Lotus Elan

Gearbox (Transmission) - Fault Finding

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Lotus Service Bulletin
Class 111
Number 1971/19
Type Elan & +2
Date 23.4.1971
Title: Gearbox (Transmission) - Fault Finding
Reason: To give advice to Service personnel in diagnosing and rectifying faults to be found in the gearbox (transmission).
Charges: U . K. - Warranty
EXPORT - Factory
- Distributor

FIRST, ascertain that a problem exists. Check the car on the road with the Customer driving. Let him (or her) demonstrate the defect. This will show exactly what the problem is and also provide an opportunity to check that the Customer is using the gearbox correctly.

Proceed as follows:-



It must be remembered that any leaking oil will be blown backwards by the car's motion, thus giving a false location of an oil leak. The following gives some of the less obvious possible locations.

  1. Extension Housing Seal: Check that oil is not leaking from the welch plug in the end of the propeller shaft yoke. Check that oil is not leaking from the gear lever pivot, reverse stop plug or the turret screw.
  2. Extension Housing to Gearbox Casing Gasket: Check that oil is not coming from the top cover plate or from the rear cover plate/gear lever pivot. Ensure that the rear cover is correctly fitted (i.e. vent hole to the rear). Check that oil is not leaking from the speedometer drive, or drive blanking plug. Check, that oil is not coming from the extension housing retaining bolt threads.
  3. Main Drive Gear Retainer: Before replacing the oil seal, check for presence of oil inside the retainer bore. If no oil can be seen, then the seal is not leaking. This points the leak to either the main drive gear retainer gasket, or past the threads of the retaining bolts. Ensure that the oil is not leaking past the crankshaft rear oil seal .


  1. Gear Noise: Some noise is inevitable with a new gearbox, or when new gears have been fitted. Those noises will decrease as the mating parts 'bed-in'. Do NOT dismantle a new gearbox or attempt rectification until the gearbox has been in Service for at least 1,000 miles (1,600 km.) unless the noise is indicative of a serious failure, or if continual running will result in serious damage. If the noise is still excessive after 1,000 miles (1,600 km.), it will then be necessary to dismantle the gearbox and examine the individual gears. Careful testing prior to dismantling will direct the examination to the defective gear(s), (i.e) drive or over-run side of gears, constant mesh if in all gears, etc. If the noise occurs on the over-run in either 1st, 2nd, or 3rd gears inspect the main drive gear on the over-run side of the teeth for incorrect bearing pattern. When the bearing can be seen to be heavy at the dog teeth end, with about half the tooth length showing contact, the main drive gear only should be replaced. These wear conditions produce a known source of noise problems. Knocks or clicks can be seen as a bright point on the gear tooth surface usually at 'the tip or end of the tooth adjacent to a damage mark on the outside of the tooth. With good diagnosis these can be stoned down and rebuilt. This will eliminate the necessity of fitting a new gear for what is in fact, a very minor and easily rectified error. Gear teeth should have a smooth finish and the wear pattern should be evenly disposed on each tooth.
  2. Knocking or Tapping: This is usually caused by a gear tooth imperfection (burr, high spot, chip etc.),. It may be evident in one particular gear or in all gears if the Main drive pair are at fault.
  3. Bearing Noise: This is a growling noise. It is indicative of a bearing breaking up. If the noise is evident in the intermediate gears only, then the mainshaft spigot bearing is suspect. If the noise is evident in all gears, including neutral, then the main drive gear (probably) or the countershaft rollers (possibly) are suspect. Note: If with the car stationary and the engine running, a noise is evident when the clutch pedal is depressed, DO NOT suspect the gearbox. It should be obvious that, under these conditions. no part of the gearbox is moving and thus cannot cause a noise. Literal descriptions of audible noises are always open to misinterpretation and dispute. While the foregoing descriptions will be helpful, it is advisable for Dealer personnel to accumulate sufficient experience to be able to diagnose noises quickly and accurately and it is most important that the car owner should demonstrate the defect.


Hissing noise from base of gear lever whilst on drive and over-run: Check the surface finish of the synchroniser sleeve selector fork groove. The finish should be smooth and flat with no nicks or burrs. Note: The 'sizzle' noise may be amplified by a damaged or badly fitted gear lever boot. Check the run-out on the synchroniser sleeve. This should NOT be more than .020 in. (.51 mm.).


