2 Mu-7 Questions.......

[thailoht]

With the mfg suggested 29 psi of air for the 16" OEM tires, what would be the appropriate amount of air pressure for 20" tires on a MU-7?

Also, does anyone know the total amount of fluid contained in the entire transmission system - pan + tubular lines & cooler?

I know that 3 liters of transmission fluid drains out when the drain bolt that is next to the filter pan is opened. How much more fluid is contained in the rest of the transmission system?

[Kwasaki]

1st point Courtesy of who use to be MRO.

So in order to know what the proper pressures should be, we need to know:

1. The car manufacturers' recommended pressures for the OEM tires.

2. The Load rating of the OEM tires (e.g. 112V, 111H, 109S etc)

3. The Load rating of the new tires..

With the cold pressure recommendations given, it’s a good idea when have to drive to a garage to get air, when using a gauge you have already put heat into the tyre so knock off 2 psi and / or check in the morning.

If your changing to different profile tires.

The correct rule is: Adjust the OEM recommended PSI pressures by subtracting or adding the load rating of the new tire from the load rating of OEM new tire.

Examples:

If the OEM tire is 109S and the new tire is 112V, and the OEM pressure is 29PSI:

109 - 112 = -3

29PSI - 3 = 26 PSI

If the OEM tire is 112H and the new tire is 111R, and the OEM pressure is 32PSI:

112 - 111 = 1

32PSI + 1 = 33 PSI.

If you didn't swap your spare tire, you should be able to look at it to determine the OEM load rating that corresponds to the vehicle manufacturers recommended pressures.

This site is good info although most of it supports OEM.

http://en.wikipedia....code#Load_index

If your new load index is a full 6 points lower than than OEM tires, I would be very concerned that you've got an unsafe fitment (it sounds like you have a passenger car tire on an SUV or pickup).

Have a look at the table here to see how the load index corresponds to the weight rating of the tire: http://en.wikipedia....code#Load_index

6 points lower load index means between 150-210KG less weight capability per tire, so 600-840KG less vehicle weight safely supported.

Normally you wouldn't go down on load index, you'd either keep it the same or perhaps go up. I'm never going to hit the maximum GVM of the car, so I normally try to keep it in the -1 to +3 range, if you're perhaps going to have a full load on board, use a 0 to +3 range when buying tires.

If above +3, the tire is so far out of original spec that pressures would have to be dangerously low to maintain any ride quality.

Second point.

Usually if you drain an auto transmission the best thing to do is top up with new fluid to the correct level, run the engine in all gears 4wd, 2wd whatever and drain it again and refill.

There is another way where you disconnect a hose and wait until new fresh looking fluid is seen running out, forget the procedure of how to do and carrying that out.

[thailoht]

1st point Courtesy of who use to be MRO.

So in order to know what the proper pressures should be, we need to know:

1. The car manufacturers' recommended pressures for the OEM tires.

2. The Load rating of the OEM tires (e.g. 112V, 111H, 109S etc)

3. The Load rating of the new tires..

With the cold pressure recommendations given, it’s a good idea when have to drive to a garage to get air, when using a gauge you have already put heat into the tyre so knock off 2 psi and / or check in the morning.

If your changing to different profile tires.

The correct rule is: Adjust the OEM recommended PSI pressures by subtracting or adding the load rating of the new tire from the load rating of OEM new tire.

Examples:

If the OEM tire is 109S and the new tire is 112V, and the OEM pressure is 29PSI:

109 - 112 = -3

29PSI - 3 = 26 PSI

If the OEM tire is 112H and the new tire is 111R, and the OEM pressure is 32PSI:

112 - 111 = 1

32PSI + 1 = 33 PSI.

If you didn't swap your spare tire, you should be able to look at it to determine the OEM load rating that corresponds to the vehicle manufacturers recommended pressures.

This site is good info although most of it supports OEM.

http://en.wikipedia....code#Load_index

If your new load index is a full 6 points lower than than OEM tires, I would be very concerned that you've got an unsafe fitment (it sounds like you have a passenger car tire on an SUV or pickup).

Have a look at the table here to see how the load index corresponds to the weight rating of the tire: http://en.wikipedia....code#Load_index

6 points lower load index means between 150-210KG less weight capability per tire, so 600-840KG less vehicle weight safely supported.

Normally you wouldn't go down on load index, you'd either keep it the same or perhaps go up. I'm never going to hit the maximum GVM of the car, so I normally try to keep it in the -1 to +3 range, if you're perhaps going to have a full load on board, use a 0 to +3 range when buying tires.

If above +3, the tire is so far out of original spec that pressures would have to be dangerously low to maintain any ride quality.

Second point.

Usually if you drain an auto transmission the best thing to do is top up with new fluid to the correct level, run the engine in all gears 4wd, 2wd whatever and drain it again and refill.

