3.54 gearset into 3.08 housing

M

mikecoombs

Active Member
I'm just starting to build up a diff to go with my 4HP22 conversion. Plan is to use 2200 gearset in a '76 3500 casing. Object being to get lower gearing to compliment the overdrive boxs higher final ratio and improve the around town performance. Has anyone tried this?
 
I assume the goal is to have the 4 pin diff and lower 3.54 ratio? I cannot be certain but I think I've read of the 2200 differential assembly also has the 4 pin diff, only the 2000 differential is 2 pin?
 
They are the same part numbers for both 3500 and 2200 diffs so i'm presuming that means they are in fact the same 4 pinion centre which is a must for the V8. However standard centre is my backup plan, primary plan is to fit an ATB centre and bespoke half shafts and drive shaft so I don't have to worry about breaking another one,,,The lower ratio is more to give the car more pickup and delay the onset of pinging. With the overdrive transmission the top speed should still be higher and cruise RPM lower
 
Ah I understand now, so in theory yes it should all work. Going from 3.08 to 3.54 is quite a step, have you compared the gear ratios from first to top? I'd assume that you'd lose any benefit of fitting the 4HP22 if you dropped the final drive ratio as it would make 1st almost redundant.
 
The 4HP22 i am using (from a disco) has the first three ratios about the same as the BW35/65. My issue with the BW 1st is that it relies on the torque converter to get the car moving. The Torque converter has a max ratio of just over 2:1 which means the engine is between 1000 and 2000 RPM. Which is somewhat below the optimum torque range; hence the off line movement is slow and it isn't terribly fuel efficient.

The difference in diff gearing is from 6:2 to 7:2 that is the overall gearing of Torque Converter plus Final Drive is 7:1 instead of 6:1 So 3rd would become 7:1 Given the new top (Overdrive) is 0.74 I won't lose anything up that end as result will be 2.61;1 overall; which is still a lower RPM than 3.08:1 will give. First on the other hand will be lower by 0.46 which should take the stress off the torque converter and get the revs up into the efficient area quicker.

That is the plan anyhow...I have a V8 diff which broke a couple of pinion teeth years ago and condequently donated a half shaft to my spare - now the car's diff) so I am pulling it to bits and plan to use the new gearset in that casing. so far the "don't remove the tube off the end of the drivshaft" bit in the manual didn't work out because it came out stuck to the diff end...Anyway I pland to get all three splined shafts made bespoke so they don't break (again).
 
Gotcha, makes complete sense now :)

I'm sure there would be a few people interested in how much the uprated input and output shafts cost once you've done it
 
I've sourced a gear set from a 2200 now but the diff I had planned to use is a "C" suffix one and has 5/16" crownwheel mounting bolts. I broke the pinion gear on this diff so it was already partly dismantled. The New Crown wheel is post suffix 'C' so has the later 3/8" bolts. Fortunately I have a spare diff that is suffix "F" so plan be is to pull it down though first up I'm trying to find someone who has a suitable ATB unit (a type of LSDiff) which would negate the need.
 
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