Disengagement of gear on drive or overrun:

Checks with gearbox still in car: Check gear linkage adjustment. Ensure that there are no damaged or distorted components and that there is no excessive free movement. Check for broken or cross-threaded gear lever cap (see also Service Bulletin 1970/10). Replace any necessary component's and adjust linkage. Note: If linkage is adjusted and the problem is cured, there is normally no need to take further action. Consideration should however, be given to removing the gearbox to rectify any damage to the gearbox components caused by the 'jump out' . Ensure there is adequate clearance between the gear lever and the centre console, with the lever in gear. Replace cap or lever as necessary.

Checks with gearbox removed from car: Ensure there is adequate clearance at each end of the selector rails in gear and also at the over-run stop when the gear is engaged. Ensure that the interlock plungers and detent ball are free and fully seating in the groove in the rails. Remove the gearbox top cover and check the selector mechanism. Fit selector rail with solid end (Part No. 2824E-7K335-A).

Forward gears only: Check the mainshaft end-float. It should not exceed .030 in. (.76 mm.). Remove the mainshaft assembly and dismantle the area required (i.e. if it jumps out of 1st. gear remove the components associated with 1st gear). Check that the tab washer retaining the mainshaft nut is intact. The tab washer should prevent the nut from turning. If the bearing is retained by a circlip, ensure that the circlip directly behind the mainshaft bearing is of the correct type and is correctly seated in its groove. Examine the gear and sleeve dog teeth for back-angling (1st and 3rd gears only), which must be evenly disposed. Check ail dog teeth for damage (chipped teeth etc.) Check that the sleeve is a good sliding fit on the hub. If either the gear or the sleeve is damaged, then the damaged component and the synchro ring should be renewed. Examine the appropriate selector fork for wear. If the wear is excessive, then the forks should be renewed. Ensure the selector forks are fitted the correct way around. Check hub and sleeve assembly for damage and renew if necessary.

Reverse gear only: Check that the reverse idler gear can be fully engaged with both mainshaft and countershaft gears. Ensure that the idler gear bush is correctly positioned in the bore of the gear and not misplaced. Cheek that the bush is a good fit on the idler shaft. If the idler gear is damaged it should be renewed. Also check associated components (cluster gear, 1st/2nd hub and sleeve assembly, etc.), which may have been damaged. Check that the 1st/2nd gear sleeve is a sliding fit on its hub. Replace gear and bush assembly.


  1. Difficult selection - Stiff movement of lever throughout its travel, or in one plane:
  2. Baulking - Gear will not go in first time but will go in on second or third attempt:
  3. Notchiness - Undue increase in effort when engaging a gear:

Checks with gearbox still in car: Check clutch operation (see Section 'Q' of the Workshop Manuals). Engage gear once, pull out and re-engage. There should be no baulking with clutch disengaged. Examine selector rails. Remove gearbox.

Checks with gearbox removed from car: Check that the selector rails with the selector forks disconnected, slide freely when the selector balls, or plungers and springs are removed. Hold the rails not being checked, in the neutral position. Check that all the interlock plungers and the detent balls and springs are fitted. Check that their operation is not restricted by swarf, etc.,(see also mainshaft checks). Clean out swarf, fit new components and check operation. Check that the correct selector rail is fitted (compare with a new part). Check that the notches for the interlocks and the balls are correct. Ensure that the 'flat, to allow oil dispersion is machined on the rail.

Mainshaft: Check the mainshaft end-float. It should not exceed .030 in. Maximum(.76 mm.) Remove the mainshaft and measure the end-float of the gears (see Technical Data in the Workshop. Manuals). Check that the tab washer retaining the mainshaft nut is intact. The tab washer should prevent the nut from rotating, If the bearing is retained by a circlip, ensure that the circlip directly behind the mainshaft bearing is of the correct type and is correctly sealed in it's groove. Remove. Remove the 3rd/4th or 1st/2nd synchroniser assembly (which one to remove obviously depends on which gear was difficult to engage). Check that the insert springs are correctly assembled, ensuring the ends of both springs pick up in the same blocker bar and that they are both either positioned in a clockwise or anti-clockwise direction as viewed from the front. Check also that the inserts are not damaged. Examine the synchroniser ring insert slots for signs of damage. Renew only the components that are damaged. Do not renew the complete synchroniser assembly, unless either the sleeve or hub itself is damaged. Dismantle the mainshaft and rebuild, using new components as required to give correct end-floats. Check that the sleeve is a good sliding fit on the hub. Inspect the dog teeth on the gear, sleeve and synchroniser ring. Check for damage and offset chamfering. If the synchroniser ring only is damaged then renew only the synchroniser ring. If either the gear or sleeve is damaged renew this part and the synchroniser ring. Note. Sleeve teeth can have up to .020 in. (.51 mm.) 'flat' across each apex, before the gear needs to be replaced. Renew synchroniser assembly.