There is another way where you disconnect a hose and wait until new fresh looking fluid is seen running out, forget the procedure of how to do and carrying that out.

Thanx Kwasaki and especially to the one 'formerly known as MRO' - (Is this going to play out as one of those " - formerly known as Prince' scenarios or were you just quoting from one of his previous posts?)

Anyway, it's exactly this type of in-depth detail that makes this thread so fulfilling!

It admittedly took me a while to 'absorb' the technical points that were made about tyre inflation rates but I appreciate the info!

Second point: I will resort to disconnecting the hose method, if I can't determine the overall amount of if that amount is greater than 6 liters.

[Kwasaki]

Thanx Kwasaki and especially to the one 'formerly known as MRO' - (Is this going to play out as one of those " - formerly known as Prince' scenarios or were you just quoting from one of his previous posts?)

Anyway, it's exactly this type of in-depth detail that makes this thread so fulfilling!

It admittedly took me a while to 'absorb' the technical points that were made about tyre inflation rates but I appreciate the info!

Second point: I will resort to disconnecting the hose method, if I can't determine the overall amount of if that amount is greater than 6 liters.

The technical point about the tyre sizes was saved from one of MRO posts because I thought it was great info that would be needed again.

The Wilki site can be looked up by anyone.

Yep !! they say flushing through is the best way to change trans fluid, the only thing I remember is flushing through near the trans cooling rad.

[transam]

You must remember that the stock wheel size and corresponding tyre profile is all linked to the suspension and so ride quality. MU7 uses truck leaf spring rear suspension and so the factory tyre/wheel combo is important. If you use low profile tyres with higher pressures ride comfort will suffer cos the stock tyres has more side wall give.

Auto trans fluid is a very robust cocktail and seldom breaks down unless a heat problem/clutch pack failure. Personally l have never done a complete fluid evacuation, even on drag race rides unless there was a problem. Use your nose and eyes. The converter holds a lot of fluid and much of it won't drain out. If it is still pink and smells sweet then l would just empty the sump and top up.

I hear that Toyota main agents ''can'' have an auto trans oil evacuation system to change it all, perhaps Isuzu has similar.

PS, Tip, don't look at the oil colour on the stick, put a few drop on something chrome or a shiny spoon to see all.

[Jitar]

Some tyre dealers have told me "plus" fitments (bigger rim diameter and lower profile tyres) need ~5 psi more pressure than OEM but I do not think this is correct.

Recommended tyre pressures are derived from load inflation tables and testing. The simplified approach described by MRO approximates this. Toyo have a fairly detailed guideline at: http://marktg.toyoti...lationtable.pdf

Both suggest load index and inflation pressure of upgraded tyres should be similar to OEM, assuming similar tyre type and use.

The theory is fine but in reality pickup based vehicles run on various size tyres with load index ranging from 90's to ~120. The bigger tyre sizes have safe loads way above actual load so pressure is more related to ride, steering response and wear. The best bet is to select your replacement tyres with a similar load index to the OEM tyres, start with the OEM pressure that corresponds to your driving style and conditions (light or heavy load etc), add or subtract a few psi (if the new tyres index is different) and see how they feel and keep an eye on tread wear.

[thailoht]

You must remember that the stock wheel size and corresponding tyre profile is all linked to the suspension and so ride quality. MU7 uses truck leaf spring rear suspension and so the factory tyre/wheel combo is important. If you use low profile tyres with higher pressures ride comfort will suffer cos the stock tyres has more side wall give.

Auto trans fluid is a very robust cocktail and seldom breaks down unless a heat problem/clutch pack failure. Personally l have never done a complete fluid evacuation, even on drag race rides unless there was a problem. Use your nose and eyes. The converter holds a lot of fluid and much of it won't drain out. If it is still pink and smells sweet then l would just empty the sump and top up.

I hear that Toyota main agents ''can'' have an auto trans oil evacuation system to change it all, perhaps Isuzu has similar.

PS, Tip, don't look at the oil colour on the stick, put a few drop on something chrome or a shiny spoon to see all.

Some tyre dealers have told me "plus" fitments (bigger rim diameter and lower profile tyres) need ~5 psi more pressure than OEM but I do not think this is correct.

Recommended tyre pressures are derived from load inflation tables and testing. The simplified approach described by MRO approximates this. Toyo have a fairly detailed guideline at: http://marktg.toyoti...lationtable.pdf

Both suggest load index and inflation pressure of upgraded tyres should be similar to OEM, assuming similar tyre type and use.

