3.64 or 3.92 Diff Choices
Discussion
For a 2011 Roadsport SV 150 kit, the standard diff is a 3.64 BMW.
I have asked for the lower ratio 3.92 diff but this apparemtly is a Sierra diff.
Caterham seem to favour the 3.64 BMW diff. Any ideas what the benifit is?
I really fancied the lower ratio 3.92 one after reading about the upgrades EVO made.
It will be mated to a standard 5-speed gearbox.
Thanks
I have asked for the lower ratio 3.92 diff but this apparemtly is a Sierra diff.
Caterham seem to favour the 3.64 BMW diff. Any ideas what the benifit is?
I really fancied the lower ratio 3.92 one after reading about the upgrades EVO made.
It will be mated to a standard 5-speed gearbox.
Thanks
It depends on what you intend to do with the car, but the 3.92 is short enough that you might find it a bit wearing for road use, which is no doubt why Caterham favour the taller diff for the roadsport.
Bottom line is that the 3.92 will give you better acceleration, but higher revs at any given road speed. Some people it won't bother, some will find it drives them nuts 'cos they feel as though they should be changing up a gear even when they're in top.
Bottom line is that the 3.92 will give you better acceleration, but higher revs at any given road speed. Some people it won't bother, some will find it drives them nuts 'cos they feel as though they should be changing up a gear even when they're in top.
The Sierra diff has a been very noisy and there’s been many many complaints hence the change to BMW. If I were you I would get the 3.62 BMW unit along with the six speed box which suits it well.RedCat7 said:
Shame the 6-speed box is nearly £3k.
Actually, I'd mis-read your original post. Sorry!The 6 speed box (with direct drive in top) would potentially be a pain, but the 5 speed box with its overdriven top gear (0.82:1) won't be nearly as bad with the short diff.
Might be quite a good compromise, in fact.
Standard diff for a 5 speed is 3.92. The 3.62 (presumably replaced with the new BMW 3.64 unit) is standard for the 6 speed box. Unless you want to go touring a lot, I wouldn't bother fitting a 3.64 with a 5 speed box as it will be too tall and ruin the acceleration for a 150 bhp car. if you want to lower the diff, look for the rare 4.1 unit - unfortunately never fitted as standard to any production car ISTR but available every now and then as special one-offs.
The problem with the Ford units is the diff whine even from new units. Sometimes they need setting up and Road & Race can get this sorted. Sometimes though its apparently due to the crown wheel and pinions being mixed up in the past so unmatched items cause the whine. This is a fundamental problem that is a bit of a showstopper to gettting fixed...
The problem with the Ford units is the diff whine even from new units. Sometimes they need setting up and Road & Race can get this sorted. Sometimes though its apparently due to the crown wheel and pinions being mixed up in the past so unmatched items cause the whine. This is a fundamental problem that is a bit of a showstopper to gettting fixed...
I understand the BMW diff is iron? 
Tell them to supply the kit without the diff, and buy a ATB diff complete with brand new casing from Quaife, for the same price as a nasty open diff from Caterham. You can be sure it's shimmed up properly then, instead of having all the backlash problems with the Caterham supplied diffs.
Quaife are a pleasure to deal with by the way.
Tell them to supply the kit without the diff, and buy a ATB diff complete with brand new casing from Quaife, for the same price as a nasty open diff from Caterham. You can be sure it's shimmed up properly then, instead of having all the backlash problems with the Caterham supplied diffs.
Quaife are a pleasure to deal with by the way.
Sorry to say this, but the QUAIFE made Diff. ARE DEFINITELY NOT quieter than any other.
I have a new R300 from Sept. 2010.
My Diff was a QUAIFE, with ATB, and with plenty of "scissor" noise when decelerating in 6° Gear (in the other gears it was not so loud, let's say "acceptable").
(It's not my first Caterham, Diff's were never silent, but this is the first with this kind of , for me unacceptable, noise; Really a pain I mist say)
Dealer took another QUAIFE ATB Diff, sent it to R&R, Phil did his Job.
Dealer came, put this second diff. in my car, we went for a Drive, 5 km later, ...here we were : This Diff. also made the same scissor noise when lifting the accelerator pedal in 6th. Gear.
Next step for me is BMW unit, Iron or not....
I hope at least it will solve the problem, as until now, nobody in any forum reported about it.
..and I hope it's really coming from the diff. One of my hypothesis is, that in 6th gear, there is a resonnance in the whole transmission, due to any self frequency being excited when the accelerator is released. In this cas, not sure that the noise will go away with the BMW Diff., as the ratio is the same.
I have a new R300 from Sept. 2010.
My Diff was a QUAIFE, with ATB, and with plenty of "scissor" noise when decelerating in 6° Gear (in the other gears it was not so loud, let's say "acceptable").
(It's not my first Caterham, Diff's were never silent, but this is the first with this kind of , for me unacceptable, noise; Really a pain I mist say)
Dealer took another QUAIFE ATB Diff, sent it to R&R, Phil did his Job.
Dealer came, put this second diff. in my car, we went for a Drive, 5 km later, ...here we were : This Diff. also made the same scissor noise when lifting the accelerator pedal in 6th. Gear.
Next step for me is BMW unit, Iron or not....
I hope at least it will solve the problem, as until now, nobody in any forum reported about it.
