550a transmission no reverse

[west25346]

Just purchased a 1985 550a dozer near new under carrige runs great all kinds of power in forward but reverse doesn't act like it fully goes in gear.Machine will move in reverse for 20 feet then stops moving. Pressure gage on dash spikes almost to max level when throttled up in reverse. Are the reverse clutches worn?Is there something else I should look for? Are the clutch packs removable from the top?Any advice will be appreciated, I have ordered a tech manual but won't get it till next week.Some times there are shortcuts people have done to make the job easier , hoping the engine does not have to come out to access the transmission components.Thank you