Please explain gearbox differences

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3 rib, 5 rib, 6 rib, etc just describes the external gearbox castings.

3 rib gearboxes were fitted to 1600 Type 1 engines and have the following codes, CA, CB, CC, CD (1968-71), CE, CF, CG, CH (1972-75), CU, CV, CW, CX (1976-79).
CB, CF and CW 'boxes had mountain ratios installed, CC, CG and CV had limited slip differentials, CD, CH and CX had mountain ratio and limited slip diffs.

5 rib gearboxes were fitted to 1700 and 1800 Type 4 engines, codes are CK, CL (1700 1972-73), CM and CN (1800 1974-75). CL and CN had limited slip diffs.

6 rib gearboxes were fitted to 2000 Type 4 engines and had CP and CT (1976-79) codes. CT having a limited slip diff.
 
The 6 (and I think 5) rib gearboxes also have taller ratios, lowering the engine RPMs at cruising speeds. They're also stronger than the 3 rib gearboxes.
 
So my 72 would have a 3 rib? Where are the ribs for counting? I knew it would be about gear ratios etc but I read about people having 1700 or 2ltre with 6 rib box etc. Although my knowledge is getting better I do like to try and understand this stuff but really didn't understand what it was all about

My next post will be about mild lowering as that is something else I know nothing about 😄
 
If you are looking to reduce your revs and increase speed you can fit a beetle gearbox or mostly these days we get early 3 rib boxes rebuilt with a 4.57 Ring & Pinion (final drive) which gives you approx the same ratios as a 6 rib box/freeway flyer. Its also cheaper than finding a 6 rib and having it rebuilt or buying a freeway flyer.
 
A freeway flyer is certainly the better option. No kit to faff around with and a bus box is designed to take the extra weight and strain of a bus, a beetle box isn’t.
 

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