The theory is fine but in reality pickup based vehicles run on various size tyres with load index ranging from 90's to ~120. The bigger tyre sizes have safe loads way above actual load so pressure is more related to ride, steering response and wear. The best bet is to select your replacement tyres with a similar load index to the OEM tyres, start with the OEM pressure that corresponds to your driving style and conditions (light or heavy load etc), add or subtract a few psi (if the new tyres index is different) and see how they feel and keep an eye on tread wear.

Thanx guys! The Load Inflation Tables will be the reference point I'll use to determine the inflation setting for my tyres.

Going 2 for 2: Transmission fluid stats....

I discovered that the transmission for the Isuzu MU-7 (and D-Max, etc?) 3.0L engine holds a total of 8.7L - 8.8L of transmission fluid. Dropping the transmission 'pan' is supposed to release ~ 4.8L of transmission fluid.

[Kwasaki]

Some tyre dealers have told me "plus" fitments (bigger rim diameter and lower profile tyres) need ~5 psi more pressure than OEM but I do not think this is correct.

Recommended tyre pressures are derived from load inflation tables and testing. The simplified approach described by MRO approximates this. Toyo have a fairly detailed guideline at: http://marktg.toyoti...lationtable.pdf

Both suggest load index and inflation pressure of upgraded tyres should be similar to OEM, assuming similar tyre type and use.

The theory is fine but in reality pickup based vehicles run on various size tyres with load index ranging from 90's to ~120. The bigger tyre sizes have safe loads way above actual load so pressure is more related to ride, steering response and wear. The best bet is to select your replacement tyres with a similar load index to the OEM tyres, start with the OEM pressure that corresponds to your driving style and conditions (light or heavy load etc), add or subtract a few psi (if the new tyres index is different) and see how they feel and keep an eye on tread wear.

Exactly right that's what I did with the Chevi truck.

[Kwasaki]

Auto trans fluid is a very robust cocktail and seldom breaks down unless a heat problem/clutch pack failure. Personally l have never done a complete fluid evacuation, even on drag race rides unless there was a problem. Use your nose and eyes. The converter holds a lot of fluid and much of it won't drain out. If it is still pink and smells sweet then l would just empty the sump and top up.

I hear that Toyota main agents ''can'' have an auto trans oil evacuation system to change it all, perhaps Isuzu has similar.

PS, Tip, don't look at the oil colour on the stick, put a few drop on something chrome or a shiny spoon to see all.

Dropping the transmission 'pan' is supposed to release ~ 4.8L of transmission fluid.

I believe this sort of thing is done at a service schedule, for changing filters.

This is not a bad site for info :-

http://autorepair.about.com/od/otherodddiyjobs/ht/trans_filter.htm

[thailoht]

Auto trans fluid is a very robust cocktail and seldom breaks down unless a heat problem/clutch pack failure. Personally l have never done a complete fluid evacuation, even on drag race rides unless there was a problem. Use your nose and eyes. The converter holds a lot of fluid and much of it won't drain out. If it is still pink and smells sweet then l would just empty the sump and top up.

I hear that Toyota main agents ''can'' have an auto trans oil evacuation system to change it all, perhaps Isuzu has similar.

PS, Tip, don't look at the oil colour on the stick, put a few drop on something chrome or a shiny spoon to see all.

Dropping the transmission 'pan' is supposed to release ~ 4.8L of transmission fluid.

I believe this sort of thing is done at a service schedule, for changing filters.

This is not a bad site for info :-

http://autorepair.ab...rans_filter.htm

Treating this car as a 'keeper', my whole intent is change to a higher quality of transmission fluid, thus the system flush questions.

[Kwasaki]

I believe this sort of thing is done at a service schedule, for changing filters.

This is not a bad site for info :-

http://autorepair.ab...rans_filter.htm

Treating this car as a 'keeper', my whole intent is change to a higher quality of transmission fluid, thus the system flush questions.

Sorry don't understand but up to you " a higher quality of transmission fluid " never heard of such a thing other than a company sales pitch.

[thailoht]

I believe this sort of thing is done at a service schedule, for changing filters.

This is not a bad site for info :-

http://autorepair.ab...rans_filter.htm

Treating this car as a 'keeper', my whole intent is change to a higher quality of transmission fluid, thus the system flush questions.

Sorry don't understand but up to you " a higher quality of transmission fluid " never heard of such a thing other than a company sales pitch.

'Synthetic' (as opposed to mineral based fluids)

[transam]

I believe this sort of thing is done at a service schedule, for changing filters.

This is not a bad site for info :-

http://autorepair.ab...rans_filter.htm

Treating this car as a 'keeper', my whole intent is change to a higher quality of transmission fluid, thus the system flush questions.

Sorry don't understand but up to you " a higher quality of transmission fluid " never heard of such a thing other than a company sales pitch.

There is synthetic fluid for auto trans which is the ultimate.

