FD gear box and high rpm shifting

[Grant Monkhouse]

I have been looking at the synchro problem we face when using our gear boxes, namely destroying the synchros and only being left with a couple of gears out of the 5 we have.

This problem is more common when cars are pushing 500Hp and upwards, then the problem of breaking the I out shaft shows itself

A few pieces I have come across suggest a couple of things;

1, polishing the synchros
2, grinding the synchros, removing every other tooth or sometimes even more
3, extra springs, now I\'m not too clued up on our boxes to know if they use springs or not??
4, chryo treatment of parts, I don\'t know how much this is but would most certainly be the greatest cost.

All these modifications obviously require the gear box to be rebuilt. If these modifications were to work I\'m sure there would be a few people pushing higher power if they needed it instead of spending ££££\'s on a dog box etc or even on the OSGiken uprgrade.

This still leaves us with the tiny input shaft:(

Once I have done some more reading up on this I will share my thoughts. What would any body think too the modifications? Would they work?

I know we can get Gboxes for £150~ but if you constantly break them like a few people do, namely CJR(Chris) on his track day car, then having a stock box modified whilst having it rebuilt would be good if it wasn\'t to break again.

Obviously there are other ways to help the Gbox last, braces, sump plates, solid mount it to the chassis etc, all of which I will be doing/have done to my FD Gbox that I am using in my RX4.

This isn\'t just for FD Gboxes but all of the boxes we have as they are very similar.

From what I have read so far a number of cars in PR ran modified stock boxes deep Into the low 9seconds!! That\'s +-600 rwhp afaik:)

[Ed_RX7parts]

Grant i cant report back on real world experience but i have a new OSG gearkit and i cryo\'d it all before it was rebuilt....i know they supposedly use different ( stronger) material in the OSG gearkits but i thought a little extra wouldnt hurt so i got it done at the same time i did my billet E shaft and titanium engine studs:yes

The gearlkit came witha new thicker shaft too so hopefully i would like to think it will be pretty

this will be the last engine so thought might as well go all out:mmmm

[Grant Monkhouse]

How much was the OSG gear set and how much to install? Aren\'t the ratios shorter too?

[Ed_RX7parts]

Got the gearkit cheap at £1800 or £1900

Rebuild was £360......Yeh gearing is different.

[Grant Monkhouse]

That is fairly cheap but still more than what I would want to fork out. Going to learn some more about modifying the standard box and see what I can come up with and see what the costs are total.

I think the tiny input shaft will still be the down fall even if the other mods work

[Ed_RX7parts]

yep i agree....the input shaft is one of the reasons i got the kit.

i made contact with a guy in oz that made kits with interchangable gearings.....well priced to but i wanted to got the tried and tested route.....i\'ll try a find his details.

[Ed_RX7parts]

tbh...i think braCing and cryo would be your best bet grant.

[Ed_RX7parts]

or possibly get the three speed kit...but doesnt come with the input shaft.

[Grant Monkhouse]

Yeh iv got lots of bracing going into the build. Iv made one bracket out of 6mm steel, Tig welded for at the rear of the box onto my chassis using the PPF mounts as I don\'t need a ppf on my rx4:D iv also made a 6mm plate for in between between the gear box and cover plate but it extends out beyond it so I can weld or bolt more bracing to the chassis at the front are of the box, if it manages to move or twist I will be running serious power or I don\'t know what I\'m doing:(

Chryo treatment isn\'t that expensive is it?? But all parts have to be removed cleaned and seperated to do it, can\'t just it in the freezer and hope for the best lmao.

[Grant Monkhouse]

I\'m not to fussed about having interchangeable gearings as I can do that with changing the rear gear, I have options to go from a 3.9-1 to 5.1-1 on the diff, plus rear tyre size will help alter that too

[Ed_RX7parts]

got all my cryo done for cheap....about £140...for e shaft, suds and gearkit with shaft

by cover plate do you mean sump?....does the fd box have a sump?

[Ed_RX7parts]

yep all have to be clean and seperate....thats why i did it all when i did.

[Grant Monkhouse]

got all my cryo done for cheap....about £140...for e shaft, suds and gearkit with shaft

by cover plate do you mean sump?....does the fd box have a sump?

Yeh the sump bit, it has a magnet in the bottom to catch all the broken synchros and input shafts when they pussy out. Lol

It has a plastic piece on the inside that I think helps the oil cover all the gears when spinning

[Ed_RX7parts]

if you added rigidity to this would it not help?....might be worth someone knocking one up in billet...possibly with cooling fins. pretty sure the guru box was like this.

[Grant Monkhouse]

I have made a plate to make it rigid, 6mm steel to go between the sump cover and the box, I think I should have made it a little thicker but its will take a lot to force to bend 6mm steel and the aluminium all bolted together.

There\'s someone on rx7 club that has made a 3/4" plate like I have but that\'s just getting really thick, not sure if he milled it CNC\'d it??

Will see I f I have a picture of the box sump sandwich plate and post it up in here, would be nice if anyone else had any ideas on this or any info about how the gear boxes work etc.