253 motor M21 gearbox

[HK1837]

To be honest, unless it is original as TH400 I'd run a 308 and late trimatic (like VL). 308 with M21 is nice with 3.36, bit too tall as 3.08.

[wbute]

It depends what sort of driving you are doing. I reckon 3.08 is awesome for highway and my brothers red wb with 3.08 flogs my wb with 3.36 around town, which goes against logic. You can rev the 3.08 out so much further between gear changes and that is where the gain is.

[Aus]

the car is plated as L32 M20 i am restoring the car for sunday club day driving would original spec be better? your right i had a HX ute which had a late tri and 308 and 3.08 it was a great highway car with 205 tyres great ute.

[wbute]

I suppose it depends on what the original diff ratio was? 3.36 is a good compromise for what you are doing I reckon behind 253 with M20.

[GNW1974]

Wasn't the 3.36 a performance option for the LC 253 in HQ's? The ute I have is definatley 3:36 optioned and I have information from another site that this was the standard option for the HC 253 HQ's. The 3:55 diff was another performance option on this model.

THe 3:08 was an economy option for the 308 HQ's and the 3:36 was standard spec.
Also lists the following ratios for what i assume are M20 and M21 boxes.
• Manual Transmission (4 speed on 6 cylinder and 253 V8):
o 1st: 3.05:1
o 2nd: 2.19:1
o 3rd: 1.51:1
o 4th: 1.00:1
o Reverse: 3.05:1
• Manual Transmission (4 speed for 308 V8 and optional on 253 V8):
o 1st: 2.54:1
o 2nd: 1.83:1
o 3rd: 1.38:1
o 4th: 1.00:1
o Reverse: 2.54:1

[HK1837]

3.08 was always the standard diff with 253 and M20 in almost all HQ and HJ, there is no economy axles listed (except where 3.55 is standard eg 253 M20 HJ LS). 3.55 was standard in HX and HZ for the same engine/box. HQ had 3.36 as standard if 253 and M21 was ordered, but GMH obviously realised this as a mistake as HJ-HZ got 3.55 with 253 and M21. All of this is reflected in the vehicle ID I have recorded. Rarely do vehicles have diff ratios other than what is standard. I don't think you could get 253 and M21 on commercials though, only on passenger vehicles.
3.36 was always standard with 308 and M21 in HQ-HZ.

There was also the M22 which was the standard box on HQ 6cyl commercials and optional on all other HQ 6cyl. Also fitted to many HJ-WB tonners. Ratios are:
3.74:1
2.68:1
1.68:1
1:1
3.74:1

[HX76King]

Just checking to see if I understand this completely.

I already have the m21 and a 253 that I am planing to warm up so the best diff ratio for this combo is a 3.55 from what I can gather from what you have said.

Also why is this, does the 253 not have enough torque/power?:knockout:

[GNW1974]

3.08 was always the standard diff with 253 and M20 in almost all HQ and HJ, there is no economy axles listed (except where 3.55 is standard eg 253 M20 HJ LS). 3.55 was standard in HX and HZ for the same engine/box. HQ had 3.36 as standard if 253 and M21 was ordered, but GMH obviously realised this as a mistake as HJ-HZ got 3.55 with 253 and M21. All of this is reflected in the vehicle ID I have recorded. Rarely do vehicles have diff ratios other than what is standard. I don't think you could get 253 and M21 on commercials though, only on passenger vehicles.
3.36 was always standard with 308 and M21 in HQ-HZ.

There was also the M22 which was the standard box on HQ 6cyl commercials and optional on all other HQ 6cyl. Also fitted to many HJ-WB tonners. Ratios are:
3.74:1
2.68:1
1.68:1
1:1
3.74:1

I have just re read the information I have about standard diff options on HQ 253 cars and with the M20/3.08 option you are totally correct, but it also lists the high performance transmission option, which I assume means a M21 box. This was standard with a 3.36 diff. The HQ ute I have bought is an M20 /3.36 combination so I am assuming this diff would have been an upgrade when bought. The 3.55 diff on this combination was then specified as the performance option.

I was looking a a reproduction of a Holden brochure and it lists the 308 and 350 with a RAC engine rating of 51.2 HP so we can't believe everything we read.