[2unique]

With the mfg suggested 29 psi of air for the 16" OEM tires, what would be the appropriate amount of air pressure for 20" tires on a MU-7?

Also, does anyone know the total amount of fluid contained in the entire transmission system - pan + tubular lines & cooler?

I know that 3 liters of transmission fluid drains out when the drain bolt that is next to the filter pan is opened. How much more fluid is contained in the rest of the transmission system?

Running mine on 34 psi but my set up is 0.9 of an inch greater in diameter than stock set up.

Sent from Android, please excuse errors in type or judgement.

[thailoht]

With the mfg suggested 29 psi of air for the 16" OEM tires, what would be the appropriate amount of air pressure for 20" tires on a MU-7?

Also, does anyone know the total amount of fluid contained in the entire transmission system - pan + tubular lines & cooler?

I know that 3 liters of transmission fluid drains out when the drain bolt that is next to the filter pan is opened. How much more fluid is contained in the rest of the transmission system?

Running mine on 34 psi but my set up is 0.9 of an inch greater in diameter than stock set up.

Sent from Android, please excuse errors in type or judgement.

I have the same wheel set up as you and the installers filled my tires to 35 psi.

But what about this: According to info from the above tire website, tire pressures are calculated according to the load weight that will be on the tires. With that in mind, all we have to do is locate the recommended inflation rate cart for our model of tires and find the recommended tire pressure that corresponds to our vehicles gross weight.

What do you think?

[Kwasaki]

I believe this sort of thing is done at a service schedule, for changing filters.

This is not a bad site for info :-

http://autorepair.ab...rans_filter.htm

Treating this car as a 'keeper', my whole intent is change to a higher quality of transmission fluid, thus the system flush questions.

Sorry don't understand but up to you " a higher quality of transmission fluid " never heard of such a thing other than a company sales pitch.

There is synthetic fluid for auto trans which is the ultimate.

DOT4 .?

[transam]

Think this stuff would be the ultimate but you need a healthy bank balance with the quantity required.

[Kwasaki]

Think this stuff would be the ultimate but you need a healthy bank balance with the quantity required.

Toyota HFM/ATF in the wife's little Toyota, must read what says on the container.

As for synthetic don't know really, could be dodgy.

" There are a number of aftermarket synthetic ATF fluids that claim to meet numerous OEM requirements therefore you must refer to the product label for approved applications.

Make sure the product meets the specific requirements for your vehicle application before using it, as transmission shift problems and possible damage could occur using the wrong type of ATF."

[transam]

Oddly enough, l found that auto fluid used in the power steering on any ride l have had has degraded far quicker than the trans. Even on my Vigo the steering fluid is now naff after a mere 60K.

[2unique]

With the mfg suggested 29 psi of air for the 16" OEM tires, what would be the appropriate amount of air pressure for 20" tires on a MU-7?

Also, does anyone know the total amount of fluid contained in the entire transmission system - pan + tubular lines & cooler?

I know that 3 liters of transmission fluid drains out when the drain bolt that is next to the filter pan is opened. How much more fluid is contained in the rest of the transmission system?

Running mine on 34 psi but my set up is 0.9 of an inch greater in diameter than stock set up.

Sent from Android, please excuse errors in type or judgement.

I have the same wheel set up as you and the installers filled my tires to 35 psi.

But what about this: According to info from the above tire website, tire pressures are calculated according to the load weight that will be on the tires. With that in mind, all we have to do is locate the recommended inflation rate cart for our model of tires and find the recommended tire pressure that corresponds to our vehicles gross weight.

What do you think?

i found a website but forgot to bookmark before clearing cache which suggested 32psi but I didn't like that feel when i drove, it was also where i was able to enter the 2 different wheel tyre set ups and auto-calculate the diameter difference

I'll have a search later...

[thailoht]

I have the same wheel set up as you and the installers filled my tires to 35 psi.

But what about this: According to info from the above tire website, tire pressures are calculated according to the load weight that will be on the tires. With that in mind, all we have to do is locate the recommended inflation rate cart for our model of tires and find the recommended tire pressure that corresponds to our vehicles gross weight.

What do you think?

i found a website but forgot to bookmark before clearing cache which suggested 32psi but I didn't like that feel when i drove, it was also where i was able to enter the 2 different wheel tyre set ups and auto-calculate the diameter difference

I'll have a search later...

Cool, I'll be anxiously waiting to learn what that site calculates my tire pressure to be.

In the meantime, I lowered my tyre pressure to 30 psi, keeping in mind that even tyre wear is my ultimate goal.......I sure wouldn't want these babies to wear out prematurely due to under or over inflation and be faced with having to shell out more big bucks for a replacement set of 20" tyres anytime soon. It makes me wonder what everyone else has been doing??!

Have you installed those new shocks, yet?