laygear, but not at the same time. Moss supplied cage bearings (made in Tiawan) fit fine with either Moss or VB suppled layshaft. I an ordering a layshaft from each source (although I doubt this is any problem). The friend sent me one of the VB cage bearings which he claims doesn't fit. I measured everything, and it looks okay (0.118" diameter rollers and loose cage), so I will have to try it on the 16th (club tech session) to see what goes. Meanwhile I have a complete set of Moss cage bearings ready for assembly. If something goes awry, assembly of the second gearbox can wait for more parts.

You wrote: "When i pressed the rear extension down, it caused the mainshaft to slip forwards through the mainshaft bearing which misaligned everything inside the gearbox because it also pushed the input shaft with its bearing out about 1/4".

To avoid that problem, install the front cover temporarily before installing the rear housing.

You said: "If i didn't have access to a press nothing would have been possible for me."

I've done a few 1600 type units, no press and no problem. For assembly use some longer bolts or long studs and nuts to draw the housing together.

You wrote: "I am an amature and this was my first gearbox rebuild".

So now you're not an amature any more. Congratulations.
Barney Gaylord

Thanks Barney, I have started another thread on my gearbox rebuild and some issues that still need resolving. If you have any comments that would be fantastic. -ryan
Ryan Kew

My first gearbox was a 58 coupe in my parents garage 30 years ago. All I had was hand tools and a now oil soaked repair manual. I learned more about transmissions from that car than I have learned since and I have done over a hundred at my repair shop.
Go for it MGAs really are simple and easy to leasn on. Back the I had to just figure it out no BBS and all the great people to help like now.
Just DO IT,
Randy
R J Brown

This thread was discussed between 01/10/2005 and 06/10/2005

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.