18 replies to this topic

[ac427]

 

The later sets with the lines are fairly obvious what they are.

 

For the earlier sets, look carefully on the Laygear, you might see a Part Number Stamped in to it;-

 

DAM3169   Standard Ratios

DAM3168   Close Ratios 

If you can't see the number, just count the teeth on the 1st Motion Shaft (this is the first gear that drives the largest end of the Laygear) - 17 tooth is standard ratios, 18 tooth is close ratios.

I mentioned too that the drop gears came in a few ratios, the standard types have unmarked gears, there's also single line available on the Primary and Input Gears and also a twin Line Primary Gear for the 1275. These all used the same Idler Gear and give Over-drive ratios. The plain gears are 29 tooth, the single line Primary Gear is 30 and twin line Primary is 31. The plain Input Gear is 29 tooth and the single line 28 tooth. Personally, I'd suggest sticking with the 1:1 Ratios here, and changing the Final Drive ratio to get the outcome you are seeking, the geartrain losses are higher when using these overdrive gears.

 

Here's a cheat sheet I put together a few years back for the all synchro gearsets;-
 

 

Hopefully it makes some sense. If you look across the top, pick out which Laygear you have, then look down the column, where there's a X, that gear will fit and mesh in that set. Pretty much all the early gears go together, with the exception of 1st Motion and Laygears and in the lined sets, only lines of matching number will go together. I haven't included the drop gears as I only use the 1:1 sets.

 

 

 

Did the MG Metro Turbo gearbox get a different different set of ratios to the ones listed in your table?

 

Are there any external markings on a gearbox case that might show which gearset / ratios are fitted?

Edited by ac427, 06 March 2022 - 06:09 PM.

[Spider]

Did the MG Metro Turbo gearbox get a different different set of ratios to the ones listed in your table?

 

Are there any external markings on a gearbox case that might show which gearset / ratios are fitted?

 

Oddly, the MG and MG Turbo Models only used the standard Single Line gear sets. I can understand this for the Turbo Models, but the non-Turbo model surely could have benefited from closer ratios. Compounding this, they initially had 3.44 final drive ratios, but then pushed these taller to 3.21 with the Turbo Model it seems also got a set of 'economy' drop gears.
 

[ac427]

 

Did the MG Metro Turbo gearbox get a different different set of ratios to the ones listed in your table?

 

Are there any external markings on a gearbox case that might show which gearset / ratios are fitted?

 

Oddly, the MG and MG Turbo Models only used the standard Single Line gear sets. I can understand this for the Turbo Models, but the non-Turbo model surely could have benefited from closer ratios. Compounding this, they initially had 3.44 final drive ratios, but then pushed these taller to 3.21 with the Turbo Model it seems also got a set of 'economy' drop gears.
 

 

Great stuff, thank you.

 

I have a 1430cc engine with what i was old was a Metro Turbo gearbox. It's developed the 1st to 2nd gear crunch and i've not looked at for at least 15 years.

 

When i did drive it, i remember the first gear being so low i was into second almost straight away.  So i think i probably have the 3.44 diff and single line gears. I remember wishing at the time that i had more evenly spaced gear ratios.

 

I can't remember where my drop gears were sourced from. I am sure i have seen a list of drop gear ratios but can't find it. Would you happen to have one to hand?

Edited by ac427, 06 March 2022 - 08:28 PM.

[Spider]

The Drop Gear Ratios are easy enough to calculate. As mentioned in a previous post, Primary Gears came in 29, 30 and 31 tooth types. Input Gears cam in 29 and 28 teeth.

29 : 29 = 1:1
29 : 28 = 1.3057:1
30 : 29 = 1.3044:1
30 : 28 = 1.0714:1
31 : 29 = 1.0689:1
31 : 28 = 1.1071:1

 

Note these all give over drive. So put another way, the drive comes off the crank, is sped up, shoved in to the gearbox, where it cold be anything from 4:1 to 1;1, then in to the final drive, where it's slowed down.

While the final drive ratios off the shelf don't give fine steps like the drop gears will, you would still be better off tinkering with the final drive ratios and leaving the drops at 1:1.

It does sound like you could have twin line gears.

I always work from a cruising speed (in top gear) vs rpms and work back from tat to sort final drive ratios.,