Type 9 Taller First Gear

[smdl]

Hi, Folks.

I'm new to the forum, and am currently in the process of building a Locost chassis that is being adjusted to suit my preferences. As my car is using mechanicals that closely parallel those used by US Caterhams, I hope you won't mind me asking a few questions.

I am using a Focus SVT Zetec with a Sierra Type 9 out of a Merkur XR4Ti. I was planning on using the Sierra diff from the Merkur in a De Dion format, but am using Miata front uprights/hubs/wheels (due to the favorable geometry), and I would like the bolt-pattern to match front and rear. So, I am now considering using Miata both front and rear, which will likely result in a 3.9 - 4.3 final drive. Now to my concern:

With such a low (numerically high) final drive ratio, I am concerned about the effectiveness of the 3.36:1 first gear in the Type 9. I really would like to avoid having a useless first gear, and wonder if there is reasonable and local source for a taller first gear. I believe that one can be sourced by BGH Geartech in the UK, and I can go there if necessary, but would prefer to find something in North America (I am in Vancouver, Canada).

So, are my concerns valid? Will the first gear be a problem? If so, what options are there for a taller first gear?

Thanks for your time!

Shaun Laughy

[slomove]

Hi Shaun, the tall first gear is maybe not a real problem but it is definitely not great. I used to have that and finally changed to a semi-close T9 with 2.83 first gear. I got that through MSI/Vacaville and believe it was assembled by Quantum Mechanics (somewhere East Coast?). Very satisfied, also with somewhat shorter 2nd and 3rd. I heard however, that the gears Quantum Mechanics was using are permanently out of stock. You may want to cantact MSI for more info.

On the other hand, many if not most Seven drivers use unmodified T9s and just live with it. The BGH box is not exactly cheap, anyway.

Gert

[Elv15]

You might be interested in this program that shows various speeds for a number of different gearboxes and ratios:

http://locost7.info/gearcalc.php

[Doug Liedblad]

Shaun

I first installed a T9 from an Xr4Ti in my Caterham using the bellhousing designed for crossflow to Zetec conversion.

It turned out to have the wrong input shaft length. About 1/2 inch too short.

It worked for awhile but then started making noise. By this time (1000 miles) I was very tired of a 3.36 (or maybe a 3.65) first gear so just bought a Semi helical close ratio box made by SPC. Gears by Quaife. It has a 2.39 first but a .87 5th.

First gear is now great, but 5th is too low for the freeway with 14 inch wheels. (4000 RPM at 70) unless I use my 16 inch wheels (3500 RPM)

The BGH box can use the stock 5th (.82) so might be a good choice.

Doug

[smdl]

Good info, everyone -- thanks.

Elv15, I do have the GearCalc program, which was a big help, but I was looking for a more subjective evaluation by those that have the same box.

I plan to have the Type 9 rebuilt anyway, as the Merkur had 180,00 KMs on it and I know that they are marginal in that application due to the power and weight of the car. So, it makes sense to me to solve the low first gear issue (if it really is an issue) up front while it is apart. Sounds like I might want to take care of it while I'm in there.

I will chat with Woody on the subject and see if he had any sources. I am just in the process of purchasing a Raceline water rail from him, and I have found him to be very helpful

Just curious, but what final drive ratios do Caterhams use?

Thanks again,
Shaun

[Doug Liedblad]

Shaun

They generally use either a 3.92 which I have or a 3.62 which would also help my freeway driving. I like the 3.92 for the track.

These are for the Sierra dif used on the DeDion cars.

There are other ratios available from ~3.3 to 4.11

I believe similar are available for live axle but I don't know the numbers like I do for the Sierra.

Doug

[smdl]

Thanks, Doug.

Shaun

[JohnCh]

I have a 3.62 diff/3.65 1st gear (standard Type-9), which provides the same overall 1st gear ratio as a 3.92 diff/3.65 1st gear combo. The short 1st gear was fine when I had a crossflow, but after dropping the Westfield's weight by over 10% and swapping in a Duratec, it is useless. Anything even approaching full throttle results in massive wheel spin and no forward progress -- even with LSD.

I am planning to buy the BGH long 1st gear transmission in the near future. It uses a 2.98 1st gear, but keeps the remaining gears the same (although you can get a 0.87 5th gear if you wish). Given all the work Brian does to improve the transmission, I think the price is reasonable, but the shipping is a killer. Group Buy anyone? :)

-John

[Roll a 7]

My diff is a 3.62 ZF with a clutchpak. Trans is the Cat 6 speed which does not have overdrive. The trans is a pain for Hwy/Frwy driving because of the higher RPMs, but great for track/autocross.

[smdl]

I have a 3.62 diff/3.65 1st gear (standard Type-9), which provides the same overall 1st gear ratio as a 3.92 diff/3.65 1st gear combo. The short 1st gear was fine when I had a crossflow, but after dropping the Westfield's weight by over 10% and swapping in a Duratec, it is useless. Anything even approaching full throttle results in massive wheel spin and no forward progress -- even with LSD.

I am planning to buy the BGH long 1st gear transmission in the near future. It uses a 2.98 1st gear, but keeps the remaining gears the same (although you can get a 0.87 5th gear if you wish). Given all the work Brian does to improve the transmission, I think the price is reasonable, but the shipping is a killer. Group Buy anyone? :)

-John

John, can you let me know what the BGH unit costs and, if you know, what the approximate shipping costs are? We are pretty close to each other.

Thanks,
Shaun

[smdl]

One other question: Can anyone tell me what the bolt-pattern/bolt circle/PCD is on Caterhams?

Thanks,
Shaun

[JohnCh]

Shaun,

Price depends on the model. I plan to go for the Heavy Duty E2 which is 620GBP. Pricing and options are located here. I did some preliminary costing on the shipping side and it appears to fall into the $450-$600 range. BGH told me that a crated gearbox weighs 32kg and is 34"x11"x11" Interestingly I believe this places it under the weight limit for checked baggage on international flights...

-John

[JohnCh]

The PCD for new Caterhams is the same as Westfield: 4x108mm. If you want a 15" wheel as opposed to a 13" wheel, then you will have a lot more options for affordable, light weight wheels by going with the Miata setup you discussed earlier.

-John

[Sean-og]

Shaun,

Price depends on the model. I plan to go for the Heavy Duty E2 which is 620GBP. Pricing and options are located here. I did some preliminary costing on the shipping side and it appears to fall into the $450-$600 range. BGH told me that a crated gearbox weighs 32kg and is 34"x11"x11" Interestingly I believe this places it under the weight limit for checked baggage on international flights...

-John

John,

The BGH web page lists prices for exchange. Do you know the price for an outright purchase of a complete box?

[JohnCh]

Doh! I was in a hurry when I posted the price and forgot to mention the 95GBP core charge -- something I don't plan to get back.

-John