focus218 Posted November 11, 2018 Report Share Posted November 11, 2018 I have a 1985 KP36. I've made a lot of mods on it mainly on the mechanical part. 1. Changed the stock 2K for a 4K motor (Brand new cylinder block) 2. Put a Weber DGV 32/36 3. Switched the T40 gearbox with a T50. 4. Put new Headers and new Radiator with a low temp racing thermostat. All these are great. The problem I have is on the freeway. My Differential is a stock KP36 (picture attached) one with a ratio of 43:10 (4.3) so travelling long distance is a pain and hard to reach top speeds. I need to get me a 3.9 ratio differential in so I will be able to cruise at 100-130 KMH with the engine at low RPMs. Is there a way I can only switch my Final Diff Gears without removing my entire rear axle? Any suggestions ??? Quote Link to comment Share on other sites More sharing options...
coln72 Posted November 12, 2018 Report Share Posted November 12, 2018 Can you run a taller wheel/tyre combo....? Quote Link to comment Share on other sites More sharing options...
focus218 Posted November 12, 2018 Author Report Share Posted November 12, 2018 3 hours ago, coln72 said: Can you run a taller wheel/tyre combo....? No. The factory tire settings were 165/65/12. The ones I have are 175/70/13 with extra 8 mm spacers in order for the front tires to not touch the shock absorbers. At the rear when I get some extra weight in, the tires escape the wheel arches just a few millimeters. So taller tires are not an option. Quote Link to comment Share on other sites More sharing options...
LittleRedSpirit Posted November 12, 2018 Report Share Posted November 12, 2018 Its a jap style diff so you can remove axles, then the centre, and put a complete taller ratio centre in if you like. Or you can remove the one you have and have different gears fitted to it if you can find them. Quote Link to comment Share on other sites More sharing options...
focus218 Posted November 13, 2018 Author Report Share Posted November 13, 2018 I am not familiar with how many diffs there are out there, if I were to buy this one which seems to be the only one available, would it fit? https://www.ebay.co.uk/itm/Toyota-corolla-AE86-t18-4age-m-t-T-series-diff-gears-3-7-ratio/263714728652 Quote Link to comment Share on other sites More sharing options...
LittleRedSpirit Posted November 13, 2018 Report Share Posted November 13, 2018 The link is for T series diff gears. They are 6.7 inches. The KP diff is 6 inches. Quote Link to comment Share on other sites More sharing options...
Banjo Posted November 14, 2018 Report Share Posted November 14, 2018 (edited) Hi Michalis, Off memory, the JAP 4.31:1 ratio diff was fitted to Corollas with auto transmission. Manual transmission models, were often fitted with 4.11:1 ratio diffs. The 3.89:1 ratio diffs were not fitted to any Corollas as standard, from memory. However, I am led to believe, that the Datsun 1200 & 120Y series, used the 3.89:1 ratio diffs, of the same origin as Toyota, & that if you can get hold of a 3.89:1 crown wheel & pinion set new, a good diff reconditioning company should be able to swap them over, & lap them in for you. A lot od Datsun 1200 utes had 3.89:1 ratio diffs. Others on this forum may be able to confirm or correct my thoughts, as I haven't actually done it myself, but I do have it on my "bucket list", as I have a KE30 with a 1.43:1 ration diff in it, that I would love to fit a 1.389:1 diff into it. Here is a listing I found, that has a number of 3.89:1 & 3.9:1 ratio diffs http://www.difflap.com.au/ratios/gearratios_ad.htm Cheers Banjo Edited November 14, 2018 by Banjo Quote Link to comment Share on other sites More sharing options...
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