..and I hope it's really coming from the diff. One of my hypothesis is, that in 6th gear, there is a resonnance in the whole transmission, due to any self frequency being excited when the accelerator is released. In this cas, not sure that the noise will go away with the BMW Diff., as the ratio is the same.
Edited by ZAGATO72 on Sunday 16th January 20:07
Edited by PEGJY on Sunday 16th January 20:19
If there was an easy fix it would have been done. What is apparent, since Ford stopped manufacturing Sierra diffs, is that the remanufactured units using patent parts are just not as quiet as the Ford originals (in general). It is maybe not surprising bearing in mind the resources Ford had to develop and tool up for the process. I understood that all crown wheels and pinions for the Sierra diff where manufactured in one location in an effort to maintain QC.
Realistically, Caterham’s only option was to move to a product still in production by a large manufacture.
Realistically, Caterham’s only option was to move to a product still in production by a large manufacture.
We got a Quaife milled unit mid 2010 as a replacement for our original (Nov 2009). The original had alot of "unhealthy grinding" noise on engine braking, but was quiet under power. The Quaife is much better under engine braking, but has a bit of a whine under power. Once it's done a few more thousand miles I'll probably get Dave at TF Motorsport to tweak the backlash to try reduce the whine, but it's not bad enough to get me to fork out for the BMW unit. The car's so noisy anyway that the improved unit is "good enough".
For me it is exact the opposite: Both QUAIFES were really silent under power and terrificly noisy under engine braking.
But terrific only in 6° Gear !!
May be a pb. with the gearbox itself....?
But I know at least one person having the same noise in 5° Gear with a fiv-speeder, so I'm confident it comes from the diff.
I will report when I have the BMW unit.
Would be really interesting to have the opinion of someone who drove with the new BMW unit onboard !
But terrific only in 6° Gear !!
May be a pb. with the gearbox itself....?
But I know at least one person having the same noise in 5° Gear with a fiv-speeder, so I'm confident it comes from the diff.
I will report when I have the BMW unit.
Would be really interesting to have the opinion of someone who drove with the new BMW unit onboard !
It's always going to be noisey in a Caterham, as you're sitting on top of it, with only a piece of aluminium sheet as a sound amplifier.
It's the backlash that seems to be the problem with the Caterham ones.
I don't know which diffs they have been using recently though, or who builds them, but from what I've read of other peoples posts they don't seem to be shimmed very well.
Either way, I'd rather put up with some wine, than bolt a chunk of pig iron, and a carrier into my Nice light car!
I'm interested to see, and hear what folks think of the new ones though, when they get finaly into the system.
My Quaife will be realy quiet I know, as I'll be using a SC box!
It's the backlash that seems to be the problem with the Caterham ones.
I don't know which diffs they have been using recently though, or who builds them, but from what I've read of other peoples posts they don't seem to be shimmed very well.
Either way, I'd rather put up with some wine, than bolt a chunk of pig iron, and a carrier into my Nice light car!
I'm interested to see, and hear what folks think of the new ones though, when they get finaly into the system.
My Quaife will be realy quiet I know, as I'll be using a SC box!
Edited by mickrick on Monday 17th January 15:01
The current noise under engine braking is really awful.
I had a 1.6K and it was also noisy from the diff., but not at all the same kind of noise and the level was really lower.
In my case it is however interesting to notice, that despite the top job of R&R, who checked that the pinion and crown wheels were genuine FORD ones, swapped the bearings and preloaded them as they should, set-up the teeht meshing properly, ...the noise did not change at all !
This was very very disappointing and strange !
I had a 1.6K and it was also noisy from the diff., but not at all the same kind of noise and the level was really lower.
In my case it is however interesting to notice, that despite the top job of R&R, who checked that the pinion and crown wheels were genuine FORD ones, swapped the bearings and preloaded them as they should, set-up the teeht meshing properly, ...the noise did not change at all !
This was very very disappointing and strange !
Interesting - the comments about the noise form the sierra diffs....Obviously i guess it depends on the other 'outside' noises, aeroscreen or windscreen etc, but myself and a few pals run various '7esque' cars and never noticed any substanial diff whine/noise. Maybe we've been lucky! FWIW i've a 7 inch sierra 3.92 with a BGH type 9 and i like the acceleration. With 15 inch wheels 80mph is about 3800 revs.
RedCat7 said:
Thanks all. You have confirmed what I thought. Low ratio is best for 5-speed but it means missing out on the newer, quieter (better?) BMW unit. Can't really win. At the moment I'm swaying towards my original low ratio plan and praying I get a quiet one!
In your situation I'd go for the BMW diff. In the metric chassis the diff mounts cause any noise from the diff to be transferred through, so that pretty much any sierra diff will appear noisier than in an imperial chassis. If you go for the 3.9 ratio you're likely to not enjoy cruising much at all. If you go for the 3.6 you can pull back a little on the gearing when you want to by fitting 13" wheels and tyres. I strongly suspect that the BMW diff is going to be significantly better than the sierra part and the two are NOT interchangeable.This means that if you wanted to change after the build you'd be looking at nearly two grand, as the BMW requires new propshaft and driveshafts. I don't believe the part is going to be significantly heavier than the sierra part either, that thing weighs a tonne in the first place!
my 2p anyway
Gassing Station | Caterham | Top of Page | What's New | My Stuff