Violent fore and aft forced vibration of the gear lever:

Using feeler gauges, measure the clearance between the over-run stop tube and the rear end of the 3rd/Top selector fork boss with 3rd gear engaged. This dimension should not be greater than .005 in. (.127 mm.). If it is in excess of this figure it will be necessary to fit a new stop tube (Part No. 2821E-7A072-B), and a graded clip so that the gap is reduced to less than .005 in. (.127 mm.). The graded clip has a basic part number of '2821E-7K714' plus a suffix which varies with the thickness. Do not fit a graded clip which is too large; this can lead to 3rd gear 'jump out. The Service stop tube is colour-coded RED. A plain tube without a circlip is fitted in Production. Circlips must not be fitted with the plain tube. Check the mainshaft end-float which should not exceed .030 in. (.76 mm.). If it does, check that the tab washer retaining the mainshaft nut is intact. The tab washer should prevent the nut from rotating . If the bearing is retained by a circlip ensure that the circlip directly behind the mainshaft bearing is correctly seated in its groove. Remove the selector mechanism and rails to gain access to the 3rd/4th synchroniser sleeve. Measure the run-out of the side of the fork groove, with the sleeve in the 3rd gear position, using a suitable dial indicator. Place a dummy propshaft on the end of the gearbox to simulate a load. The run-out should be measured while rotating the input shaft to simulate driving conditions. This should be repeated three or four times with the gear dog teeth engaging on different teeth on the sleeve. If the run-out. exceeds .020 in. (.51 mm.) the synchroniser assembly should be renewed.


A characteristic grating or crashing noise which occurs when engaging a gear:

Checks with gearbox still in car: Check clutch operation (see Section 'Q' of Workshop Manual). Note: If, it is found that the crashing is caused by defective clutch operation, consideration should be given to whether any further work is required. This decision should be based on the severity of the crashing and the length of time it has been evident.

Checks with gearbox removed from car: Check that all the synchroniser rings are fitted. Dismantle the mainshaft and examine the dog teeth on the gear and sleeve, renew damaged components and rebuild the mainshaft with synchroniser rings. Remove the mainshaft assembly and dismantle the area required (i.e. if it crashes in 1st gear, only dismantle the components associated with 1st gear). With the synchroniser still assembled check that the insert springs are correctly fitted. They should run anti-clockwise (starting from the tang) when viewed from either side, also the spring tangs should be located in the same insert. Check the inserts themselves are undamaged. Inspect the dog teeth on the synchroniser ring, sliding gear and the gear. If either the sleeve or the gear is damaged then renew this part and the synchroniser ring. Inspect the synchroniser ring for wear of
the internal thread. Examine the gear cone finish for signs of grooving or chatter marks. The cone should have a smooth lightly polished surface. When the blocker ring is screwed onto the cone it should grip the cone when turned under hand pressure; if it does not, determine whether the gear or synchroniser ring is at fault


Impossible to disengage gear:

Check the gearchange linkage. Remove the gearbox top cover and reset the linkage correctly. Check that the selector forks or selector lever is securely attached to the selector rails. Check that all the interlock plungers are fitted. Secure the fork or selector arm to the rail. Remove the old pin or screw from the inside of the gearbox. Examine the selector rails. Ensure that they are free to move . Check that they are not distorted or jammed by foreign matter between the selector rails and the gearbox casing. Dismantle and rebuild with interlock plungers (check that the interlock plungers that should have been fitted are not loose in the bottom of the casing). Note: If gears are difficult to disengage check the mainshaft end-float.


Screeching Noise from gearbox when driving in any forward gear. Most noticeable in 2nd gear:

To overcome this problem, select parts to give a minimum clearance of .004 in. (.102 mm.) between the blocker ring and synchroniser hub recess.


When replacing any parts in the gearbox check that the new components are free from any possible defects such as back-angling, chamfering, pits and clearances etc. This is particularly important with regard to damage on gear teeth, as a nick or burr on a tooth will necessitate a second repair. Storage and handling of gears during repair is also vitally important. Where damage has been found to a gearbox part, such as dog teeth, it is important that the casing be washed out prior to re-assembly as these particles will only cause further damage. It may be necessary to remove the cluster gears where excessive foreign matter has been found.

New circlips, roll pins and gaskets must be fitted where these have been removed or disturbed and Hylomar sealer should be applied to all bolt threads on re-assembly to prevent oil leakage.